9.1a). Third, natural or close to natural distur-
bance regimes and landscape mosaics should be
maintained, as most species are likely to be
well adapted to these over evolutionary and eco-
logical time (Bengtssonet al. 2003; Lindenmayer
et al. 2008).
9.2.3 Metacommunities in human-
dominated landscapes: effects of habitat
loss and fragmentation
From an applied perspective, a crucial question con-
cerns the effects of land use changes under the differ-
ent metacommunity perspectives. The intensification
of agriculture and forestry during the last century
has resulted in an unprecedented loss of natural
habitats and increased distances betweenthe remain-
ing ones (fragmentation). In addition, management
intensification has resulted in an increase in the area
covered by monocultures of certain crops and tree
species in large patches. At the same time, intensifi-
cation has resulted in an increased disturbance fre-
quency and intensity, to a larger extent in agriculture
than in forestry. Note that a similar drastic increase in
disturbance frequency also has taken place on most
fishing grounds. The high frequency of disturbance
is expected to favour certain species only. Traits such
as rapid exploitation and high dispersal ability may
make these specific species more likely to persist in
such landscapes (Tremlova and Mu ̈nzbergova 2007).
What are the expected consequences of these pro-
cesses on different types of metacommunities? To
discuss this question, we first need an idea of what
kinds of metacommunity dynamics were dominant
in the landscapebeforethe onset of land use changes.
Then a short scenario related to the effects of frag-
mentation and habitat loss will be discussed.
Assume a fairly homogeneous landscape in
which communities can mainly be described as
close to theneutralordispersal-drivenmetacommu-
nity types, because dispersal distances between
patches are negligible. Although species may be
dispersal limited, the short distances between suit-
able patches allows persistence of many species and
a high local and regional diversity. If this landscape
is broken up into smaller fragments by human ac-
tivities, the situation will first approach the patch
dynamics perspective. Locally and regionally, sort-
ing by dispersal ability will take place, because
species that are poor dispersers but, presumably,
good competitors will not be able to persist (Nee
and May 1992). As intensification of land use pro-
ceeds, species with poor dispersal will approach
remnant metapopulations in which extinctions are
not balanced by colonizations (Eriksson 1996).
Long-lived species such as plants may persist for a
long time, but finally go extinct. The end result will
be scattered patches with similar community com-
position, dominated by the best dispersers in the
region or those common in the intensively managed
matrix. That is, the metacommunity will again ap-
pear to be dispersal driven, but with low local and
regional diversity and impaired ecosystem services.
Alternatively, assume an originally heterogeneous
and mosaic landscape, in which niche differences
and environmental variation result in a high diversi-
ty of species. This metacommunity will be closer to a
species sortingperspective, and to variable degrees
patch dynamics. When such landscapes are fragmen-
ted and dispersal is made more difficult, the result
will first be sorted remnant metacommunities in
patches of varying quality and composition. Further
land use intensification may have different conse-
quences. In remnant patches of sufficient quality
and size, species adapted to local conditions and
with high competitive ability can remain for a long
time, and the species sorting perspective prevails.
Alternatively, if local extinction rates are higher,
there will be a shift from competitive dominants to
species sorted by dispersal, and the dispersal-domi-
nated perspective will be more applicable.
A third scenario concerns disturbance-driven mo-
saic landscapes, where disturbances, e.g. fire or
wind-throws, are major causes of local extinctions
(e.g. Bengtssonet al. 2003). At moderate to high dis-
turbance frequencies the role of species sorting will
be reduced, and communities will be dominated
by fast resource trackers with high dispersal ability.
Depending on disturbance frequency such land-
scapes will originally appear to be dominated by
dispersalorpatch dynamics.However,somespecies
may also persist in these landscapes by escaping in
time rather than space, e.g. by having dormant stages
waiting for the next disturbance. Human activities
altering disturbances and increasing fragmentation
will increase the role of dispersal for speciesDIVERSITY AND ECOSYSTEM SERVICES 121