7
Network Theory: An Evolving
Approach to Landscape
Conservation
Timothy H. Keitt
125
7.1 Introduction
Habitat loss and fragmentation are ongoing and significant problems
throughout the globe (Turner 1996; Riitters et al. 2000). Future biodiversity
scenarios highlight the importance of habitat conversion to human
land uses as the leading driver of biodiversity loss worldwide (Sala
et al. 2000). Particularly disturbing is the habitat loss occurring within
protected areas (Liu et al. 2001). Unchecked, current rates of habitat
loss may have profound implications for future biodiversity (Pimm et al.
1996).
Given the magnitude of the problem, a case-by-case viability approach
to conservation may be impractical. Even conceptually straightforward
goals, such as the estimation of a species’ extinction risk within a fixed
period of time, are, in practice, exceedingly difficult to accomplish without
large amounts of accurately measured field data (Dennis et al. 1991; Fieberg
and Ellner 2000; Coulson et al. 2001). Confidence intervals on extinction
risks estimated via population viability analyses (PVAs) are typically so
large as to render the estimated value meaningless (Ludwig 1998). Brook
et al. (2000) examined the output of a number of different PVAs and
concluded that these models do provide precise predictions of extinction
risk. However, their conclusions are unwarranted because their results
demonstrate that PVA models are on average unbiased, but not necessarily precise for any one species. According to the analysis of Brook et al.,
individual PVAs are, in fact, likely to be imprecise for the single species
targeted by the PVA (Ellner et al. 2002).
The viability approach is further limited by the difficulty of obtaining
sufficient high-quality data across a large number of species. Scarce funding
for conservation may be better spent mediating direct causes of habitat loss
than attempting to elucidate subtleties of population demography across
many species. As a result of these problems, a broader-scale approach,
targeted at entire landscapes, may be necessary to maintain significant
biodiversity in the future.
Network Theory: An Evolving
Approach to Landscape
Conservation
Timothy H. Keitt
125
7.1 Introduction
Habitat loss and fragmentation are ongoing and significant problems
throughout the globe (Turner 1996; Riitters et al. 2000). Future biodiversity
scenarios highlight the importance of habitat conversion to human
land uses as the leading driver of biodiversity loss worldwide (Sala
et al. 2000). Particularly disturbing is the habitat loss occurring within
protected areas (Liu et al. 2001). Unchecked, current rates of habitat
loss may have profound implications for future biodiversity (Pimm et al.
1996).
Given the magnitude of the problem, a case-by-case viability approach
to conservation may be impractical. Even conceptually straightforward
goals, such as the estimation of a species’ extinction risk within a fixed
period of time, are, in practice, exceedingly difficult to accomplish without
large amounts of accurately measured field data (Dennis et al. 1991; Fieberg
and Ellner 2000; Coulson et al. 2001). Confidence intervals on extinction
risks estimated via population viability analyses (PVAs) are typically so
large as to render the estimated value meaningless (Ludwig 1998). Brook
et al. (2000) examined the output of a number of different PVAs and
concluded that these models do provide precise predictions of extinction
risk. However, their conclusions are unwarranted because their results
demonstrate that PVA models are on average unbiased, but not necessarily precise for any one species. According to the analysis of Brook et al.,
individual PVAs are, in fact, likely to be imprecise for the single species
targeted by the PVA (Ellner et al. 2002).
The viability approach is further limited by the difficulty of obtaining
sufficient high-quality data across a large number of species. Scarce funding
for conservation may be better spent mediating direct causes of habitat loss
than attempting to elucidate subtleties of population demography across
many species. As a result of these problems, a broader-scale approach,
targeted at entire landscapes, may be necessary to maintain significant
biodiversity in the future.