Adaptiveness of Defence Strategies Against Cuckoo Parasitism. Modelling, Analysis and Simulation. (MAS)

摘要

Host bird species of the Eurasian Cuckoo, Cuculus canorus, ofther display egg-discrimination behavior but chick-rejection behaviour has never been reported. In this paper, we analyse a host-cuckoo association in which both population dynamics and evolutionary dynamics are explored in a discrete-time model. We introduce four host types, each with their own defense behavior, displaying either egg or chick rejection, neither or both. we also introduce fitness functions for each of these host types. Although we can characterize the long term behavior in many cases by a simple heuristic argument which is in accordnace with common wiers in ecology, there are a number of other phenomena that are not explained within this framework: we describe stable oscillatory behavior and coexistence of two defensive host types. We analyse the secnarios in which chick rejection may establish itself and give a first explanation as to why this defense trait has never been recorded in nature. We find that chick rejectors generally are at an intrinsic disadvantage with respect to a host type that rejects eggs. Host benefit more from rejecting cuckoo eggs than cuckoo chicks, and our model suggests that this is chiefly responsible for the absence of chick rejection. Moreover, even though it seems that chick rejection must be useful as an extra defense, it is shown that hosts with both defense strategies are less likely to establish themselves in competition with egg-rejectors than hosts which reject chick only. These results provide insight in the extent to which adaptations may be perfected by natural selection.