Invasive Species

Invasive species are one of the leading drivers of loss of native biodiversity and changes in ecosystem function. Defined by their non-native, harmful, and quickly spreading characteristics, invasive species are a growing focus of ecological research.  These species threaten human health, cause financial damage, and alter ecosystem function.  For these reasons, the need is urgent for new management approaches and stronger policy on invasive species.  Aquatic systems have not been immune to these invasions.  In fact, invasive species are a top threat to many aquatic systems including the Great Lakes, where over 183 non-native species are known.  CAC researchers led by David Lodge and Gary Lamberti are looking for ways to control and prevent the spread of invasive species in aquatic ecosystems.  To do this, they are collaborating with biologists, economists, and mathematicians to understand what happens at each stage of the invasion process.

Pathways of Invasion

How do organisms end up in new places? Increasing trade, especially international trade, is the answer.  In the first stage of any Great Lakes invasion, for example, organisms are moved from their native environments through shipping, as hitchhikers in ballast water, on cargo, or on ship’s hulls.  Other major pathways of invasion into the Great Lakes and many other ecosystems globally include the pet, nursery, and watergarden trades, recreational boating, and bait dumping.  CAC researchers have looked at some of the ways species are introduced and are now working to determine what specific pathways have the highest risk of introducing potentially invasive species.  Some of this work includes developing models of recreational boater movement, as well as models to determine the riskiest global shipping routes for potentially harmful species introductions.  A better understanding of pathways provides direct guidance on how to prioritize management and policy efforts.  Much of this on-going work is led by Lodge in collaboration with two collaborators at The Nature Conservancy, John Andersen, Director of the Great Lakes Program, and John Randall (Director of the Global Invasive Species Initiative.


Once introduced to a new area, why are some species able to thrive and reproduce while others simply die off?  Researchers at CAC have shown that several factors influence successful establishment, including the similarity of native and foreign habitats, the number of individuals introduced and the frequency of introductions, and species traits such as fecundity. CAC researchers, led by Lodge and colleagues, are using population models to estimate the risk of establishment of non-native species from unintentional releases like those that commonly occur in ships' ballast water.  

Spread and Impacts

What is it about a zebra mussel, an invasive species brought over from the Caspian Sea in ballast water, which allows it to out-compete native mussels and reach very high and harmful densities? Why do only some non-native species cause such harm? Why does a rusty crayfish, invasive in many parts of the Upper Midwest, have such harmful impacts in its non-native range as compared to its native range? CAC researchers, including Lamberti and Lodge, are investigating these later stages of the invasion process, the harmful spread and impact of some species. By learning more about the biology of the species themselves, how these species interact in their new environment, and how those interactions affect community and ecosystem function, researchers are better able to forecast the impact of future invasions.  For example, researchers from the Lodge, Feder, and Lamberti laboratories are investigating the roles of predation, hybridization, and competition in the dominance of the rusty crayfish in its non-native environment.  Past work has shown that all of these factors are important in explaining the dominance of this crayfish to other crayfish but there are still more questions to be answered. Center researchers are also conducting extensive statistical analyses of non-native and native species in the Great Lakes to discover characteristics that distinguish invasive from non-invasive species, and species that become nuisances from those that do not.  Such analyses, like those published on fishes and mollusks, can provide the basis for species screening protocols like those adopted in Australia but not yet in the U.S.  In a recently published analysis, Lodge and colleagues demonstrated that species screening provides both environmental and economic benefits.

Risk Analysis

To inform management agencies of the best ways to control and prevent these harmful species, researchers at CAC together with their mathametics and economic collaborators, are developing risk analyses to screen for both high-risk pathways and high-risk species.  This collaboration will also guide management in the allocation of resources to prevention or control to reduce the probability of future invasion disasters in the best way possible.  CAC work on ecology and economics shows that risk assessment and risk management must go hand-in-hand because ecological and economic forces interact strongly and because natural resource management targets cannot be set independently of the costs of achieving those goals. The systematic study of risk at every stage in the invasion process provides the quantitative insight to target management interventions in the most cost-effective way possible.  Lodge recently led the development of policy and management guidance on invasive species for the Ecological Society of America.

Selected Publications

Kolar, C.S. and D.M. Lodge.  2002.  Ecological predictions and risk assessments for alien species. Science 298:1233-1236.

Leung, B., D.M. Lodge, D. Finnoff, J.F. Shogren, M. Lewis, and G. Lamberti.  2002.  An ounce of prevention or a pound of cure: bioeconomic risk analysis of invasive species. Proceedings: Biological Sciences (formerly Proc Royal Soc London B) 269: 2407-2413.
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Drake, J.M. and D.M. Lodge.  2004.  Global hotspots of biological invasions: evaluating options for ballast-water management. Proc. R Soc London B 271:575-580.
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Lodge, D.M., S. Williams, H. MacIsaac, K. Hayes, B. Leung, S. Reichard, R.N. Mack, P.B. Moyle, M. Smith, D.A. Andow, J.T. Carlton, and A. McMichael.  2006. Biological invasions: recommendations for U.S. policy and management [Position Paper for the Ecological Society of America]. Ecological Applications 16:2035-2054.
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Drake, J.M. and D.M. Lodge.  2006.  Allee effects, propagule pressure and the probability of establishment: risk analysis for biological invasions.  Biological Invasions 8:365-375.
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Bossenbroek, J.M., L.E. Johnson, B. Peters and D.M. Lodge.  Westward expansion of the zebra mussel in North America: forecasting a low probability-high impact event. Conservation Biology 21 (3), 800–810.
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Keller R.P., D.M. Lodge and D.C. Finnoff.  2007. Risk assessment for invasive species produces net bioeconomic benefits.  Proceedings of the National Academy of Sciences 104:203-207.
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Keller, R.P. and D.M. Lodge. 2007. Species invasions from commerce in live aquatic organisms: problems and possible solutions. BioScience 57:428-436.
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Keller, R.P., J.M. Drake, and D.M. Lodge. 2007. Fecundity as a basis for risk assessment of nonindigenous freshwater mollusks. Conservation Biology 21:191-200.
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Costello C., J.M. Drake and D.M. Lodge.  2007. Evaluating an invasive species policy: ballast water exchange the Great Lakes.  Ecological Applications 17 (3): 655-662.
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Fowler, A. D.M. Lodge, and J. Hsia. Failure of the Lacey Act to protect U.S. ecosystems against animal invasion. In press and forthcoming in September issue.
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