Insularity and adaptation in coupled victim-enemy associations

Employing a mathematical model we show how insularity, genotypic interactio ns and victim life-history/demography can influence adaptation in a simple enemy-victim interaction where genotypes migrate between a large source and a smaller, initially unoccupied, isolated habitat. We find that when there are explicit costs to heightened enemy virulence and victim resistance, la rge/close islands resemble their immigration sources, whereas small and/or distant islands tend to be occupied only by the least defended victims and least virulent enemies. In a model with no explicit cost to genotypic ident ity, frequencies do not differ on average between source and island. Despit e these trends in genotype frequencies, for a range of realistic conditions , both cost and cost-free genotypic interactions yield an increase in the f requency of resistant encounters as a function of isolation. Moreover, in m odels with explicit costs, maximal island to island variation in genotypic frequencies is found on islands of intermediate distance from the source. I n contrast, the model without explicit costs produces more variable communi ties, attaining maximum variability in genotypic frequencies at the most is olated islands. We hypothesize that adaptive patterns in mainland-island co mparisons may differ substantially from those generated by centre-periphery comparisons in continental systems.