Niche Conservatism, Tracking, and Ecological Stasis
Niche Conservatism, Tracking, and Ecological Stasis
A Hierarchical Perspective
At the heart of the concept of ecological stasis is the general hypothesis that ecological niches, broadly defined as positions of species along environmental gradients, remain relatively stable over time. To further investigate this concept, we designed a hierarchical sampling strategy for a well-studied interval of previously documented evolutionary-ecological stability, the Middle Devonian of New York State. Fossil assemblages were sampled at the scale of members, and formations; i.e., at timescales of tens of thousands to about a million years. In each case, gradients of fossil assemblages were diagnosed using detrended correspondence analysis and these gradients were used to parameterize the niches of individual taxa. In a seeming paradox, members exhibit minor niche modification, whereas formations appear more conservative. We attribute this to either an incomplete representation of environments within members or fluctuations in parameters that are not reflected in the environmental gradients studied here. Overall, the results indicate a tendency toward niche conservatism over the millions of years duration of the Hamilton Group, despite minor local and regional fluctuations over the shorter timescale of members. This result is consistent with a model of habitat tracking by taxa and may explain the pattern of prolonged stability known as "coordinated stasis".
Keywords: Devonian, ecological stasis, ecological evolutionary subunits, gradient analysis, hierarchy theory, niche conservatism, sloshing bucket hypothesis
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