Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Demography of a Large Herbivore, the Greater Kudu Tragelaphus strepsiceros, in Relation to Rainfall

Norman Owen-smith
Journal of Animal Ecology
Vol. 59, No. 3 (Oct., 1990), pp. 893-913
DOI: 10.2307/5021
Stable URL: http://www.jstor.org/stable/5021
Page Count: 21
  • Read Online (Free)
  • Download ($18.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Demography of a Large Herbivore, the Greater Kudu Tragelaphus strepsiceros, in Relation to Rainfall
Preview not available

Abstract

(1) The study was conducted from 1974 to 1984 in two areas of the Kruger National Park differing in mean rainfall. Age-class specific survival rates were estimated by individual registration of the kudus present in each female-young social unit, using natural markings. (2) The kudu populations in both study areas increased in 1974-78 then declined in 1978-83. Because of high annual variability in juvenile recruitment, no stable age distribution was attained. (3) The survival rates of juveniles (including prenatal losses), yearlings and old females (> 6 years of age) were significantly correlated with the preceding annual rainfall total. Rainfall over the late wet season exerted the strongest influence. A negative relation was evident between survival and preceding biomass density of kudus, which was statistically significant for juveniles. For prime females only a weak relation between survival rates and both variables combined was shown in the lower rainfall study area. (4) Survival rates were significantly correlated with resource supply relative to population demand, as indexed by the rainfall/biomass ratio, except in the case of prime females. Data points for both study areas fitted closely similar regression lines, indicating that the higher kudu density in one area counterbalanced the higher mean rainfall there. (5) Juvenile survival post-conception functioned as the key factor causing population fluctuations as well as being density-dependent. Prime females in the age range 2-5 years conferred a degree of population resilience to drought, due to their insensitivity to resource limitations. (6) Rainfall is presumed to act through its effects on the food supply, in particular of high quality components such as forbs. However, the effects of wet season rainfall on juvenile survival appeared to be partially density-independent. Predation was probably responsible for a background mortality level of 5-10% per annum even among prime-aged animals. Although all mortality was probably mediated by predation, except during a severe drought year, fluctuations in mortality were evidently dependent on nutritional well-being as influenced by rainfall relative to kudu density. (7) Where the resource supply fluctuates widely between years, as is the case where it is controlled by rainfall, density-dependent effects may become evident only after controlling for such fluctuations. This is especially true for herbivores dependent on food quality as well as quantity. The influence of rainfall variability on population dynamics can be opposite in sign for browsing and grazing ungulates.

Page Thumbnails

  • Thumbnail: Page 
893
    893
  • Thumbnail: Page 
894
    894
  • Thumbnail: Page 
895
    895
  • Thumbnail: Page 
896
    896
  • Thumbnail: Page 
897
    897
  • Thumbnail: Page 
898
    898
  • Thumbnail: Page 
899
    899
  • Thumbnail: Page 
900
    900
  • Thumbnail: Page 
901
    901
  • Thumbnail: Page 
902
    902
  • Thumbnail: Page 
903
    903
  • Thumbnail: Page 
904
    904
  • Thumbnail: Page 
905
    905
  • Thumbnail: Page 
906
    906
  • Thumbnail: Page 
907
    907
  • Thumbnail: Page 
908
    908
  • Thumbnail: Page 
909
    909
  • Thumbnail: Page 
910
    910
  • Thumbnail: Page 
911
    911
  • Thumbnail: Page 
912
    912
  • Thumbnail: Page 
913
    913