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Again, why do we care? Helps determine community structure Agent of natural selection Can influence species density or distribution 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.” Ripple & Beschta 2004 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 Stable equilibrium points Total predator response Prey growth rate w/o predation Unstable equilibrium point Prey density California Channel Islands Island fox Urocyon littoralis Golden eagle Aquila chrysaetos Roemer, Donalan, and Courchamp 2002 Roemer et al. 2002 No pigs Pigs Roemer et al. 2002 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. Swift fox population ecology • Density • Home Range • Reproduction • Survival • • • • Methods Mark / Recapture Radio-telemetry Den Watches / Observations Den Camera Grassland Community Characteristics • Vegetation structure • Small mammal diversity & density • • Predator diversity & density • • • Methods Vegetation surveys Small mammal trapping Spotlight surveys Scent station surveys Regulation? Coyote predation is the primary source of swift fox mortality Swift fox population densities vary between different landscapes BUT: Coyote control has had mixed results in enhancing swift fox populations Swift fox densities are not related to coyote densities Coyote predation on swift foxes is not density-dependant Landscape-mediated predation Grass height high Shrub density low high low Landscape-mediated predation Grass height high high low Shrub density low Landscape variable 95% home range Annual Winter Summer Fall Mean basal area - - - - Mean grass height - - - - Mean shrub height ¹ - - - - 0.10 0.25 - - SD basal area - - - - SD shrub height ¹ - - - - 0.10 (0.003) 0.25 (0.11) - - - - Mean grasshopper mice captures 0.09 0.41 - - Mean deer mice captures 0.07 - - - Total captures - 0.13 - - Per capita prey biomass - - - - Species richness - 0.25 - - 0.05 - - - 0.21 (.007) 0.79 (0.01) Mean shrubs / 100m² ¹ model R² (p-value) Prey base variable Mean kangaroo rat captures Shannon-Werner diversity model R² (p-value) 0.25 R² = 0.40 P = 0.005 Swift fox population density is negatively related to grass height 0.15 0.1 0.05 0 0 5 10 15 20 Mean grass height (cm) Swift fox survival is positively related to shrub density 1.2 Adult fox survival Density 0.2 1 0.8 0.6 R² = 0.71 P = 0.02 0.4 0.2 0 0 2 4 Shrub density Juvenile survival? 6 Swift fox What’s the point? Black footed ferret San Clemente Loggerhead shrike Island fox Lethal predator control is Steven’s kangaroo rat pervasive and not always Desert tortoise all that effective Aplomado falcon Red wolf Predation may be the Wyoming toad proximate cause of mortality, Green macaw Hawaiian crow but not the ultimate cause Piping plover ‘Ne ‘Ne ‘Alae ‘Ula Landscape management may ‘Io be a more effective alternative Island night lizard Galapagos tortoise to lethal predator control Giant woolly flying squirrel Loggerhead sea turtle California gnatcatcher
