Insect Dynamics in Heterogeneous Environments and the Relevance of Retrospective Life Tables and Cyclic Budgets: An Integrated Approach

Abstract

The analysis of cumulative, time-independent survivorship data for insect populations as obtained by using trace methods and their use in constructing retrospective life tables are reviewed. The reliability of the estimates obtained by such methods is examined by placing empirical data in the broader context of a model of the spatiotemporal dynamics of age-structured populations in heterogeneous environments. For the case of stable, average populations, the information contained can be displayed as a cyclic budget quantifying the mortality during development, the sex ratio and the fecundity as key (k) factors. Because of the time-independent nature of the display, prereproductive losses of adult females, typically those due to migration and failure to find reproductive resources, can be interpolated. The whole, therefore, can be viewed as a numerical description of a life-history strategy. The mathematical relationship between the “true” mortality function, which in general depends on age, time, population density, and location, and the age-dependent “apparent” mortality as determined from trace methods for a particular sampling area is established. These apparent death rates are then correlated with the k-factors appearing in the budget.