A New Threat to Native Species? 

When exotic species are introduced to a new area, they pose a threat to native flora and fauna, through competition for food, predation, and the infectious diseases that they bring with them. Another potential impact is ‘parasite spillback’: new species can pick up parasites from native fauna and act as reservoirs, allowing the parasites to ‘spill back’ into the native species, causing further outbreaks of disease.

Until now, little research has been carried out about the role this mechanism has in causing the decline and loss of native species. Dr Daniel Tompkins from Landcare Research and his colleagues have been awarded a Marsden grant, to explore this issue in more detail.

In preliminary work, the team has identified that freshwater fish is one of the most likely communities in which parasite spillback could be a cause of native species decline and local extinction. Therefore, the team will study the interaction of New Zealand native freshwater fish with introduced trout.

Trout are known to harbour high numbers of parasites. In New Zealand, 11 species of parasitic worms are reported from the brown trout alone, all but one of which are parasites of native fish. Therefore, spillback effects on native New Zealand freshwater fish are likely, and may help to explain why trout have displaced native species from some freshwater areas and not others.

Dr Tompkins will use a combination of field surveys, examination of fish, exposure to parasites, and mathematical modelling to assess the importance of parasite spillback as a cause of native species loss. A major objective will be to test whether the presence of brown trout, and the parasite abundance within them, is indeed associated with increased infection of the four native fish species being investigated. The team will also extend their studies to similar fish communities overseas.

This will be the first time the role of parasite spillback in native species loss has been tested in New Zealand, advancing knowledge of what might be a significant cause of extinction in native species worldwide.

Total Funding:    $586,110
Researchers:    Dr Daniel Tompkins, Landcare Research Limited, Dunedin.
Associates:    Professor Robert Poulin, University of Otago
Professor Colin Townsend, University of Otago