Using two-species Integrated Population Models to estimate competitive outcomes and coexistence mechanisms in stage-structured systems
Résumé
Most communities of competing species have an age or stage structure, with possible competition between and within species at various life-stages. Predicting competitive outcomes and inferring coexistence mechanisms in such stage- or age-structured communities typically requires fitting dynamical models to data, from which invasion criteria and eventually coexistence indicators can be derived. Methods that allow to fully propagate parameter uncertainty and demographic stochasticity while estimating interaction strength and invasion or coexistence criteria are particularly indicated. These should ideally make the best out of multiple data sources, each of which can be relatively scarce by statistical standards. Here, we embed a mathematical model of stage-structured competition between two species, producing analytical invasion criteria, into a two-species Integrated Population Model framework. The community-level IPM fulfills the above requirements, and allows to combine for both species multiple data sources (counts, capture-recapture, fecundity data) into a single statistical framework. Our Bayesian formulation of the IPM fully propagates parameter uncertainty. Model fitting demonstrates that we can predict correctly coexistence through reciprocal invasion when present, though cases with extinction are little harder. Prior specification can have a relatively large influence on the results, with some priors leading to nonidentifiability in species interaction parameters, so we recommend to always plan for some form of prior sensitivity analysis in such Bayesian dynamic community model fitting exercises.