TAILIEUCHUNG - Insect Ecology - An Ecosystem Approach 2nd ed - Chapter 6

6 Population Dynamics POPULATIONS OF INSECTS CAN CHANGE DRAMATICALLY IN SIZE OVER relatively short periods of time as a result of changes in natality, mortality, immigration, and emigration. Under favorable environmental conditions, some species have the capacity to increase population size by orders of magnitude in a few years. | 6 Population Dynamics I. Population Fluctuation II. Factors Affecting Population Size A. Density-Independent Factors B. Density-Dependent Factors C. Regulatory Mechanisms III. Models of Population Change A. Exponential and Geometric Models B. Logistic Model C. Complex Models D. Computerized Models E. Model Evaluation IV. Summary POPULATIONS OF INSECTS CAN CHANGE DRAMATICALLY IN SIZE OVER relatively short periods of time as a result of changes in natality mortality immigration and emigration. Under favorable environmental conditions some species have the capacity to increase population size by orders of magnitude in a few years given their short generation times and high reproductive rates. Under adverse conditions populations can virtually disappear for long time capacity for significant and measurable change in population size makes insects potentially useful indicators of environmental change often serious pests affecting human activities and important engineers of ecosystem properties that also may affect global conditions. The role of insects as pests has provided the motivation for an enormous amount of research to identify factors affecting insect population dynamics to develop models to predict population change and more recently to evaluate effects of insect populations on ecosystem properties. Consequently methods and models for describing population change are most developed for economically important insects. Predicting the effects of global change has become a major goal of research on population dynamics. Insect populations respond to changes in habitat conditions and resource quality Heliovaara and Vaisanen 1993 Lincoln et al. 1993 see Chapter 2 . Their responses to current environmental changes help us to anticipate responses to future environmental changes. Disturbances in particular influence population systems abruptly but these effects are integrated by changes in natality mortality and dispersal rates. Factors that normally regulate

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