Aim To investigate relative niche stability in species responses to various types of environmental pressure (biotic and abiotic) on geological time-scales using the fossil record.
Location The case study focuses on Late Ordovician articulate brachiopods of the Cincinnati Arch in eastern North America.
Methods Species niches were modelled for a suite of fossil brachiopod species based on five environmental variables inferred from sedimentary parameters using GARP and Maxent. Niche stability was assessed by comparison of (1) the degree of overlap of species distribution models developed for a time-slice and those generated by projecting niche models of the previous time-slice onto environmental layers of a second time-slice using GARP and Maxent, (2) Schoener’s D statistic, and (3) the similarity of the contribution of each environmental parameter within Maxent niche models between adjacent time-slices.
Results Late Ordovician brachiopod species conserved their niches with high fidelity during intervals of gradual environmental change but responded to inter-basinal species invasions through niche evolution. Both native and invasive species exhibited similar levels of niche evolution in the invasion and post-invasion intervals. Niche evolution was related mostly to decreased variance within the former ecological niche parameters rather than to shifts to new ecospace.
Main conclusions Although the species examined exhibited morphological stasis during the study interval, high levels of niche conservatism were observed only during intervals of gradual environmental change. Rapid environmental change, notably inter-basinal species invasions, resulted in high levels of niche evolution among the focal taxa. Both native and invasive species responded with similar levels of niche evolution during the invasion interval and subsequent environmental reorganization. The assumption of complete niche conservatism frequently employed in ecological niche modelling (ENM) analyses to forecast or hindcast species geographical distributions is more likely to be accurate for climate change studies than for invasive species analyses over geological time-scales.
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