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Study shows invasive species can have cross-ecosystem impacts

Hermina Fourie, sampling for invasive trout and native fish species

C·I·B funded MSc student and co-author, Hermina Fourie, sampling for invasive trout and native fish species such as mountain catfish (Amphilius natalensis) and chubby head barb (Barbus anoplus). Photo credit: Michelle Jackson

A recent study by C·I·B post-doctoral fellow, Michelle Jackson, found that invasive species can have effects that reach across different ecosystems.

Competition and sharing of resources, such as food and space, is important for the structuring of ecological communities. Species that use the same resource may compete with one another, and a new invasive species is often more successful when it can use a resource that is not preferred by native species.

Studies on the sharing of resources usually consider species that occur in the same habitat, for example, the diets of invasive fish often overlap with the diets of native fish. However, species that are not in the same habitat may also compete for the same resources. For example, flying insects, which are an important diet item of birds, bats and spiders, often have an aquatic larval stage. These larvae are also important in the diet of many fish species. To examine this notion further, Michelle assessed the diet of native fish, invasive fish and native spiders in six streams in South Africa.

Michelle’s study showed that spiders were more likely to share resources with invasive trout than native fish, including the mountain catfish (Amphilius natalensis) and chubby head barb (Barbus anoplus). The likelihood of spiders overlapping into the trophic niche of invasive brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) was as high as 26% and 51%. In contrast, the likelihood of spiders overlapping into the trophic niche of native fish was always less than 5%.

“The results suggest that native spiders share resources with invasive fish, adding to the growing body of evidence that invaders can have cross-ecosystem impacts. Competition for resources across the aquatic–terrestrial ecotone should be considered as a far reaching impact of invasive fishes” according to Michelle Jackson, lead author of the paper published in the journal, Ecology and Evolution.

Mountain catfish (Amphilius natalensis)

The native fish species, the mountain catfish (Amphilius natalensis)




Read the paper in Ecology and Evolution

Jackson, M.C., Woodford, D.J., Bellingan, T.A., Weyl, O.L.F., Potgieter, M.J., Rivers-Moore, N.A., Ellender, B.R., Foerie, H.E. and Chimimba, C.T. 2015. Trophic overlap between fish and riparian spiders: potential impacts of an invasive fish on terrestrial consumers. Ecology and Evolution 6(6): 1475-1752.

For more information, contact Michelle Jackson at mjackson@zoology.up.ac.za