Native species can evolve antipredator behaviour quickly

Posted on July 2, 2014

Invasive predators can have rapid and devastating effects on native populations. It’s commonly assumed that this occurs mainly because prey species are poor at detecting and responding to novel predators. However, there are other possible explanations. In theory, prey may be able to respond effectively to invasive predators if the predator releases scent cues that are similar to those released by native predators (e.g., because the predator species are related). Alternatively, alarm cues may be released by prey when they are consumed or digested by predators, or prey may learn to associate the scent of novel predators with alarm cues from their fellow prey. A further possibility is that prey respond to cues specific to the new predator. A recent study by Michigan-based researchers was the first to explicitly explore these alternatives experimentally. It focussed on the responses of the zooplankton species Daphnia mendota to different types of predators, including the spiny water flea (Bythotrephes longimanus), which is native to Europe and Asia but invaded the Great Lakes of North America in 1982. The behaviour of D. mendota was recorded by placing Daphnia in tall columns filled with water that had previously contained predators. Relative to the depths that they maintained in pure water, Daphnia moved significantly lower in water that had the scent of spiny water fleas or yellow perch (a native fish predator). They responded more strongly to water that had contained starved spiny water fleas than to water in which spiny water fleas had either consumed Daphnia, digested Daphnia, or digested copepods (a different type of plankton prey). They also showed a significant adaptive response to water that had previously housed mysid shrimp (a native invertebrate predator) although in this case the movement was upwards. Under field conditions, this shift would take them away from mysids, which normally dwell in relatively deep water. In contrast , Daphnia showed no response to predator species that were taxonomically similar to spiny water fleas. So Daphnia responses couldn’t be explained in terms of predator relatedness or predator diet. Taken together with other experiments that ruled out learning, these findings showed that Daphnia were responding to cues that were specific to invasive spiny water fleas. It’s possible that this ability could have been retained from an ancestral species that coevolved with spiny water fleas, but given the long time span involved, this is unlikely. This leaves one explanation – that in the 25 years since Bythotrephes were introduced, Daphnia have been subjected to strong evolutionary selection for antipredator behaviour to counter the invading species.

Reference: Bourdeau, P.E. et al. 2013. Finely tuned response of native prey to an invasive predator in a freshwater system. Ecology 94(7), 1449–1455.