Conservation planning in a changing world
219
provide matrix habitats suitable for a substantial
proportion of native species, although typically not
for certain habitat - specialist forest dwellers (Bhagwat
et al. , 2008 ). Therefore, it can be argued that for
successful conservation within reserves, a whole -
landscape approach is needed that accounts for maintaining suitable matrix habitat.
8.5 EMERGENT GUIDELINES FOR
CONSERVATION
Theories are nets cast to catch what we call ‘ the
world ’ : to rationalize, to explain, and to master it.
We endeavour to make the mesh ever fi ner and
fi ner.
(Karl R. Popper, 1959 , p. 59)
MacArthur & Wilson (1967) and MacArthur (1972)
have described ‘ habitat patches ’ such as farmer ’ s
woodlots surrounded by fi elds and recent fi re burns, as
number of planthopper colonists increased by threefold relative to patches separated by matrix habitat
only. The effectiveness of stepping stones and corridors
was signifi cantly lower in a high - resistance matrix
(one that provides only low rates of interpatch dispersal), with stepping stones failing to improve connectivity for the planthoppers relative to controls
(Baum et al. , 2004 ).
To test whether the type of interpatch matrix can
contribute signifi cantly to patch isolation, Ricketts
(2001) conducted a mark – recapture study on a butterfl y community inhabiting meadows in a naturally
patchy landscape. The relative resistances of the two
major matrix types (willow thicket and conifer forest)
to butterfl y movement between meadow patches were
estimated. For four of the six butterfl y taxa (subfamilies
or tribes) studied, conifer forest was 3 – 12 times more
resistant than willow thicket. For the two remaining
taxa (the most vagile and least vagile in the community), resistance estimates for the two differing matrix
types were not signifi cantly different, indicating that
responses to matrix differ even among closely related
species. These results suggest that the surrounding
matrix can signifi cantly infl uence the ‘ effective isolation ’ of habitat patches, rendering them more or less
isolated than patch size and/or isolation would indicate
(as Figure 8.13 ).
In a study conducted in grasslands in western
Victoria, Australia, Williams et al . (2006) assessed how
both the spatial attributes of remnant patches (area
and isolation) and the landscape factors (extent of
urbanization and maximum inter - fi re interval) infl uence the persistence of native plant species. They found
that, on average, 26 per cent of populations of native
species distributed across 30 remnants became locally
extinct between the 1980s and 2001. While area and
isolation had little effect on the probability of local
extinction, urbanization and longer maximum inter -
fi re intervals corresponded with increased extinction
risk (Williams et al. , 2006 ).
Most nature reserves are now surrounded by
human - dominated landscape matrix, which is often
inhospitable to many species. For example, intensively
cultivated agriculture landscape is unable to support
forest - dwelling species. Modifi cation of this agricultural matrix, therefore, may provide opportunities for
reducing patch isolation and thus the extinction risk of
populations in fragmented landscapes.
Tropical agro - forestry systems, where crops are
grown under the shade of native tree species, often
Figure 8.13 A modifi ed species incidence function for a
hypothetical species in a series of habitat islands. The
occupancy of the species depends primarily on the area and
isolation of the habitat island but also varies between
Landscape A and Landscape B as a function of the quality
of the matrix habitat. Black circles indicate occupied habitat
islands and white cells unoccupied habitat islands. The grey
remnants and solid line indicate that a species would inhabit
these remnants when in a landscape with matrix
composition ‘ B ’ (favourable) but would not in matrix
composition ‘ A ’ (less favourable; dashed line). From
Whittaker et al. (2005) and based on original ideas
developed by Mark V. Lomolino and James E. Watson.
219
provide matrix habitats suitable for a substantial
proportion of native species, although typically not
for certain habitat - specialist forest dwellers (Bhagwat
et al. , 2008 ). Therefore, it can be argued that for
successful conservation within reserves, a whole -
landscape approach is needed that accounts for maintaining suitable matrix habitat.
8.5 EMERGENT GUIDELINES FOR
CONSERVATION
Theories are nets cast to catch what we call ‘ the
world ’ : to rationalize, to explain, and to master it.
We endeavour to make the mesh ever fi ner and
fi ner.
(Karl R. Popper, 1959 , p. 59)
MacArthur & Wilson (1967) and MacArthur (1972)
have described ‘ habitat patches ’ such as farmer ’ s
woodlots surrounded by fi elds and recent fi re burns, as
number of planthopper colonists increased by threefold relative to patches separated by matrix habitat
only. The effectiveness of stepping stones and corridors
was signifi cantly lower in a high - resistance matrix
(one that provides only low rates of interpatch dispersal), with stepping stones failing to improve connectivity for the planthoppers relative to controls
(Baum et al. , 2004 ).
To test whether the type of interpatch matrix can
contribute signifi cantly to patch isolation, Ricketts
(2001) conducted a mark – recapture study on a butterfl y community inhabiting meadows in a naturally
patchy landscape. The relative resistances of the two
major matrix types (willow thicket and conifer forest)
to butterfl y movement between meadow patches were
estimated. For four of the six butterfl y taxa (subfamilies
or tribes) studied, conifer forest was 3 – 12 times more
resistant than willow thicket. For the two remaining
taxa (the most vagile and least vagile in the community), resistance estimates for the two differing matrix
types were not signifi cantly different, indicating that
responses to matrix differ even among closely related
species. These results suggest that the surrounding
matrix can signifi cantly infl uence the ‘ effective isolation ’ of habitat patches, rendering them more or less
isolated than patch size and/or isolation would indicate
(as Figure 8.13 ).
In a study conducted in grasslands in western
Victoria, Australia, Williams et al . (2006) assessed how
both the spatial attributes of remnant patches (area
and isolation) and the landscape factors (extent of
urbanization and maximum inter - fi re interval) infl uence the persistence of native plant species. They found
that, on average, 26 per cent of populations of native
species distributed across 30 remnants became locally
extinct between the 1980s and 2001. While area and
isolation had little effect on the probability of local
extinction, urbanization and longer maximum inter -
fi re intervals corresponded with increased extinction
risk (Williams et al. , 2006 ).
Most nature reserves are now surrounded by
human - dominated landscape matrix, which is often
inhospitable to many species. For example, intensively
cultivated agriculture landscape is unable to support
forest - dwelling species. Modifi cation of this agricultural matrix, therefore, may provide opportunities for
reducing patch isolation and thus the extinction risk of
populations in fragmented landscapes.
Tropical agro - forestry systems, where crops are
grown under the shade of native tree species, often
Figure 8.13 A modifi ed species incidence function for a
hypothetical species in a series of habitat islands. The
occupancy of the species depends primarily on the area and
isolation of the habitat island but also varies between
Landscape A and Landscape B as a function of the quality
of the matrix habitat. Black circles indicate occupied habitat
islands and white cells unoccupied habitat islands. The grey
remnants and solid line indicate that a species would inhabit
these remnants when in a landscape with matrix
composition ‘ B ’ (favourable) but would not in matrix
composition ‘ A ’ (less favourable; dashed line). From
Whittaker et al. (2005) and based on original ideas
developed by Mark V. Lomolino and James E. Watson.