Ecological niche evolution, speciation, and feedback loops: Investigating factors promoting niche evolution in Ordovician brachiopods of eastern Laurentia

Abstract

Quantifying the relative stability of ecological niches of taxa during intervals of environmental change including determining the environmental controls of niche expansion, stability, and contraction is important for understanding of how taxa and communities change through time. In this study, we used ecological niche modeling to quantify trends in niche dynamics and the stability of eastern Laurentian brachiopod genera during the Sandbian through Katian Stages of the Late Ordovician Epoch. Niche dynamics were quantified using ordination methods to assess niche stability, expansion, and unfilling between time slices, and D and I statistics were calculated to assess niche similarity and equivalency between time slices. Brachiopod genera exhibited substantial niche expansion and limited niche stability between their reconstructed Sandbian and early Katian niches. Conversely, comparisons between early Katian and late Katian niches indicated high levels of niche stability, similarity, and equivalency but limited niche expansion or unfilling. No singular abiotic or biotic causal driver is consistent with the observed patterns. Patterns of niche dynamics and stability are best explained by a feedback loop linking tectonics, sea level, and climate with geographic connection and disconnection of depositional basins, speciation, and dispersal processes. During the Sandbian to early Katian interval, intermittent dispersal events between basins alternated with basin isolation; this cycle fostered increased diversification, which manifests as niche expansion at the genus level. During the late Katian, basin connectivity increased facilitating widespread regional dispersal events. The lack of isolation and spread of invasive taxa hindered speciation. This diminished niche expansion, and genera exhibited niche conservation as the primary niche response. These results indicate that generic niche analysis can be a useful proxy for underlying diversity dynamics and emphasize the importance of incorporating dispersal and isolation when considering evolutionary patterns and processes. Investigations of niche response over long intervals should consider both broader ecological and geographic context that incorporates the influence of diversity and dispersal.