This is fascinating....
http://www.telegraph.co.uk/earth/main.jhtml?view=DETAILS&grid=&xml=/earth/2008/01/10/scieleph110.xml
Eco-damage threatens elephants and ants
By Roger Highfield, Science Editor
Last Updated: 7:01pm GMT 10/01/2008
Biologists have often complained conservation efforts are
focused too much on charismatic big animals to the exclusion of vast
numbers of insects, plants and other small creatures.
Now a study has shown that if elephants, giraffes and other
picture-postcard animals disappear from the eastern African savanna, the
ecological damage may extend, ironically, to the acacia trees they eat and
cascade all the way to down to affect ants too.
The study is a cautionary tale about the rapid and unanticipated
consequences of human interference and how these effects extend deeper and
wider than we realise, one that will spur efforts to ensure that
conservation efforts focus more on the way species interact.
The finding is a dramatic example of the web of life in which unrelated
species depend directly on each other so that, in this case, four species
of ants rely on the whistling thorn tree, Acacia drepanolobium, for food
(nectar) - and shelter, in the form of bulbous swellings, while the trees
rely on the ants - up to 100,000 each - to guard them against browsing
animals that may want a quick chew.
To reveal what happens when a "cog" is removed from this particular web
of life, Todd Palmer of the University of Florida and colleagues closed off
patches of acacias in their study site over a ten-year period, so that
elephants, giraffes and other large mammals could not feed on the trees.
As a result, ant colony size decreased and a parasitic ant species
became dominant over the others.
These effects led to more attacks by stem-boring beetles and reduced
tree growth and survival.
Acacias which had been fenced off from wild herbivores looked sickly
compared to their unfenced counterparts.
The findings of the study published in the journal Science serve as a
cautionary tale of how people can influence the ecosystem as their impacts
cascade down unexpected paths.
"Throughout sub-Saharan Africa these large mammals are threatened by
human population growth, habitat fragmentation, over-hunting, and other
degradation, so we have to wonder how their loss will affect these
ecosystems," says Palmer.
"The last thing you would think is that individual trees would start to
suffer as well, and yet that's exactly what we see."
One irony of the findings is that the trees have developed their
relationship with the ants to protect themselves against plant-eating
mammals - and yet because of that relationship, the trees wind up actually
needing the mammals.
"If you get rid of the large mammals, it shifts the balance of power,
because the trees default on their end of the bargain," Palmer said.
"When the trees opt out, their hard-working employees starve and grow
weak, which causes them to lose out. So, ironically, getting rid of the
mammals causes individual trees to grow more slowly and die younger.
"However, as for the critical issue of whether the overall number of
species in the study site changed, "we don't know enough about these big
species and the myriad ways they affect ecosystems to be able to predict
the "system-wide" consequences of their loss," he says.
But the message is clear.
"That's the tragedy of human-induced alteration of landscapes... we are
changing the globe in such enormous ways, whether via greenhouse gases,
acidification of oceans, nitrogen deposition, habitat degradation, land
conversion, and other means... and we know so very little about so many
species.
"Although we have certainly put a lot of time and effort into studying
big mammals like elephants and giraffes, we still know appallingly little
about the complex interactions - both direct and indirect - that these
species have with other members of the communities in which these
extraordinary creatures live. "
He says conservation efforts often focus too much on solely conserving
species.
"It's important that conservation biologists continue to learn not only
about individual species, but also the complex web of interactions in which
these species are embedded, when thinking about how to maintain the
integrity of ecological systems."