Cave features, seasonality and subterranean distribution of non-obligate cave dwellers.

Enrico Lunghi,Gentile Francesco Ficetola,Raoul Manenti

doi:10.7717/peerj.3169

Abstract

Seasonality impacts species distributions through changes of the environmental conditions that affect the presence of individuals at a given place. Although the dynamics of cave microclimates are well known, only a few studies have evaluated the effects of such dynamics on non-strictly cave species. Here we assessed if species exploiting subterranean environments show changes in habitat occupation related to seasonal variation of cave microclimates. We surveyed 16 caves in central Italy every month for one year. Caves were subdivided into longitudinal sectors of three meters. In each sector we measured cave morphology and microclimatic features, assessed the occurrence of eight non-troglobitic taxa (orthopterans, spiders, gastropods and amphibians), and related species distribution to environmental features and sampling periods. The occurrence of most species was related to both cave morphology and microclimatic features. The survey month was the major factor determining the presence of species in cave sectors, indicating that cave-dwelling taxa show strong seasonality in activity and distribution. For multiple species, we detected interactions between sampling period and microclimatic features, suggesting that species may associate with different microhabitats throughout the year. The richest communities were found in sites with specific microclimates (i.e., high humidity, warm temperature and low light) but seasonality for species richness was strong as well, stressing the complexity of interactions between outdoor and subterranean environments.

Highlights

Seasonality plays a major role in species distributions by altering the presence of individuals in a given place at a stated time (Murray, Webster & Bump, 2013)
Analysis with mixed models We identified the relationship between species and cave features using generalized linear mixed models (GLMMs) assuming binomial error
The species surveyed in our study belong to two different types of nonstrictly cave dwelling organisms: usually epigean species normally considered to exploit caves during certain part of the year or during part of the day, and species resident close to cave entrances (e.g., Meta and Metellina spiders)

Summary

Introduction

Seasonality plays a major role in species distributions by altering the presence of individuals in a given place at a stated time (Murray, Webster & Bump, 2013). Subterranean environments, from small crevices to deeper holes and caves, are sometimes used as shelters to avoid unfavorable outdoor conditions (Biswas, 2014; Lunghi, Manenti & Ficetola, 2014; Manenti, 2014), as these environments possess specific microclimatic features which differ from those of surface habitats (Romero, 2009) Even in such environments the microclimate may not be stable, and fluctuations of primary microclimatic features (temperature, humidity, illuminance) contribute to creating areas characterized by heterogeneous conditions, especially in zones not far from the surface (Campbell Grant, Lowe & Fagan, 2007; Culver & White, 2005; Romero, 2012). Only a few studies have evaluated the effect of cave microclimatic dynamics on non-strictly cave species (Camp et al, 2014; Lunghi, Manenti & Ficetola, 2015; Mammola, Piano & Isaia, 2016), leaving incomplete knowledge about species-habitat associations across seasons

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Discussion

Conclusion