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Submitted to: African Journal of Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/13/2010 Publication Date: 2/2/2012 Citation: Augustine, D.J. 2012. Response of native ungulates to drought in semiarid Kenyan rangeland. African Journal of Ecology. 48:1009-1020. Interpretive Summary: The distribution and abundance of native large herbivores (primarily elephant, zebra and several antelope species) were studied on a commercially-managed ranch in central Kenya over a 3-year period that encompassed severe drought and above-average rainfall. Total biomass of large herbivores averaged 7556 kg/km2. Responses of the native species to severe drought were variable. Impala densities were similar to or greater than densities for similar habitat in national parks, and varied from 12 – 16 km-2 during and following the drought to 24 – 29 km-2 following above-average rainfall. Dik-dik densities were greater than densities reported for protected areas, and were surprisingly stable throughout the study despite the wide annual fluctuations in rainfall. Elephant migrated off the ranch during drought but were present at high densities (2.9 – 5.3 km-2) during wet seasons. This finding supports previous studies indicating that a portion of the Laikipia-Samburu elephant population migrates to bushland habitats in central Laikipia during wet periods. Results show that high densities of native browsing herbivores can occur on rangeland managed for commercial beef production, and suggest native herbivores need to move over large areas (>100 km2) in response to locally variable thunderstorms. Technical Abstract: The distribution and abundance of native ungulates were measured on commercially-managed, semiarid rangeland in central Kenya over a 3-year period that encompassed severe drought and above-average rainfall. Ungulate biomass density averaged 7556 kg/km2 over the study and was dominated by elephant (Loxodonta africana), impala (Aepyceros melampus), dik-dik (Madoqua kirkii) and cattle (Bos taurus). Responses of native ungulates to severe drought were variable. Impala densities were similar to or greater than densities for similar habitat in protected areas, and varied from 12 – 16 km-2 during and following the drought to 24 – 29 km-2 following above-average rainfall. Dik-dik densities were also greater than densities reported for protected areas, and were surprisingly stable throughout the study despite the wide annual fluctuations in rainfall. Elephant migrated out of the region during drought but were present at high densities (2.9 – 5.3 km-2) during wet seasons, consistent with telemetry studies emphasizing the importance of Acacia bushland habitat on commercial rangelands for the migratory portion of the Laikipia-Samburu elephant population. Results show that substantial densities of native browsing and mixed-feeding ungulates can occur on rangeland managed for commercial beef production, and suggest that the capacity for ungulates to move over large spatial scales (>100 km2) and to shift distributions in response to locally variable thunderstorms may be important for sustaining these populations. |
