Where do nivicolous myxomycetes occur? – Modeling the potential worldwide distribution of Physarum albescens
2021
To identify potentially suitable areas for the mostly alpine ecological guild of nivicolous (snowbank) myxomycetes, the worldwide distribution of a distinct morphospecies, Physarum albescens, was modelled with a correlative spatial approach using the software MaxEnt from 537 unique occurrence points. Three models were developed, first with only the 19 bioclimatic variables plus elevation from the WorldClim database, second with regularization to correct for pseudo-absence, and third with additional categorical environmental layer on snow cover. All three models showed high mean AUC (area under the curve) values (>0.970). Output maps were comparable, with the third model perhaps the most realistic. For this model, snow cover, precipitation of the coldest quarter (of the year), and elevation predicted best the distribution of Ph. albescens. Elevation alone is a good predictor only in some regions, since (i) elevation of the occurrence points decreases with increasing latitude, and (ii) elevation wrongly predicts the species’ occurrence in arid mountain ranges. The model showed mountains in humid climates with highest incidence, which confirmed field studies: a long-lasting snow cover fluctuating with comparatively mild summers is the decisive factor. As such, the model can serve as a predictive map where fructifications of nivicolous myxomycetes can be expected. Limitations of the model are discussed: cryptic speciation within a morphospecies, including the evolution of reproductively isolated units which may lead to local adaptation and niche differentiation, and wider ranges for myxamoebal populations.
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