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Introduced rats indirectly change marine rocky intertidal communities from algae- to invertebrate-dominated

Island and Ocean Ecosystems, BRB

Available Online

Croll, Donald A.

Kurle, Carolyn M.

Tershy, Bernie R.

It is widely recognized that trophic interactions structure ecological communities, but their effects are usually only demonstrated on a small scale. As a result, landscape-level documentations of trophic cascades that alter entire communities are scarce. Islands invaded by animals provide natural experiment opportunities both to measure general trophic effects across large spatial scales and to etermine the trophic roles of invasive species within native ecosystems. Studies addressing the trophic interactions of invasive species most often focus on their direct effects. To investigate both the presence of a landscape-level trophic cascade and the direct and indirect effects of an invasive species, we examined the impacts of Norway rats (Rattus norvegicus) introduced to the Aleutian Islands on marine bird densities and marine rocky intertidal community structures through surveys conducted on invaded and rat-free islands throughout the entire 1,900-km archipelago. Densities of birds that forage in the intertidal were higher on islands without rats. Marine intertidal invertebrates were more abundant on islands with rats, whereas fleshy algal cover was reduced. Our results demonstrate that invasive rats directly reduce bird densities through predation and significantly affect invertebrate and marine algal abundance in the rocky intertidal indirectly via a cross-community trophic cascade, unexpectedly changing the intertidal community structure from an algae- to an invertebrate-dominated system.

An overview of introduced predator management in inhabited landscapes

Available Online

Russell, James C.

Stanley, Margaret C.

Predators play a critical role in ecosystems; however, when overly abundant, they can disrupt natural processes and cause extinctions of species. In particular, oceanic islands have endured many impacts of introduced mammalian predators. Whereas knowledge and management of introduced mammalian predators on islands is well advanced in natural landscapes, in inhabited landscapes, spanning rural and urban environments, comparatively less is known. We summarise key issues from the natural and social sciences in the management of introduced mammalian predators in inhabited landscapes of AotearoaNew Zealand. We describe the shift in focus over the past few decades from management of introduced mammalian herbivores to predators in rural environments, and the growth in management of introduced mammalian predators in urban environments, both seeking to emulate conservation gains made in forested landscapes. We discuss the circumstances around companion animal management at the interface of the natural and social sciences. We summarise surveys of attitudes towards introduced mammalian predators, the role of biodiversity comanagement between Ma¯ori and Pakeha, and the importance of also considering non-biodiversity benefits from introduced predator management. We describe the rise of community predator control and large landscape projects aspiring for a Predator Free New Zealand, and how such an aspiration must be concurrent with habitat restoration. We make recommendations for further research on the basic population biology of predators in inhabited landscapes, and more long-term studies. Such studies should be integrated with examination of the motivations for predator management, as well as the biodiversity and social outcomes of such management. We conclude by remarking that introduced predator management is only one component of a robust national strategy for conservation of native biodiversity in New Zealand.

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