Science Inventory

Density Dependent Functional Forms Drive Compensation in Populations Exposed to Stressors

Citation:

RAIMONDO, S. Density Dependent Functional Forms Drive Compensation in Populations Exposed to Stressors . ECOLOGICAL MODELLING. Elsevier Science BV, Amsterdam, Netherlands, 265:149-157, (2013).

Impact/Purpose:

To explore uncertainty of density dependence in population model predictions.

Description:

The interaction between density dependence (DD) and environmental stressors can result in a compensatory or synergistic response in population growth, and population models that use density-independent demographic rates or generic DD functions may be introducing bias into management decisions. Understanding the relationship between DD and stressor impacts on demographic endpoints is needed to ensure models applied in management have the potential to detect compensatory and synergistic interactions between the two. This relationship was explored through the development of a DD demographic model for the sheepshead minnow (Cyprinodon variegatus) containing data-defined functions of DD for adult survival, fecundity, and juvenile growth. Concentration response curves were developed for organism-level effects in chronic laboratory studies with four chemicals (estradiol, trenbolone, trifluralin, chlordane) causing impacts varying in endpoint and magnitude. Concentration-response curves were also developed for three hypothetical chemicals (HC) that affected only adult survival (HC A), fecundity (HC B), or juvenile growth (HC C). Population growth rate (PGR) was determined across a range of densities and concentrations for each chemical. PGR contours revealed DD-stressor interactions ranging from compensatory to synergistic, which were a function of the combination of DD forms applied in the model and the organism-level impacts of the stressor. The strongest compensation occurred where DD survival was included in the model. When DD survival was omitted, DD fecundity and growth were drivers of PGR, but had limited compensatory influence. These interactions reflect model sensitivity to demographic rates and models applied in management should consider species life history when including specific DD functions for important endpoints.