Modelling interactions of toxicants and density dependence in wildlife populations

• Published in: Journal of Applied Ecology
• Main Authors: Schipper, Aafke M., Hendriks, Harrie W. M., Kauffman, Matthew J., Hendriks, A. Jan, Huijbregts, Mark A. J.
• Other Authors: Stephens, Phil
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2013
• Subjects: peregrine falcon
• Online Access: http://dx.doi.org/10.1111/1365-2664.12142; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2F1365-2664.12142; https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1365-2664.12142

Summary A major challenge in the conservation of threatened and endangered species is to predict population decline and design appropriate recovery measures. However, anthropogenic impacts on wildlife populations are notoriously difficult to predict due to potentially nonlinear responses and interactions with natural ecological processes like density dependence. Here, we incorporated both density dependence and anthropogenic stressors in a stage‐based matrix population model and parameterized it for a density‐dependent population of peregrine falcons F alco peregrinus exposed to two anthropogenic toxicants [dichlorodiphenyldichloroethylene ( DDE ) and polybrominated diphenyl ethers ( PBDE s)]. Log‐logistic exposure–response relationships were used to translate toxicant concentrations in peregrine falcon eggs to effects on fecundity. Density dependence was modelled as the probability of a nonbreeding bird acquiring a breeding territory as a function of the current number of breeders. The equilibrium size of the population, as represented by the number of breeders, responded nonlinearly to increasing toxicant concentrations, showing a gradual decrease followed by a relatively steep decline. Initially, toxicant‐induced reductions in population size were mitigated by an alleviation of the density limitation, that is, an increasing probability of territory acquisition. Once population density was no longer limiting, the toxicant impacts were no longer buffered by an increasing proportion of nonbreeders shifting to the breeding stage, resulting in a strong decrease in the equilibrium number of breeders. Median critical exposure concentrations, that is, median toxicant concentrations in eggs corresponding with an equilibrium population size of zero, were 33 and 46 μg g −1 fresh weight for DDE and PBDE s, respectively. Synthesis and applications . Our modelling results showed that particular life stages of a density‐limited population may be relatively insensitive to toxicant impacts until a critical threshold is ...