Emerging lessons: Invasive species effects that cross habitat boundaries

Background/Question/Methods

Invasion of a species in one habitat can change fluxes of materials and organisms to adjacent or distant habitats, with consequences for food webs and ecosystem processes.  Here we summarize findings from experimental and comparative studies of invasive aquatic and terrestrial species that affect linked stream-riparian ecosystems.  

Results/Conclusions

In Japan, invading rainbow trout triggered changes in feeding behavior of native char that decreased aquatic insect emergence 35% and riparian spiders 65%.  Similarly, brook trout that replace cutthroat trout in western U.S. streams reduced emergence flux by 36% and spiders by up to 20%, owing to their higher production and different foraging traits.  Reciprocally, invasion of western U.S. riparian areas by Russian olive has altered stream organic matter budgets and nutrient dynamics, presumably via its ability to fix nitrogen, and because its low-quality leaf litter is decomposed slowly and underutilized by native stream animals.  Strong cross-habitat effects of species additions or losses can be caused by species with novel functional traits, trophic mismatches between invaders and native food webs, and relatively subtle differences in behavior of invasive species versus natives they replace.