Exploitative competition and ecological effective abundance

Abstract

This study analyzes the effect of exploitative competition and density dependence by using an individual-based simulation model. There are two components of exploitative competition (leftovers and resource-recovery competition). In leftovers competition, individuals compete for food resources that have been left by others. In resource-recovery competition, the consumption of foods by individual predators affects growth rates of food populations. An individual-based simulation was conducted to examine how these two types of competition affect density-dependent processes. In the simulation, individual predators search for food organisms within their home range. Food organisms reproduce in three different ways: replacement, recruitment and neighborhood recruitment. In replacement, all food organisms die and are replaced with a new food population. In recruitment, food organisms do not disappear during simulation unless they are eaten by predators, and new food organisms are recruited based on their density. In neighborhood recruitment, food organisms reproduce depending on their abundance within the neighborhood area. The simulation was conducted by varying the number of predators, the home range size of individual predators, the area of simulation, the reproductive rates of food organisms, and the reproductive modes of the food organisms. The number of food organisms taken by an individual predator, and the number of predators over several different scales, were measured. A multiple regression was conducted to examine the relationships between several different estimations of predator abundance and the number of food organisms taken by an predator. The effects of different types of exploitative competition differed depending upon the spatial scale or estimated population density. The number of predators within the home range of an individual predator is negatively related to individual food gain. This suggests that leftovers competition can be detected within the home range of an individual predator. In the case in which the food population was regulated over the whole simulation area, the number of predators in the whole area was positively related to food gain of individual predator in the case of recruitment and neighborhood recruitment of reproduction of food, but positively in replacement. In the case in which a food population was regulated in smaller parts of the whole area, the estimated number of predators within a food population were related to food gain of an individual predator but the total population size does not affect the food gain.