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

distinct species assemblages due to differences in environmental conditions [19]. This informa- tion is crucial for understanding the distribution patterns of vertebrates and identifying factors that influence species composition in karst and volcanic caves across different elevations [20]. We predicted that more abundant species such birds and mammals would show a higher β- diversity between cave types, between karst and volcanic caves at different altitudinal zones, and between environments in both cave types, whereas less abundant species such as reptiles and amphibians would have a lower β-diversity. We also predicted that the difference in verte- brate β-diversity would be primarily due to species richness rather than to species replacement [21,22]. Finally, caves in closer proximity to each other would be expected to have more similar species. Materials and methods Ethics statement Our study was non-invasive and adhered to the legal requirements of Mexican law (NOM- 059-SEMARNAT-2010). Vertebrates were sampled during field expeditions under the field permits SGPA/DGVS/10344/21 provided by the Secretarı´a de Medio Ambiente y Recursos Naturales of Mexico (SEMARNAT). Study area The study area is located in the region of central Veracruz, at the intersection of the Sierra Madre Oriental and the Trans-Mexican volcanic belt [23]. The area exhibits high topographic heterogeneity with an elevation gradient (300 to 2,400 m a.s.l.) with two climatic areas: from warm at the lower part, to temperate at mountain mid-elevations, to cold at the higher regions

[24]. The orographic and climatic differences within the area allow the presence of six vegeta- tion types [24] from the dry environments at elevated temperatures (tropical semideciduous forest and tropical oak forest), to the humid temperate areas (humid montane forest, pine-oak forest), to the cold and dry areas at the higher parts of the gradient (pine and fir forests) [23]. In addition, from a biogeographic perspective, this area is located at the confluence between the Nearctic and Neotropical regions, and it thus has a significant biogeographic value and an even greater biodiversity value [23,24]. For this study, 12 caves of karst origin and 4 of volcanic origin were selected, comprising an area from the northeast of the Nauhcampate´petl volcano (19˚29031@N, 97˚09000@O) to the southeast of the Citlalte´petl volcano (19˚020N, 97˚160O). Modified cave topographies were used for each cave to carry out exploratory visits and adjust the methodology for vertebrate sampling. According to altitudinal zonation, the elevation gradient was divided into four altitudinal zones: Z1 (300–599 m a.s.l), Z2 (600–899 m a.s.l), Z3 (900–1199 m a.s.l.), and Z4 (2100–2400 m a.s.l.). There was a mean difference of 200 m between the altitudinal zones. Four karst caves were located at Z1: Maguey (MY), Atoyac (AY), nacimiento de 7 aguas (NC), and ojo de agua grande (OJ). Eight karst caves were located at Z2: Pinoltepec (PN), la Reja (RE), el Aire (AI), la Palma (PL), el boquero´n de Capulapa (BQ), el so´tano de Tepeapulco (TP), and la cueva Pin-

tada (PI), as well as the volcanic cave de Tenampa (TN). Two caves were located at Z3: el so´tano ka´rstico de los Maltos (MT), of karst origin, and the volcanic cave of la Garganta (GT). Finally, the caves de la Escalera (ES) and del Volcancillo (VC), both of volcanic origin, were located at Z4 (Table 1). The cave at the highest altitude (cueva del Volcancillo) was located at 2392 m a.s.l., and the cave at the lowest altitude (cueva del Maguey) was located at 339 m a.s.l. The average distance between all caves was 43.4 km, between karst caves it was 33.3 km, and between volcanic caves it was 14.3 km. PLOS ONE Vertebrates in caves of Neotropical hotspot PLOS ONE | https://doi.org/10.1371/journal.pone.0306105 August 9, 2024 3 / 19