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Efficient experimental designs for studying stress and population density in animal populations

Sibly, Richard M.
Ecological applications 1999 v.9 no.2 pp. 496-503
animals, carrying capacity, confidence interval, environmental factors, experimental design, food availability, interspecific competition, labor, life tables, parasitism, population density, population growth, predation, stress response, surveys
The first signs of environmental stress in field surveys are losses of species or their declining abundances. Interpretation of field survey data can be difficult, however, because species numbers in any case change with time and location, as a result of density dependence acting through or together with changing levels of food supply, predation, parasitism, interspecific competition, migration, environmental variables, and so on. As a first step toward resolving these difficulties it is argued that single‐species microcosm experiments are needed that establish the joint effects on populations of stress levels and population density. Inter alia these will show how carrying capacity changes with stress levels in the absence of variation in other physical and biotic variables. Until now population effects of stressors have generally been assessed experimentally by calculating population growth rates in Life Table Response Experiments (LTREs), but these are time consuming and labor intensive and have only been performed at low population density. It is argued that measurements made at low density may underestimate population stress responses. To undertake the proposed experiments, faster and more efficient techniques for measuring population growth rates and their associated confidence intervals are needed, and some suggestions are made as to how these might be achieved.