“Top Down” predator controls of ecosystem processes: Can coyotes (Canis latrans) dampen prey population cycles and influence herbivory rates on the Sevilleta NWR? Robert R. Parmenter, Lucina Hernandez, and John Laundre Department of Biology, University of New Mexico, and Instituto de Ecologia, Durango, Mexico
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Robert R. Parmenter, Lucina Hernandez, and John Laundre
“Top Down” predator controls of ecosystem processes: Can coyotes ( Canis latrans ) dampen prey population cycles and influence herbivory rates on the Sevilleta NWR?. Robert R. Parmenter, Lucina Hernandez, and John Laundre Department of Biology, University of New Mexico, - PowerPoint PPT Presentation
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“Top Down” predator controls of ecosystem processes:
Can coyotes (Canis latrans) dampen prey population cycles and influence herbivory
rates on the Sevilleta NWR?
Robert R. Parmenter, Lucina Hernandez, and John Laundre
Department of Biology, University of New Mexico,
and Instituto de Ecologia, Durango, Mexico
Estimating coyote impacts on small mammal prey:
• Need coyote density estimates
• Need coyote energy requirements and prey energy equivalences, coupled with digestive assimilation efficiencies
• Need small mammal prey density estimates
• Need coyote diet composition data
• Need estimates of prey productivity
Coyote Density Estimation• Statistics derived from basin-and-range
topographic regions of shrub-steppe in Utah.
• Absolute densities (D=N/A) calculated from 8 coyote populations enumerated during radio-collar studies (i.e., known numbers of coyotes, N, and known home range sizes, A).
• Verified coyote enumeration using radioactive markers in scats.
(Data from Dr. F. F. Knowlton and colleagues, Utah State University)
Development of Scat Index
• Collected coyote scats along measured lengths of dirt roads on valley flats.
• First, cleared roads of scats, then resampled at a later date (several days to a week).
• Scat Index computed as # scats per 24-hour period per mile of road.• Index then correlated with known coyote
Available = Observed + Est. Reprod.Reproduction: 1 litter/season:F-A: 4.5/litter; M-J: 3/litter; A-O: 2/litter, N-J: 1/litter.
Rodent Productivity Vs. Predation
0
2000
4000
6000
8000
10000
12000
Den
sity
(No.
/Sq.
Km
.)
No. rodents eaten per season Total rodents available
S F S F S F S F S F S F S F S F S F S F
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Rodent Productivity Vs. Predation
0
2000
4000
6000
8000
10000
12000
Den
sity
(No.
/Sq.
Km
.)
No. rodents eaten per season Total rodents available
S F S F S F S F S F S F S F S F S F S F
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Availability = Observed + Estimated Reproduction
Rodent Productivity Vs. Predation
0
2000
4000
6000
8000
10000
12000
Den
sity
(No.
/Sq.
Km
.)
No. rodents eaten per season Total rodents available
S F S F S F S F S F S F S F S F S F S F
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
Availability = Observed + Estimated Reproduction
Reproduction: 1 litter/6 months,
which doubles population.
Coyote Impacts on Small Mammals:
• At Sevilleta, potential average reduction of rabbit productivity by 46%
• At Sevilleta, potential average reduction of rodent productivity by 32%
• In west Texas, coyote presence resulted in an average ~50% reduction of rabbits and kangaroo rats compared to coyote removal areas (Henke & Bryant 1999)
Tentative Conclusions
• Coyote predation results in substantial removal of prey biomass, prey densities.
• Coyote predation influences small mammal prey population dynamics, but cannot consistently prevent episodic population outbreaks (associated with precipitation dynamics).
• Experimental coyote manipulations needed to verify these calculations.