Oral Presentation Australian Society for Limnology Congress 2013

Invasion ecology – from stream theory to conservation practice (#1)

Colin Townsend 1
  1. University of Otago, Dunedin, 9054, New Zealand

During a lifetime of ecological research one theme has resurfaced repeatedly: the role of top predators in aquatic ecosystems and the impacts of predators when they invade new regions. My work started in an area of England whose streams should have held brown trout but didn’t, seeking to unravel the cause and consequences of the absence of trout. Then I moved to New Zealand, whose streams shouldn’t have had brown trout but did. This invasion is responsible for the local extinction of certain native fish, although particular kinds of refuge habitat allow the natives to persist in some streams. We have studied why trout and the natives cannot coexist, focusing on predation, competition and changes to host-parasite relationships. But most effort has been directed at the consequences of replacement of natives by trout, developing an understanding of effects on individual populations, community food-web interactions, and ecosystem functioning in terms of changes to productivity and nutrient cycling. The understanding that comes from fundamental and theoretical studies is crucial to the development of biosecurity policy aimed at preventing deleterious introductions as well as the management of vulnerable native species in the face of established invasions. Human global pressures, including invasions and the effects of acid deposition, continue more or less unabated. Back in England, however, brown trout have returned to some of the streams that lacked them because acid deposition has declined, and stream pH has increased, as a result of the shift in industrial production to other parts of the globe.