Third, homogenization of landscapes and
increased disturbances associated with land use
intensification ‘select’ species with particular traits
such as high dispersal ability, generalistic resource
and habitat requirements, and ability to rapidly ex-
ploit abundant resources. In essence, homogeneous
landscapes are creatinga weedy world(this term was
originally coined by Carl Folke; note the similarity
with classicalr-selected species (MacArthur and
Wilson 1967), such as ruderals and rats).
Fourth, because different organisms are likely to
differ in their sensitivity to habitat loss and increased
isolation, and in their response to intensification, dif-
ferent landscapes will contain different sets of species
(metacommunities) and the strength of trophic inter-
actions in patches will vary between landscapes. For
example, if predators have lower population sizes or
lower dispersal rates than their prey, then increased
isolation, smaller habitat patches and increased inten-
sification is predicted to decrease ratios of predators
to prey, resulting in less predator control of prey, e.g.
pests. However, predators may spill over from more
productive matrix habitats to small patches or to in-
tensively cultivated areas, resulting in higher preda-
tion. Thus, the mechanisms for different levels of
predation need to be understood in a spatial context
(Oksanen 1990; Poliset al. 1997; van de Koppelet al.
2005; Chapter 5)
Finally, as a consequence of the third and fourth
points above, homogeneous landscapes are likely
to show a lower diversity and biomass of many func-
tional groups, except those deliberately favoured by
agriculture or forestry through planting (note that
planting is not the case in fisheries, which exacer-
bates these effects). Changes in diversity and species
composition are often associated with changes in size
distributions, which in turn may entail less efficient
ecosystem services (Bengtsson 1998).
9.3 A selection of empirical studies
9.3.1 Applied questions allow experimental studies on management scales
A major issue in ecology is on which scales
phenomena and processes should be studied (e.g.
Peterson and Parker 1998). Scale refers to the size or
duration (spatial and temporal scale) of phenome-
na, and it is a general problem that conclusions
about a system depend on the scale at which we
view it. For example, there have been thousands of
laboratory and small plot experiments in applied
ecology. Often, such small-scale studies have been
used to guide management at larger scales, as in
forestry where the majority of experiments have
been made on plots smaller than a hectare (100
100 m) monitored over much less than a forest
generation. Still it is assumed that they inform us
about the large-scale and long-term effects of vari-
ous forestry practices, despite the fact that this as-
sumption often is unlikely to hold. Management
advice based on small-scale studies is risky.
However, management of real ecosystems is
carried out on large scales, and different manage-
ment practices can provide information about the
dynamics of ecosystems on larger scales. While
small-scale experimental model systems can be in-
structive, any advice on, for example, corridors
or land use should be relevant at the scales at
which decisions about land use are made. In agri-
cultural landscapes such decisions are made at the
scale of single fields to farms or even landscapes
with many farms. These decisions are made by
farmers, advisors and land use planners based on
socioeconomic factors, naturally given landscape
and soil features, but also on individual feelings
and prevailing ideologies. This creates variation in
management that can be used to examine the effects
of various land use practices in a pseudo-experi-
mental way.
An example of this is how different farming sys-
tems affect biodiversity and ecosystem services.
The original question was if organic farming –
a system characterized by using no pesticides
and no inorganic fertilizers and consequently
usually more perennial semi-permanent grasslands
with nitrogen-fixing plants – had higher biodiversi-
ty than conventional farming systems. Clearly,
plot experiments on the scale of a few metres are
almost useless for answering such a question. It
should be answered at the management scale
of fields or preferably farms. However, at this
larger scale, landscape structure, such as the
amount of natural habitat or the diversity of habi-
tats, is important for species richness of manyDIVERSITY AND ECOSYSTEM SERVICES 123