organisms from plants to insects and birds (Steffan-
Dewenteret al. 2002; Bentonet al. 2003). How can
we distinguish farming system effects from such
landscape effects?
A straightforward way is to account for the
effect of landscape by examining farms (or fields)
situated in different landscapes, but making sure
that organic and conventional farms are evenly
distributed over the landscapes. The simplest way
is to choose matched pairs of organic/conventional
farms along a gradient of landscape heterogeneity,
and then analysing the results with an analysis of
covariance or similar models. This approach was
used by Weibullet al. (2000) and has since then been
extensively used by a variety of authors in Ger-
many, the UK and Sweden (Roschewitzet al. 2005;
Fulleret al. 2005; Rundlo ̈f and Smith 2006). With
this design, it is also possible to examine whether
there are interactions between the farming system
and landscape structure. For example, organic
farming might have a large effect in homogeneous
agricultural landscapes but not in small-scale mo-
saic landscapes.
However, in order to extract the variables that
best describe the habitat and landscape factors
that organisms are likely to respond to, the biology
and ecology of the organisms under study must be
understood. Here, we often encounter an imbalance
in our knowledge: Most field biologists working on
an organism group have an intuitive feeling for
which local habitat factors influence the presence
of species. On the other hand, understanding re-
gional influences on species distributions require
that we also have a good idea about the factors
affecting dispersal and movements of organisms
in the landscape. Such knowledge is more difficult
to obtain and for many organisms quite scanty.
Hence, while the local factors included in an analy-
sis often capture what organisms really respond to,
regional scale variables are often merely informed
guesses, and determined by the availability and res-
olution of the landscape maps used to measure, for
example, proportion of habitats, landscape heteroge-
neity and edge zones. Thus, almost by default region-
al influences will contribute less to the explained
variation in species distributions and diversity than
the more precisely known local habitat factors. In
view of this, major advances in metacommunity ecol-
ogy will require more studies of how organisms dis-
perse and how they utilize the matrix between focal
patches.9.3.2 Biodiversity in human-dominated landscapes: local or landscape management?
The intensification of agriculture in recent decades is
a good example of how management practices affect
whole landscapes as well as the quality of habitat
patches. How these qualities affect organisms and
their interactions are exactly the kind of applied
question that metacommunity theories should try to
explain. In the UK, the major changes in agricultural
landscapes took place in the 1970s as it joined the
European Union (Chamberlainet al. 2000), similar to
many other Western European countries.
It is well established that modern agriculture (and
forestry, e.g. Bengtsson et al. 2003) has resulted
in declines in biodiversity (Donald et al.2001;
Tscharntkeet al. 2005; Biesmeijeret al. 2006). In agri-
cultural landscapes the reasons are well known: Sim-
plified crop rotations, farm specialization, increased
use of pesticides and herbicides, heavy fertilization
and loss of marginal and natural habitats, singly or
together, have affected various organisms negative-
ly. For organisms depending on traditionally man-
aged habitats such as semi-natural grasslands, their
habitats nowadays occur as isolated patches in a sea
of crops or forest.
To reverse this trend, intuitively we would sug-
gest that diversity could be restored by increasing
the amount of seminatural habitats and landscape
heterogeneity, and decreasing the use of pesticides
and other intrants. This has led to suggestions that
organic farming practices would result in a higher
farmland biodiversity, because organic farming is
supposed to have, among other things, a higher
crop diversity, more complex crop rotations with
more semi-permanent fields like leys and pastures,
and not using pesticides, herbicides and inorganic
fertilizers. Organic farms are also more likely to be
mixed farms with both animal and crop produc-
tion. However, all these features of organic farming
may not be realized on single farms, although pes-
ticides, herbicides and inorganic fertilizers always
are prohibited. In many landscapes organic farmers124 APPLICATIONS