Microhabitat analyses support relationships between niche breadth and range size when spatial autocorrelation is strong

Abstract

Multiple evidence of positive relationships between nice breadth and range size (NB-RS) suggested that this can be a general ecological pattern. However, correlations between niche breadth and range size can emerge as a by-product of strong spatial structure of environmental variables. This can be problematic because niche breadth is often assessed using broad-scale macroclimatic variables, which suffer heavy spatial autocorrelation. Microhabitat measurements provide accurate information on species tolerance, and show limited autocorrelation. The aim of this study was to combine macroclimate and microhabitat data to assess NB-RS relationships in European plethodontid salamanders (Hydromantes), and to test whether microhabitat variables with weak autocorrelation can provide less biased NB-RS estimates across species. To measure macroclimatic niche, we gathered comprehensive information on the distribution of all Hydromantes species, and combined them with broad-scale climatic layers. To measure microhabitat, we recorded salamander occurrence across > 350 caves and measured microhabitat features influencing their distribution: humidity, temperature and light. We assessed NB-RS relationships through phylogenetic regression; spatial null-models were used to test whether the observed relationships are a by-product of autocorrelation. We observed positive relationships between niche breadth and range size at both the macro-and microhabitat scale. At the macroclimatic scale, strong autocorrelation heavily inflated the possibility to observe positive NB-RS. Spatial autocorrelation was weaker for microhabitat variables. At the microhabitat level, the observed NB-RS was not a by-product of spatial structure of variables. Our study shows that heavy autocorrelation of variables artificially increases the possibility to detect positive relationships between bioclimatic niche and range size, while fine-scale data of microhabitat provide more direct measure of conditions selected by ectotherms, and enable less biased measures of niche breadth. Combining analyses performed at multiple scales and datasets with different spatial structure provides more complete niche information and effectively tests the generality of niche breadth-range size relationships.

Updating salamander datasets with phenotypic and stomach content information for two mainland Speleomantes

“…These features force Speleomantes to select only specific microclimatic conditions: they need high moisture and relatively cold temperatures to survive 2 . Therefore, Speleomantes often inhabit subterranean environments 3 , 4 , where their preferred microclimatic conditions are realized 5 . Nonetheless, subterranean environments also may be chosen by Speleomantes because predator pressure is lower if compared to epigean ones 6 , 7 .…”

Photographic database of the European cave salamanders, genus Hydromantes

“…We also considered a population introduced into the French Pyrenees, which probably includes individuals of different Hydromantes species, if not hybrids; 48 there, we photographed 47 individuals. The surveyed sites included forest, natural caves, mines and artificial springs (see Table 1); in all of them, the presence of Hydromantes was previously assessed 4,48,49 . Each site was surveyed once between August and October 2018 in order to avoid repeated photos on the same individual.…”

Drivers of change in the realised climatic niche of terrestrial mammals

“…A species' niche – the set of environmental conditions in which the species can persist (Peterson et al 2011) – represents the essential ecological characteristics of a species, and niche breadth – the ‘distance through' a niche along particular lines in the niche space (Colwell and Futuyma 1971) – is an important trait that allows adaptation to environmental change (Thuiller et al 2005, Pacifici et al 2015, Ficetola et al 2020). Niche breadth is considered a key correlate of species sensitivity to habitat change (Swihart et al 2003) and climate change (Thuiller et al 2005, Chown et al 2010).…”