Information Technology Reference
In-Depth Information
alistic network but not the structure of the habitat landscape. We anticipate that
the tendency to study full ecological networks on real ecological landscapes will be
an important area in the near future. This will integrate networks of networks. The
spatial component of networks has already generated important contributions which
we will review in the following section. A next step will be to integrate all sections,
that is, to study the spatial component of networks of ecological interactions.
14.4. Spatial Networks
We have thus far examined where we are in bridging the gap between structural
understanding and system dynamics in food webs and plant-animal mutualistic
networks. Such ecological networks depict relationships which principally aect the
population growth rates of the interacting species. An altogether dierent type of
ecological network, that representing spatial dynamics, has been also studied. Spa-
tial dynamics inuences both the organization and stability of communities [Tilman
and Kareiva (1997); Hanski and Gilpin (1997); Bascompte and Sole (1998)] and
hence, the spatial aspects in which ecological processes take place cannot be ig-
nored. For example, in fragmented landscapes, the spatial distribution of habitat
patches can inuence on the dispersal movements of individuals [Wiens (2001)]. In
plants, gene ow mediated by animals is a key demographic process which serves
to shape the spatial pattern of intraspecic genetic variability [Barrett and Harder
(1996)]. In animal societies, the relationships between individuals are often deter-
mined by the common use of resources patchily distributed across the landscape
[Gibbons and Lindenmayer (2002)]. All these cases can be described and analyzed
as networks in which nodes represent habitat resources and links indicate dispersal,
gene ow, or social interactions. By considering spatial dynamics from a network
perspective, we can shed light into problems as diverse as species persistence in
spatially-extended environments and gene ow in plant populations.
14.4.1. The structure of spatial networks
The spatial dynamics which result from the dispersal of individuals from one popula-
tion to another have been successfully studied using the metapopulation framework
[Hanski and Gilpin (1997)]. In this approach, the probability for an empty habi-
tat patch to be colonized depends, among other factors, on the distance between
that patch and the rest of occupied patches [Ovaskainen and Hanski (2004)]. By
considering dierent functional forms for the probability of an individual to reach
a patch located at a particular distance (i.e., the dispersal kernel), we can build
stochastic networks of connected patches in fragmented landscapes. The structure
of the resulting networks of patches provides a straightforward way to quantify
the robustness of a patchy population to habitat loss [Urban and Keitt (2001)].
It also provides useful information for conservation planning because it allows the
identication of the most important patches | termed keystone patches | that
