Small Mammal Abundance and Diversity in Relation To Prairie Dog Reintroduction Sites
Ty Werdel
Chadron State College
10 August 2013
Introduction:
Prairie Dogs ( Cynomys spp.
) are considered ecosystem engineers and keystone species in
North American grasslands (Ceballos, List, and Pacheco, 1998). They have great impacts on abiotic and biotic features: influencing environmental heterogeneity, plant succession, hydrology, nutrient cycling, biodiversity, and landscape architecture (Ceballos, List, and
Pacheco, 1998). Studies have shown that prairie dog colonies create habitat for mammals, birds, reptiles, amphibians, and arthropods (Ceballos, List, and Pacheco, 1998). This results in greater species richness in association with prairie dog colonies. Many species may be dependent upon prairie dogs or their colonies for survival. The black-footed ferret, mountain plover, ferruginous hawk, swift fox, and burrowing owl have all become endangered or nearly endangered due to the population decline of prairie dogs (Prairie Dog Coalition). In the last 150 years prairie dog populations have declined by 90-98%. They historically occupied millions of hectares of land, but due to encroachment on habitat by human populations and extermination their range is disappearing. The Gunnison’s prairie dog’s ( Cynomys gunnisoni ) range is generally considered the southwest or Four Corners region of the United States. This species was selected to be reintroduced within the Sevilleta National Wildlife Refuge in 2010 because they were present in the area historically before their eradication by ranchers. Their reintroduction within the refuge gives researchers the opportunity to study the effects of C. gunnisoni upon the ecosystem. Much of the research done on the relationship between small mammals and prairie dogs has been with the black-tailed prairie dog ( Cynomys ludovicianus ).
Small mammals, in habitats including prairie dogs, utilize prairie dog burrows for shelter: some cannot dig their own burrows in the hard ground, while others simply exploit them because of their presence (Ceballos, List, and Pacheco, 1998). The burrows also provide escape from predators and denning opportunities. Small mammal species richness, diversity, and abundance have been shown to be higher in areas with prairie dogs when compared to similar habitats without prairie dogs (Ceballos, List, and Pacheco, 1998). Certain species of small mammals are also more apt to live in areas of short grass and bare ground, such as pocket mice ( Perognathus ) and kangaroo rats ( Dipodomys ) (Bock and Bock, 2006). Over the range of an ecosystem, small mammal species richness, diversity, and abundance will be higher because of the differing habitats created by prairie dog presence (Fascinating Facts).
The research conducted is important to the scientific community because the relationship between small mammals and C. gunnisoni has not been well documented. I evaluated how small
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mammal species have responded to the presence of C. gunnisoni by measuring small mammal species diversity and relative abundance between control sites and reintroduction sites. This will help to further understand the relationship between C. gunnisoni and the ecosystem which they inhabit.
Methods:
Trapping Location and Design:
This research was conducted within the boundaries of the Sevilleta National Wildlife
Refuge in Socorro County, New Mexico. Small mammal trapping was done on two 16 ha treatment plots (prairie dog reintroduction study plots) and two 16 ha control study plots. The plots are labeled A , B , C , and D . A and C are control study plots (no prairie dog reintroduction), while B and D are the prairie dog reintroduction study plots. These plots are located in a transition zone between Chihuahuan and Plains grassland ecosystems along Test Well Road on the east side of the refuge. 169 Sherman Live Traps, along with trap shades, were placed in each plot covering a 9 ha grid. The grid consisted of traps being placed at 25 m intervals, with thirteen traps in each row. Flags were placed and numbered at each trap to aid in data recording.
Trapping Periods:
Each plot was trapped once a week for four nights. Control plot A was trapped 3-7 June
2013, control plot C was trapped 10-14 June 2013, treatment plot B was trapped 17-21 June
2013, and treatment plot D was trapped 24-28 June 2013.
Trapping Procedure:
The traps were moved and set up at a given locality on Monday afternoon each week.
The traps were then baited and set each night for four nights, and then checked at dawn each following morning. Each trap was baited with steamed, crimped oats tossed into the trap after it is placed on the ground. Each morning transects were walked up and down and open traps were closed. Traps were not reopened until they were re-baited that evening. When a closed trap was encountered, it was first checked to see if an animal was present. If a trap contained an animal, that animal was then processed. While checking for animals on Friday morning, traps were picked up, emptied, and returned to storage boxes, ready for placement at another locality the following week.
Animal Processing:
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For each capture, the trap number was recorded and the animal was removed from the trap. Each animal was identified to species, then sexed, and aged (juvenile or adult). Specific measurements (total length, length of tail, length of foot, and length of ear) were taken only for those genera which required them for species identification: Peromyscus , Onychomys ,
Perognathus , and Reithrodontomys .All measurements were taken to the nearest millimeter.
Reproductive status was then determined by examination of the genitalia (lactating, vaginal, pregnant, or scrotal). In order to recognize recaptures during the week, all new captures were clearly marked on their ventral side with a permanent marker (red for females and blue for males). This was not necessary on the fourth morning. Before releasing the individual, it was weighed to the nearest gram. Recaptures were only identified by species and the sex was recorded. Animals that perished during captivity on plots were noted in the comments on field data sheets.
Results:
Small Mammal Diversity and Distribution:
Ten species of small mammals representing three families (Heteromyidae, 4 spp;
Sciuridae, 1 spp; Cricetidae, 5 spp) were captured during the research period. Species captured were Merriam’s kangaroo rat (
Dipodomys merriami ), Ord’s kangaroo rat ( Dipodomys ordii ), banner-tailed kangaroo rat ( Dipodomys spectabilis ), silky pocket mouse ( Perognathus flavus ), spotted ground squirrel ( Spermophilus spilosoma ), southern plains woodrat ( Neotoma micropus ), northern grasshopper mouse ( Onychomys leucogaster
), Mearn’s grasshopper mouse
(Onychomys arenicola), brush mouse (Peromyscus boylii), and deer mouse ( Peromyscus maniculatus ).
Among control and treatment plots there were no significant differences in species richness. The control plots yielded 8 (Plot A) and 7 (Plot C) different species, while the treatment plots produced 7 (P lot B) and 6 (Plot D) different species (Fig. 1). Perognathus flavus and
Onychomys leucogaster were more abundant within treatment plots than control plots.
Dipodomys merriami was only captured within treatment plots and genus Peromyscus was only captured within control plots. Dipodomys spectabilis was more abundant in Plot D than any of the other plots (Fig. 2.).
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9
8
7
6
3
2
1
5
4
0
Fig.1
. Treatment and control species richness.
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7 7
A B C
Plot
4
6
D

Fig. 2. Total small mammals by species caught in each plot. Species code is derived from first 2 letters of genus combined with first 2 letters of species.
70
63
61
60
50
41
42
40
30
20
C
D
A
B
20
10
3
1
12
5
8
6 6
9
1
2 2
1
2 2
8
4
7
3
1
2
3
4
5
0
DIME DIOR DISP NEMI ONAR ONLE PEBO PEMA PGFV SPSP
Species
Small Mammal Abundance:
The study resulted in a total of 324 individual small mammals captured across all plots.
The most abundant species captured over all plots was Perognathus flavus with 207 unique individuals, followed by Dipodomys spectabilis (41), Dipodomys ordii (25), Onychomys leucogaster (21), Spermophilus spilosoma (14), Neotoma micropus (5), Dipodomys merriami (4),
Onychomys arenicola (3), Peromyscus boylii (3), and Peromyscus maniculatus (1). Total abundance between control and treatment plots was not significant statistically, but there is a trend with more individuals captured in the treatment plots than the control plots (Fig. 3). The average number of individuals captured on control and treatment plots yields a P-value of 0.3168
(Fig. 4).
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Fig. 3. Total unique individual small mammals captured per plot.
120
100
80
60
40
20
68
90
70
96
0
A B C D
Plot
Fig 4. Average total number of individuals captured among control and treatment plots.
100
90
80
70
60
50
40
30
20
10
0
69
93
Control Treatment
Conclusions:
With a limited amount of research time, it is difficult to assess exactly how prairie dogs are influencing small mammal diversity and abundance. Prairie dogs have the ability to influence small mammals in many different ways by impacting abiotic and biotic features. They can influence environmental heterogeneity, plant succession, hydrology, nutrient cycling,
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landscape architecture, and biodiversity. My results showed that small mammal species diversity and distribution did not seem to be influenced by the reintroductions, but the data does show a trend of abundance being higher on reintroduction sites which supported previous research and my own hypothesis. The data from this study also supports previous research in the fact that short term studies may not collect enough data to show significant trends. The fact that total overall abundance of small mammals was low could be due to only having one trapping period per site. This was not a long enough time for significant data to be collected.
The fact that I trapped only in the in a period of drought could have also affected mammal activity. This may have caused low abundance and less variation between all plots. This was a baseline study and the first year C. gunnisoni was researched on the Sevilleta National Wildlife
Refuge, so future research can be built upon the data gathered during this study. Suggestions for future research include extending trapping periods, increasing the amount of traps, and trapping during different seasons. There is also potential for future research on specific species.
Future researchers could also combine vegetation maps, prairie dog burrows, and trapping data with GIS and spatial mapping. This would enable researchers to see what types of plants and what burrows small mammals are utilizing. With more data in the future, significant trends are likely to surface.
Citations
Bartz, S.E., L.C. Drickamer, and M.J.C. Kearsley. "Response of Plant and Rodent Communities to
Removal of Prairie Dogs (Cynomys Gunnisoni) in Arizona." Journal of Arid Environments 68.3
(2007): 422-37. Print.
Bock, Carl E., and Jane H. Bock. "Response of birds, small mammals, and vegetation to burning sacaton grasslands in southeastern Arizona." Journal of Range Management Archives 31.4 (2006): 296-
300. Print.
Ceballos, G., R. List, and J. Pacheco. "Influence of Prairie Dogs (Cynomys Ludovicianus) on Habitat
Heterogeneity and Mammalian Diversity in Mexico." Journal of Arid Environments 41.2 (1999):
161-72. Print.
Clark, Tim W., Thomas M. Campbell, III, and Denise E. Casey. "Prairie Dog Colony Attributes and
Associated Vertebrate Species." Western North American Naturalist 42.4 (1982): 572-82. Print.
"Fascinating Facts about Prairie Dogs." Prairie Dog Coalition . N.p., n.d. Web. 07 Aug. 2013.
<http://www.prairiedogcoalition.org/facts-about-pd.php>.
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