The nature of dispersal barriers and their impact on regional species pool richness and turnover

Abstract

Aim:We document realized and potential global species ranges based on empirically vetted species concepts in conjunction with global climate databases and climate suitability modelling. From this we investigate the nature of dispersal barriers and illustrate how they generate ecological uniqueness. Location: Holarctic.Methods: Fifty-two small body-size (i.e. < 5 mm) land snail taxa within the genera Euconulus, Pupilla and Vertigo were considered. These represent ~10% of all small body-size Holarctic land snails and are among the most proficient known passive dispersers. Their potential climatic ranges were determined using Maxent modelling based on 9205 occurrence records. From these we inferred the location, width and nature of isolating barriers and tested for their effects on regional species pool richness and turnover.Results: Use of unvetted traditional taxonomic concepts and unverified occurrence records would have created up to threefold higher or lower estimates of speciesspecific climatic tolerances than the actual values. Modelling must thus only use high quality occurrence data. All but one taxon were shown at a global scale to possess multiple isolated areas of appropriate climate. While oceans represented the most common barrier (37%), intra-continental barriers were in total almost twice as frequent (inappropriate climate -29%, habitat/history -27% and the Greenland ice sheet -7%). These barriers restricted taxa to only a subset of their potential range, with European taxa possessing approximately twice the global occupancy rates as North American ones (median scores of 62 vs. 34%). As a result, regional taxa pools were three times smaller than their potential sizes, with 50% change in composition occurring over ~2600-km distances. Main conclusions:Even for these readily dispersing taxa, isolation barriers prevented species from saturating their potential global range, reduced the size of regional species pools by 2/3, and generated ecological uniqueness between them.

Intercontinental dispersal and niche fidelity drive 50 million years of global diversification in Vertigo land snails

“…Very few cases of vicariance were inferred for Vertigo , and only once as the sole inferred process, namely, the (most likely Pleistocene) segregation of three geographically isolated subspecies within the Holarctic V. lilljeborgi clade. Climate modelling indicates that these three subspecies occupy highly disjunct regions, separated by vast areas with unfavourable climate (Nekola et al., 2022). Although we did not find that vicariance is a main driver of diversification in Vertigo at the continental scale (as most continents separated prior to the origin of Vertigo ), it still may operate at subcontinental scales, which requires further in‐depth study.…”

“…Species distribution data are presented in Table S1 in Appendix S1. Although Europe and Asia form a single land mass, we considered them separate due to consistent differences in climatic niche models for land snail species (see Nekola et al., 2022). Non‐native occurrences, for example, the recent anthropogenic introductions of Vertigo pygmaea in North America, were not considered when coding geographic ranges.…”

Ecological Niche Modelling Approaches: Challenges and Applications in Vector-Borne Diseases

“…As aforementioned, presence-background models (with Maxent the most popular) contrast the environmental characteristics of sites of known occurrence against those associated with background locations where presence/absence is unmeasured [127]. Being this essential to predict the probability of presence, it is crucial to outline the calibration area as the area that has been accessible to the species (M) [58,128], as the species will be absent from outside of this area for reasons unrelated to A [129] (such as geographical barriers [130] or anthropogenic range contractions [131]). Defining M has strong implications in several aspects of ENM, for instance:…”