Population

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 periods.This 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 population size, such as resource availability and predation, also are affected by disturbance. As a result, population regulation may be disrupted by disturbance for some insect species. Models of population change generally do not incorporate effects of disturbance. This chapter addresses temporal patterns of abun

Dynamics dance, factors causing or regulating population fluctuation, and models of population dynamics.

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