Héctor T. Arita

Flight and echlocation in the ecology and evolution of bats

Flight and echolocation are key characters distinguishing most bats from other mammals.The number of ecolological niches for bats is limited by the concurent constraints of the mammalian physiology and reproductive system and the high cost of flight and echolocation. The recent discovery of a biomechanical coupling between echolocation and flight highlights the need to incorporate both chracters as parts of a single adaptive complex in future research on the ecology and evolution of bats.

Male dominance, paternity, and relatedness in the Jamaican fruit‐eating bat (Artibeus jamaicensis)

We analysed variation at 14 nuclear microsatellite loci to assess the genetic structure, relatedness, and paternity of polygynous Jamaican fruit‐eating bats. A total of 84 adults captured in two caves exhibited little genetic differentiation between caves (FST = 0.008). Average relatedness among adult females in 10 harem groups was very low (R = 0.014 ± 0.011), providing no evidence of harem structure. Dominant and subordinate males shared paternity in large groups, while dominant and satellite males shared paternity in smaller groups. However, our results suggest that male rank influences paternity. Dominant males fathered 69% of 40 offspring, followed by satellite (22%) and subordinate males (9%). Overall adult male bats are not closely related, however, in large harem groups we found that subordinate and dominant males exhibited relatedness values consistent with a father‐offspring relationship. Because dominant and subordinate males also sired all the pups in large groups, we propose that their association provides inclusive fitness to them.

Conservation Biology of the Cave Bats of Mexico

The available information on use of caves by Mexican bats was examined to determine the effectiveness of a conservation strategy based on diversity. Diversity was estimated by species richness, or the number of bat species present in a cave. Sixty of the 134 Mexican species of bats regularly roost in caves. Seventeen of these species tend to roost in caves with low species richness (segregationists), 14 tend to roost in caves with high species richness (integrationists), and 29 show no tendency in terms of the species richness of the caves (indifferent). Of the 215 caves included in this study, 80% support few (three or less) species, whereas only 10% harbor six or more species. In general, species that share caves with many species form small or medium-sized colonies, and there is no positive correlation between species richness and total number of individuals in the caves. Few of the fragile and vulnerable species of Mexican bats roost in caves with high species richness or with large populations. A conservation plan based solely on diversity is not adequate for the protection of cave bats in Mexico.

Neotropical-Nearctic Limits in Middle America as Determined by Distributions of Bats

The Neotropical-Nearctic transition in Middle America was analyzed using distributional patterns of bats. The 169 non-insular bat species of Middle America were classified into four categories: shared with North and South America, shared only with North America, shared only with South America, and endemic. A theoretical biogeographic index was developed and compared with null frequency distributions based on the multivariate hypergeometric model. A total of 1,054 half-by-half-degree quadrats were used to determine the biogeographic zone (Nearctic, Neotropical, or transitional) of sites in Mexico and Central America. The null distribution allowed statistical assessment of each quadrat, permitting the quantitative determination of the limit between the two biogeographic regions. Results showed a pattern that coincided with previous studies in the position of the southern limits for the Nearctic region but differed in locations of Neotropical areas, and in the extent of the transitional zone, which was much broader in the present study.

The tropics: cradle, museum or casino? A dynamic null model for latitudinal gradients of species diversity.

Several ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid-domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one- or two-dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients.

Structure and Social Dynamics of Harem Groups in Artibeus jamaicensis (Chiroptera: Phyllostomidae)

The Jamaican fruit-eating bat ( Artibeus jamaicensis ) is one of the most common Neotropical chiropterans, but comparatively little is known about structure and dynamics of its social groups. In two caves of the Yucatan Peninsula, Mexico, we found Jamaican fruiteating bats forming harem groups, consisting of 4–18 females and 1–2 males, inside solution cavities that develop on the ceiling of caves. Other individuals roosted solitarily in the same caves, but outside solution cavities. We identified three types of males: dominants (one in each harem group), subordinates (present only in the largest harems), and satellites (not associated with a harem). Dominants were larger and heavier than males of the other two categories. During the 2-year study, harem groups always roosted in the same cavity and presented a high degree of stability, with few changes in composition. Satellite males and solitary females, in contrast, shifted roosting sites frequently and never formed cohesive groups. Adult females performed more movements from and to harem groups than males, and those movements were less frequent during the breeding season. Harems of the Jamaican fruit-eating bat presented subordinate males in large groups and differ from those of other phyllostomids in the lower degree of cohesiveness shown by females.

Species Diversity and Distribution in Presence-Absence Matrices: Mathematical Relationships and Biological Implications

The diversity of sites and the distribution of species are fundamental pieces in the analysis of biogeographic and macroecological questions. A link between these two variables is the correlation between the species diversity of sites and the mean range size of species occurring there. Alternatively, one could correlate the range sizes of species and the mean species diversity within those ranges. Here we show that both approaches are mirror images of the same patterns, reflecting fundamental mathematical and biological relationships. We develop a theory and analyze data for North American mammals to interpret range‐diversity plots in which the species diversity of sites and the geographic range of species can be depicted simultaneously. We show that such plots contain much more information than traditional correlative approaches do, and we demonstrate that the positions of points in the plots are determined to a large extent by the average, minimum, and maximum values of range and diversity but that the dispersion of points depends on the association among species and the similitude among sites. These generalizations can be applied to biogeographic studies of diversity and distribution and in the identification of hotspots of diversity and endemism.

THE CONSERVATION OF CAVE-ROOSTING BATS IN YUCATAN, MEXICO

Seventeen species of bats roost in the caves of Yucatan, Mexico. To identify those caves that would be important in a conservation plan for bats, 36 Yucatan caves were surveyed during a one-year study. Three criteria were considered for the identification of critical sites: a high species richness, an unusually large multispecies population size, and the presence of species of special concern (rare, threatened, or endangered). Most sites were small caves that supported only few (less than five) species, whereas a few caves supported very rich assemblages of more than nine species. The distribution of bat species among caves was highly nested, with smaller assemblages being subsets of larger communities. This distribution produced a pattern in which rare species tend to be present only in those caves with the highest species richness, whereas common species are present in all kinds of caves. A classification of the caves based on the presence or absence of bat species produced six groups. One of such groups included the largest caves, which also harboured the most diverse assemblages, contained the largest populations, and supported several species of concern. Many of these large caves are targetted for development as tourist sites, so a conservation strategy for these sites should take into consideration the social and economic pressures associated with such plans.

Morphological assembly mechanisms in Neotropical bat assemblages and ensembles within a landscape

Empirical studies on bat assemblages have shown that richness is not appreciably influenced by local processes such as ecological interactions. However, most of these studies have been done in large areas that include high heterogeneity, and they analyse all bat species within such areas, and thus they may be not reflecting local but supra-community conditions. We followed an ecomorphological approach to assess how bat assemblages of species from the families Phyllostomidae and Mormoopidae, and ensembles of frugivorous bats, are assembled in local habitats within a single landscape. We measured the volume of the space defined by wing morphology and quantified the average distance between species within such a volume. Then, we related these measures to local richness. Such relationships were contrasted against relationships with random assemblages to test for statistical differences. At the ensemble level of organization, we found that the frugivorous bat morphological assembly mechanism is different from random patterns, and it corresponds to the volume-increasing model. On the other hand, bat assembly mechanisms may be ubiquitous at the assemblage level, because groups of species coexisting in a local habitat and delimited only by phylogeny include more than one ecological group with no potential to interact. Assembling processes are crucial to an understanding of species diversity in local communities, and ecomorphological analyses are very promising tools that may help in their study.

Conservation Biology of Nectar-Feeding Bats in Mexico

Nectar-feeding bats (tribe Glossophagini) are an important component of the rich chiropteran fauna of Mexico. Because of biological features associated with their specialized diet, nectar-feeding bats might be more vulnerable to extinction than other bats. Twelve species of glossophagines occur in Mexico. Most have restricted distributions, with two species endemic to the country and two species endemic to Middle America. Compared with other neotropical bats, nectar-feeding species are smaller in body mass and have smaller distributions but have similar local densities. In Mexico, most nectar-feeding bats are associated with tropical and subtropical dry areas (tropical deciduous forests and scrubland). Highest species richness occurs along the warm and dry Pacific versant, including the Balsas Basin. Caves are the main roosts of four of the Mexican nectar-feeding bats, and another six species use caves as alternate roosts. Critical faunas analyses performed using three criteria (species richness, presence of rare species, and phylogenetic value) indicated different sets of critical areas for conservation, nonetheless all criteria identified an area of the Pacific versant and lowlands of southeastern Mexico as priority areas for conservation efforts.