Intercontinental-wide consequences of compromise-breaking adaptations: the case of desert rodents

Abstract

Desert rodent assemblages from around the world provide convergent, but independent crucibles for testing theory and deducing general ecological principles. The heteromyid rodents of North America and the gerbils of the Middle East and their predators provide such an example. Both sets of rodents face predation from owls and vipers, but the North American species possess unique traits that may represent macroevolutionary breakthroughs: rattlesnakes have infra-red sensitive sensory pits, and heteromyids have cheek pouches. To test their significance, we brought together two gerbils (Middle East), two heteromyid rodents (a kangaroo rat and a pocket mouse; North America) in a common setting (a vivarium in the Negev Desert), and quantified the “opinions” of the rodents towards the North American sidewinder rattlesnake and the Middle Eastern Saharan horned viper and the foraging behavior of each in the face of these snake predators plus owl predators. Gerbils are fairly evenly matched in their anti-predator abilities, while the heteromyids differ widely, and these seem to match well with and may determine the types of mechanisms of species coexistence that operate in the communities of each continent. Evolutionary history, macroevolutionary traits, and risk management therefore combine to determine the characteristics of the organisms and the organization of their communities.

Divergent Behavior Amid Convergent Evolution: A Case of Four Desert Rodents Learning to Respond to Known and Novel Vipers

“…Pocket mice and kangaroo rats provide examples of opposite strategies in managing risk from snakes (as shown here), and other predators such as owls [28,32]. Why the stark difference?…”

“…The most likely explanation is that our systems were devoid of environmental heterogeneity. During the exposure period, we found species-specific—spatially explicit—responses to the distribution of risk posed by each snake and in combination with barn owls [28,30,32,56]. However, in the enclosed systems, where individual gerbils forage without competition, the response of both species to the risk of predations is similar.…”

“…Despite being naïve to the dangers of the sidewinder rattlesnake at the start of the experiments, both gerbils quickly learned to respond to the snakes and both rank them as a risk. In out measurements in the aviary they both ranked snakes as a lower risk than (lower GUDs) than owls [28,30,32]. The results of the comparison between the gerbils highlight the importance of competition to species that have less spatial segregation than the North American heteromyids [44,47].…”

“…Overall, the gerbelline species were willing to take more risk investigating the predators, while the heteromyids preferred to avoid both species. This reluctance to take risk in the heteromyids, suggests an overall greater “respect” to risk posed by snakes, possibly due to their evolution alongside snakes that have heat-sensing capabilities [32].…”

“…The fur-lined cheek pouches, hypothesized to give the heteromyids an advantage in maximizing harvest, under similar risk conditions, did not appear to function in such a manner in the presence of the snakes [32]. The greater sensitivity of heteromyids to the interaction with the snakes meant that despite having the ability to forage quickly in the presence of the predators, the heteromyids simply avoided these patches resulting in higher giving up densities than their gerbilline counterparts.…”