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Transcript
Effect of Habitat Fragmentation on Red Fox (Vulpes
vulpes) Population Health In Northern York County,
Pennsylvania
Jeremy M. Hamsher
York College Department of Biological Sciences
The ever increasing suburbanization of the rural countryside of
America leaves many questions about the future of wildlife in these
areas. An effect of this rapid population increase is habitat
fragmentation. Fragmentation separates populations of organisms
from food sources, water and other con-specifics (Gaines 1997).
However, while fragmentation detrimentally effects some species, it
may allow others to exploit new resources (Gehring 2003). The
organisms that can exploit a fragmented landscape can move from a
population under control to an overpopulated burden on the
ecosystem (DeStefano 2003). When fragmentation occurs, organisms
get pushed into smaller and smaller parcels of land and while their
overall numbers may not increase, their density does. A species
which is adapted over a wide variety of environments may be better
able to respond to landscape changes from human impact. Today,
wildlife managers face many problems ranging from trying to retain
biodiversity in a region to managing overabundant species in the
same area (DeStefano 2003).
In northern York County, Pennsylvania little is known about the
effect of fragmentation on the red fox (Vulpes vulpes). Along with the
effects of fragmentation, little is known about the population structure
and overall health. The effect of fragmentation in York County is
important because it could be used as a management model for other
similar areas. The niche breadth of the red fox has yet to be
characterized for this broken landscape. By determining the
population dynamics in response to human-induced fragmentation,
management plans can be developed to help maintain healthy
populations of this species in human rich environments
(Gehring 2003).
• Stomach contents reveal food availability and what style of predation
foxes are using.
Figure 1.
15
5
0
• Using a canine tooth and counting the cementum annuli rings as
described in Novak 1987 shows what the age structure of a
population is and can indicate if there is a reproductive problem
within a population.
• Habitat fragmentation and the extent of fragmentation can be
detrimental or beneficial to a species depending on its ability to
adapt (Gehring 2003 and DeStefano 2003).
• Habitat fragmentation may affect predators such that it changes the
spatial availability of resources (Gehring 2003).
• Species with a broader niche and adaptability impose fewer
constraints on an organism and allow it to distribute itself throughout
the fragmented landscape. The effect of fragmentation on large
carnivores is not known (Gehring 2003).
OBJECTIVES
• Assess population health
• Determine if habitat fragmentation has a
detrimental effect on red fox distributions
and densities
METHODS
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Body Weight (kg)
Figure 1.
The frequency distribution of body weights (Kg) for
37 female and 34 male foxes.
Female Mean Body Weight = 4.273 Kg
Male Mean Body Weight = 5.462 Kg
When analyzed using an unpaired T test, the
means were not found
to be significantly different.
Figure 2.
Number of
Individuals
• Mange is a key factor in determining population health. Mange
caused by the mite Sarcoptes scabiei, is an important factor in the
mortality of foxes (Storm et al. 1976). High incidence of mange
occurs when fox density is high and may be a regulating force in the
control of fox populations (Storm et al. 1976).
10
8
6
4
2
0
Male
Female
29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
Femur Length (cm)
Figure 2.
The frequency distribution of femur lengths(cm) for
32 female and 34 male foxes as an index of growth
and maturity.
Female Mean Femur Length = 35.88 cm
Male Mean Femur Length = 36.998 cm
When tested using an unpaired T test, the means
were found to be not significantly different.
Figure 3.
10
Male r2= 0.04222
Female r2= 0.01103
8
6
4
2
0
25 30 35 40 45 50
Femur Length (cm)
Figure 3.
Correlation between femur length (cm)
and body weight (kg)
for both male and female red fox to
show current trends of
growth and development. Both r2
values
show little correlation between femur
length and body weight.
1. Locate various trapping locations by habitat type and levels of habitat
fragmentation using digital photo-orthoquads
2. Trap foxes at each location using #1 ½ foothold traps and dirt hole sets
3. Take morphological measurements of foxes captured
4. Record incidence of mange and degree to which the animal is affected
5. Remove a canine tooth for age analysis
6. Examine stomach contents
7. Trap rodents using a mark-recapture survey to determine food availability at
each location
Nothing
27
Mange Index
Male
Female
10
Stomach Contents
Bones
3
Table 2.
Body Weight
(Kg)
INTRODUCTION
• Morphological measurements such as those provided in Storm et al.
1976, Lefebvre et al. 1999, Pils 1978 gives clues as to how well the
populations are doing physically.
Carrion
41
RESULTS
Figure 4.
2
Male
r
= 0.01608
10
Female r2=0.02274
8
6
4
2
0
20.0 22.5 25.0 27.5 30.0 32.5
Head Circumference (cm)
Figure 4.
Correlation analysis of head circumference (cm)
and body weight (Kg). This is an index of current
growth anddevelopment rates for males and
females. Both r2 values show little correlation
between body weight and head circumference.
Body Weight
(Kg)
The impact of expanding human populations on wildlife often has
a negative and detrimental effect. York County has experienced
population growth of 25.2% every ten years, but the effects this
growth has on wildlife is unknown. The objective of this study is to
assess the overall population health of the red fox (Vulpes vulpes) in
northern York County, Pennsylvania and determine if habitat
fragmentation has had an affect on fox populations. Foxes will be
captured at locations of varying landscape types by using foothold
traps. Population health will be assessed by examining occurrence of
mange and age structure will be determined by counting cementum
annuli rings in a canine tooth of adults and the lack of root closure in a
juvenile canine tooth. The red fox helps maintain the delicate balance
of predator and prey in ecosystems, but little is known about their
population structure in Pennsylvania. The effects of population
increase on these predators needs to be established to help with
management and for the good of the species.
REVIEW OF LITERATURE
Number of
Individuals
PROJECT SUMMARY
Table 1.
Male
Mange Present
6%
Mange Not Present
42%
Total %
48%
Two Sided P Value= 0.0271
Female
18%
34%
52%
Table 3.
Age Structure
Juvenile
6
Adult
28
Examining the morphological data, it
appears that the foxes are not getting enough
to eat at the current time. They are primarily
feasting on carrion. The age structure is
interesting because it does not coincide with
the published literature of Storm et al (1976)
and Pils (1978). Normal ratios are from 1.5-7.5
young for every adult. Here, the ratios have
flip flopped to 4.7 adults for every juvenile.
This, if in fact is the actual age structure of the
population could illustrate a serious deficiency
in breeding. The occurrence of mange for this
population does appear to be consistent with
the results of other published studies regarding
mange occurrence rates. At this point, there
can be no correlation made between amount of
fragmentation and population health and
density. There was no definitive data that
showed one location had a higher population of
foxes. More research needs to be conducted.
LITERATURE CITED
•DeStefano, Stephen and DeGraaf, Richard M. 2003. Exploring the ecology of
suburban wildlife. Frontiers in Ecology and Environment.
1(2):95101.
•Gaines, M.S. et al. 1997. The effects of habitat fragmentation on the genetic
structure of small mammal populations. Journal of Heredity. 88:294
304.
•Gehring, Thomas M. and Swihart, Robert K. 2002. Body size, niche breadth
and ecologically scaled responses to habitat fragmentation:
mammalian
predators in an agricultural landscape. Biological
Conservation. 109: 283-295.
•Lefebvre, Christine et al. 1999. Prediction of body composition of live and
post-mortem red foxes. Journal of Wildlife Diseases. 35(2): 161-170.
•Novak, Milan et al., ed. Wild Furbearer Management and Conservation in North
America. Ontario. 1987.
•Pils, Charles M. and Martin, Mark A. 1978. Population dynamics, predator-prey
relationships and management of the red fox in Wisconsin. Technical
Bulletin No. 105 Department of Natural Resources Madison, Wisconsin.
•Storm, Gerald et al. 1976. Morphology, reproduction, dispersal and mortality
midwestern red fox populations. Wildlife Monographs. 49:82 p.
ACKNOWLEDGEMENTS:
Dr. Karl Kleiner for mentoring me and input on the ecological
perspectives of this project.
Dr. Bradley Rehnberg for giving input on the physiological
perspectives
Jim Payne for the use of his foxes
All of the landowners that allowed me to trap on their property
of