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- Title
Vegetation modification and resource competition in grazing ungulates.
- Authors
Murray, Martyn G.; Illius, Andrew W.
- Abstract
The prevalence of interspecific competition in animal communities is the subject of a long-running debate, chiefly because the underlying processes of resource exploitation and resource supply are often poorly understood. To provide some insight into these processes within a guild of grazing herbivores, two hypothetical mechanisms of exploitation competition were tested by measuring food intake of topi (Damaliscus lunatus ) and wildebeest (Connochaetes taurinus ) when foraging on different sward structures in the Serengeti National Park. According to our bite quantity hypothesis, wildebeest, which have relatively wide mouths, can graze down vegetative swards to a height below that which can be tolerated by topi; and according to our bite quality hypothesis, the narrower-mouthed topi can reduce the leafy component of differentiated swards (i.e. swards in which seed-bearing stems have developed) through selective feeding to a level below that which can be tolerated by wildebeest. On differentiated swards with erect growth form, the topi selected 20% more green leaf in their diet, as measured by a calibrated visual technique, and also obtained higher short-term intake rates. Greater selectivity alone provided topi with a metabolisable energy intake estimated to be 16% higher than that of wildebeest. On vegetative swards, it was estimated that wildebeest could maintain positive energy balance on 2-cm swards, 1 cm shorter than the threshold height for topi. Our findings indicate the conditions under which each ungulate species may limit the other's use of natural pastures through interspecific competition: bite quantity competition may apply on short grazing lawns; bite quality competition is expected on differentiated swards with a limited supply of green leaf. We suggest that herbivory by one species can modify the vegetation in a way that makes it less profitable to competing species. In effect the vegetation is ‘captured’ as a resource by one species. Thus modification of vegetation is argued to be a critical component of resource competition in herbivores.
- Subjects
BOTANY; ECOLOGY; RESOURCE exploitation
- Publication
Oikos, 2000, Vol 89, Issue 3, p501
- ISSN
0030-1299
- Publication type
Article
- DOI
10.1034/j.1600-0706.2000.890309.x