Community Ecology Processes, Models, and Applications

9.3.3 Local and regional effects on ecosystem services

The species most likely to profit from organic farming
and other agri-environmental schemes decreasing
agricultural intensity can be termed ‘the common
biodiversity’ (I owe this term to Anki Weibull, and
have found it very useful to distinguish these species
from the red-listed species that often – and rightly so –
are the major concern in conservation biology). These
species are not rare, but may be declining. They are
common enough to have direct effects on ecosystem
services, such as predators controlling pests, insects
pollinating fruits and vegetables, or earthworms
maintaining soil fertility. The common biodiversity
provides farmers, landowners and society with a
number of ecosystem goods and services whose va-
lues usually are unknown and thus never enter the
economic calculations that constrain how ecosystems
are managed. Clearly, a useful community ecology
should provide a better understanding of ‘the ecology
of ecosystem services’.
Many ecosystem services provide interesting
cases of natural habitats interacting with crops,
with the quality of the matrix of agricultural fields
between natural habitats playing an important role.

Pollinators often rely on semi-natural and less dis-

turbed habitats, but still use flowering crops for

nectar and pollen. However, biological control of

pests in crops provides an even better example of

how metacommunity theories concerning species

interactions in spatially structured habitats natural-

ly interact with very applied questions. There is

also a direct economic benefit of biological control

for farmers.

Two types of biological control are discussed in

the literature. One is control of pests by specialized

predators. In this case the trick is to maintain both

predators and pests so that control continues over

time, either naturally or by continuous addition of

predators. This has been quite successful in, for

example, greenhouses. The second is the control of

pests by generalist predators, which do not depend

on, but readily feed on, the pest. The latter type

often relies on predators being present in the fields

when potential pests emerge or colonize. These

predators usually depend on habitats surrounding

the fields for persistence. Early examples were po-

lyphagous insects such as carabids feeding on cere-

al aphids (Ekbomet al. 1992) and parasitoids on

rape seed beetles (Thies and Tscharntke 1999), but

Spiders

Generalist predator guild

Crop field Edge zones, ley

Intra-guild

Spiders Movement predation

Carabids

Aphids

Collembola

(detritivores)

Interactions = mechanisms

Biological

control

Context

Collembola

(detritivores)

Pest insects

Carabids

Plant

material

Insect

larvae

etc.

Figure 9.3The biological control of a pest in a crop, for example aphids, is only a part of the interactions that the
predators (and pest) are involved in, and proper management requires that all interactions in the food web are managed.
In this case, including the edge habitat results in a basic food web question in a spatial context, incorporating predator–
prey dynamics and spatial subsidies.

DIVERSITY AND ECOSYSTEM SERVICES 127