It is important that we should understand the underlying concepts of interspecific
competition if we are to comprehend how species might or do actually interact in
the field. There are several applications where we need to be aware of potential com-
petition: (i) in conservation where we might have to protect an endangered species
from competition with another dominant species; (ii) in managed systems such as
rangelands and forests where there could be competition between domestic species
and wildlife – for example an increase in livestock or the expansion of rangeland
might cause the extinction of wildlife species, or wildlife might eat food set aside for
the domestic animals; and (iii) if we want to introduce a new species to a system,
for example a new game bird for hunting, and there could be competition from other
resident species.Let us imagine a situation where we want to conserve a rare species but we are
concerned about possible competition from a common species. For example, roan
antelope (Hippotragus equinus), a fairly rare species, were released in Kruger National
Park, South Africa, as part of a conservation program. There were concerns that the
numerous wildebeest would exclude the roan antelope. In this case the management
response was to cull the wildebeest (Smuts 1978). More recent evidence indicates
that predators, supported by an abundant zebra population, are limiting and even
excluding this rare species (Harrington et al. 1999; McLoughlin and Owen-Smith 2003).
Thus, apparent competition is the dominant process here. A similar example
involved the extremely rare Arabian oryx (Oryx leucoryx). A few of the last remain-
ing individuals of this species were captured in Arabia in the early 1960s and taken
to the San Diego zoo. There numbers increased and some have been successfully rein-
troduced to Oman (Stanley Price 1989).
In both of these examples it would be important to detect whether there was com-
petition with resident species. We have seen that simple measures of overlap or even
changes of overlap with season may not be good indicators of competition. Similarly,
observations that an increase in a common species is correlated with a decrease in
the rare species does not mean that competition is the cause because of the problem
of apparent competition. These measures are necessary but not sufficient. In addi-
tion we would need a measure of: (i) resource requirement; (ii) availability of
limiting resources and demonstration that one is in short supply; and (iii) the pre-
dation rates on both the target species and alternative prey.
A second kind of problem comes from changes in habitat. Assume there is
coexistence and habitat partitioning between two species along the lines of
Rosenzweig’s shared preference hypothesis described above. Since studies of diet and
habitat selection would show that both species prefer the same habitat, one may be
tempted to manage an area by increasing the preferred habitat at the expense of the
other habitats. In this case, however, only one species, the dominant, would benefit
and the other would decline. The breeding habitats of the yellow-headed and
red-winged blackbirds (Orians and Willson 1964) may be a case in point. Both species
prefer deeper-water marshes but one may predict that increasing the depth of a marsh
where both occur, thereby leaving little shallow water, may well result in the exclu-
sion of the red-winged blackbird.
In Lake Manyara National Park, Tanzania, there is a habitat consisting of open
grassland on the lake shore which is used by wildebeest. Adjacent to this shoreline
is savanna consisting of longer grass with scattered trees and shrubs preferred by AfricanCOMPETITION AND FACILITATION BETWEEN SPECIES 159
9.10 Applied aspects of competition
9.10.1Applications
9.10.2Conservation