A lot of work has gone into studying the predatory effects of invasive species, but little is known about their effects as prey. Researchers looking through 3,905 publications have revealed that native predators seem to benefit from the arrival of nonnative prey – but only until the invaders overtake the native prey population.
Because predators and nonnative prey share no evolutionary history, the prey typically don’t have the right defenses (weaponry, chemicals, and otherwise) while the predators might not be efficient at either catching or eating them. If they’re just supplementing the prey base – that is, providing more food options for predators – then nonnative species should have a neutral to positive effect. If, however, they begin displacing native prey, their overall effect might depend on their quality and relative abundance.
So, to quantify the effect of nonnative prey on native predators, Ohio State’s Lauren Pintor and University of Georgia’s James Byers reviewed the literature for studies on the growth rate, fecundity, survival and population abundance of native predators living among or without nonnative prey. After sorting through thousands of studies, they ended up with 52 publications and 109 data points.
When native predators have access to both nonnative and native prey at the same time, predator abundance and individual growth rate increased after the invaders showed up. Though, studies that only examined the effects of nonnative prey species in isolation from other prey found that the invaders either similarly or negatively affected native predators.
“We whole-heartedly caution against interpreting the increase in native predator population abundance or growth rate in the community context following invasion of non-native prey as evidence that non-native species are not harmful to native biodiversity and ecosystems,” the authors wrote in the November issue of Ecology Letters. “Our data simply suggest that non-native prey may not be overly impacting the native prey base for native predators.”
These apparent benefits arrived indirectly sometimes. For example, the positive effects of cane toads (Bufo marinus) on five of Australia’s native snake predators – which are susceptible to the toads’ toxins – may have been the result of cane toads poisoning giant lizards that see snakes as prey.
[h/t Science News]