Applications from food web and ecosystem theory - Ecological Applications: Toward a Sustainable World - page 265

Fig. 9.17 Links between
pressure caused by
human activities, state
in terms of community
composition and
ecosystem processes,
and management
response to reduce the
pressure. Adverse
effects on ecosystems
sometimes involve
processes with clear
value in human terms -
ecosystem services such
as recreational
opportunities, water
quality, natural fl ood
control, harvestable
wildlife and general
biodiversity. (From
Begon et al., 2006.)

Pressure State

Human pressures on ecosystems
• Pollution
• Physical habitat change
• Changed disturbance regimes
• Harvesting
• Invasions

Altered structure and functioning
• Lower biodiversity
• Eutrophication
• Decreased ecosystem services
• Increased human health risk

Response

Societal/management response
• Set objectives to reduce pressures and
improve state
• Devise indicators of ecosystem health
• Monitor performance

mortality, changed patterns of nutrient cycling, and more frequent outbreaks of tree
pests and diseases. These properties may serve as indicators of ecosystem health -
successful restoration ( response ) will be evident when the indicator trends reverse.
Ruf and Beck (2005) note the potential value of predatory soil mites as indicators
of forest health. This is a very diverse group of organisms with, for example, 800
species in Europe in total, and up to 60 to be found at a given site. The predatory
mites occupy a unique position in the soil food web, straddling the three pathways
of energy and nutrients - from primary production (of plant roots), as well as fungal-
based and bacteria-based decomposer chains (Figure 9.18). As such, they are well
placed as integrators of the degrading effects of human pressures to serve as eco-
system health indicators. For example, characteristic sets of predatory mite species
dominate the community at different levels of soil acidity.

9.8.3 Ecosystem
health in an
agricultural landscape
- bats have a ball

Predatory mites could equally well serve as ecosystem health indicators in agricul-
tural soils. But at a rather different scale, bats might be used to the same end (Wick-
ramasinghe et al., 2003). Intensifi cation of agriculture has placed increasing pressures
on the agroecosystem, including unintended effects of fertilizers, herbicides and
pesticides on nontarget species, as well as the loss of traditional farmland habitats
such as hedges. Recognizing that organic farming prohibits the use of agrochemi-
cals, and that organic farmers are more likely to leave hedges and riparian vegetation
intact, bat activity and bat species richness were assessed in southern Britain in 24
carefully matched pairs of farms, one organic and the other conventional in each
pair. There was no statistical difference in bat species richness, with a total of 14 of
the 16 British bat species observed on organic farms compared to 11 on conventional
farms. In most cases, however, the organic farm received more visits from bats and
recorded more feeding activity (measured by acoustic surveys of feeding 'buzzes')
than its conventional counterpart. Overall, bat numbers were 61% higher and feeding
activity 84% higher on organic farms, probably refl ecting the greater preponderance
of hedges and other linear habitats along which bats fl y and where their insect prey
tend to be most common. In addition, agrochemical use on conventional farms may
reduce abundance of both terrestrial insects and, through deterioration in water
quality, of the adults of aquatic insects upon which bats prey.