2006-7 annual report - Nature Conservation Foundation

Survival of mammal populations in rainforest fragments
Assessing the conservation value of rainforest fragments
on lands outside protected areas, such as private
lands, is gaining increasing attention in global conservation
priorities. NCF, in a study by Hari Sridhar, examined
mammal populations in tropical rainforest fragments
and assessed their status through comparisons
with earlier studies.
The study estimated mammal densities using linetransect
sampling, in five protected rainforest patches
within the Indira Gandhi Wildlife Sanctuary and four
private rainforest fragments on the Valparai plateau. As
many as 24 out of 28 mammal species recorded in protected
rainforests, also persisted in fragments on private
land. Comparisons between fragments and sanctuary
sites showed that 8 out of 10 species evaluated
maintained similar densities in these two strata (see
figure).
The lion-tailed macaque (Macaca silenus), an
endangered Western Ghats endemic, achieved much
higher density and average troop sizes in the private
fragments compared to the sanctuary. Densities in fragments
(total number of individuals divided by fragment
area) could have however been artificially inflated because
all species also use larger areas around the fragments
to forage or move through—a sort of artificial
‘compression’ effect. Nevertheless, the persistence of
most mammals in fragments can be attributed to low
hunting pressure, the ability to use surrounding plantations,
lowered predation pressures, and increased food
availability in and around fragments for terrestrial and
arboreal mammals. For example, fruit trees such as jackfruit
and shade trees in coffee plantations around frag-
ments provide leaves and fruits for arboreal mammals
such as Indian giant squirrels and lion-tailed macaques.
The relatively degraded private fragments also contain
grass and secondary vegetation used by ungulates such
as gaur and barking deer.
We then examined what habitat parameters
were best correlates or predictors of the arboreal mammal
densities. Across sites, these turned out to be different
for different species. Indian giant squirrel (Ratufa
indica) abundance was negatively correlated to canopy
overlap, lion-tailed macaque abundance was negatively
correlated to patch area and canopy overlap, while Nilgiri
langur (Trachypithecus johnii) abundance showed
no significant correlates and was similar across most
sites.
Comparison with estimates from earlier studies
showed that the densities of all three arboreal mammal
species have increased in the last decade, especially in
the private fragments. The persistence and increase in
abundance of mammals in private fragments can be attributed
to a number of reasons—proximity to large
contiguous forests that have remained largely protected
for over a century, low hunting pressure, species’
ability to use matrix habitats, lack of predators, and
high food availability. The relative importance of each
of these needs investigation. While the persistence of
mammals in private fragments is encouraging, effects
of high densities due to the effects of fragmentation or
‘compression’ on long-term population dynamics, behavioural
changes, and social organization also needs
to be looked into.
28
Mammal densities in Indira Gandhi Wildlife Sanctuary (IGWLS) and in fragments on private lands. (Bars = 95% C. I.).
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