The study of ecology involves investigations of specific organisms and environments and the development of general conclusions about how the natural world works. These generalizations are called theories. The goal of ecology, like all sciences, is to develop theories that aptly describe what human beings know about the natural world. For example, the statement "islands have fewer species than similar sized environments on the mainland because islands have higher extinction rates and lower immigration rates" is a theory. It does not describe the situation of a particular island but proposes a generalization regarding patterns and mechanisms for all islands.
Theoretical ecology is a branch of ecology that particularly focuses on the development of theory. To accomplish this, theoretical ecologists usually develop models of the patterns and processes about which they are interested in generalizing. These models usually consist of a series of mathematical equations intended to quantify the phenomenon under study. Ecologists do not pretend that their models include everything involved in the study system. In fact, the models are intentionally simplified representations of what they are studying. This simplification enables the ecologist to analyze in detail certain aspects of their system.
Virtually all aspects of ecology are of interest to theoretical ecologists. In the 1920s and 1930s ecologists Alfred Lotka and Vito Voltera developed some of the first theoretical models of ecology. These simple models consisted of equations intended to describe the growth of two interacting populations over time. The two populations could be competitors or predator and prey. These famous equations are referred to as the Lotka-Voltera model. These equations predicted the conditions in which one species would drive the other to extinction and also what conditions permitted coexistence of the two species. Although very simple models, the results prompted ecologists to think more deeply about species interactions and eventually to develop more complex, but realistic, models and theories.
A number of theoretical models have been developed to describe how animals make foraging choices. For example, optimal foraging theory predicts that animals should forage in a way that maximizes the net intake of energy in the shortest period of time. Other theoretical models have been developed to explain how plants compete for resources, why animals sometimes behave altruistically toward kin but not unrelated individuals, why some species of plants reproduce many times in their lifetime while other species reproduce only once, how disease spreads through a population, and why sexual reproduction evolved.
One important value of developing models is that the formal process of modeling requires the ecologist to be very thorough and precise in defining the assumptions of the model. Thus, modeling helps ecologists think more clearly about the issues they are studying in the natural world. Another value of these theoretical models is that they often suggest field experiments that can be conducted to test certain predictions made by the model. Data collected from the field often then prompt the theoretical ecologists to revise their models or theories. Thus data collection and theory building work together to advance the ecological understanding of the world.
Mark A. Davis
Gotelli, N. J. A Primer of Ecology, 2nd ed. Sunderland, MA: Sinauer and Associates Inc., 1998.