PARENT SESSION
Oral Session #45: Herbivory: Effects on Plants. Presiding: T. Craig.
Wednesday, August 8, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Cascading effects of mammalian herbivores on ecosystem dynamics in a coastal dune system.

McNeil, Sean¹, Cushman, J.¹, ¹

ABSTRACT- Herbivores can have large effects on individual plants (growth, tissue chemistry and resources allocated to reproduction), and these effects can cascade into ecosystem-level processes by altering nutrient cycling. In a coastal dune system in northern California, we evaluated the influence of black-tailed deer (Odocoileus hemionus columbianus) on the growth and fecundity of silver bush lupine (Lupinus chamissonis), and the consequences of these effects for C:N ratio of leaf tissue, litter deposition, and soil nitrogen pools and mineralization rates. Results from three- and four-year exclosure experiments show that deer browsing significantly reduced growth rates of lupines. These negative effects of herbivory translated into significant reductions in fecundity. Deer browsing significantly decreased C:N ratios of leaf tissue and the amount of litter collected underneath each lupine, which led to faster nitrogen mineralization rates in the soil underneath browsed shrubs. However, there was no detectable difference of nitrogen pools between browsed and unbrowsed lupines. We also found that deer browsing indirectly reduces the abundance of tip-galling nematodes on these lupines. In conclusion, we have shown that a single herbivore species directly reduces the growth and reproduction of an influential plant species, thereby indirectly altering a key ecosystem process.

KEY WORDS: ecosystem ecology, animal-plant interactions, mammalian herbivory, nitrogen mineralization