Landscape management - Ecological Applications: Toward a Sustainable World - page 282

long-lived species, such as grizzly bears ( Ursus arctos ) in the Rocky Mountains of
North America, may persist for some time even after changes to the landscape
around their reserves have already sealed their fate - extinction within a few genera-
tions. Thus, the particular value of studies such as that on the wood thrush (Section
10.2.2) and on grizzly bears (Carroll et al., 2005) lies in identifying probable future
extinctions so that plans can be made in time. In the case of the grizzlies, Carroll's
team showed that a doubling of reserve area produces a 47% increase in the probabil-
ity of population persistence in highly 'developed' landscapes and a 57% increase in
semideveloped landscapes. However, increasing connectivity between reserves is
much more infl uential, increasing the probability of population persistence by 81%
in undeveloped settings and by an impressive 350% in semideveloped parts of the
species' range.

10.3 Landscape
harvest management

Harvesting rarely takes place in a homogeneous landscape. In the ocean, some areas
are heavily exploited while little or no fi shing takes place in others. This is another
situation where an understanding of both landscape (actually waterscape) structure
and metapopulation dynamics is necessary when devising management strategies.
Ter re st r i al landscapes can be even more patchy. Irregular disturbances produce a
mixture of early successional, mid-successional and late-successional patches, each
with different mixes of products that people can exploit. In this section I explore
how a landscape perspective can be used to guide harvesting behavior in the ocean
(Section 10.3.1) and on land (Section 10.3.2).

10.3.1 Marine
protected areas

I noted in Section 7.2.4 how easy it is to imagine the potential benefi ts for harvest
management of setting aside zero-fi shing zones (marine protected areas). Thus, for
species that are relatively sedentary and do not venture outside, individuals within
the zero-fi shing zone may be protected from fi shing and achieve higher density. It
is also possible that the unfi shed population will consist of larger and more fecund
individuals, leading to a further elevation of density. If such a density increase leads
to net migration from the zero-fi shing zone to fi shed areas, then the marine pro-
tected area may contribute to sustainable exploitation of the fi shery at large.
Despite the elegance of this reasoning, however, there have been very few cases
where the potential benefi ts of marine protected areas have actually been shown to
occur. And there are important gaps in our knowledge, particularly relating to pat-
terns of dispersal of larval stages away from protected areas and towards fi shed
zones. Robinson et al. (2005) have helped to bridge this gap by modeling the move-
ment of 'virtual fi sh larvae' (i.e. theoretical 'particles' with appropriate properties)
within the region as a whole. Their simulation models were run for 90 days (the
average larval duration) and incorporated three-dimensional knowledge of ocean
currents in late winter when high abundances of fi sh larvae are observed in the
region. They tracked, through the ocean at large, fi sh larvae 'released' in each of ten
coastal marine protected areas. You can see in Figure 10.7, fi rst, that the different
marine protected areas do not operate as isolated systems - each can contribute and
receive fi sh recruits from one or more other areas. This metapopulation structure
may help counter local extinctions and enhance genetic diversity (a component of
biodiversity - Box 10.1). Second, there is clearly a major fl ow of recruits away from
the protected areas to other areas of the coast and the open ocean, possibly contri-
buting to the maintenance of exploited fi sh populations.