Assessing Density-Dependence: Where Are We Left?

Abstract

The history of density dependence started in 1798 with Malthus’ sentence: population, when unchecked, increases in a geometrical ratio. The famous controversy between Lack, Andrewartha and Birch and others in the 1950s and 1960s remained largely unsolved: while the impossibility of long term exponential growth required density-dependence, density-independent environmental variation in vital rates was often dominant in empirical studies. Fifty years later, where are we left? I revisit first the representation of density-dependence in dynamical models, whether deterministic or stochastic, and I emphasize the lack of theory for the simultaneous occurrence of density-dependence and environmental variation. I then review approaches to detect and measure the intensity of density-dependence, in two steps: based on population size estimates and in demographic parameter analyses. I discuss then how the question of density-dependence could be efficiently revisited, taking advantage of progress in our understanding of spatio-temporal dynamics, statistical procedures, access to individual characteristics, and possibilities of experimental approaches.