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

Effective number of species in caves at different altitudinal zones Many species of vertebrates were observed in karst and volcanic caves across altitudinal zones. Our findings indicate that the species diversity of almost all vertebrate classes was higher in karst caves at mid-altitudes (600–899 m a.s.l.). According to altitudinal zonation, terrestrial diversity is highest at mid-altitudes [49]. Mid-altitudes are characterized by a greater variety of forests (i.e, cloud forest, oak forest, and dry forest), which decreases at higher and lower alti- tudes [49]. In fact, there is a variety of habitats in this region [24]. This variety of forests that composes the altitudinal landscape and surrounds caves [50] can serve as habitats for verte- brates and promote local diversity [51,52]. The effective number of species in karst caves at mid-altitudes indicated a higher species richness (q0) of birds and mammals, whereas reptiles were the class with the lowest species richness. In volcanic caves, all vertebrate classes showed high species evenness due to more constant effective species numbers for all orders of q (0,1,2,3). The communities with the lowest richness were those at the highest (Z4) and lowest (Z1) altitudinal zones. Caves located at mid- altitudes may offer more stable environmental conditions that promote the presence of verte- brate species [53] such as birds and mammals, as we found in our study. In addition to envi- ronmental conditions, caves located at mid-altitudes may offer habitat resources such as

nesting sites for bird communities and shelter for mammals, particularly bats, as has been doc- umented in other cave systems along altitudinal gradients [54]. Effective number of species in cave environments Vertebrate diversity in caves is used as an indicator of habitat quality for troglobitic, trogloxenic, and troglophilic vertebrates [1], and the distribution of vertebrates inside karst caves seems to depend on several factors such as the size and distribution of entrance spaces, organism mobility, and food dis- tribution [55]. Our results indicate that, regardless of the environment occupied by vertebrates, all groups show the same pattern of higher species richness (q0) and a few common (q1), dominant (q2), and very dominant species (q3). Our findings indicate that birds and reptiles in the euphotic environment of karst and volcanic caves, mammals in the aphotic environment of both cave types, and amphibians in the aphotic environment of karst caves showed a relatively similar pattern of effective number of species. Mammals showed a similar pattern in the aphotic environment of karst and volcanic caves due to the presence of bats such as Artibeus jamaicensis (Chiroptera:Phyllostomi- dae), Balantiopteryx io (Chiroptera:Emballonuridae), Myotis keaysi (Chiroptera:Vespertilionidae), or Corynorhinus mexicanus (Chiroptera:Vespertilionidae). The disphotic environments of karst and volcanic caves showed the lowest number of species for all orders of q (0,1,2,3). Most mammals were recorded in the aphotic environment, birds and reptiles in the eupho-

tic and disphotic environments, and amphibians in the disphotic and aphotic environments. The euphotic environment is a transition zone between surface and subsurface environments, where there is a distinct gradient of several abiotic factors, especially light, temperature, and humidity [56]. These conditions may be important for vertebrates such as birds and reptiles, which presented the highest biodiversity and abundance in the euphotic environment. We found that the innermost environment in the caves (aphotic environment) was also attractive to vertebrates such as bats and amphibian species. This indicates that the high richness of these species responds to different resources in the aphotic environment such as shelter, microcli- matic conditions, food, and water [57,58]. Beta diversity between cave origins, altitudinal zones, and cave environments We hypothesized that bird and mammal species would show a higher β-diversity between karst and volcanic caves along the altitudinal zones, while reptile and amphibian species would PLOS ONE Vertebrates in caves of Neotropical hotspot PLOS ONE | https://doi.org/10.1371/journal.pone.0306105 August 9, 2024 13 / 19