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Indirect Predator Effects Consumptive and Nonconsumptive Indirect Effects ESRM 450 Wildlife Ecology and Conservation Indirect Predator Effects Occur when predators cause a change in some property of a transmitter species, which in turn has an effect on a 3rd species within the community, the receiver Predator Change in some property Transmitter Indirect Effect Prey species Change in some property Receiver + or - Consumptive Indirect Effects Occur when predators cause a change in the density of a transmitter species, which in turn has an effect on the receiver • Also called density-mediated indirect interactions (DMII) Schmitz et al. (2004) Ecol Lett Predator Consumption reduces density Transmitter Indirect Effect Prey species Change in some property Receiver + or - Cougar (Felis concolor) Consumption reduced density prior to ~1930 Mule deer (Odocoileus hemionus) (Transmitter) Indirect Effect + Reduced herbivory on tree saplings Black oak (Receiver) Ripple and Beschta (2008) Biol Cons Implications for Conservation • After ~ 1930, cougars largely eliminated from Yosemite NP • Mule deer population grew, herbivory on black oak (Quercus kelloggii) intensified, park landscape became less forested • Yosemite ecosystem has changed because of historical predator control – No longer serves as a benchmark Ripple and Beschta (2008) Biol Cons Non-consumptive Indirect Effects Occur when predators cause a change in a trait of the transmitter species, which in turn has an effect on the receiver • Also called trait-mediated indirect interactions (TMII)1 - Trait commonly modified: behavior - “Behaviorally Mediated Indirect Interactions” (BMII)2 Schmitz et al. (2004) Ecol Lett Dill et al. (2003) Ecology Predator Intimidation alters trait (behavior, morphology) Transmitter Indirect Effect Prey species Change in some property Receiver + or - Tiger shark (Galeocerdo cuvier) Intimidation increases use of seagrass meadow edges Dugong (Dugong dugon) (Transmitter) Indirect Effect - Intense herbivory (reduced coverage, altered species composition) Seagrass (Receiver) Heithaus et al. (2011) In prep Implications for Conservation • Loss of tiger sharks from Shark Bay ecosystem could shift dugong herbivory away from meadow edges – Alter patterns of seagrass biomass and species composition • Ultimately, larger dugong population (closer to K) would likely overgraze seagrass Pisaurina mira ‘Sit-and-wait’ Dominant herb Solidago rugosa used heavily (low P. mira risk) Preferred grasses and forbs avoided (high risk from P. mira) Melanopuls femurrubrum Responds by shifting foraging behavior Schmitz (2008) Science