Ecosystem management and
conservation
21
Most of the previous chapters have focused management and conservation on indi-
vidual species and their direct interactions with the next trophic level. Management
and conservation threats are usually stated in terms of overharvesting (Chapter 19),
overpredation (Chapters 10 and 17), disease (Chapter 11), pests (Chapter 20), or
habitat loss (Chapter 17; Griffith et al. 1989). Although these issues are correct as
far as they go, they hide a common feature: population declines occur through a com-
bination of factors, derived from complex interactions between environment and biota,
which together overwhelm the ability of a species to withstand them. These are the
effects of ecosystem dynamics and they often dictate the fate of individual species.
Natural ecosystem complexity arises from factors such as non-linear biotic inter-
actions, evolutionary history and assembly history of species, and often-unpredictable
environmental disturbance.
Human interference, from both exploitation and stewardship, can alter ecosystem
dynamics with results that can be opposite to what is intended. For example, fences
were put up in central Botswana and Kruger National Park, South Africa intended
to protect the cattle industry in the former and wildlife in the latter, but they both
altered migrations and caused a collapse of wildlife populations; placement of
artificial water holes in Hwangi Park, Zimbabwe, Kruger Park (du Toit et al. 2003),
and the Sahel of northern Africa resulted in local overuse of resources and unwanted
ecosystem effects (Sinclair and Fryxell 1985); and crude attempts at biological con-
trol through the introduction of exotic predators to control exotic prey in Hawaii,
Australia, New Zealand, and many other areas have resulted in the extinction, or near
extinction, of endemic species and the complete failure of the control of pests
(Serena 1994). Thus, what at first seems an obvious conservation solution may not
be with closer examination.
The fundamental problem is that by ignoring some aspects of ecosystem dynamics
- historical legacy, community interactions, and disturbance at different scales – inap-
propriate conservation efforts can result, curing the symptoms rather than the cause
of a threat to a species. Ecosystem dynamics have now been well described (e.g. Boyce
and Haney 1997). Here we put the various aspects that we have discussed in the rest
of the book into the context of the ecosystem to show how these are pertinent to
management and conservation. We start by providing some definitions.
Communitiesare complexes of interacting populations. They involve both direct
and indirect effects of competition, predation, and parasitism. They contain major
players, called dominantandkeystonespecies, and combinations of many other
minor species. Although species combinations are fluid, there are usually identifiable
365
21.1 Introduction
21.2 Definitions
