Transcript The Effects of Coyote Removal in Texas: A Case Study in

The Effects of Coyote Removal
in Texas:
A Case Study in Conservation
Biology
Adapted from activity by
Margaret Carroll
Department of Biology
Framingham State College
National Center for Case Study Teaching in Science website;
http://ublib.buffalo.edu/libraries/projects/cases/case.html
Plains of West Texas
• Shortgrass prairie
• chaparral
Primary Producers:
• Grasses, herbaceous
flowering plants
(forbs)
• Mesquite, yucca
Herbivores & Scavengers
• Jackrabbits &
cottontails
• Ground squirrels
• Rats (3 species)
• Mice (7 species)
Ord’s Kangaroo Rat
Mesopredators
•
•
•
•
Badgers
Bobcats
Skunks
Grey fox
Top Predator
• Coyote
What does this food web look like?
• Ideas –
• Draw on board
Part I
• Predator removal
• The Nature Conservancy wants to
determine the effects of coyote removal in
West Texas
• Your group has been asked to submit a
proposal
Part I
Questions
• What specific question do you intend to
answer?
• What type of experimental treatment and
control will you use?
• What variables do you intend to monitor?
Part II
• Congratulations! Your proposal has been
funded.
• Experimental design:
– Four, 5,000 ha sites
– 2 controls, 2 treatments
– Similar ecological communities represented
Part II – Experimental Design
Figure 1. Location of experimental sites in West Texas. Sites 1 and 2 were
the control sites. Coyotes were removed from sites 3 and 4 and from a 5-km
border (figure from Henke and Bryant 1999, used with permission).
Part II-Experimental Design
• Experimental design:
– Four, 5,000 ha sites
– 2 controls, 2 treatments
• All coyotes removed from treatment sites
& 5 km border
• No manipulation of control sites
• Animal community monitored on all sites:
– 1 year prior to treatment
– 2 years following coyote removal
Part II
Question
• Make two predictions concerning the
effects of coyote removal on the fauna of
West Texas.
Part III - Mesopredators
• Mesopredator populations monitored for 3
years
• Total abundance of badgers, bobcats,
skunk and fox found on treatment and
control sites plotted each year
• Use these data to interpret the impact of
coyote removal on the community of small
mammalian predators
Part III - Mesopredators
Figure 2. Relative abundance of mammalian mesopredators in the experimental
sites before and after treatment. Error Bars represent one standard error (figure
modified from Henke and Bryant 1999, used with permission).
Part III - Mesopredators
Questions
• What effect does coyote removal have on
the mesopredator populations?
• Predict what might have happened to the
rodent populations as a result of changes
in the mesopredator populations.
Part IV – Rodent Population Size
• You decide to analyze data on rodent
population size next
• As a measure of population size, you
compare rodent biomass in grams per
hectare in treatment vs. control areas over
3 years
Part IV – Rodent Population Size
Figure 3. Biomass of rodents in the experimental sites before and after coyotes were
removed from the treatment sites. Error Bars represent one standard error (figure
modified from Henke and Bryant 1999, used with permission).
Part IV – Rodent Population Size
• Questions
• What do you think is the primary factor
controlling rodent population growth?
• Given the changes in population size,
what other changes might you expect in
the rodent community?
Part V – Rodent Diversity
• Population size of individual rodent
species shows Ord’s kangaroo rat doing
very well in treatment areas
• Examine the data:
Part V – Rodent Diversity
Figure 4. Diversity of rodents in the experimental sites before and after coyotes were
removed from the treatment sites. Rodent diversity was estimated using Simpson's
Index. Error Bars represent one standard error (figure modified from Henke and Bryant
1999, used with permission).
Part V – Rodent Diversity
Questions
• In one sentence summarize the meaning of the graph
shown in Figure 4.
• How does the competitive success of Ord's kangaroo rat
change in the absence of coyotes?
• What term could be used to describe the role of the
coyote in this community?
• Propose one possible cause for the decline in rodent
diversity in the control areas after treatment begins.
• In your report to The Nature Conservancy, how will you
summarize the impact of coyote removal in this
community?
References
• Henke, S.E., and F.C. Bryant. 1999. Effects of
coyote removal on the faunal community in
Western Texas. Journal of Wildlife Management
63:1066-1081.
• Carroll, M. 2002. The effects of coyote removal
in Texas: A case study in conservation biology.
National Center for Case Study Teaching in
Science website:
http://ublib.buffalo.edu/libraries/projects/cases/case.html ; site visited 9/06