Landscape management - Ecological Applications: Toward a Sustainable World - page 275

managers must put the microscope back in its box and take up a telescope - but
let's call it, more aptly, a 'macroscope' (Brown, 1995). In other words, the scale
of consideration needs to be increased to include a much larger landscape.
Some important general principles of landscape ecology are described in Box 10.1
before I proceed to a systematic exploration of ecological applications at the
landscape level.

Box 10.1 Landscape
theory

Patches, patch dynamics and landscapes
Habitats are invariably patchy in the distribution of abiotic conditions, resources and enemies. This
patchiness affects the performance of individual organisms, the distribution of populations and
the composition of communities. Box 8.1 noted how communities, when viewed at a large enough
scale, often consist of a mosaic of patches at different successional stages. The patch dynamics
concept of communities views the habitat as a set of patches, with patches being disturbed and
recolonized by individuals of various species. Landscape ecology takes an even broader view, being
concerned with the way individuals, populations and communities behave in the patchwork of
habitats that occur in a region.

Metapopulations
A population that exists as a discrete entity is made up of individuals distributed over an area of
suitable habitat, where rates of birth and immigration add individuals to the population and rates
of death and emigration subtract them. This is the simple view of population dynamics. Where a
species exists as a metapopulation (a collection of subpopulations linked by dispersal), each sub-
population might also be considered, in isolation, to behave according to the simple view of dynam-
ics. But, by contrast, the dynamics of the metapopulation as a whole are mainly determined by the
rate of extinction of individual subpopulations, and the rate of colonization - by dispersal from
existing subpopulations - of habitable but uninhabited patches, creating or restoring a subpopula-
tion in that part of the landscape (Hanski, 1999). Note the intrinsic importance in metapopulation
dynamics of dispersal and migration (dealt with in detail in Chapter 4). The metapopulation concept
has particular relevance to metapopulation conservation and to harvest management.

Metacommunities and Island Biogeography Theory
So far, most of my discussion of applications from community ecology (Chapters 8 and 9) has
treated the community as a more or less discrete entity. By analogy with metapopulations, however,
if communities are viewed through the 'macroscope' a metacommunity may be discerned - a set
of local communities that are linked by dispersal of multiple, potentially interacting species (Leibold
et al., 2004). When looked at like this, you can see that the particular community that assembles
in a patch of habitat is infl uenced by other habitat patches and other habitats in the vicinity. The
metacommunity concept is relevant to harvest management, pest control and restoration and
conservation of biodiversity.
The number of species in a community is a balance between the principal process that adds
species (colonization from other communities in the region) and the principal process that sub-
tracts species (extinction). Macarthur and Wilson's (1967) 'Island Biogeography Theory' has been
very infl uential in ecology, and is equally applicable to oceanic islands and to 'habitat islands' such
as lakes, mountain tops and forest patches. In essence, the theory holds that there is a continual
turnover of species - because of species extinction and colonization events - but that a balance is
achieved that mainly refl ects two things (Figure 10.1). The fi rst is island size - larger islands have
a higher equilibrium number of species because of higher colonization rates (large islands are
bigger 'targets') and lower extinction rates (large islands have larger average population sizes).
The second is isolation from colonist sources - isolated islands have lower colonization rates and
therefore lower equilibrium numbers of species. See Begon et al. (2006) for a more detailed treat-
ment of Island Biogeography Theory.