Bat Population Dynamics: An Individual-based Model Approach

Temperate zone bats are subject to serious energetic constraints due to their high surface area to volume relations, the cost of temperature regulation, the high metabolic cost of flight, and the seasonality of their resources. To my knowledge, there are no individual-based mathematical models for any bat species. The model developed here for a female bat is primarily based on life history and energetics. It describes the growth of an individual female bat using a system of differential equations modeling the dynamics of two main compartments: storage (lipids) and structure (proteins and carbohydrates). The model is parameterized for the little brown bat, Myotis lucifugus, because of information available on energy budgets and changes in body mass throughout its life history. However, with appropriate modifications the conceptualization might be applied to other species of bats with similar life histories.

The dynamic estimates of daily energy budgets resulting from the model reasonably compare to previous estimates obtained through different methodologies. Sensitivity analysis using statistical screening design techniques identifies the individual parameters driving the model output and indicates the individual characteristics that might play an important role in survival, reproduction, and consequently in population dynamics. The individual model is used to test hypotheses related to strategies used by temperate bats to meet their energy demands. A complete corroboration of the model is not possible due to the lack of a data set independent of that used to construct and calibrate the model.

The individual model is integrated into a structured population model. Characteristics of the individuals determine the structure and, subsequently the dynamics of the population. This methodology uses and integrates the information on bat biology and physiology that has been collected primarily at the individual level. Survival and reproductive rates estimated from simulated populations under varying density dependence are comparable to those reported in the literature for natural populations of M. lucifugus. The population model provides insight into possible regulatory mechanisms of bat population sizes and dynamics of survival and extinction. A better understanding of population dynamics can assist in the development of management techniques and conservation strategies, and to investigate stress effects.