Unexpected consequences of control: competitive vs. predator release in a four-species assemblage of invasive mammals

Abstract

Invasive species are frequently the target of eradication or control programmes to mitigate their impacts. However, manipulating single species in isolation can lead to unexpected consequences for other species, with outcomes such as mesopredator release demonstrated both theoretically and empirically in vertebrate assemblages with at least two trophic levels. Less is known about the consequences of species removal in more complex assemblages where a greater number of interacting invaders increases the potential for selective species removal to result in unexpected changes in community structure. Using a replicated Before-After Control-Impact field experiment with a four-species assemblage of invasive mammals we show that species interactions in the community are dominated by competition rather than predation. There was no measurable response of two mesopredators (rats and mice) following control of the top predator (stoats), but there was competitive release of rats following removal of a herbivore (possums), and competitive release of mice following removal of rats.

Dietary niche differentiation among three species of invasive rodents (Rattus rattus, R. exulans, Mus musculus)

“…Stokes et al (2009) in Australia, and Harris and Macdonald (2007) in the Galápagos Islands, demonstrated that native rats (R. fuscipes and Nesoryzomys swarthi, respectively) suffered from interference competition rather than resource competition with the larger, non-native black rats. Furthermore, removal of black rats can result in population increases in coexisting rodents such as house mice (Harper and Cabrera 2010;Ruscoe et al 2011). The average body masses of the three coexisting rodents in our study differed 4-10 fold.…”

Biology and Impacts of Pacific Island Invasive Species. 11.Rattus rattus,the Black Rat (Rodentia: Muridae)

“…Stokes et al (2009) in Australia, and Harris and Macdonald (2007) in the Galápagos demonstrated that native rats (Rattus fuscipes and Nesoryzomys swarthi, respectively) suffered from interference competition with nonnative R. rattus. Furthermore, removal of R. rattus can result in population increases in coexisting nonnative rodents on Pacific islands, which has been observed with M. musculus in New Zealand (Ruscoe et al 2011) and in the Galápagos (Harper and Cabrera 2010).…”

Red foxes colonizing the tundra: genetic analysis as a tool for population management

“…Also, to increase the efficiency of this action as well as avoiding unmotivated culling, an evaluation of the spatial scale where measures are necessary is highly recommended. Even though predator control has been successful in the case of Arctic fox conservation (Angerbjörn et al 2013), there are examples of unexpected consequences of predator removal (Ruscoe et al 2011). Therefore, continuous assessment of removal strategies and consequences is central.…”