Premium
Vegetation modification and resource competition in grazing ungulates
Author(s) -
Murray Martyn G.,
Illius Andrew W.
Publication year - 2000
Publication title -
oikos
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.672
H-Index - 179
eISSN - 1600-0706
pISSN - 0030-1299
DOI - 10.1034/j.1600-0706.2000.890309.x
Subject(s) - wildebeest , biology , interspecific competition , grazing , competition (biology) , ecology , herbivore , foraging , agronomy , national park
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.