FEEDBACK LOOPS IN ECOLOGICAL NICHE EVOLUTION, DISPERSAL, AND SPECIATION: EXPLORING ECOLOGICAL NICHE EVOLUTION IN EASTERN LAURENTIAN UPPER ORDOVICIAN BRACHIOPODS

Quantifying the relative stability of ecological niches of taxa during intervals of environmental change 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. 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. Niche patterns 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, fostering increased diversification, which manifests as genus-level niche expansion. During the late Katian, basin connectivity increased, facilitating widespread regional dispersal events. The lack of isolation and spread of invasive taxa hindered speciation, thus diminishing niche expansion, resulting in increased genus-level niche conservation. These results indicate that generic niche analysis can be a useful proxy for underlying diversity dynamics. Investigations of niche response over long intervals should consider both broader ecological and geographic context that incorporates the influence of diversity and dispersal.