Abstract
Caves are not colonised by all taxa present in the surface species pool, due to absence of light and the tendency to food limitation when compared to surface communities. Under strong species sorting during colonisation and later by the restrictive environmental filter, traits that are not adaptive in subterranean habitats may be filtered out. We tested whether cave communities were assembled by the restrictive regime propitiated by permanent darkness or by competitive exclusion due to resource scarcity. When compared to surface communities, the restrictive subterranean regime would lead to lower functional diversity and phenotypic clustering inside the caves, and the opposite should be expected in the case of competitive exclusion. Using isopods (Oniscidea) as model taxa, we measured several niche descriptors of taxa from surface and cave habitats, used a multivariate measure of functional diversity, and compared their widths. We found phenotypic overdispersion and higher functional diversity in cave taxa when compared to surface taxa. On the one hand, the dry climate outside of caves hampered the survival of several taxa and their ecological strategies, not viable under severe desiccation risk, culminating in the clustering of functional traits. In contrast, this restriction does not occur inside of caves, where isopods find favourable conditions under lower predation pressures and more amenable environmental parameters that allow occupation and subsequent diversification. Our results showed that, at least for some taxa, caves may not be such a harsh environment as previously thought. The high functional diversity we found inside caves adds an additional reason for the conservation of these sensitive environments.
Highlights
All cave communities throughout the world have a remarkable feature in common: the complete darkness in deeper zones, which leads to the absence of photosynthetic producers and to the dependence on surface food intake [1]
Using oniscidean isopods as a model taxon, we aimed to test whether cave communities were assembled by the restrictive regime caused by permanent darkness, leading to phenotypic clustering and lower functional diversity when compared to surface communities, or by limiting similarity caused by competitive exclusion due to resource scarcity, leading to phenotypic overdispersion and higher functional diversity when compared to surface communities
Our ecological conclusions remain valid, because functional diversity is independent of species identity [16]
Summary
All cave communities throughout the world have a remarkable feature in common: the complete darkness in deeper zones, which leads to the absence of photosynthetic producers and to the dependence on surface food intake [1]. PLOS ONE | DOI:10.1371/journal.pone.0151958 March 22, 2016
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