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Again, why do we care? Agent of natural selection Helps determine community structure Can influence species density or distribution

Wolves in Yellowstone Wolves in Yellowstone Wolves were extirpated in mid-1920’s Elk densities doubled within 10 years Willow, cottonwood, and quaking aspen density decreased while mean dbh increased Wolves reintroduced in 1996

Ripple & Beschta 2004

“If similar top-down effects hold true in other regions,… wolf recovery may represent a management option for helping to restore riparian plant communities and conserve biodiversity.”

Wolves produce carrion Keystone?

Regulation Errington (1946) – the idea of ‘Doomed Surplus” 1970’s -1990’s – top down vs. bottom up regulation Now – multiple states of equilibrium Predation rate Prey density Total predator response Prey growth rate w/o predation Stable equilibrium points Unstable equilibrium point

California Channel Islands

Roemer, Donalan, and Courchamp 2002 Island fox Urocyon littoralis Golden eagle Aquila chrysaetos

Roemer et al. 2002

No pigsPigs Roemer et al. 2002

LANDSCAPE-LEVEL INFLUENCES ON SWIFT FOX DEMOGRAPHICS AND COMMUNITY STRUCTURE IN SOUTHEASTERN COLORADO LANDSCAPE-LEVEL INFLUENCES ON SWIFT FOX DEMOGRAPHICS AND COMMUNITY STRUCTURE IN SOUTHEASTERN COLORADO

Historic Grassland Disturbance Regime Current Disturbance Regime What will these changes do to predator / prey interactions? Hint – think about Gause and Huffaker’s work. What will these changes do to predator / prey interactions? Hint – think about Gause and Huffaker’s work.

Vegetation structure Small mammal diversity & density Predator diversity & density Vegetation structure Small mammal diversity & density Predator diversity & density Methods Vegetation surveys Small mammal trapping Spotlight surveys Scent station surveys Methods Vegetation surveys Small mammal trapping Spotlight surveys Scent station surveys Grassland Community Characteristics Swift fox population ecology Density Home Range Reproduction Survival Density Home Range Reproduction Survival Methods Mark / Recapture Radio-telemetry Den Watches / Observations Den Camera Methods Mark / Recapture Radio-telemetry Den Watches / Observations Den Camera

Regulation? Coyote control has had mixed results in enhancing swift fox populations Coyote control has had mixed results in enhancing swift fox populations Coyote predation on swift foxes is not density-dependant Coyote predation on swift foxes is not density-dependant Coyote predation is the primary source of swift fox mortality Coyote predation is the primary source of swift fox mortality Swift fox densities are not related to coyote densities Swift fox population densities vary between different landscapes Swift fox population densities vary between different landscapes BUT:

Landscape-mediated predation low high Shrub density Grass height

Landscape-mediated predation low high Shrub density Grass height

Landscape variable 95% home range AnnualWinterSummerFall Mean basal area---- Mean grass height---- Mean shrub height ¹---- Mean shrubs / 100m² ¹ SD basal area---- SD shrub height ¹---- model R² (p-value)0.10 (0.003)0.25 (0.11) Prey base variable Mean kangaroo rat captures---- Mean grasshopper mice captures Mean deer mice captures Total captures Per capita prey biomass---- Species richness Shannon-Werner diversity model R² (p-value)0.21 (.007)0.79 (0.01)

R² = 0.40 P = R² = 0.71 P = 0.02 Swift fox population density is negatively related to grass height Swift fox population density is negatively related to grass height Swift fox survival is positively related to shrub density Swift fox survival is positively related to shrub density Juvenile survival?

Swift fox Black footed ferret San Clemente Loggerhead shrike Island fox Steven’s kangaroo rat Desert tortoise Aplomado falcon Red wolf Wyoming toad Green macaw Hawaiian crow Piping plover ‘Ne ‘Alae ‘Ula ‘Io Island night lizard Galapagos tortoise Giant woolly flying squirrel Loggerhead sea turtle California gnatcatcher Swift fox Black footed ferret San Clemente Loggerhead shrike Island fox Steven’s kangaroo rat Desert tortoise Aplomado falcon Red wolf Wyoming toad Green macaw Hawaiian crow Piping plover ‘Ne ‘Alae ‘Ula ‘Io Island night lizard Galapagos tortoise Giant woolly flying squirrel Loggerhead sea turtle California gnatcatcher What’s the point? Lethal predator control is pervasive and not always all that effective Lethal predator control is pervasive and not always all that effective Landscape management may be a more effective alternative to lethal predator control Landscape management may be a more effective alternative to lethal predator control Predation may be the proximate cause of mortality, but not the ultimate cause