56-6 Measuring and Modeling Ecological Rates with Neutral Theory

Session: Phylogenetic and Computational Approaches in Paleobiology and Paleoecology, Part II

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The pace of change in ecological communities is at the heart of several classic paleobiological problems, as well as emerging ones like the uniqueness of ecological change in the Anthropocene. Timeseries of community composition are common in paleontology and more accessible than ever in datasets like BioDeepTime. Yet there has been no unproblematic way to measure rates of change in paleocommunities: traditional rates (ecological distance divided by time) appear faster when measured over shorter time intervals, preventing straightforward interpretation of rates when timescales vary. Similar problems arise when there is variation in sampling intensity or taxonomic resolution. Here we develop an approach that mitigates these issues using Hubbell’s neutral theory, a model of ecological change in which species drift up and down in abundance in a community of fixed size J. Community change is faster when J is smaller, so 1/J provides a process-based rate metric that can be estimated from empirical timeseries. We develop a likelihood function for changes in community composition under neutral theory, and show that it accurately estimates rates of change in simulated data even when timescale, taxonomic rank, and sampling intensity vary. We use the Neotoma database of Quaternary pollen cores to demonstrate the power of this method in exploratory analyses for comparing rates between sites as well as for considering change in rates through time, whether in a single timeseries or across many of them. Finally, our probabilistic framework can be used to test hypotheses about the causes of ecological change, which we demonstrate with tests for a rate shift associated with anthropogenic disturbance. We outline future directions including model extensions, descriptive paleoecology, and tests of the causes and timing of ecological change in the Holocene.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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