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The process of faunal relaxation has important consequences for conservation.

Protected areas (national parks and other reserves) are often small islands carved out

of much larger ecosystems. A barrier is created by altered habitat surrounding them

that many species find difficult or impossible to cross – particularly large mammals

and sedentary birds, reptiles, and amphibians. Thus, a park should lose species over

time. The rate of loss should be higher and the eventual number should be lower for

smaller parks. There is some evidence that this loss is already occurring (Newmark

1987).

Ecosystem function is a general term that covers three different components: pro-

cesses, products or “goods,” and services. Box 21.1 lists some examples of each. Processes

involve rates of flow of nutrients, growth of biomass, etc. Services are processes that

are of benefit to human society, for example pollution control, and goods are the

end result of these, such as clean water (Schulze and Mooney 1993; Mooney and

Ehrlich 1997; Kinzig et al. 2001; Loreau et al. 2002; Srivastava and Vellend 2005).

Ecosystem function is often linked to biodiversity (Schulze and Mooney 1993; du

Toit and Cumming 1999). The argument is that the more species there are in a

system, the greater the ability of the system to withstand shocks to it (Walker 1992,

1995; Naeem 1998; Tilman 1999; Loreau 2000). This can be illustrated in two ways

(Fig. 21.4). First, ecosystem function would be related to the number of species

linearly if all species had equal contribution to the function (e.g. productivity) and

acted independently (Fig. 21.4a). However, we know this equality of function is unlikely

ECOSYSTEM MANAGEMENT AND CONSERVATION 381

21.14 Ecosystem function

Ecosystem processes

1 Hydrology

2 Biological productivity

3 Biogeographical cycling and storage

4 Decomposition

5 Resilience

6 Robustness–fragility

Ecosystem services

1 Maintaining hydrological cycles

2 Regulating climate

3 Purifying water and air

4 Pollinating crops and natural systems

5 Generating and maintaining soils

6 Cycling nutrients

7 Detoxifying pollutants

8 Providing aesthetic quality

9 Providing baseline research

Ecosystem goods

1 Food and clean water

2 Construction materials

3 Medicinal plants

4 Wild genes

5 Replacement species

6 Biological control agents

7 Tourism

Box 21.1The three
categories of ecosystem
function.