Ecosystem engineering by invasive exotic beavers reduces in-stream diversity and enhances ecosystem function in Cape Horn,Chile |
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Authors: | Christopher B Anderson Amy D Rosemond |
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Institution: | (1) Institute of Ecology, University of Georgia, Athens, GA 30602, USA;(2) Omora Ethnobotanical Park, University of Magallanes, Puerto Williams, Chile;(3) Institute of Ecology and Biodiversity, Casilla 653, Santiago, Chile |
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Abstract: | Species invasions are of global significance, but predicting their impacts can be difficult. Introduced ecosystem engineers,
however, provide an opportunity to test the underlying mechanisms that may be common to all invasive engineers and link relationships
between changes in diversity and ecosystem function, thereby providing explanatory power for observed ecological patterns.
Here we test specific predictions for an invasive ecosystem engineer by quantifying the impacts of habitat and resource modifications
caused by North American beavers (Castor canadensis) on aquatic macroinvertebrate community structure and stream ecosystem function in the Cape Horn Biosphere Reserve, Chile.
We compared responses to beavers in three habitat types: (1) forested (unimpacted) stream reaches, (2) beaver ponds, and (3)
sites immediately downstream of beaver dams in four streams. We found that beaver engineering in ponds created taxonomically
simplified, but more productive, benthic macroinvertebrate assemblages. Specifically, macroinvertebrate richness, diversity
and number of functional feeding groups were reduced by half, while abundance, biomass and secondary production increased
three- to fivefold in beaver ponds compared to forested sites. Reaches downstream of beaver ponds were very similar to natural
forested sections. Beaver invasion effects on both community and ecosystem parameters occurred predominantly via increased
retention of fine particulate organic matter, which was associated with reduced macroinvertebrate richness and diversity (via
homogenization of benthic microhabitat) and increased macroinvertebrate biomass and production (via greater food availability).
Beaver modifications to macroinvertebrate community structure were largely confined to ponds, but increased benthic production
in beaver-modified habitats adds to energy retention and flow for the entire stream ecosystem. Furthermore, the effects of
beavers on taxa richness (negative) and measures of macroinvertebrate biomass (positive) were inversely related. Thus, while
a generally positive relationship between diversity and ecosystem function has been found in a variety of systems, this work
shows how they can be decoupled by responding to alterative mechanisms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Ecosystem engineer Exotic Invasion Secondary production Subantarctic |
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