Abstract
Eleven years after invasive Norway rats (Rattus norvegicus) were eradicated from Hawadax Island, in the Aleutian Islands, Alaska, the predicted three-level trophic cascade in the rocky intertidal, with native shorebirds as the apex predator, returned, leading to a community resembling those on rat-free islands with significant decreases in invertebrate species abundances and increases in fleshy algal cover. Rats had indirectly structured the intertidal community via their role as the apex predator in a four-level trophic cascade. Our results are an excellent example of an achievable and relatively short-term community-level recovery following removal of invasive animals. These conservation successes are especially important for islands as their disproportionately high levels of native biodiversity are excessively threatened by invasive mammals.
Highlights
Eleven years after invasive Norway rats (Rattus norvegicus) were eradicated from Hawadax Island, in the Aleutian Islands, Alaska, the predicted three-level trophic cascade in the rocky intertidal, with native shorebirds as the apex predator, returned, leading to a community resembling those on rat-free islands with significant decreases in invertebrate species abundances and increases in fleshy algal cover
Community recovery after invasive animal eradication is difficult to measure for many reasons, including natural stochasticity and uncertain baselines by which to compare altered landscapes
We sought to: (1) document longer-term recovery of breeding intertidal-feeding marine birds (Black Oystercatchers and Glaucous-winged Gulls), (2) examine changes in the marine rocky intertidal community related to the direct and indirect impacts of marine bird recovery, and (3) better understand the time required for recovery of marine rocky intertidal communities on islands after rat removal
Summary
Eleven years after invasive Norway rats (Rattus norvegicus) were eradicated from Hawadax Island, in the Aleutian Islands, Alaska, the predicted three-level trophic cascade in the rocky intertidal, with native shorebirds as the apex predator, returned, leading to a community resembling those on rat-free islands with significant decreases in invertebrate species abundances and increases in fleshy algal cover. Our results are an excellent example of an achievable and relatively shortterm community-level recovery following removal of invasive animals These conservation successes are especially important for islands as their disproportionately high levels of native biodiversity are excessively threatened by invasive mammals. The direct effects of invasive animals on islands are well documented[7,8,9,10,11], and there is increasing evidence of their multiple indirect effects as w ell[6, 12,13,14,15] Because of these deleterious impacts, the removal of invasive animals has become an important global conservation strategy, with over 900 successful animal eradications on almost 800 islands since 1 95025. Understood than the direct deleterious effects of invaders and the recoveries of multiple native species once invaders and their direct mechanisms of control (frequently predation) are removed (but see[30,31])
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