Environmental Engineering Reference
In-Depth Information
Fig. 8.17 Mean
latitudinal range sizes
of bird species in early-
successional areas
(cle ared for ag r icult ure
- shown as 0 years
since abandonment),
young and old
secondary forest
(var y ing in age from 1
to 35 years) and mature
forests, in six tropical
forest studies in Central
and South America.
Mature forests are
labeled as 100 years old
although some are
older. The six data sets
included a total of 631
species of breeding
birds, the latitudinal
ranges of all of which
are known. (After Dunn
& Romdal, 2005, where
the original studies are
cited.)
50
45
40
35
30
25
0
25
50
75
100
Years since abandonment
host plants. For example, the success in open patches of the legume Lotus wrightii
benefi ted several butterfl y species such as the orange sulfur ( Colias eurytheme ) and
western green hairstreak ( Callophrys affi nis ).
8.5.3 When late
succession matters
most - range fi nding
for tropical birds
Species can differ dramatically in the size of their geographical ranges. Dunn and
Romdal (2005) compared the range sizes of bird species characteristic of different
successional stages of tropical forests between northern Mexico and central Peru.
They found on average that species with the largest average latitudinal ranges
occurred in early-successional (cleared) areas, intermediate ranges were associated
with young secondary forests, smaller ranges were linked to old secondary forests
and the smallest ranges of all were associated with mature forests (Figure 8.17). At
one end of the spectrum, bird species from early-successional stages more often
extend outside the tropics and are thus more likely to be conserved by conservation
programs directed at other biomes. On the other hand, mature forest specialists may
be especially at risk of extinction because they are both habitat-restricted and have
small range sizes. They deserve special consideration.
8.5.4 Controlling
succession in an
invader-dominated
community
When endangered animal species are associated with a particular successional stage,
their conservation depends on intervention to maintain habitat at an appropriate
point in the successional timetable. An intriguing example is provided by a giant
New Zealand insect, the weta Deinacrida mahoenuiensis (Orthoptera; Anostostoma-
tidae), a species believed extinct after being formerly widespread in forest habitat.
The weta was rediscovered in the 1970s in an isolated patch of gorse ( Ulex euro-
paeus ). Ironically, in New Zealand gorse is an introduced weed that farmers spend
much time and effort attempting to control. Its dense, prickly sward provides a
refuge for the giant weta against other introduced pests, particularly rats ( Rattus
spp.), but also hedgehogs ( Erinaceus europaeus ), stoat s ( Mustela erminea ) and possums
( Tr i ch os ur u s vulpecula ), which readily captured wetas in their original forest
home.
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