The future of the savannah ecosystems: ecological islands or faunal enclaves?

ummary Various savannah reserves are examined to determine whether they are likely to lose substantial numbers of large herbivores if they become isolated. The relationship between the number of ungulate species and the size of each reserve is examined and compared to predictions established from existing island biogeographic studies. In the case of the savannah reserves, no significant relationship was found. However, when the data were re-analysed for reserves of similar habitat, significant though low z-values of 0.04 and 0.08 were established. For discrete ecosystems rather than reserves a steeper z-value of 0.14 was found. It is suggested that the z-value for the savannah ecosystems is lower than the typical value of 0.22 for other land mass islands because of the ubiquitous distribution of most large herbivore species and their long history of co-evolution. The significance of island biogeographic theory to the design of nature reserves is limited, at least in the savannahs. Most of the variation in the number of species in areas which can be practically established as reserves can be explained by habitat and landscape diversity. Whether the savannah reserves became faunal islands will be decided by political and economic policies and practices rather than the principles of ecological design. The design of reserves in the past is considered to have been based on sound ecological principles in most cases, even though these were not recognized at the time. Resume Diverses reserves a savane sont examinees afin de determiner si elles sont susceptibles de perdre un nombre important de grands herbivores si elles deviennent isolkes. La relation entre le nombre d'especes d'ongules et la taille de chaque reserve est examinee et comparee aux predictions etablies a partir d'etudes sur des ilots biogeographiques isoles. Dans le cas des reserves e savane, aucun type de relation significative n'a ete trouve. Cependant, lorsque les donnees furent analysees a nouveau pour des reserves a habitat similaire, des valeurs significatives bien que faibles de z= 0.04 a 0.08 ont eteetablies. Pour des ecosystemes discrets au lieu de reserves, une valeur plus raide de z= 0.14 fut trouvee. Il est suggere que la valeur de z pour les ecosystemes de savane est plus faible que la valeur typique de 0.22 pour les autres ilots de massifs terrestres a cause de la distribution uniquiste de la plupart des especes de grands herbivores et la longue histoire de leur co-evolution. L'application de la theorie des ilots biogeographiques au cas de reserves naturelles est limitee, du moins en ce qui concerne les savanes. La plupart des variations du nombre des especes dans les zones qui pourraient etre erigees en reserve peuvent etre expliquees par la diversite des habitats. Les reserves a savane deviendront des ilots faunistiques davantage selon les decisions politiques et economiques que les principes ecologiques. On considere que la gestion des reserves fut base dans le passe sur les principes ecologiques de base, meme si ceux-ci n'etaient pas encore reconnus a cette epoque.

[1]  M. Soulé,et al.  Benign neglect: A model of faunal collapse in the game reserves of East Africa , 1979 .

[2]  L. Harris,et al.  Isolation and extirpations in wildlife reserves , 1977 .

[3]  S. Cobb.  The distribution and abundance of the large herbivore community of Tsavo National Park,Kenya , 1976 .

[4]  S. McNaughton,et al.  Serengeti Migratory Wildebeest: Facilitation of Energy Flow by Grazing , 1976, Science.

[5]  D. Western.  Water availability and its influence on the structure and dynamics of a savannah large mammal community , 1975 .

[6]  R. May.  Islands biogeography and the design of wildlife preserves , 1975, Nature.

[7]  M. Norton-Griffiths.  Counting the Serengeti migratory wildebeest using two‐stage sampling , 1973 .

[8]  J. Terborgh.  CHANCE, HABITAT AND DISPERSAL IN THE DISTRIBUTION OF BIRDS IN THE WEST INDIES , 1973, Evolution; international journal of organic evolution.

[9]  J. Diamond,et al.  Biogeographic kinetics: estimation of relaxation times for avifaunas of southwest pacific islands. , 1972, Proceedings of the National Academy of Sciences of the United States of America.

[10]  James H. Brown.  Mammals on Mountaintops: Nonequilibrium Insular Biogeography , 1971, The American Naturalist.

[11]  R. Bell.  A grazing ecosystem in the Serengeti , 1971 .

[12]  D. J. Pratt,et al.  A Classification of East African Rangeland, with an Appendix on Terminology , 1966 .

[13]  H. Lamprey.  ESTIMATION OF THE LARGE MAMMAL DENSITIES, BIOMASS AND ENERGY EXCHANGE IN THE TARANGIRE GAME RESERVE AND THE MASAI STEPPE IN TANGANYIKA , 1964 .

[14]  H. Lamprey.  ECOLOGICAL SEPARATION OF THE LARGE MAMMAL SPECIES IN THE TARANGIRE GAME RESERVE, TANGANYIKA† , 1963 .

[15]  Edward O. Wilson,et al.  The Nature of the Taxon Cycle in the Melanesian Ant Fauna , 1961, The American Naturalist.

[16]  D. Vesey-Fitzgerald,et al.  Grazing Succession Among East African Game Animals , 1960 .

[17]  C. B. Williams.  Area and Number of Species , 1943, Nature.

[18]  J. Terborgh.  Faunal Equilibria and the Design of Wildlife Preserves , 1975 .

[19]  D. Western.  The structure, dynamics and changes of' the Amboseli Ecosystem , 1973 .