| dc.description.abstract | In nature species react to a variety of endogenous and exogenous ecological factors.
Understanding the mechanisms by which these factors interact and drive population
dynamics is a need for understanding and managing ecosystems. In this study we
assess, using laboratory experiments, the effects that the combinations of two exogenous
factors exert on the endogenous structure of the population dynamics of a sizestructured
population of Daphnia. One exogenous factor was size-selective predation,
which was applied on experimental populations through simulating: 1) selective predation
on small prey, 2) selective predation on large prey and 3) non-selective predation.
The second exogenous factor was pesticide exposure, applied experimentally in
a quasi-continuous regime. Our analysis combined theoretical models and statistical
testing of experimental data for analyzing how the density dependence structure of
the population dynamics was shifted by the different exogenous factors. Our results
showed that pesticide exposure interacted with the mode of predation in determining
the endogenous dynamics. Populations exposed to the pesticide and to either selective
predation on newborns or selective predation on adults exhibited marked nonlinear
effects of pesticide exposure. However, the specific mechanisms behind such nonlinear
effects were dependent on the mode of size-selectivity. In populations under nonselective
predation the pesticide exposure exerted a weak lateral effect. The ways in
which endogenous process and exogenous factors may interact determine population
dynamics. Increases in equilibrium density results in higher variance of population
fluctuations but do not modify the stability properties of the system, while changes in
the maximum growth rate induce changes in the dynamic regimes and stability properties
of the population. Future consideration for research includes the consequences
of the seasonal variation in the composition and activity of the predator assembly in
interaction with the seasonal variation in exposure to agrochemicals on freshwater
population dynamics. | |
