1 / 32

Effects of Soil Type and Fertility and Large Herbivores on East-African Savanna Small Mammals

Effects of Soil Type and Fertility and Large Herbivores on East-African Savanna Small Mammals. Bradley J. Bergstrom Biology Department, Valdosta State University, Valdosta, GA. Mpala Research Centre. Habitat Manipulations: Large-Herbivore Exclusion & Prescribed Burns.

brilliant
Download Presentation

Effects of Soil Type and Fertility and Large Herbivores on East-African Savanna Small Mammals

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Effects of Soil Type and Fertility and Large Herbivores on East-African Savanna Small Mammals Bradley J. Bergstrom Biology Department, Valdosta State University, Valdosta, GA Mpala Research Centre

  2. Habitat Manipulations: Large-Herbivore Exclusion & Prescribed Burns Rodent populations responded positively to fencing (Keesing 1998) Was it: a) release from diffuse competition for resources, or b) improved cover? Burns should enhance forage, but short-term effect negative on rodents due to loss of cover. This effect may persist, depending on response of larger herbivores (Sensenig 2004),

  3. Native Large Mammalian Herbivores “Megaherbivores” Mixed Feeders, Ruminants Zebra: grazer, non-ruminant

  4. Black Cotton soil • Vertisol of volcanic origin • More productive grassland substrate • Dominated by Acacia drepanolobium • More sparsely bushed • Single dominant small (Murid) rodent: Saccostomus mearnsi

  5. Saccostomus mearnsi (pouched mouse)

  6. Red soil • Sandy loam • More densely bushed, with greater diversity of woody species • Less productive grassland • Several co-dominant small rodents…

  7. Aethomys sp. (bush rat) Acomyssp. (spiny mouse)

  8. Arvicanthis sp. (grass rat) Tatera sp. (gerbil)

  9. Mus musculoides (pygmy mouse) Elephantulus rufescens

  10. Boma • Cattle enclosure of traditional pastoralists • Cleared of woody vegetation • Ringed with cut thorn-scrub (Acacia) • Becomes highly enriched over years of use

  11. Glade • Abandoned boma site, attracts native large herbivores (feeding and bedding) • Dense grassy understory, woody plants suppressed • Effect lasts for decades, sustained by herbivory • Some glades become closely cropped “grazing lawns”

  12. Ungrazed Glade in Red Soil Augustine and McNaughton (2006)

  13. Ungrazed Glade in Black Cotton • KLEE (Kenya Long-Term Exclosure Experiment [Young et al. 1997] overlaid on old glades • Rankest grass on “Zero” plots; also dense on “W” plots (native ungulates, but not elephant or giraffe)

  14. Methods • Live-trapping (Shermans) mid-August to mid-December • 100-trap grids and transects (10-m spacing), each trapped 4 consecutive days and nights • Black Cotton sites: grazed, partly grazed, and ungrazed glades; burned and unburned non-glades • Red-soil sites: grazed and ungrazed glades and non-glades (“bush”) • Structural meas. of understory: dead/live stem density, bare soil; grass height

  15. Red-Soil Glade Exclosures: High densities & dramatic treatment effect ▪Treatment Effects: all P < 0.1 (Mann-Whitney) for Total Small Mammal and Three Most Common Species

  16. Red-Soil Bush Exclosures: Half the densities of glades but still dramatic treatment effect ▪Treatment Effect: Total Mammal P = 0.01, Individual Species P > 0.1 (Mann-Whitney)

  17. Live stems n.s. (P > 0.5)

  18. Live stems, R2 = 35.4% (P = 0.041)

  19. Small Mammal Densities and Species Richness (Min-Max per plot) 10-10 adjacent to exclosures

  20. Conclusions I • Both Soil Types: Arvicanthis (diurnal) found only in exclosures. • Saccostomus dominant in all Black-cotton treatments and controls, but limited to exclosures in Red-soil (grazing yields bare patches in Red-soil, more so than Black Cotton). • Black Cotton small-mammal density and diversity naturally lower than Red Soil (“matrix,” i.e., grazed, non-glade controls). • Red Soil species richness 2X higher (7-8 species caught > 2 times vs. 4 species for Black Cotton) • Red Soil grazing treatment effect more dramatic; glades all grazing lawns, densities inside 2X.

  21. Conclusions II • Small-mammal density strongly positively related to Grass Height and Grass Density—especially dead stems—within each soil type. • Small mammals avoid high-nutrient foraging areas without sufficient cover. • Large-mammal herbivory removes small-mammal cover. • Question: • What is natural? e.g., where is/was Arvicanthis naturally common?

  22. Literature Cited • Augustine, D.J., and S.J. McNaughton. 2006. Interactive effects of ungulate herbivores, soil fertility and variable rainfall on ecosystem processes in a semi-arid savanna. Ecosystems 9:1-16. • Keesing, F. 1998. Impacts of ungulates on the demography and diversity of small mammals in central Kenya. Oecologia 116:381-389. • Sensenig, R.L. 2004. Spatial ecology of fire in an East African savanna: effects of burn size and patchiness on the foraging ecology of herbivores of varying body size. Proposal to NSF for Dissertation Improvement Grant. • Young, T.P., B. Okello, D. Kinyua, and T.M. Palmer. 1997. KLEE: a long-term multi-species herbivore exclusion experiment in Laikipia, Kenya. African Journal of Range and Forage Science 14:94-102. Acknowledgments Valdosta State University National Science Foundation Mpala Research Centre Truman Young Ryan Sensenig Bernard Agwanda National Museums of Kenya John Mpaiyan Jake Goheen Todd Palmer Rob Pringle Corinna Riginos

More Related