On the development of a trait-based approach for studying Neotropical bats

New World bats are involved in key ecological processes and are good indicators of environmental changes. Recently, trait-based approaches have been used in several taxa to better understand mechanisms underlying species assemblages, biotic interactions, environmental relationships and ecosystem functions. However, despite the relevance of bats on ecosystem dynamics, so far, there is no conceptual framework that relies on the measurement of bat traits to address functional studies. Here, we present a set of 50 bat biological traits, which are suitable to assess environmental stressors and can potentially affect ecological processes. Several examples were provided to show the applicability of this framework in the study of Neotropical bat ecology. We suggest some considerations regarding trait-based approach including the importance of intraspecific variation, correlations between traits, response-effect framework, global dataset, and future directions to assess the reliability of functional relations across species and Neotropical regions by using traits. This could be helpful in tackling ecological questions associated with community assembly and habitat filtering, species diversity patterns along environmental gradients, and ecological processes. We envision this paper as a first step toward an integrative bat functional trait protocol held up with solid evidence.


INTRODUCTION
Global biodiversity loss is a major concern that has motivated ecologists to explore the links between biodiversity and ecosystem functioning (Gross et al., 2017), especially under different scenarios of human impact (García-Morales et al., 2016). The necessity to transfer this knowledge into management planning is critical, as the massive loss of biodiversity is threatening the ecosystem services from which humans depend on (Millennium Ecosystem Assessment, 2005). Accordingly, several approaches have been conducted to monitor biodiversity, of which measures of taxonomic diversity (i.e., species richness, evenness, diversity) are the most widely used ones (Cadotte et al., 2011;Mayfield et al., 2010;García-Morales et al., 2016). However, taxonomic diversity indices (e.g., Shannon, Simpson) ignore species differences in ecological roles (Villéger et al., 2010;Córdova-Tapia & Zambrano, 2016). Alternatively, functional diversity approach has been a core topic research in community ecology and conservation biology over the last decades (García-Morales et al., 2016;Gross et al., 2017), due to the inclusion of ecological attributes of species associated to ecosystem functioning (Gómez-Ortiz & Moreno, 2017). In line with this, functional diversity provides a comprehensive framework of causes, consequences, and mechanisms in the relations between species diversity and ecological processes (Córdova-Tapia & Zambrano, 2016).
Moving from ecological studies based on the taxonomic structure of communities to investigations that include functional diversity measures and relationships with ecosystem processes requires, mainly, a functional trait-based approach. Functional traits are traditionally defined as any morphological, physiological, behavioral, or phenological characteristic that, in addition to impact the fitness of an organism (Violle et al., 2007), reflects interactions with the environment either by mirroring the impact on some ecosystem process (effect traits) (Lavorel & Garnier, 2002;Luck et al., 2012) and/or by responding to environmental changes (response traits). Values measured by a functional trait in the same spatio-temporal dimension are called functional attributes (Lavorel et al., 1997). Thus, functional trait-based approach is a promising tool to address plenty of ecological questions that contribute to biodiversity conservation (Castillo-Figueroa, 2018a; Jung & Threlfall, ISSN On-Line: 1807-0205 ISSN Printed: 0031-1049 ISNI: 0000-0004-0384-1825 2018). For example, several studies show that functional traits explain the impact of human-made landscapes on ecological groups of animals , the influence of climate change on species distributions and phenology (Robbirt et al., 2011), the effect of chemical elements on community assembly (Rubach et al., 2011;Van den Brink et al., 2013), and the distribution of functional diversity at macro-ecological scale (McGill et al., 2006;Hortal et al., 2015;González-Maya et al., 2017), to name a few examples.
The concept of functional traits has been, however, criticized because of its vague meaning, as all the traits of an organisms affect, at least indirectly, the fitness of an individual (Mlambo, 2014). Focusing on functionality rather than the performance of the organism seems to be a more comprehensive definition of functional trait. Hence, real functional traits are those that modulate ecological processes, whereas the other traits can be categorized as biological ones (Mlambo, 2014). In this sense, before reaching functional traits is essential to list, describe and study biological traits that can potentially be functional.
Plant communities are the main biological group in which functional trait-based approach has been widely developed (Cornelissen et al., 2003;Hortal et al., 2015). Plant ecologists have been able to conceptualize the linkages between individual plant traits and ecosystem processes, including mechanisms and ecological factors such as competition, intra-and inter-specific variation, and environmental filtering across several ecosystems (Siefert et al., 2015). This field has advanced in the last few years with global databases like TRY (Kattge et al., 2020), LEDA (Kleyer et al., 2008) Global Wood Density (Chave et al., 2009), as well as handbooks and protocols (Cornelissen et al., 2003;Salgado-Negret et al., 2015). Undoubtedly, plant functional trait-based approaches have been a successful model that animal ecologists have adopted in handbooks and frameworks of traits in zoological groups such as terrestrial invertebrates (Moretti et al., 2017), fishes (Zamudio et al., 2015), birds (López-Ordoñez et al., 2015), and amphibians (Cortés-Gómez et al., 2015). Nevertheless, so far, there is no such protocol for mammalian traits, mainly due to the challenge of developing a single handbook that integrates the striking ecological complexity of this group. Although several but isolated investigations using functional traits have been conducted in mammals, it is necessary to start selecting biological traits of mammal groups to accomplish a complete and solid functional trait handbook.
Chiroptera is one of the most ecologically important taxa among mammals. Accounting for 1,411 recognized species (Mammal Diversity Database, 2020), bats represent a fifth of mammalian diversity (Hutson et al., 2001;Frick et al., 2019), with many opportunities for investigating ecological questions in a comparative framework (Brokaw & Smotherman, 2020). New World bats, in particular, consist of 400 species (Arita et al., 2014) and display a variety of morphological (Findley et al., 1972;Santana et al., 2011aSantana et al., , 2012Castillo-Figueroa, 2020a), ethological (Vandoros & Dumont, 2004;Voss et al., 2016;, physiological (Schondube et al., 2001;Saldaña-Vázquez et al., 2015;Tschapka et al., 2015), and reproductive traits (Fleming et al., 1972;Kerth, 2008;Vela-Vargas et al., 2016;Stukenholtz et al., 2018). Moreover, this group has a high diversity of feeding habits (Wilson, 1973), trophic niches (Giannini & Kalko, 2004), and habitat use Denzinger & Schnitzler, 2013;Voss et al., 2016), which are reflected in their multiple ecological roles in the ecosystems they inhabit (Lacher et al., 2019;Castillo-Figueroa, 2020b). Even though ecological studies using traits have long been conducted in bats (Findley & Wilson, 1982;Norberg & Rayner, 1987;Fleming, 1991), recently some investigations have focused on functional diversity measures based on traits Mancini et al., 2019;Pereira et al., 2019;Farneda et al., 2019;Ramírez-Mejía et al., 2020), many of which have lacked an ecological criterion to select the most suitable functional traits. Because the success of trait-based approaches depends on trait selection (Hortal et al., 2015), conceptual frameworks that define the ecological relations of traits becomes imperative to better apply this approach into functional ecology studies. Here, we present a synthetic conceptual framework which emphasizes in the main biological traits of Neotropical bats by defining an extensive set of features. We then show how our framework might aid to perform different studies on bat ecology through several examples from literature that includes: trait-related responses to habitat fragmentation, land use management, elevational gradients, seasonal changes and seed dispersal networks. We also emphasize the importance of testing, either empirically or experimentally, these biological traits in order to discover the real functionality of each trait. Finally, we discuss issues regarding trait-based approach in Neotropical bats encompassing intraspecific variation, correlations between traits, response-effect framework, global dataset, and future directions regarding their application in functional ecology and biodiversity conservation.

Functional ecology and trait selection
Neotropical bats play key ecological roles in arthropod suppression, vertebrate predation, seed dispersal, pollination, and fertilization (Kasso & Balakrishnan, 2013;Castillo-Figueroa, 2020b). Furthermore, bats have broad geographical ranges and can be affected by several environmental gradients including habitat fragmentation (Meyer et al., , 2016Rocha et al., 2017), agricultural management , urbanization (Jung & Threlfall, 2018), climate change (Sherwin et al., 2012), among others. In fact, bats have been considered as bioindicators of disturbance due to idiosyncratic responses to environmental variation (Fenton et al., 1992;Medellín et al., 2000;Jones et al., 2009a). Consequently, effect and response traits may reflect the relations with ecological processes and the impact of environmental conditions on this group, yet there are few studies using functional traits and, in most cases, the selection seems to be arbitrary because of the absence of functional interpretations of traits. Easy measurable traits are usually chosen, rather than traits more related to functional components (Raunkiaeran Shortfall sensu Hortal et al., 2015).
We selected 50 bat biological traits according to studies that directly relate traits to environmental conditions, but we also included traits potentially linked to, either directly or indirectly, individual performance and ecosystem process (Table 1). However, more research is needed to clarify direct linkages with ecosystem functioning as the available information that relates traits with ecological processes is very scarce. This paper, therefore, helps to provide a list of potential traits that need to be investigated in-depth for an understanding of their functionality.
The selected traits were grouped into two main types of traits: Morphological (21 traits) and Life history traits (29 traits) (Fig. 1). The former includes six functional complexes (size, wings, pollex, hindlimbs, head, and tail) and the latter is divided into six functional dimensions following the proposal of Gómez-Ortiz & Moreno (2017): reproductive, physiological, behavioral, trophic niche, spatial niche, and echolocation (Table 1). We focused on the selection of traits that can be measured directly and quantitatively, but we also presented categorical traits, which have been extensively used in several ecological studies (Cisneros et al., 2016;Farneda et al., 2019;Ramírez-Mejía et al., 2020). In all the traits we indicated the pertaining group (functional complex or functional dimension), the value of the trait (attribute), the way to measure (description), and the source of information where the trait can be obtained (trait obtaining). We also present the ecological information of each trait based on an extensive literature revision of bat ecology.

Study cases from literature
We reviewed the available information that employed the usage of trait-based approach in Neotropical bats by searching in Scopus and Google scholar databases (consulted the 25/09/2020) with the terms "Neotropical Bats" OR "New World bats" AND "Trait-based approach". We obtained 135 document results from Scopus and 541 from Google Scholar. After reviewing carefully each one of the documents we obtained a total of 19 study cases that employed this approach. For each case we recorded location, morphological and natural history traits, and the application of the study. Five of those cases were illustrated to show the type of research questions that can be pursued under trait-based approach.

Size complex
Body size is probably one of the most informative traits, and it is also one of the easiest features to measure in bats (MacNab, 2007;Safi et al., 2013;Giannini et al., 2012). In the past few years, body size has been the core of ecological and evolutionary studies (Safi et al., 2013; Figure 1. Schematic model of biological traits of Neotropical bats. Life history traits in black boxes whereas morphological traits are depicted in white boxes.  Giannini et al., 2012;Arevalo et al., 2020). Size has remarkable implications in essential functions such as aerodynamic performance (Norberg & Rayner, 1987;Arevalo et al., 2020), echolocation (Barclay & Brigham, 1991;Jones, 1999;López-Cuamatzi et al., 2020;Arevalo et al., 2020), basal metabolic rate (MacNab, 2003), biomechanical properties (Swartz & Middleton, 2008), dietary habits (Norberg & Fenton, 1988), foraging habitats (Muscarella & Fleming, 2007) and other life history traits (Safi et al., 2013). Body measurements, therefore, can be a reliable proxy for general size, being informative regarding environmental changes and ecosystem functions as well Body mass: related to morphometric structures including skull size (Aguirre et al., 2002), length of the digestive tract (Bonaccorso, 1979), biomechanics structures of postcranial skeleton (Swartz & Middleton, 2008) and wings (Norberg & Rayner, 1987). Body mass is also linked to other functions associated to wingbeat frequency (Jones, 1999;Norberg & Norberg, 2012), pulse duration (Jones, 1999), peak frequency (Jones, 1999;Thiagavel et al., 2017;López-Cuamatzi et al., 2020), bite force (Aguirre et al., 2002), basal metabolic rate (Kleiber, 1947;Soriano et al., 2002), quantity, quality and time invested in food handling (Fleming, 1991;Gómez-Ortiz & Moreno, 2017), hardness and size of the food (Aguirre et al., 2003), and niche partitioning . In frugivorous bats, body mass is positively related to foraging height (Rex et al., 2011), food transit time (Laska, 1990), and the consumption of large-sized and low-quality fruits (low concentration of sugars and proteins), with a longer time in handling, processing and intestinal transit (Fleming, 1991;Saldaña-Vázquez, 2014a). Large species are more likely to disperse heavier fruits (López & Vaughan, 2004), colonize and dominate urban environments (Saldaña-Vázquez & Schondube, 2016;Jung & Threlfall, 2018) as well as other human-dominated landscapes (e.g., coffee plantations) (Frank et al., 2017), but are prone to be more vulnerable to habitat loss (Martínez-Ferreira et al., 2020) and fragmentation (Farneda et al., 2015). Body size also determines the foraging habitats of frugivorous bats (Muscarella & Fleming, 2007); that is, small bats with low wing loading and low aspect ratio can potentially forage both in the understory and canopy of forests because of their greater maneuverability. Conversely, larger species with high wing loading and high aspect ratio are less maneuverable and tend to forage in the canopy (Norberg & Rayner, 1987;Muscarella & Fleming, 2007). It has been found that body mass is positively correlated with colony size, which is associated with lower individual predation risk and with certain morphological features such as the absence pelage markings (Santana et al., 2011b). Also, to some extent, body size seems to be positively related to home range in some fig-eating stenodermatines (Kalko et al., 1996).
Total length: this trait comprises the length from the tail, if any, to the head. Total length is associated to body size, developmental stage, and the amount of resources and energy required by bats (Gómez-Ortiz & Moreno, 2017).
Forearm length: a reliable proxy for body size (Dietz et al., 2006;Safi et al., 2013;Thiagavel et al., 2017). In phyllostomid bats, forearm length is positively related to nose leaf length (Arita, 1990). Studies conducted in silvopastoral agricultural systems have shown an increase of forearm length because of the availability of food and roosting sites (Ballesteros-Correa, 2015; Castillo-Figueroa & Pérez-Torres, 2018; Chacón-Pacheco & Ballesteros-Correa, 2019). This trait can be converted to a categorical variable, and the species may be classified in three groups, according to Muñoz (2001) as follows: small (< 40 mm), medium (40 mm-60 mm) and large (> 60 mm). Maneuverability is also related to size; small bats are more likely to perform a better flight performance in highly cluttered habitats than large and fast-flying bats (Thollesson & Norberg, 1991;Stockwell, 2001;Denzinger et al., 2016). Particularly, for insectivorous bats, forearm length is a significant predictor of peak frequency and wing morphology; that is, small species with low wing loadings and low aspect ratios tend to emit higher frequency calls, whereas large species with high wing loading and high aspect ratio are characterized by emit lower frequency signals (Norberg & Rayner, 1987;Thiagavel et al., 2017;Núñez et al., 2019). It has been also found a positive correlation between forearm length and prey size (Houston et al., 2004). For stenodermatinae bats, species that use leaf tents as diurnal roosts display short forearm length than bats that use other type of roosts (Garbino & Tavares, 2018).
Length of the third digit: measure of hand-wing length. A high ratio between third digit length and forearm length indicates long wings and thereby fast flights and low energy expenditure (Dietz et al., 2006;Castillo-Figueroa, 2020a). Lower values of length of the third digit in relation to length of the fifth digit indicate short wings adapted to a slow flight in narrow habitats (Dietz et al., 2006;. Altogether with forearm length and length of the fifth digit, this trait is a good proxy of wing morphology (Findley et al., 1972).
Length of the fifth digit: measure of the wing width. A high ratio between the length of the fifth digit and forearm length indicates wide wings with high maneuverability and hovering capacity (Dietz et al., 2006;Castillo-Figueroa, 2020a), slow flights and low wing loading (Lisón, 2012). A high ratio between the length of the third digit and the fifth digit indicates long wings, adapted to fast flight in uncluttered habitats and open areas (Dietz et al., 2006). This measure together with forearm length and length of the fifth digit is a good proxy of the wing morphology (Findley et al., 1972).
Wing loading: defined as the relationship between weight and wing area, wing loading reflects the flight speed and the ability to load items during the flight (Giannini & Brenes, 2001). Small bats have low wing loadings (Norberg & Rayner, 1987;Thollesson & Norberg, 1991), whereas large bats that carry heavier fruits, preys and pups (in the case of reproductive females), usually have higher wing loadings (Norberg & Rayner, 1987;Thollesson & Norberg, 1991). This trait is positively related to higher heart mass, thus compensating for the energy expenditure generated by rapid flights (Rodríguez-Durán & Padilla-Rodríguez, 2008). Bats with high wing loadings are suitable to better exploit uncluttered habitats with few dodges and obstacles, whereas in highly cluttered areas bats with low wing loadings are more likely to use efficiently these habitats (Norberg & Rayner, 1987;Kalcounis & Brigham, 1995;Marinello & Bernard, 2014). Due to this, bats with high wing loading are more tolerant to urban and suburban areas because this trait favor high-speed flight at low-energy cost, allowing for the exportation of open environments which are quite common in cities (Jung & Threlfall, 2018;Ramírez-Mejía et al., 2020). Wing loading is also related to echolocation traits. Bats with high wing loading and high aspect ratio are likely to produce long-duration signals and low frequency calls (Norberg & Rayner, 1987;Jones, 1999). By contrast, bats with low aspect ratio and low wing loading are more likely to generate echoes characterized by high frequency and short-duration signals (Norberg & Rayner, 1987;Jones, 1999). High wing loading in frugivorous bats also indicates higher flexibility in the use of space and a higher ability to move between fragments (Farneda et al., 2015;Frank et al., 2017), contrary to species with low wing loading which are prone to be negatively affected by habitat loss and fragmentation (Frank et al., 2017;Martínez-Ferreira et al., 2020).
Aspect ratio: reflects the wing width in relation to the body (wing narrowness) and is positively related to flight efficiency and flight speed (Norberg & Rayner, 1987;Thollesson & Norberg, 1991) and inversely related to flight energy expenditure (Giannini & Brenes, 2001). Species with a higher aspect ratio have constant and high-speed flights at low-energy costs generally in upper strata (Blood & McFarlane, 1988;Saunders & Barclay, 1992), as well as long commuting flights (Giannini & Brenes, 2001). By contrast, species with lower values in aspect ratio have slower but more maneuverable flights generally in low strata (Blood & McFarlane, 1988;Thollesson & Norberg, 1991;Saunders & Barclay, 1992). Species that forage in open and uncluttered areas, like many aerial insectivores, have high aspect ratios, whereas species typical of cluttered spaces such as forest interiors have low aspect ratios (Norberg & Rayner, 1987). Bats with high aspect ratio and high wing loading tend to produce echolocation calls of low frequency and long duration, whereas bats that display low aspect ratio and low wing loading are more likely to emit calls of high frequency and short duration (Norberg & Rayner, 1987;Jones, 1999). In frugivorous bats, low aspect ratio explains higher diversity of fruits consumed because of slow and highly maneuverability flights that allow to forage in all forest strata (Laurindo et al., 2020). It has been found that bats with low aspect ratio tend to be negatively affected by habitat loss and fragmentation (Martínez-Ferreira et al., 2020), whereas bats with high aspect ratio seems to be more tolerant to human-made landscapes such as urban and suburban areas, since they are able to exploit open environments (Jung & Threlfall, 2018).
Tip shape index: wingtip shape estimates wingtip geometry (Norberg & Rayner, 1987) and indicates maneu-verability within dense vegetation (Findley & Wilson, 1982). Tip shape varies depending on the forest strata used by particular species, being higher in understory vegetation (Olaya-Rodríguez et al., 2019). According to this index, wingtips can be triangular (I = 0), rounded (I > 0), or pointed (I < 0) (Norberg & Rayner, 1987;Norberg, 1990Norberg, , 1994. Bats with large tip shape index (rounded) perform low flight speed, whereas bats that display small tip shape (pointed) can make flights with high roll acceleration (Thollesson & Norberg, 1991). Tip shape index is also related to echolocation traits. Pointed wingtips are related to calls with low frequency and long duration, whereas rounded wingtips are associated to echoes characterized by high frequency and short duration (Norberg & Rayner, 1987). In the case of insectivorous bats, rounded wings are related to generalist diet because of higher maneuverability that allow to exploit a high diversity of habitats and prey items, whereas pointed wings are related to specialist diet as a consequence of less maneuverable flights that restrict bat foraging to a narrow range of habitats and preys (Magalhães de Oliveira et al., 2020).
Wing span: measure showing the amplitude of the extended wings over the long axis of the body (Thollesson & Norberg, 1991). Higher flight speed is common in bats that present shorter wing span and thinner body, whereas lower flight speed is common in bats that display longer wing span and large wing area (Thollesson & Norberg, 1991). Similar to birds, this trait can be related to size, dispersion capacity and flight performance (Claramunt et al., 2012).

Pollex complex
The pollex (thumb) is the only structure of the forelimbs that has not been drastically modified for powered flight in bats (Granatosky, 2018). However, the pollex is very important in other functions such as terrestrial quadrupedal locomotion (Granatosky, 2018), food manipulation, perching and climbing over several types of substrates (Walldorf & Mehlhorn, 2013). The length of the pollex can vary from being vestigial (Furipteridae), very small (Thyropteridae) to very developed (e.g., Desmodus rotundus). This body complex is probably, one of the less investigated in terms of ecological variations.
Length of the pollex without claw: related to food handling and locomotion. This trait is not integrated into the membrane and therefore has a function to grip, hold and scale (Walldorf & Mehlhorn, 2013). The pollex varies considerably in size across guilds. Species that use the pollex to manipulate food, move or perch, display longer pollex length (Myers et al., 2016). In the case of blood-eating bats and particularly in Desmodus rotundus, longer pollex allows them to propel themselves from the ground to fly.

Hindlimbs complex
Depending on the guild, the legs can be involved in key roles including prey capture (Fish et al., 1991), walking on the ground (Dietz, 1973), and food handling (Vandoros & Dumont, 2004). The claws have a key function saving energy expenditure by perching with the tendon locking mechanism in roosting sites (Quinn & Baumel, 1993).
Length of the foot without claw: related to the perching behavior, the capture of some preys and locomotion. The foots are useful in food-handling behaviors and are related to the type of suspension during food consumption (Vandoros & Dumont, 2004).
Length of the foot with claw: related to the absolute drag force (air resistance) and the type of prey consumed (Fish et al., 1991). Higher values of the length of the foot with claw generate more absolute drag force but allow the capture of larger preys such as fishes and other vertebrates. Piscivorous bats have large foots, long and sharp claws (Denzinger et al., 2016) that can rotate 180 degrees to hook the slippery fishes they catch from the water (Fish et al., 1991). In nectarivorous bats that rely on landing on the flowers/inflorescences as foraging strategy, claws are useful in resource exploitation of flowers (Vieira & Carvalho-Okano, 1996;Tschapka, 2003;Sazima et al., 2003). Large claws also are used in the manipulation of fruits (Uieda & Vasconcellos-Neto, 1984) and preys (Fish et al., 1991).
Length of the tibia: measurement related to size (Swartz & Middleton, 2008;Giannini et al., 2012). This trait has been poorly studied, but it is likely related to moving on surfaces such as foliage, soil, woods, among others. In bats with developed uropatagium, the width and maneuverability of this membrane is related to the length of the tibia.
Length of calcaneus: process that articulates with the posterolateral surface of the proximal region of the calcaneus (tarsal bone) (Adams & Thibault, 1999). The calcaneus helps the uropatagium to change its curvature giving rigidity and flexibility simultaneously, thus being important in the aerodynamics of the flight by avoiding wind resistance, and improving maneuverability and hovering (Adams & Thibault, 1999). In the case of insectivorous species, the calcaneus has a key role in prey capture, as it helps to stretch the uropatagium to catch insects and take them to the mouth (Webster & Griffin, 1962).

Head complex
The head integrates the bulk of sensory functions in bats. Particularly, New World bats have a broad spectrum of morphological adaptations in the olfaction, which in some species are important for detecting resources such as ripe fruits (Mikich et al., 2003;Bianconi et al., 2007) insects , shelter and mates (Brokaw & Smotherman, 2020). Indeed, external nasal morphology is strongly related to diet and foraging ecology (Brokaw & Smotherman, 2020). Echolocation is a key feature for bats to detect and track preys and avoid obstacles as well. By doing so, the external ears receive the echoes of the environment and the tragus filters this information for localizing auditory targets (Chiu & Moss, 2007). Thus, ear and nose traits are key to the acquisition of food, spatial orientation, and intraspecific and interspecific communication.
Length of the external ear: main structure of the acoustic system of bats that maximize the distance in which they can receive sound signals. This trait allows to locate potential preys, members of the same species (Balcombe & Fenton, 1988), and detect predators (Fenton, 1980). Larger ears contribute to detect low auditory threshold of ultrasonic uptake, amplify incoming soundwaves from its surrounding, and improve the sensitivity of echolocation and directionality (Obrist et al., 1993;Huihua et al., 2003;Håkansson et al., 2017). Large ears may also hamper aerodynamic performance as they generate wind resistance during the flight (Gardiner et al., 2011a), precluding high-speed aerial acrobatics (Razak, 2018). During slow flights, however, large ears contribute to lift generation (Håkansson et al., 2017). Importantly, ear size is also related to foraging strategy and foraging habitats; that is, gleaning bats with large ears use them for passive listening and detecting preys, whereas bats with small ears usually fly faster in uncluttered habitats (Norberg & Rayner, 1987;Gardiner et al., 2011a;Håkansson et al., 2017). Therefore, length of the ear size is associated to the composition of preys consumed, which may affect the ability of each species to regulate particular group of arthropods.
Length of tragus: this structure is a skin flap located lateral to the ear canal that is likely to affect the incoming acoustic signal, but also may generate spectral cues for vertical sound localization (Chiu & Moss, 2007). The tragus has a functional contribution to the directivity patterns (Müller, 2004), and to elevation-dependent spectral cues which enable successful prey capture performance (Chiu & Moss, 2007). The degree of inclination aids in detecting and processing acoustic signals (Müller, 2004). For gleaning animalivores, the tragus is more developed, providing gain for frequencies (10-20 kHz) to capture preys more efficiently (Müller, 2004;Razak, 2018).
Length of nose leaf: typical structure of phyllostomid bats. This trait is mainly related to nose-emitted echolocation (King et al., 2013), and the length of the nasal spear correlates with the length of the forearm (Arita, 1990). Larger leaf-nose can be potentially associated with an increased ability to direct sound during echolocation in the vertical plane, allowing thus a more precise detection of food items in the dense foliage such as insects, fruits, and nectar (Martínez-Ferreira et al., 2020). This because a more developed leaf-nose favor a higher directionality of sonar beam, which gives two principal advantages to the species by, firstly, reducing the echoes from the periphery of the bat, minimizing thus the information that should be processed to detect objects and, secondly, enhancing the detection range by focusing the sound energy into an specific target (Martínez-Ferreira et al., 2020). Species that use hearing to locate roost or food have more developed nose leaf spears as is the case of species of Phyllostominae (Arita, 1990) and Lonchorhininae subfamilies (Brokaw & Smotherman, 2020). Conversely, species that use vision or smell to locate the food, do not have large nose leaves, as is the case of Desmodontinae species (Arita, 1990). Secondary sexual dimorphism has been found in this structure in Phyllostominae bats , probably because females forage more intensely during pregnancy and breastfeeding, so they have developed significantly larger nose leaves than males to improve their foraging efficiency . In response to environmental conditions, leaf nose manipulation modulates the shape of the sound beam by adjusting the directionality (Martínez-Ferreira et al., 2020). For example, in structurally complex vegetation the leaf nose can modify frequency and intensity of the emitted sound, thus adjusting the search volume and the perception of vegetation structure, which ease the navigation in clutter habitats (Arita, 1990). In this sense, forest loss affect negatively species with large leaf-nose that forage in the dense foliage (Martínez-Ferreira et al., 2020).
Inner nostril width ratio: reflects the separation between receptors in bats (nostrils). Considering that the maximum separation of the nostrils is restricted by the cranial width (Stoddart, 1979), lower values of the inner nostril width ratio indicate wider nostrils and higher values entails narrow nostrils (Brokaw & Smotherman, 2020). Wider separation between nostrils increase the effective area and the ability to detect different chemical signals from the environment (Stoddart, 1979). Diet, foraging habitat, foraging strategy, and echolocation are related to nostril separation (Brokaw & Smotherman, 2020). Insectivorous bats that use uncluttered habitats, exhibit aerial foraging, and employ the oral mode of echolocation, show lower inner nostril width ratio (Brokaw & Smotherman, 2020).

Tail complex
Although the structures of forelimb are mainly responsible for flight performance, the structures that support the tail membrane (uropatagium) are important for aerial locomotion, especially in maneuverability and thrust during horizontal takeoffs (Gardiner et al., 2011b;Adams et al., 2012). Moreover, uropatagium performs a key role in prey capture for insectivorous bats (Webster & Griffin, 1962;Saunders & Barclay, 1992;Kalko, 1995), carrying pups during the reproductive season (Adams & Thibault, 1999), and in thermoregulation through blood perfusion (Reeder & Cowles, 1951).
Tail length: the tail and the surrounding membrane (uropatagium) are involved in flight performance by providing greater maneuverability (Gardiner et al., 2011b). These structures also provide thrust and horizontal displacement during the flight (Adams et al., 2012). Species with tails and larger uropatagia have better flight control (Gardiner et al., 2011b).
Uropatagium area: as a membrane structure, the uropatagium is an aerodynamic surface related to wing loading and should be included in flight performance assessments (Marinello & Bernard, 2014). Larger uropatagium improves flight agility (Gardiner et al., 2011a(Gardiner et al., , 2011bAdams et al., 2012) and prey capture (Kalko, 1995). Species that consume evasive flying preys, such as moths, have a larger uropatagium (Saunders & Barclay, 1992). Similarly, other bat guilds including piscivores and animalivores also have a large uropatagium area (Marinello & Bernard, 2014). The uropatagium is also useful when carrying pups during the reproductive season and its manipulation is largely controlled by the calcaneus (Adams & Thibault, 1999). Also, it has been proposed that nectar-eating bats uropatagium serves to transport pollen from one flower to another (Aguilar-Rodríguez et al., 2019).

Reproductive dimension
Bats have a diversity of mating systems and reproductive strategies in response to environmental conditions (Crichton & Krutzsch, 2000). Many of the reproductive traits are heavily determined by the distribution of food resources through time and space as well as ambient temperature (McGuire & Boyle, 2013;Saldaña-Vázquez et al., 2020). In the Neotropics, reproductive patterns of many species can be synchronized with rainy seasons (Mello et al., 2004;Kunz et al., 2009), due to the increase of resources, mainly fruits and insects (Altringham, 2011). Nonetheless, with some exceptions, reproductive traits are poorly investigated in New World bats and the effects of habitat perturbation on reproduction are still unknown.
Litters per year: reflects reproductive output (Barclay & Harder, 2003), availability and demand of trophic and spatial resources (Gómez-Ortiz & Moreno, 2017). Bats tend to employ different reproductive strategies to produce offspring in favorable environments during specific times of the year (Fleming et al., 1972;Mello et al., 2004). For example, there is a correspondence between fruit abundance and arthropod biomass with rainfall, thus influencing reproductive timing for frugivorous and insectivorous bats, respectively (Crichton & Krutzsch, 2000). It is important to highlight, however, that food availability rather than climatic factors underlies the timing of repro-ductive events in Neotropical bats (Crichton & Krutzsch, 2000).
Litter size: related to bat fecundity (Barclay & Harder, 2003). Litter size is influenced by several characteristics such as maternal body mass, pup mass and food intake (Speakman, 2008). In the case of insectivorous bats, dietary characteristics including the capacity to obtain calcium may constrain litter size (Barclay, 1994).
Gestation duration: reflects the demand of trophic and spatial resources (Gómez-Ortiz & Moreno, 2017). The length of the pregnancy is a key period in bat reproduction (Crichton & Krutzsch, 2000), which is influenced by availability of food, and environmental factors. Bats with long gestation periods are unable to react faster to shortterm environmental fluctuations, thus their reproduction strategy lies into predictable seasonal changes to maximize reproductive success (Crichton & Krutzsch, 2000).
Lactation duration: this is the most energetically costly period (Speakman, 2008), in which bats increase the consumption of food during the early weeks of lactation to milk production and export (Kunz et al., 1995). Therefore, food availability is a key factor in determining the ability of females to obtain nutrients for reproduction (Gómez-Ortiz & Moreno, 2017). Bats display a correspondence between lactation, or at least a part of it, and the peak of food availability (Crichton & Krutzsch, 2000).
Reproductive status: related to fertility and timing of pregnancy  and can be influenced by environmental conditions (Vela-Vargas et al., 2016). Rather than temperature cycles (Crichton & Krutzsch, 2000), rainfall seasonality may be the critical factor in Neotropical bat reproduction by influencing either directly reproductive activity or indirectly the availability of food resources (Mello et al., 2004;Montiel et al., 2011). During oestral cycle, hormone concentrations, mainly progesterone and estradiol, determine reproductive status in bats . Based on the monitoring of the reproductive status of males and females, four basic reproductive patterns of Neotropical bats can be distinguished: (1) reproduction all the year (e.g., Desmodontinae), (2) a long reproductive period with a short period of reproductive inactivity (e.g., Vespertilionidae) (3) bimodal seasonal polyoesstry defined by two reproductive peaks during the year (e.g., frugivorous from Phyllostomidae) and, (4) seasonal monoestry characterized by a single reproductive period during the year (e.g., Noctilionidae) (Fleming et al., 1972;Mello et al., 2004).
Sexual maturity age: the more time needed to reach adult age, the more demand for trophic and spatial resources (Gómez-Ortiz & Moreno, 2017). This trait is also related to demography. Thus, generalist bats that become adults in a short time (e.g., four months) are more likely to have a higher abundance of adults in bat colonies (Mello & Fernandes, 2000).
Mating systems: related to reproductive success, the protection of the offspring and the demand for trophic and spatial resources (Gómez-Ortiz & Moreno, 2017). Mating systems are a consequence of bat that live in groups, where all the possible combinations to find a mate during reproduction are included (Davies et al., 2012). These systems entail intraspecific interactions where antagonistic reactions can occur in both sexes (i.e., sexual conflicts) (Davies et al., 2012). More broadly, mating systems can be classified into monogamic when male mates with only one female and the parental investment is the same for both sexes or polygamic when different combination between males and females can occur during breeding season (i.e., polyandria, polygyny, promiscuity). Species such as Vampyrum spectrum are monogamous, Carollia perspicillata, Artibeus lituratus and the bulk of the bats are polygynous, and Eptesicus fuscus are promiscuous (Altringham, 2011).

Physiological dimension
Physiological traits are among the most important in terms of the relationships with ecosystem processes. The way in which bats obtain the maximum amount of energy has remarkable effects on the interaction with their environment (Ayala-Berdon et al., 2013). Due to the experimental difficulties of their measurements but also the key information provided, these measurements are considered as "hard traits" (sensu Hodgson et al., 1999). Bat ecology is constrained by different environmental factors that encompass mean atmospheric temperature and humidity (McCain, 2007), as well as the availability of food resources (Montiel et al., 2011). Hence, several adaptations in physiological functions including echolocation, digestion, flight, thermoregulation and movement have been accomplished in the natural history of this mammal group.
Digestive capacity: directly related to diet diversity (Saldaña-Vázquez et al., 2015). In nectarivorous bats, rates of hexose assimilation as well as affinity of sucrase for its substrate affect the food quantity that an individual is capable to digest (Ayala- Berdon et al., 2013). Bats with higher digestive capacities can maintain a constant nutrient intake independently of diet quality (Ayala-Berdon & Schondube, 2011; Saldaña-Vázquez & Schondube, 2013). Also, high digestive capacity of bats to acquire and store energy from food intake can confer the ability to survive at montane and cold environments efficiently (Ayala-Berdon et al., 2013;Cruzblanca-Castro et al., 2018;Ortega-García et al., 2020). This means that physiological capacities to process energy are likely to influence spatial distribution of bats (Ayala-Berdon et al., 2013;Cruzblanca-Castro et al., 2018).
Gut size: gut plays a central role in diet diversity, especially in frugivorous bats (Saldaña-Vázquez et al., 2015). Larger gut size increases energy intake in low-quality food items (Karasov et al., 2011;Cruzblanca-Castro et al., 2018), enabling their digestion and potential germi-nation of pioneer plants (Saldaña-Vázquez, 2014a), but also may reduce viability of other seed species (Traveset, 1998). By contrast, shorter gut size contains a greater amount of lymph in the tissues which represents rapid assimilation of nutrients (Oliveira & Lemes, 2010). Gut size may also limit food intake volume in nectarivorous bats (Ayala-Berdon & Schondube, 2011).
Gut retention time of seeds: the time that seeds remain in the gut of an animal can prompt heavily effects for plant reproduction (Traveset, 1998). Retention of seeds may influence plant fitness through dispersal distance and gene flow (Murray et al., 1994;Shilton et al., 1999), recruitment of new individuals to plant populations (Schupp et al., 2010), and the seed germination (Baldwin & Whitehead, 2015); therefore, the role of this trait may be pivotal in effective seed dispersal. Optimum retention time enables seed scarification (Jacomassa & Pizo, 2010) and decreases minimum imbibition time, thus increasing germination probability of seeds, especially in dry ecosystems (Naranjo et al., 2003). Nevertheless, depending on the ecological context (the seeds, the dispersers, and environments), longer gut retention time can enhance seed germination (cleaning the pulp and with seed scarification) or, conversely, can reduce seed viability (damaging the seed with the acid environment of the gut) (Traveset, 1998). Overall, Neotropical bats present shorter food transit times, usually less than 1 h (Fleming, 1988;Baldwin & Whitehead, 2015), which may be the best strategy to maximize energy gain in frugivorous bats, when eating a low-quality diet (Laska, 1990). Some studies have shown that gut retention time in bats can increase germination success but does not influence germination speed (Baldwin & Whitehead, 2015). It is important to highlight that gut retention time is not only determined by intrinsic morphological and physiological features of the disperser animal, but also by extrinsic factors related to the food ingested such as nutrient composition, secondary compounds, consistency, mass, hardness and amount ingested (Laska, 1990;Cipollini & Levey, 1997;Traveset, 1998;Baldwin & Whitehead, 2015).
Type of lingual papillae: lingual physiology can be useful in elucidating dietary preferences and evolutionary patterns of feeding habits (Gregorin, 2003). Variations in papillae shape and distribution on the tongue are related to the way of capturing prey, the ingestion, and the diet (Pastor et al., 1993). For instance, in frugivorous bats that are not able to swallow big fruits, they can absorb the juice and avoid the fiber by using the mechanical and gustatory papillae (Gunawan et al., 2019), whereas nectivorous bats can perform nectar extraction by using a tongue with hair-like papillae or tongues with lateral grooves (Fleming et al., 2009;Tschapka et al., 2015;Lacher et al., 2019). The different types of lingual papillae may also vary at intra-specific level and between habitats or geographical locations (Gunawan et al., 2019).
Metabolic rate: related to the demand for trophic resources, energy expenditure (Gómez-Ortiz & Moreno, 2017) and body mass (Kleiber, 1947;Soriano et al., 2002;MacNab, 2003). Variations in metabolic rate can also be related to feeding habits; that is, highest rates of metabolism are likely to be found on nectarivores, followed by frugivores, intermediate rates in frugivorous-insectivorous, and the lowest rates in hematophagous and insectivorous guilds (Soriano et al., 2002). Several environmental factors can affect metabolic efficiency such as rain through increasing the energy cost in bat flight , ambient temperature via thermoregulation at lower and higher temperatures, elevation in which phytophagous bats can increase metabolic rate with increasing altitude (Soriano et al., 2002), and food quality that affect food volumetric ingestion and therefore energy intake (Ortega-García et al., 2020).
Body temperature: stress can elicit changes in body temperature (Muise et al., 2018;Ortega-García et al., 2020). Increasing rapidly body temperature may be critical to escape predators while roosting during day (Muise et al., 2018). The reduction of metabolic rate is related to a subsequent decreasing in heart rate and body temperature, which is strongly related to ambient temperature (O'Mara et al., 2017). For example, nights with rains, high winds and low ambient temperatures increase the use of torpor as a consequence of less energy intake (Klug & Barclay, 2013;Ortega-García et al., 2020). Other factors such as poor foraging condition may increase the use of torpor, and reproduction (e.g., lactation and early development) may influence the thermoregulatory strategies employed by bats to control body temperature (Klug & Barclay, 2013). Body mass is also related to body temperature given that large bats can better regulate their temperature than small bats regardless the guild (Soriano et al., 2002).

Behavioral dimension
Behavioral traits in New World bats are poorly known, mainly because of their cryptic lifestyles. Behavioral information is the cornerstone for many essential aspects of bats such as demography, ecological constraints, intraand interspecific interactions (Kerth, 2008). Moreover, behavioral changes are useful indicators of human-made habitat modification, as they may be an appropriate measure of sensitivity to disturbances other than traditional measures of species richness or abundance (Presley et al., 2009;Montaño-Centellas et al., 2015).
Migration: migration events during the reproductive season are necessary for some bats. Females' migrations to warmer sites improve prenatal development, thus enhancing breeding success . During migration bats flight over long distances and thereby this trait is linked to the demand for trophic and spatial resources, torpor, lethargy and temporary segregation (Esbérard et al., 2011;Gómez-Ortiz & Moreno, 2017). Furthermore, altitudinal migration over shorter distances can be performed by bats because of seasonal variation in food resources across elevational gradient (McGuire & Boyle, 2013), but also to find appropriate sites for breeding . This altitudinal movement may constitute an important factor affecting bat interactions with plant species they disperse and/ or pollinate , or insects they prey at different periods thought the year.
Sociality: bat aggregation may reduce energetic expenditure due to thermoregulatory demands in lactating mothers and juveniles (Agosta, 2002;Klug & Barclay, 2013). Ecological factors such as roost or shelter limitation could forces bats to aggregate, even in contexts where group living is detrimental (Kerth, 2008). Moreover, physiological demands, demographic predispositions including philopatry, longevity and overlapping generations influence sociality in bats (Kerth, 2008). Depending on whether bats forage in a group or solitary could influence individuals' movement paths and spatial patterns of seed rain.
Foraging strategy: the way to capture the food allows species to take advantage of habitat heterogeneity and generate a higher resource partition in ecosystems . It has been suggested that the more forage strategies, the more resources and habitats can be used by bats, which may be linked to a greater number of ecological processes (Mora-Fernández et al., 2013). Foraging strategy is related to diet; for example, insectivorous bats obtain their food primarily as aerial foragers but can also present a gleaning behavior; carnivorous, omnivorous and hematophagous bats consume some animals or parts of them (e.g., blood) that are captured in the foliage or some surface by employing different senses to locate their food . Frugivorous bats can be canopy or understory since vertical stratification is associated to resource allocation because in each of these strategies there are differences in the quantity and quality of fruits they consume (Bonaccorso, 1979;Soriano, 2000). Also, foraging strategy in frugivorous bats are related to displacements performed per night to obtain the fruits and in the associations with the fruiting patterns of the plants (Big bang for canopy bats or Steady state for understory bats) (Bonaccorso, 1979;Soriano, 2000). Foraging strategy is also related to foraging habitat, since uncluttered areas (and in some cases background) are suitable places for aerial foragers, whereas narrow habitats are suitable for bats that gather their food on the foliage , in the canopy or at understory level (Bonaccorso, 1979;Soriano, 2000). In the case of nectarivorous bats, trap-lining foraging contributes to efficiency as pollen dispersers over long distances, promoting outcrossing in plants (Muchhala & Thomson, 2010). These foraging strategies are likely to influence plants distribution patterns.
Activity pattern: bat activity represents an important niche dimension because indicates how species exploit the environment (Presley et al., 2009). The optimization of activity times is critical for the species survival (Di Blanco et al., 2017), and the bulk of these temporal events are associated with predatory and anti-predatory strategies as well as temporary segregation (Thies et al., 2006;Gómez-Ortiz & Moreno, 2017). Environmental factors such as rain ), humidity (Ferro-Muñoz et al., 2018 and temperature (Barclay, 1985;Verde, et al., 2018;Ferro-Muñoz et al., 2018) may influence energy expenditure by constraining foraging activity times. Bat activity patterns may also respond to local disturbance (Montaño-Centellas et al., 2015), habitat conversion (Presley et al., 2009), and availability to ripe fruit in the case of frugivorous (Thies et al., 2006). Other factors including moonlight intensity displays a negative relationship to bat activity, especially for those species that forages in open habitats such as water surfaces and forest canopy (Saldaña-Vázquez & Munguía-Rosas, 2013).

Trophic niche dimension
New World bats, particularly from Phyllostomidae family, show a high diversity feeding habits as well as foraging strategies to obtain their food. According to optimal foraging theory (MacArthur & Pianka, 1966;Schoener, 1971), an animal displays the best strategy to accomplish the maximum benefit with the lowest energetic cost. In line with this argument, Neotropical bats are under several ecosystem contexts in which many extrinsic and intrinsic factors influence the ability to exploit food and better maximize energetic gains (Saldaña-Vázquez, 2014a). The consequences of the interactions between bats and their food resources are reflected in ecosystem functions associated to seed dispersal, pollination, arthropod suppression, vertebrate control, and the regulation of pathogens and diseases Kasso & Balakrishnan, 2013;Lacher et al., 2019;Castillo-Figueroa, 2020b).
Diet specialization: in frugivorous bats is related to intrinsic factors including foraging behavior, mouth morphology, bite force, digestive physiology (Saldaña-Vázquez, 2014a) and body size (Saldaña-Vásquez & Schondube, 2013). Likewise, dietary specialization has shown relationships with extrinsic factors such as plant phenology (Thies & Kalko, 2004), the physical characteristics of the fruit, the non-digestible material, secondary metabolites, nutrients, fruit energy (Saldaña-Vázquez, 2014a), latitude, altitude, and ecoregion (Saldaña-Vásquez & Schondube, 2013). This trait is also a key factor that determines the structure of the bat assemblage (Saldaña-Vázquez, 2014a) and are likely related to floristic diversity and supply of resources where the species are found (Fleming, 1986;Loayza et al., 2006). Considering intraspecific characteristics, dietary specialization can differ between males and females (Alviz & Pérez-Torres, 2020) and between reproductive stages (Bohlender et al., 2018). Interestingly, this trait is not related to habitat fragmentation Farneda et al., 2015), despite that this process isolates and reduces resources for many species (Pérez-Torres, 2004). Nonetheless, narrow dietary breath is related to extinction risk in insectivorous bats (Boyles & Storm, 2007). Wing morphology seems to be related to dietary specialization. For example, frugivorous bats with low aspect ratio tend to have a high dietary breadth due to slow and highly maneuverability flights that enable to forage in all forest habitats (Laurindo et al., 2020). Similarly, for insectivorous bats, individuals with more rounded wings have a more generalist diet, whereas individuals with more triangular and pointed wings present specialized diets (Magalhães de Oliveira et al., 2020).
Bite force: reflects the performance of the whole organism and can be linked to the fitness (Anderson et al., 2008;Davis et al., 2010), because of its influence on the spectrum of available food and niche partitioning (Aguirre et al., 2003). Bite force is strongly correlated to body mass (Aguirre et al., 2002), food size and food hardness (Aguirre et al., 2003), limiting dietary selection in bats. Importantly, bite force is also related to size gap angle and bite point (Dumont & Herrel, 2003;Santana, 2015), skull and mandibular shape (Nogueira et al., 2009), as well as temporalis muscle mass, temporalis fiber length and masseter muscle mass .

Spatial niche dimension
Bats can occur in almost all the environments of the Neotropics, ranging from sea level to montane forests and paramos across different ecosystems with a diversity of vegetational physiognomies, habitat complexities, and landscapes characteristics (including man-made environments and structures). Accordingly, bats have developed different strategies, morphological adaptations and aerodynamic features to use the horizontal and vertical space. In doing so, bats can move genetic material (e.g., pollen or seeds) between sites, promoting plant reproduction (Quesada et al., 2003). Bats can also track their preys thought the space and time, being important as agents for the suppression of agricultural pests (McCracken et al., 2012).
Foraging habitat: related to echolocation conditions and foraging strategy (Schnitzler & Kalko, 2001;Schnitzler et al., 2003;Denzinger & Schnitzler, 2013;Denzinger et al., 2016). In uncluttered habitats, insectiv-orous bats generally have echolocation characterized by calls with low frequency and narrow band, adapted to detect insects over long distances . High-frequency signals are emitted in edge areas that present a component used to detect flying insects and another component to detect oscillations . In these habitats are also bats that forage water surfaces (Denzinger & Schniltzler, 2013). In highly cluttered habitats, the waves emitted are short, broadband, multi-harmonic and often modulated . In these habitats, it is difficult to distinguish the echoes coming from the food (fruits, nectar, insects, small vertebrates) from the echoes generated by the surrounding vegetation (Denzinger & Schnitzler, 2013). To solve this, they can specialize in detecting insect flutter, by using passively foraging when using other senses (sit-and wait strategy), or employing actively foraging of conspicuous local resources, or even combining passive and active foraging which is common in phytophagous bats (frugivorous and nectarivorous) (Denzinger & Schnitzler, 2013). Foraging habitat is also related to wing and ear morphology, thereby in cluttered habitats, the predominant ecoforms are wide and short wings  with low wing loading and aspect ratio (Norberg & Rayner, 1987), longer length of the fifth digit in proportion to the length of the third digit and forearm length (Dietz et al., 2006;Castillo-Figueroa, 2020a), allowing greater maneuverability and agility (Norberg & Rayner, 1987). In these habitats, bats are likely to have large ears and slow flights for passive listening to detect prey, (Norberg & Rayner, 1987;Gardiner et al., 2011a;Håkansson et al., 2017). By contrast, in uncluttered spaces, the predominant ecoforms are long wings  with high wing loading and aspect ratio (Norberg & Rayner, 1987), and smaller length of the fifth digit in proportion to the length of the third digit and forearm length (Dietz et al., 2006;Castillo-Figueroa, 2020a), thus enabling fastspeed flights (Norberg & Rayner, 1987). To reduce drag and enhance aerodynamic performance, bats have small ears that enable fast flights over open habitats (Norberg & Rayner, 1987;Gardiner et al., 2011a;Håkansson et al., 2017). In forest edges, the wings are wide and somewhat short to avoid obstacles and dodges like trunks, branches, shrubs and foliage . Prior studies have shown that tolerance of insectivorous bats to urbanization is more likely to occur in species that forage in open and edge spaces as well as in bats with flexible roosting strategies (Jung & Threlfall, 2018).
Home range: related to connectivity of species between habitat patches (Bernard & Fenton, 2003;Loayza & Loiselle, 2008). The ability to flight long distances over open areas affects the processes of seed dispersal, pollination, and arthropod control, respectively (Galindo-González, 1998;Bernard & Fenton, 2003;Kalka & Kalko, 2006;Mello et al., 2008). In frugivorous bats, seed dispersal over long distances reduces intraspecific competition and seed predation (Janzen, 1970;Muscarella & Fleming, 2007), and promote seed deposition in suitable microsites enhancing germination (Heithaus & Fleming, 1978;Galindo-González, 1998;Mello et al., 2008). In the case of nectarivores, pollen movement over short and long distances, and trap-lining foraging resulting in outcrossing pollination, thus increasing gene flow in plants (Muchhala, 2006;Fleming et al., 2009), especially in fragmented landscapes (Quesada et al., 2003). For insectivorous bats, some gleaners display high efficiency in exploitation of preys even on small forest patches where habitat suitability is very low . To some extent, home range appear to be directly related to body size in fig-eating stenodermatines (Kalko et al., 1996).
Type of roost: related to skull morphology, body size, pelage patterns, social organization and group size (Kunz, 1982;Santana et al., 2011b;Garbino & Tavares, 2018). Diurnal roosts are a fundamental resource for bats because, on one hand, they spend at least half of their lives in these sites (Kunz, 1982) and, on the other hand, roost environments allow species coexistence and are linked to morphological or behavioral adaptations of bats (Voss et al., 2016). The remarkable variety of diurnal refugia used by bats include caves, rock outcrops, termite nests, foliage, crevices and shallow grottoes, fallen trees, tree barks and vine tangles (Kalko et al., 1999;Sampedro et al., 2008;Voss et al., 2016). This is important because bats play a key role in nutrient cycling by fertilizing sites that are used as roosts (Castillo-Figueroa, 2020b), thus increasing, for instance, nitrogen content in the trees and soils (Voigt et al., 2015). The potential effect of bats in the increase of nutrients by defecating within and nearby the roost tree (nutrient hot spot hypothesis), remains to be explored in Neotropical bats (Pierson, 1998;Duchamp et al., 2010;Castillo-Figueroa, 2020b). Roosting ecology is also phylogenetically informative, and along with other traits, roost selection may explain morphological variation in bats; for example, species that use leaf tents are smaller than bats that use other type of roosts, and pelage markings such as white stripes of stenodermatines are related to foliage roosting (Garbino & Tavares, 2018). In terms of community ecology, the availability and the type of roosts may play a major role in environmental filtering of bat species at a local or regional scale (Voss et al., 2016). For instance, tolerance to urbanization is more likely to occur in insectivorous bats with flexible roosting strategies and this could influence species composition in urban environments (Jung & Threlfall, 2018).

Echolocation dimension
Echolocation is, probably, one of the most important traits of bats to perceive their environment. Bats can produce calls of extraordinary high frequencies ranging from 20 kHz to 212 kHz (Thiagavel et al., 2017). These tonal signals, emitted mainly in the larynx, can return in echoes that enable the detection, localization, and characterization of reflecting targets, including preys and obstacles in the habitat (Schnitzler et al., 2003). This allows bats to orient themselves spatially, recognize biotopes, and find their food (Neuweiler, 2000;Denzinger & Schnitzer, 2013). Therefore, identifying echolocation signals is useful to study the interactions between bats and their environments (Neuweiler, 2000), especially for insectivores' guilds, which usually escape from traditional techniques such as mist-nets (Estrada-Villegas et al., 2010). Indeed, resource partitioning by echolocation is, arguably, a key factor to understand the structuring of bat communities (Houston et al., 2004).
Duration: related to the efficiency of prey-acquisition according to the habitats (Saldaña-Vázquez, 2014b). Shortduration signals may enable the detection of different prey sizes but is limited to short ranges by atmospheric attenuation, whereas long-duration signals reach distant preys but may limit availability of small preys (Houston et al., 2004). Accordingly, in uncluttered spaces bats can emit calls of longer duration, increasing the probability to record distant objects or preys, whereas in cluttered habitats the duration of the calls is shorter, enhancing the spatial orientation and prey detection in dense foliage (Jones & Holderied, 2007;Barboza-Marquez et al., 2013;Denzinger & Schnitzer, 2013). Pulse duration is related to body mass (Jones, 1999) and wing morphology (Norberg & Rayner, 1987); that is, larger bats have high wing loading and high aspect ratio reflected in faster flights, thus allowing to search for distant preys (Norberg & Rayner, 1987). In such circumstances, bats can increase pulse duration because echoes will return late from distant targets (Jones, 1999). Conversely, small and maneuverable bats with low wing loading and low aspect ratio are capable to detect a wide range of target sizes over nearby distances by emitting shorter pulses to avoid pulse-echo overlap (Jones, 1999;Houston et al., 2004).
Interval: similar to the duration, the interval of the call can be reduced while the bat is approaching the prey since its echolocation system does not allow to discern the overlap between the emitted signal and the echo that returns, either during or soon after call emission (Kalko, 1995;Jones & Holderied, 2007;Saldaña-Vázquez, 2014b). In open habitats, where no objects can mask the echoes of the prey, bats can generate calls of longer intervals, improving the chances of detecting preys that are from far distances (Barclay, 1985). In dense habitats, intervals are short to improve aerial navigation and insect-acquisition in complex habitats (Barboza-Marquez et al., 2013;Denzinger & Schnitzer, 2013).
Frequency: in echolocation, this is probably the most variable trait (Saldaña-Vázquez, 2014b). Broadly, low frequencies and long signals reduce the probability for detect small preys, whereas high frequencies in conjunction with short signals increase the capacity to detect large preys, but only in short distances (Barclay, 1985;Kalko, 1995;Houston et al., 2004;Jones & Holderied, 2007). This because at high-frequency calls there is a high atmospheric attenuation, making these signals only operational over short ranges (Jones, 1999;Houston et al., 2004). Bats with larger ears can detect low frequency calls and improve directionality (Obrist et al., 1993;Huihua et al., 2003). Frequency is also related to size (Jones, 1999) and wing morphology (Norberg & Rayner, 1987); smaller bats with low wing loading, low aspect ratio and rounded wingtips produce higher frequency signals to move in cluttered habitats, conversely, larger bats with high wing loading, high aspect ratio and pointed wingtips use lower frequency sounds to forage on uncluttered spaces (Jones, 1999;Thiagavel et al., 2017;Núñez et al., 2019;López-Cuamatzi et al., 2020).
Intensity: the variation of this trait is minute in comparison to the other call parameters (Saldaña-Vázquez, 2014b). Bats tend to emit intense tonal signals when hunting and can also adjust the sound level of search calls according to the distance of closest obstacles in their natural habitats (Surlykke & Kalko, 2008). High intensity is found in bats that forage on uncluttered spaces due to the attenuation of the sound through space (Jones & Holderied, 2007). However, low intensity calls, typical of sit-and wait foragers, can increase the efficiency in tracking preys since their tonal signs are not overlapping with the glints in insects' echoes (Holderied et al., 2010). Intensity is unrelated to body size, being that smaller species can emit both high and low intensity sounds (Saldaña-Vázquez, 2014b).
Harmonics: the use of harmonics enhance the resolution of preys and objects without modulation of the frequency (Holderied et al., 2010;Bates et al., 2011), allowing to exploit insect preys of different size (Jones & Holderied, 2007). Bats that forage close to objects usually modulate the frequency of the calls by adding harmonics (Denzinger & Schnitzer, 2013). Harmonics allow to discriminate clutter echoes from target echoes by sacrificing delay acuity to avoid masking effect (Bates et al., 2011).

Application of the framework
Historically, body size and wing morphology, e.g., body mass, wing loading and aspect ratio, have been employed to assess species performance and ecological correlations with several environmental characteristics (Cisneros et al., 2014;Farneda et al., 2015;Cisneros et al., 2015;Cisneros et al., 2016). In our review, we found 19 study cases using trait-based approach in Neotropical bats, and most of them have focused on response traits across human-dominated landscapes (Presley et al., 2017;Farneda et al., 2019;Ramírez-Mejía et al., 2020) and elevational gradients (Rodrigues Coelho et al., 2018;Mancini et al., 2019) as is shown in Table 2 and Fig. 2. It is clear enough that this framework is particularly useful for studying biodiversity patterns and species response across human-made landscapes in the Neotropics, as specific combinations of traits may predict the ecological structure of communities in urban or rural contexts (Jung & Threlfall, 2018;Ramírez-Mejía et al., 2020).
However, effect traits have been largely neglected. To our knowledge, only one paper directly related traits to seed dispersal process through ecological network approach (Laurindo et al., 2020). Nonetheless, some physiological and behavioral studies related to foraging ecology have started to shed light on trait relations to ecological processes (Baldwin & Whitehead, 2015;Ortega-García et al., 2020;Saldaña-Vázquez et al., 2020) as we mentioned above. We consider that these studies may be a point of reference for further investigations on effect traits in bats.   (Camargo & Oliveira, 2012;Stevens et al., 2013;Hurtado et al., 2015;Castillo-Figueroa, 2018b), morphological variations among individuals (Magalhães de Oliveira et al., 2020), and between populations (Louzada & Pessoa, 2013), the use of traits would allow to assess the effect of demography on ecological functions as has been done for other taxa (Violle et al., 2012;Siefert et al., 2015). It is important to evaluate whether intraspecific variations found in frugivorous bat diet between males and females (Alviz & Pérez-Torres, 2020) and between reproductive stages of the females (Bohlender et al., 2018) affect processes such as seed rain and seed germination. Also, in the case of insectivorous bats, inter-individual variation on habitat exploitation and dietary preferences (Magalhães de Oliveira et al., 2020) may have differential impacts on insect control. An obstacle to conduct these studies has been the lack of complete and bat-adjusted list of traits. Therefore, we  , 2021; v.61: e20216124 16/27 believe that this proposal is a benchmarking to establish a bat functional traits protocol and will help in addressing ecological and functional questions. We recommend providing separately intraspecific stats (mean, ranks, standard deviation) for each trait analyzed.
Correlation between traits: many traits presented here can be correlated with each other as we pointed out in the description of the traits. Among all the 50 traits, many of them are expected to vary allometrically, but testing the relations between them may provide a better basis for functional description of Neotropical bats instead of using only those more-common traits from the literature. Moreover, empirical evidence gathered in our revision (Table 2 and Fig. 2) indicates that the analysis of a large set of different and informative traits improves the understanding of species response to human-dominated landscapes, rather than the analysis of a single or few attributes (Martínez-Ferreira et al., 2020). Frequently, traits from wing morphology and body size are used (Pereira et al., 2019;Farneda et al., 2019;Ramírez-Mejía et al., 2020), but many others from complexes such as the tail, hindlimbs, and natural history are neglected oftentimes and can provide other type of information to an in-depth understanding of bat ecology under different environmental contexts. It should be noted that we are not suggesting using simultaneously all the 50 traits. Researchers should first decide the set of suitable traits to use according to the objectives and hypothesis of their own investigations by following the theoretical framework proposed in this paper. Collinearity between traits should be evaluated posteriorly in data analysis and then they can take their own decisions about the utility of each trait. Our objective with this proposal is to conceptualize an extensive set of traits that can be useful in ecological studies of Neotropical bats and show their applicability, but researchers should test the utility of each one of them.
Response-Effect framework: as aforementioned, in animal taxa the study of the link between traits and ecological processes is still in its infancy (Hortal et al., 2015). To better understand the nature of these relationships, empirical and experimental studies should be conducted. Given the multiple interactions in which Neotropical bats participate (e.g., frugivorous, nectarivory, insectivorous, and animalivory), their impact on ecological processes becomes more important in conditions where communities have low redundancy. Measuring simultaneously traits and ecosystem processes would contribute to disentangling the mechanisms of these interactions. It is important to document those traits that are potentially related to ecological processes (i.e., gut size, bite force, lingual papillae).
In contrast, response traits have been largely studied in environmental gradients as predictors of bat assemblages (Table 2), according to the trait-based environmental filtering (Keddy, 1992). Nevertheless, few studies have parsed out variations of response traits between land-use management types across agricultural areas. This can assess the sustainability of agricultural systems for bats, providing key information in conservation planning and decision-making . Identifying also the traits that make species more vulnerable to habitat modification is fundamental to design of effective conservation strategies that reduce local extinctions of Neotropical bats (Jung & Threlfall, 2018;Núñez et al., 2019).
Global datasets: this paper is the first step toward a functional trait-based approach in New World bats. However, conducting investigations by using the traits presented here, a plethora of ecological information can be gathered from many species in several study sites across the Neotropics. Some websites like Bat Eco-Interactions platform (Geiselman et al., 2015) have successfully facilitated datasets on bat diets and interactions, promoting scientific research on bat ecology and conservation (Castaño et al., 2018;Saldaña-Vázquez et al., 2019). Additionally, remarkable trait databases such as Atlantic Mammal Traits (Gonçalves et al., 2018), Elton Traits (Wilman et al., 2014) and PanTheria (Jones et al., 2009b) are key tools in functional investigations and are successful models of global databases from which new ones can be inspired to accomplish big and detailed bat trait databases in the Neotropics. In the same way, we want to encourage the accessibility of trait information based on this list to take advantage of big data for Neotropical studies. This trait list can also be extended to other geographical regions and bat faunas.
Outstanding functional questions: the use of bat traits can be useful in several trending topics in ecology and conservation. The most obvious but also crucial is the quantification of ecosystem processes and ecosystem services. Removal experiments have shown key findings related to biodiversity-function relationships in several groups, including the assessment of traits and their effects on ecosystem function . It is wellknown the prominent role of phyllostomid bats in numerous ecological processes, nevertheless, as far as we are aware of the literature, there are very few studies that relate directly bat traits to ecosystem processes. In addition, is important to know: -How are bat traits related to ecological processes and how this can vary across environmental gradients and human-modified landscapes? -How do bat traits match with the traits of plants or animals they interact with? -There is any difference between intraspecific categories (e.g., males, females) in terms of their functional contribution? And if so, is this reflected in their traits? -How can traits explain the efficiency of bats in ecological processes different from those they are primarily involved? (e.g., carnivorous and insectivorous as seed dispersers) -What are the trade-offs between bat traits when analyzing a specific ecological process?
On the other hand, as secondary forests are nowadays quite common in the Neotropics, understanding how this forest type affect animal species becomes critical (Chua & Potts, 2018). It is important to generate indicators that effectively assess ecological resilience as well as ecological resistance, in a way that complement taxonomic studies with functional trait-based dimension using a multi-scale and multi-coverage approach (Martínez-Ferreira et al., 2020). In line with this argument, long-term studies at the Biological Dynamic of Forest Fragment Project (BDFFP) have shown the applicability of functional approach to ecological succession (Farneda et al., 2018). Thus, including the functional approach can contribute to practices of restoration ecology. The impact of agricultural systems on biodiversity and ecosystem functioning is one of the most important conservation concerns in the Neotropics (González-Maya et al., 2017). Due to this, considering the type of management is urgent to better select agriculture practices that minimize environmental impacts and improve sustainability of productive systems. Some questions rise about this regard: -Can traits be a useful tool in rapid assessment of human impacts? Can they become bioindicators? -Which bat traits are good predictors of sustainable ecological and conservation practices? -To what extent a trait can vary in the same species across environmental gradients? What are the biotic and abiotic drivers?

CONCLUSIONS
In this paper, we provided an extensive guide of biological traits for studying Neotropical bats with their respective description of measurement, definitions, attributes, trait obtention and ecological information. Experimental studies are needed to test if a trait is effectively functional or not, considering that all functional traits are biological traits but not all biological traits are functional (Mlambo, 2014). This is the first contribution to achieve a bat functional traits protocol that supports the legitimate ecological reasons of each trait by using solid evidence and not just by theoretical deductions or surmises. It is essential to identify an adequate set of traits to assess bat ecological roles in ecosystems, for which is necessary to expand the base knowledge in open access databases. Also, it is important to test for correlations between traits. Finally, we encourage to use response traits in human-made landscapes, agricultural managements, and environmental gradients. Accounting this source of information, a better understanding of ecosystem functions and anthropogenic disruptions in the Neotropics can be achieved through a trait-based approach of bats.

ACKNOWLEDGMENTS
We are in debt to the reviewers and the editor for insightful comments that substantially improved the manuscript. We are also thankful to Erin Stukenholtz for the revision of the English style.

AUTHORS' CONTRUBUTIONS
D.C.-F.: conceived the idea, contributed to the theoretical and conceptual framework, wrote the paper, prepared figures and tables, reviewed drafts of the paper. J.P.-T.: wrote the paper, contributed to the theoretical and conceptual framework, reviewed drafts of the paper. The authors declare no conflict of interests.