CANCELLED - The maintaining of individual specialization and its effects on predator-prey dynamics

Background/Question/Methods

For simplicity, many models of species interaction assume that conspecific individuals are equivalent to each other. However, the variation in ecological attributes of different sexes and age classes has long been recognized, and there is growing empirical evidence of individual variation within sex and age classes, especially on diet. I examined the ecological effect of different levels of individual variation in resource use (individual specialization) using a Holling type II one-predator-two-prey model system. The predator species is composed of three genotypes that vary in attacking rates and handling rates towards the two prey species. This variation is genetically determined by one-locus/two-allele Mendelian inheritance and the heterozygous can be underdominant/overdominant/intermediate compared to homozygous. Both of the prey species follow a logistic growth function but can differ in growth rate and carrying capacity. I explored the conditions that can lead to 1) stable coexistence of all three species while maintaining predator polymorphism, 2) the loss of predator polymorphism following the extinction of one prey species and the coexistence between the resulting monomorphic predator and remaining other prey species.  The impacts of different levels of individual specialization on these conditions are analyzed.

Results/Conclusions

With extreme high levels of individual specialization where two types of homozygous predators each have strong preference towards one of the two prey species, the heterozygous predator type couples the dynamics of each pair of homozygous predator-prey dynamics and has a contradictory effect in maintaining predator polymorphism, and in facilitating the stable coexistence between predator and two prey species.  The strength of this effect depends on the relative fitness of heterozygous. With intermediate and low levels of individual variation, the conditions described above become very complicated and no simple conclusion can be drawn. However, there is still a general tendency for individual specialization among predators elongating the persistence of predator population when compared to another equivalent predator population in which all individuals are assumed to be the same.