Two damselflies 'brought back from extinction'
Karin Theron, UCT
A beautiful purple damselfly, the Cape Bluet, and his smaller, more delicate
relative damselfly, the Ceres Stream Damsel, that were thought to be extinct for
decades, were rediscovered by scientists in November 2003 thanks to the felling
of invasive alien trees.
The very unusual purple damselfly, the Cape Bluet, which has
not been seen since 1962 and feared extinct, is now recovering as alien trees
are removed from its wetland habitat.
According to Prof Michael Samways, an expert on South African dragonflies in
the Faculty of Agricultural and Forestry Sciences at the University of
Stellenbosch, these two species were believed extinct as they had not been seen
for years despite intensive searches. The Cape Bluet had not been seen for 41
years and the Ceres Stream Damsel for an astounding 83 years. This is the latest
in a series of remarkable rediscoveries by the Stellenbosch team, which is
compiling a list of threatened species and a field guide.
It seems that these beautiful insects were on the brink of extinction when
the Working for Water Programme began removing alien trees. Suddenly, these
feared extinct species miraculously reappeared. With removal of the trees,
sunlight was able to penetrate the pools, water plants were able to grow and
these extremely rare damselflies, with their special adaptations to Cape
conditions, were able to thrive once more.
Apart from their intrinsic and aesthetic value, dragonflies and damselflies
are now recognised as indicators of riverine integrity. Among the insects most
affected by aggressive alien trees are the dragonflies and their delicate
relatives the damselflies. Some live in streams and others in the wetlands,
where the pressure upon them is enormous. Often the impacts are compounded with
cattle trampling aggravating the impact of the aliens.
This extraordinary damselfly, the Ceres Stream Damsel, is an
evolutionary curiosity that prefers pools rather than streams. It was thought to
be extinct as it had not been seen since 1920, but has reappeared in pools where
invasive alien wattle trees have been removed.
These impacts are particularly severe because populations of dragonflies and
damselflies are already pushed to the limit through drainage and conversion of
their wetland homes. With their habitats reduced and separated they find it
increasingly difficult to find new localities when one pool dries out. They are
left with nowhere to go. Also, their genetic flexibility is reduced as their
populations become increasingly small.
Clearly, it is critical to keep removing invasive aliens to protect wetlands,
including small pools, which are the special habitats of these unusual and
fascinating insects. Research continues, with more species being brought back
from the brink of extinction. The task is urgent now to record, not just how our
special fauna is declining because of alien plants, but also how do we best
manage our wetlands to ensure that our unique natural heritage recovers fully.
The biodiversity crisis is reaching such proportions that it is estimated
that as many as a quarter of all insect species will be extinct within the next
few decades. Other estimates suggest that between 7 and 30 insect species are
already going extinct every week.
These figures are important for South Africa because the country is one of
the most biodiversity-rich countries in the world. Within its borders are two
world-class biodiversity hotspots: that Cape Floristic Region and the Succulent
Karoo.
The Cape Floristic Region is rich in endemic species of insects, as well as
plants, that occur in the Western Cape and nowhere else. These insects are under
severe threat from many environmental pressures. Among these threats are
invasive alien trees. These foreign trees shade out the habitat and cause a
decline in the insect species that are normally used to very sunlit conditions.
Nowhere is it so severe as along water courses. Wattle trees are the worst of
offenders, because they stifle local vegetation and completely change the local
ecology.
More information:
For more information, contact Karin Theron at tel. 021 - 852 7771 or cell.
083 290 6737.
vinofino @ mweb.co.za
Article courtesy UCT Monday Paper
Related articles:
 Extinct?
Think again. Valuable virus reappears
|
