The Habitat Loss
Club: Rise in Sea Level Threatens to Wipe Out Only Mangrove-Dwelling Tiger
Population in the World
What
is the most significant shared characteristic between polar bears and tigers?
If you’re thinking of massive canines, try again. The answer, unfortunately, is
rapid habitat loss. Just as melting ice caps are robbing polar bears of their
land, anthropogenic factors have directly and indirectly been fragmenting tiger
habitats in all their ranges. In the past couple of decades, the Indian and
Bangladeshi governments – both countries containing a significant proportion of
the remaining tigers in the world – have taken strict action to constrain
direct anthropogenic influences on tiger population. Anti-poaching laws, the establishment
of tiger reserves, and relocation of villages to minimize human-tiger conflict are
some of the actions taken by the Indian government under what was called
Project Tiger.
While
such actions have helped stabilize tiger populations in the subcontinent, they
have only addressed direct forms of anthropogenic threats to tiger populations.
Indirect forms of anthropogenic influences such as habitat loss through climate
change, although slower, pose just as big of a threat. In their 2010 article, “Sea
level rise and tigers: predicted impacts to Bangladesh’s Sundarbans mangroves”,
Loucks examine the potential rise in sea levels caused by climate change and
its effects on the Bangladeshi portion of the Sundarbans mangrove forest, home
of the only mangrove-dwelling tiger population in the world. The threat of sea
level rises is especially big in the Sundarbans since it is extremely
low-lying. Unlike previous sea level studies that have used large meter-scale
measurements of sea level rises, Loucks and his colleagues, therefore, use a
new sub-meter digital elevation model (DEM) which provides an extremely precise
elevation model of the mangrove forest. They
create their continuous DEM from 80,584 GPS elevation points measured in mm
above sea level. Subsequently, using 4 mm year-1 as a conservative estimate
(based on the previous literature) of annual sea level rise and the year 2000
as the baseline, they predict the percentage of the Sundarbans that will go
under at eight chosen sea level rise values (0, 4, 8, 12, 16, 20, 24, and 28
cm).
Their
results, visualized in Figure 2, predict a 96% loss in tiger habitat by the
time a 28 cm rise in sea level occurs. Assuming that current sea level rise
rates are maintained, that would give us only 50-90 years. Furthermore, using average
tiger home range areas, they estimate the breeding population to decline down
to less than 20 individuals by the time of this 28cm sea level rise. What’s
most upsetting, however, is the fact that Loucks and his team’s estimation is
based on average sea level rises (which
can be exceeded) and the assumption that no forces other than sea level rise are
at work to threaten tiger populations in the Sundarbans (which is not true). So
really, this is just a conservative estimate!
Loucks
et al. (2010) demonstrates the very real threat that slow-acting, macro-level
anthropogenic factors like climate change pose to natural ecosystems. It is
especially worrisome since mangrove ecosystems are themselves one of the most biologically
productive ecosystems in the world, having environmental and economic
implications. The ecosystem services they provide include protection from
cyclones, food and building supplies, fisheries, and carbon cycling in addition
to hosting a wide range of biodiversity. Since the fates of tigers and
mangroves are so intrinsically tied to each other and both so important, as
Loucks et al. point out, I think investigations should be made into ways in
which tiger conservation and mangrove conservation/restoration efforts can be
linked, not just in the Sundarbans, but globally.
Work(s) Cited:
Loucks, C., S. Barber-Meyer, M. A. A. Hossain,
A. Barlow, R. M. Chowdury. 2010. Sea level rise and tigers: predicted impacts to Bangladesh’s Sundarbans mangroves. Climatic Change 98:291-298.
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