Explaining and predicting organisms’ abundance and its variation over space and time is a key objective of ecology. In most studies, different population dynamics are interpreted in terms of differences in the sensitivity of life history traits and age structure to density by relating population growth rate to population size or to overall population density. In this approach, it is implicitly assumed that the mean degree of competition experienced at the individual level increases linearly with total population size. This assumption holds true in spatially well-mixed populations in which individuals move at random.
However, in numerous species, animals do not wander randomly, but use spatial memory to repetitively visit a limited set of profitable places. Such memory-based recursive movements reflect decisions that are energetically advantageous when resources are predictable in space and time. This non-random use of the environment should have population-level consequences. These are however mainly still unknown. We developed a spatially-explicit individual-based model where reproduction and death depend on foraging efficiency, and compared the population dynamics of with- and without-memory individuals.
Results/Conclusions
We show that:
1) memory-based foraging leads the individually-experienced intensity of competition to increase nonlinearly with the total population size: it is smaller than expected for a wide range of population sizes, and its variability is higher than for populations of randomly moving individuals.
2) an environment consisting of renewing resource patches has a higher carrying capacity for with- than for without-memory individuals, even if with-memory individuals more heavily deplete the environment.
3) the use of memory leads to a nonlinear density-dependent response curve of the net population growth rate.
Thus, our study shows for the first time that the cognitive abilities of the individuals in a population can translate into strong differences in population dynamics, and that the total population size is not a satisfactory proxy for the intensity of competition experienced by memory-based foraging individuals. As this type of foraging seems to be very common, the long-standing assumption of a spatially well-mixed population seems prone to lead to erroneous interpretations of population dynamics. Our results should help improve the design of and the insights drawn from population dynamics studies and open a new research avenue linking individual cognition to population dynamics.