Transcript Predator-prey relationships


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
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•
•
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Methods
Mark / Recapture
Radio-telemetry
Den Watches / Observations
Den Camera
Grassland Community Characteristics
• Vegetation structure
• Small mammal diversity & density
•
• Predator diversity & density
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•
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