The effects of grazing on Texas kangaroo rats in
This presentation is the property of its rightful owner.
Sponsored Links
1 / 25

- state threatened species due to its rareness and small geographic range PowerPoint PPT Presentation


  • 69 Views
  • Uploaded on
  • Presentation posted in: General

The effects of grazing on Texas kangaroo rats in Wichita County, Texas Allan D. Nelson, Ji m R. Goetze, Elizabeth Watson, and Mark Nelson Department of Biological Sciences, Box T-0100, Tarleton State University, Stephenville, TX 76401.

Download Presentation

- state threatened species due to its rareness and small geographic range

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


State threatened species due to its rareness and small geographic range

The effects of grazing on Texas kangaroo rats in Wichita County, Texas Allan D. Nelson, Jim R. Goetze, Elizabeth Watson, and Mark NelsonDepartment of Biological Sciences, Box T-0100, Tarleton State University, Stephenville, TX 76401


State threatened species due to its rareness and small geographic range

-state threatened species due to its rareness and small geographic range

-IUCN (1986) lists habitat loss and degradation resulting from agricultural and infrastructure development as major threats


State threatened species due to its rareness and small geographic range

-habitat fragmented by extensive cultivation that occurred in the Rolling Plains region of Texas (Correll and Johnston 1970)

-changes in vegetation patterns at sites in Wichita County may also pose a threat


State threatened species due to its rareness and small geographic range

-only tracts of land unsuitable for cultivation were left in their natural state and these were fenced by ranchers and stocked with cattle but, because of the decline of ranching, some of these pasturelands are no longer grazed or, worse yet, have been invaded by introduced species such as Japanese brome

-lack of fire has allowed the increase of honey mesquite and lotebush in Wichita County and in some cases, rats use soils surrounding these woody species as burrow sites because the plants collected wind-blown soil and the Texas kangaroo rats dig burrows at their bases


State threatened species due to its rareness and small geographic range

-as mesquites mature, vegetation composition changes, sometimes favoring introduced grasses like Japanese brome, which grows densely and changes the habitat so that it is less suitable for D. elator


State threatened species due to its rareness and small geographic range

-Davis and Schmidley (1994) stated that Texas kangaroo rat burrows invariably entered the ground at the base of a mesquite and the primary threat contributing to the rarity of the species was the clearing of mesquite brush

-mesquite forest was not seen as a problem by Texas Parks and Wildlife Department


State threatened species due to its rareness and small geographic range

-Wichita County on a privately owned ranch that is moderately grazed pasture (0.3 head/ha) and mesquite density at the site is 168/ha (less than 1.0m tall)

-this site was compared to a nearby relatively large population of Texas kangaroo rat (Stangl et al. 1992, Goetze et al. 2007) where grazing is relatively intense (0.8 head/ha) and it has about 54 small mesquite/ha

-major soil association at both the study sites are the same and categorized as a clay loam called Kamay soils (Richardson et al. 1977)


State threatened species due to its rareness and small geographic range

-7.5 x 8.8 x 30 cm Sherman traps with rolled oats as bait

-based on parameters set by Stangl et al. (1992) and Stasey (2005) regarding burrow entrance diameter, angle of entry, and vegetation, we selected suspected burrows at the sites and placed three traps around each burrow entrance


State threatened species due to its rareness and small geographic range

-vegetation data quantified in May for burrows where Texas kangaroo rats were caught

-one square meter quadrats centered around burrow entrances in a north-south orientation -percentage cover, grass, forb, bare ground, and woody vegetation recorded

-vegetative richness and height were measured and the dominant grass, forb, and woody species identified (Goetze et al. 2007)


State threatened species due to its rareness and small geographic range

-data compared using SPSS 14.0 (www.spss.com)

-Mann Whitney test was used to test for significant differences in richness and percentages of grasses, forbs, bare ground, and woody vegetation between the two grazed sites

-data from a previous study (Stasey 2005) at an ungrazed site was included in a Kruskal –Wallis analysis to test for significant differences between the grazed and ungrazed sites


State threatened species due to its rareness and small geographic range

Moderately grazed (0.3 head/ha) burrows:

Burrow #1234567

Forbs

BroomweedXXXXXX

PepperweedX

Grass

Little BarleyXXXXX

BuffaloX

RescueX

Woody Vegetation

MesquiteXXXXX

NoneXX

Burrow Associations

FenceXX

MesquiteXXXXX


State threatened species due to its rareness and small geographic range

Heavily grazed (0.8 head/ha) burrows:

Burrow #12, 345, 8, 10679

Forbs

BroomweedX

Hog potatoXX

PepperweedXX

RagweedX

UnknownX

Grass

Little BarleyXXXXXXX

Woody Vegetation

LotebushX

MesquiteX

NoneXXXXX

Burrow Association

FenceX

LotebushX

MesquiteX

Old brush pileXXX

Prairie moundX


State threatened species due to its rareness and small geographic range

Means, standard deviations (in parentheses), and ranges [in brackets] and P-value using Wilcoxon Mann-Whitney test.

Heavily GrazedModerately GrazedP-value

Avg. Herb. Height7.1 (±7.9) [2.0-40.0]24.5 (±12.7) [9.0-29.4]0.0001*

% Bare Ground49.9 (±24.0) [0.0-80.0]20.7 (±18.1) [5.0-60.0]0.024*

% Forbs16.5 (±13.1) [1.0-35.0]33.7 (±22.6) [15.0-67.0]0.133

% Grasses24.60 (±18.9) [1.0-55.0]20.1 (±15.6) [1.0-45.0]0.623

% Woody 6.0 (±15.8) [0.0-50.0]26.1 (±26.5) [0.0-60.0]0.037*

% Other2.0 (±4.2) [0.0-2.0]0.0 (±0.0) [0.0-0.0]0.222

Richness6.2 (±2.4) [3.0-10.0]7.6 (±1.8) [6.0-10.0]0.137


State threatened species due to its rareness and small geographic range

-dominant plant species included little barley, common broomweed, hog potato, Virginia pepperweed, and western ragweed, which occur in disturbed habitats, and common broomweed is often an indicator of heavy grazing (Diggs et al. 1999)

-their dominance is likely caused by grazing of cattle and rodent activity around the burrows


State threatened species due to its rareness and small geographic range

-habitat dominated by short, herbaceous vegetation (2.0 - 40.0 cm in height)

-general agreement that D. elator requires a sparse, short-grassland habitat (Carter et al. 1985; Dalquest & Collier 1964; Roberts & Packard 1973; Stangl et al. 1992), and our findings support this conclusion

-data also indicates that grazing may be important in maintaining this type of habitat


State threatened species due to its rareness and small geographic range

Stasey (2005)

-trapped in a mesquite forest with an ungrazed understory dominated by Japanese brome

within 4.0 km of our heavily grazed site

-caught only two kangaroo rats on the periphery of the mesquite forest habitat with one from friable clay soil mounded around gate corner posts and the other along a fence-line berm separating the pasture from a wheat field

-surveyed seven quadrats for vegetational differences in the core of the ungrazed pastureland and found percent bare ground with a mean of 10.9%, grasses 63.7%, and forbs 16.1%, whereas the mean average herbaceous height was 49.0 cm

-average herbaceous height (P=0.001), percentage bare ground (P=0.009), and grasses (P=0.009) were significantly different when comparing the grazed sites to the ungrazed site examined by Stasey (2005)


State threatened species due to its rareness and small geographic range

Comparison of our two grazed sites with an ungrazed site (Stasey 2005)

-grazing can change percent bare ground and grass as well as herbaceous height, which appear to be important to Texas kangaroo rat habitat

-this habitat relationship is complicated by the dominance of the introduced grass, Bromusjaponicus at the ungrazed site and additional studies need to be conducted at ungrazed sites containing native vegetation

-based on the lack of D. elator at the ungrazed site and its relative abundance at the grazed sites, it appears that grazing plays a role in maintaining suitable habitat for Texas kangaroo rats


State threatened species due to its rareness and small geographic range

Lack of grazing significantly increased

-vegetation height at the ungrazed site, which on average was double the moderately grazed site and seven times greater than the heavily grazed site

-percentage of grasses, which was about three times greater on average at the ungrazed site when compared to grazed sites

-percentage bare ground, which on average was about one-half that of the moderately grazed site and about one-fourth that of the heavily grazed site

This tall, dense coverage by

grasses may impede:

movement of rats

ability to see potential

predators

(3) burrow construction

(4) their dust bathing activities


State threatened species due to its rareness and small geographic range

We hypothesize that grazing bison (Stangl et al. 1992), prolonged droughts, and natural prairie heterogeneity such as prairie mounds (Diggs et al. 1999; Goetze et al. 2007), and perhaps fire maintained the type of disturbances needed by the Texas kangaroo rat before cattle grazing and human mediated disturbances were used opportunistically as burrow sites. In areas where cattle no longer graze or at sites where native vegetation is overcome by invasive species, it appears that populations of Texas kangaroo rats have declined.


State threatened species due to its rareness and small geographic range

Of the 17 burrows examined in this study 47% are associated with human-mediated disturbances such as old brush piles and fence rows.


State threatened species due to its rareness and small geographic range

53% of 17 burrows are associated with more natural sites such as shrubs and prairie mounds.


State threatened species due to its rareness and small geographic range

At the heavily grazed site, lotebush and honey mesquite burrow associations were equal in number, supporting our hypotheses that mesquite is not a requirement. The type of shrub is probably not as important as is the accumulation of loose friable soil at the base of the shrubs.


State threatened species due to its rareness and small geographic range

Current knowledge of Texas kangaroo rat distribution and ecology is very incomplete. Surveys should be conducted at Buffalo Creek Reservoir and Lake Arrowhead State Park to ascertain if D. elator occurs in any protected natural areas (PNAs) in Wichita County, or if suitable habitat is available in PNAs.

Because moderate to heavy grazing and unburned brush piles appear to be important to Texas kangaroo rats, private landowners could be offered incentives to implement these management practices if Texas kangaroo rats are found on their property. Protected natural area managers might instigate grazing and brush clearing projects to increase availability of Texas kangaroo rat habitat.

It seems short-sighted to manage Texas PNAs as undisturbed medium to tall grass ecosystems, when natural prairie ecosystems were undoubtedly disturbed by grazing, fire, and drought. It is important that these research and management suggestions be considered to protect this unique Texas mammal.


State threatened species due to its rareness and small geographic range

Thanks to: Tarleton State University for research funds, undergraduate students Mark

Nelson & Elizabeth Watson, and the Goetze family for access to their property


  • Login