0198566123.pdf

subject to large-scale phenomena such as drought
and severe winters may not be protected from such
die-offs by population subdivision. But, where the
crashes are produced by disease epidemics, subdi-
vision may be beneficial, and the creation of linking
corridors, and translocation efforts, may be harmful.
Young noted in his review that most herbivore die-
offs were due to starvation, but carnivore die-offs
were more often attributed to disease. An epidemic
need not eliminate all the individuals in a popula-
tion for it to have a crucial role in causing the even-
tual extinction of a population from a reserve.
Combining these considerations with meta-
population modelling, Hess (1996) argues that
there should theoretically be an optimal degree of

movement within a metapopulation to enable the

movement of propagules of the target species but

not of disease. But much will depend on the nature

of the intervening landscape matrix and the extent

to which it filters target and ‘pest’ species (Ricketts

2001; Ewers and Didham 2005).

The spread of exotic competitors and predators

and of fire into reserves can also be problematic

(Spellerberg and Gaywood 1993; Lockwood and

Moulton 1994). It has been suggested that alien

plant invasion can be reduced by isolating reserves

and surrounding them with simplified cropland

oceans (Brothers and Spingarn 1992). Short and

Turner (1994) found that the decline and extinction

of certain species of native Australian mammals

280 ISLAND THEORY AND CONSERVATION

0 8

km

N

C

sa

ca

d

es

R

an

g

Peak e

Wilderness

Diamond

Figure 10.11A possible spatial and size-frequency distribution of old-growth habitat islands arranged along riparian strips at progressively
greater distances from a current wilderness area in the Willamette National Forest, USA, designed to provide the optimal degree of connectivity
between patches in a system structured by the dendritic pattern of drainage. In this hypothetical system, the most distant islands are generally
larger in order to counter presumed lower dispersal. (Redrawn from Harris 1984, Fig. 10.2.)