Mountain caves of the central region of Veracruz: A vertebrate biodiversity reservoir in a Neotropical hotspot

show a lower β-diversity. We also predicted that the difference in vertebrate β-diversity between environments would be primarily due to species richness rather than to species replacement. Our results met these expectations, confirming thus that bird and mammal spe- cies composition is similar among caves at different altitudinal zones [59]. Contrary to what is reported in the literature [58], vertebrate beta diversity is high and is mainly due to species richness rather than species replacement. In this sense, on average, up to 50% of bird and mammal species are shared between caves. Numerous studies suggest that ver- tebrate species in caves are unique, which increases β-diversity in caves at a landscape scale [60]. However, we know that small disturbances in habitats surrounding caves can increase the number of vertebrate species, particularly those of birds and mammals that occupy karst and volcanic caves and their environments [61]. These vertebrate species are affected by the conditions imposed by disturbances in the external habitat and, hence, a proportion of these vertebrate species find refuge in caves [62]. Therefore, our results suggest that disturbances in external habitats surrounding caves can reduce beta diversity, increasing β-richness and decreasing β-replacement, which leads to a reduction in regional vertebrate β-diversity in caves. Patterns of β-diversity in caves along an altitudinal gradient are the reflection of the discon- tinuous nature of cave ecosystems [63], and the diversity of vertebrates within the caves can be

related to the distribution and displacement capacity of vertebrate species [64]. The high β- diversity values observed for all vertebrate classes confirm the presence of birds, mammals, reptiles, and amphibians in different karst and volcanic caves along the altitudinal gradient studied. These results suggest that an important proportion of similar bird and mammal spe- cies use caves as habitats along this altitudinal gradient. Birds and mammals have a high dis- placement capacity, which can increase the chance of occupying caves as habitats at different altitudinal zones, unlike reptiles and amphibians [64], which may have wide distribution ranges but have a lower cursorial capacity, and therefore only a few species of reptiles and amphibians are able to inhabit caves [47]. The vertebrate diversity observed in karst and volca- nic caves contributes to maintaining the regional patterns of vertebrate β-diversity in the caves along this altitudinal gradient, and all vertebrate classes that inhabit caves play an important role in the local composition of cave biodiversity. Estimations of β-diversity inside caves are essential for assessing the degree of species com- position between different cave environments [65,66]. In both cave types, each chamber or passage may have unique cave characteristics [1] and environmental conditions (humidity and temperature [55]) that favor the presence of different species in different cave environments. The β-diversity observed in the different environments of karst and volcanic caves indicates

that species replacement and richness contributed in a similar proportion to the β-diversity of all vertebrate classes. The high β-diversity values observed for all vertebrate classes in the three environments of karst and volcanic caves confirms the higher richness of trogloxene birds and reptiles in the euphotic environment and of troglobiont mammals and amphibians in the aphotic environment. Implications for conservation Biodiversity in tropical subterranean habitats varies from place to place [67,68] and, as we found in this study, species turnover is high in karst and volcanic caves [12]. As expected, there was a relationship between species richness and distance between caves. For example, 37% of the total number of species was similar between karst and volcanic caves in close prox- imity to each other. These results are relevant because they also show that 63% of species are unique to each cave. Thus, regardless of the relative proximity between caves, each one PLOS ONE Vertebrates in caves of Neotropical hotspot PLOS ONE | https://doi.org/10.1371/journal.pone.0306105 August 9, 2024 14 / 19