Divergent Behaviour amid Convergent Evolution: Common Garden Experiments with Desert Rodents and Vipers

Desert ecosystems worldwide provide examples of convergent evolution for species and entire communities. In a series of common-garden experiments, I compare the communities of granivorous rodents and their predators from North American and Middle Eastern Deserts. I used populations of two Heteromyid rodents from the Mojave Desert and two Gerbillines from the Negev. Each population’s perception of risk of viper species, one known and one from the convergent system, was measured in three steps: initial (at first encounter), over a two month experiment of co-habitation with predators in a semi-natural arena, and post exposure. The initial and post exposure “interviews” revealed that all four rodent species fear most their native viper species. However, after two months of exposure, all four species exhibit greater fear for the sidewinder rattlesnake (Crotalus cerastes) from the Mojave, a snake capable of infra-red vision, than for the Saharan horned viper (Cerastes cerastes) from the Negev, a snake “blind” on dark nights. In the semi-natural arena (vivarium), all four species exhibited fear (higher giving-up densities in depletable food patches) of snakes and owls. As evidence of predator facilitation, all four rodents respond to owls by favoring the shrub cover and respond to snakes by favoring the open areas. More subtle responses to moonphase, particular viper species, and interactions of owls and snakes were rodent species specific. The evolutionary history with predators proved to be more important in shaping the evolution of anti-predator strategies than environmental forces of climate, substrate and food availability. Heteromyids, who evolved with heat sensing vipers exhibited fixed strategies that fluctuate in intensity based on the overall risk in the environment. The Gerbillines on the other hand reassess the risk based on the greatest threat in the environment. All species however respond to all vipers with the strategies best suited to the vipers they evolved with.