Download Indirect Predator Effects

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