Competition favors elk over beaver in a riparian willow ecosystem

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Beaver (Castor spp.) conservation requires an understanding of their complex interactions with competing herbivores. Simulation modeling offers a controlled environment to examine long-term dynamics in ecosystems driven by uncontrollable variables. We used a new version of the SAVANNA ecosystem model to investigate beaver (C. Canadensis) and elk (Cervus elapses) competition for willow (Salix spp.). We initialized the model with field data from Rocky Mountain National Park, Colorado, USA, to simulate a 4-ha riparian ecosystem containing beaver, elk, and willow. We found beaver persisted indefinitely when elk density was < or = 20 elk km_2. Beaver persistence decreased exponentially as elk density increased from 30 to 60 elk km_2, which suggests the presence of an ecological threshold. The interaction of beaver and elk herbivory shifted the size distribution of willow plants from tall to short when elk densities were > or = 30 elk km_2. The loss of tall willow preceded rapid beaver declines, thus willow condition may predict beaver population trajectory in natural environments. Beaver were able to persist with slightly higher elk densities if beaver alternated their use of foraging sites in a rest-rotation pattern rather than maintained continuous use. Thus, we found asymmetrical competition for willow strongly favored elk over beaver in a simulated montane ecosystem. Finally, we discuss application of the SAVANNA model and mechanisms of competition relative to beaver persistence as metapopulations, ecological resistance and alternative state models, and ecosystem regulation.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Competition favors elk over beaver in a riparian willow ecosystem
Series title Ecosphere
Volume 3
Issue 11
Year Published 2012
Language English
Publisher Ecological Society of America
Publisher location Washington, D.C.
Description 16 p.
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Ecosphere
First page 1
Last page 15