Abstract
BackgroundClimate is often considered as a key ecological factor limiting the capability of expansion of most species and the extent of suitable habitats. In this contribution, we implement Species Distribution Models (SDMs) to study two parapatric amphibians, Lissotriton vulgaris meridionalis and L. italicus, investigating if and how climate has influenced their present and past (Last Glacial Maximum and Holocene) distributions. A database of 901 GPS presence records was generated for the two newts. SDMs were built through Boosted Regression Trees and Maxent, using the Worldclim bioclimatic variables as predictors.ResultsPrecipitation-linked variables and the temperature annual range strongly influence the current occurrence patterns of the two Lissotriton species analyzed. The two newts show opposite responses to the most contributing variables, such as BIO7 (temperature annual range), BIO12 (annual precipitation), BIO17 (precipitation of the driest quarter) and BIO19 (precipitation of the coldest quarter). The hypothesis of climate influencing the distributions of these species is also supported by the fact that the co-occurrences within the sympatric area fall in localities characterized by intermediate values of these predictors. Projections to the Last Glacial Maximum and Holocene scenarios provided a coherent representation of climate influences on the past distributions of the target species. Computation of pairwise variables interactions and the discriminant analysis allowed a deeper interpretation of SDMs’ outputs. Further, we propose a multivariate environmental dissimilarity index (MEDI), derived through a transformation of the multivariate environmental similarity surface (MESS), to deal with extrapolation-linked uncertainties in model projections to past climate. Finally, the niche equivalency and niche similarity tests confirmed the link between SDMs outputs and actual differences in the ecological niches of the two species.ConclusionsThe different responses of the two species to climatic factors have significantly contributed to shape their current distribution, through contractions, expansions and shifts over time, allowing to maintain two wide allopatric areas with an area of sympatry in Central Italy. Moreover, our SDMs hindcasting shows many concordances with previous phylogeographic studies carried out on the same species, thus corroborating the scenarios of potential distribution during the Last Glacial Maximum and the Holocene emerging from the models obtained.
Highlights
Climate is often considered as a key ecological factor limiting the capability of expansion of most species and the extent of suitable habitats
The 77.6% (388) of the 500 occurrences analyzed for Lissotriton v. meridionalis falls in the allopatric area, while for L. italicus the percentage is only of 43.1% (173/401)
It can be reasonably assumed that the Species Distribution Models (SDMs) built for L. v. meridionalis on the considered study area are properly informed about the full set of climatic conditions relevant to the species, so that the Padano-Venetian plain and Prealps can be excluded from the study area without weakening model calibration
Summary
Climate is often considered as a key ecological factor limiting the capability of expansion of most species and the extent of suitable habitats. In this contribution, we implement Species Distribution Models (SDMs) to study two parapatric amphibians, Lissotriton vulgaris meridionalis and L. italicus, investigating if and how climate has influenced their present and past (Last Glacial Maximum and Holocene) distributions. Within the SDMs approach, wide areas with high predicted suitability/probability of presence with respect to a certain species but currently unoccupied suggest the existence of some unmeasured variables constraining the species’ distribution [17]. Cycles of glaciations during the Pleistocene, because of their limiting effects on species’ dispersal possibilities and tolerance to climatic stressors, largely contributed to shape European fauna [19], leading to the extinction of some species and influencing the distribution of other taxa [20,21,22]
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