Energy and speleogenesis: Key determinants of terrestrial species richness in caves.

Alberto Jiménez‐Valverde,Ana Sofia P S Reboleira,Policarp Garay,Alberto Sendra

doi:10.1002/ece3.3558

Abstract

The aim of this study was to unravel the relative role played by speleogenesis (i.e., the process in which a cave is formed), landscape‐scale variables, and geophysical factors in the determination of species richness in caves. Biological inventories from 21 caves located in the southeastern Iberian Peninsula along with partial least square (PLS) regression analysis were used to assess the relative importance of the different explanatory variables. The caves were grouped according to the similarity in their species composition; the effect that spatial distance could have on similarity was also studied using correlation between matrices. The energy and speleogenesis of caves accounted for 44.3% of the variation in species richness. The trophic level of each cave was the most significant factor in PLS regression analysis, and epigenic caves (i.e., those formed by the action of percolating water) had significantly more species than hypogenic ones (i.e., those formed by the action of upward flows in confined aquifers). Dissimilarity among the caves was very high (multiple‐site βsim = 0.92). Two main groups of caves were revealed through the cluster analysis, one formed by the western caves and the other by the eastern ones. The significant—but low—correlation found between faunistic dissimilarity and geographical distance (r = .16) disappeared once the caves were split into the two groups. The extreme beta‐diversity suggests a very low connection among the caves and/or a very low dispersal capacity of the species. In the region under study, two main factors are intimately related to the richness of terrestrial subterranean species in caves: the amount of organic material (trophic level) and the formation process (genesis). This is the first time that the history of a cave genesis has been quantitatively considered to assess its importance in explaining richness patterns in comparison with other factors more widely recognized.

Highlights

The subterranean domain encompasses numerous habitats, which, despite being largely unexplored, are more dominant across the entire earth than surface habitats (Culver & Pipan, 2009)
The trophic level of each cave was the most significant factor in partial least square (PLS) regression analysis, and epigenic caves had significantly more species than hypogenic ones
The subterranean fauna of this region is composed by a flourishing variety of troglophile and troglobiont species: of the 128 taxa, 33 are troglobionts, which clearly illustrates the relevance of this geographical area in the Iberian

Summary

| INTRODUCTION

The subterranean domain encompasses numerous habitats, which, despite being largely unexplored, are more dominant across the entire earth than surface habitats (Culver & Pipan, 2009). Caves (at least partially) could be considered ecotones that connect the surface and deep subterranean environments (Prous, Ferreira, & Martins, 2004; Moseley, 2009) Surface variables such as temperature and precipitation have been identified as determinants of the presence of subterranean fauna probably due to their direct relationship with surface productivity (Christman et al, 2016). Landscape-scale variables related to land use have been pointed out as significant determinants in subterranean biodiversity patterns as they condition the influx of nutrients that seep into the underground (Pellegrini et al, 2016) Another important factor that needs to be kept in mind in order to understand biodiversity patterns in caves is their speleogenesis history (Sendra et al, 2014). The caves were grouped according to their species composition similarity, and the effect that spatial distance could have on similarity was studied using correlation between matrices

| MATERIAL AND METHODS

Findings

| DISCUSSION