When big mammals are lost, so are termites
Ecologists monitor the impact on rainforest ecosystems.
By Nick Carne
The impact of losing Africa’s big animals goes beyond the obvious.
US researchers have discovered that in rainforest areas where large mammals such as elephants, buffaloes and gorillas are hunted, the abundance of termites falls by as much as 170 times.
That’s significant even in an environment with around 10,400 termites per square metre, given that the insects play a key role in plant decomposition, carbon flux and the physical properties of the soil – as well as being food for others.
And, say ecologists Amy Dunham and Therese Lamperty from Rice University, it serves as a “worthy bellwether” of how any change in an ecosystem might influence the whole.
Lamperty, who spent three months running experiments in the inland rainforests of the central African nation of Gabon, knew that termites were sensitive to habitat change but was surprised by the magnitude of the impact.
"If you go into a forest that's been hunted, you can see differences right in the understory because you don't have these big things trampling and eating all the vegetation," she says.
"So we expected we'd see differences in the vegetation, but didn't know what was likely to happen to the invertebrate populations. The termites caught us off guard."
When large animals are removed from the environment, termites lose two food sources – deadwood from trampled brush and the animal dung.
The study also found that the forest floor becomes dense with vegetation, providing a platform for increased numbers of web-building spiders. These, in turn, eat such flying insects as pollinators and are themselves a food source for insectivorous birds.
Lamperty worked in 11 regions in northeastern Gabon: five in protected forest and six in hunted forest. At each site, she established three plots and collected invertebrate samples in pitfall traps, cups placed with their lips at ground level and filled with ethanol to preserve whatever creatures fell in.
Gabon was an ideal choice, says Dunham, because of the juxtaposition of protected forests with areas near settlements that are hunted.
"It's one of the few countries that has a sizable amount of continuous forest left that can support megafauna like forest elephants," she says.
"When you have large animals like elephants that have disappeared from a forest, you're likely to have some cascading impacts, and these small things that run the world, the insects, are likely to be affected.
The next step, she says, would be to quantify the effect of termite decline on animals that depend on them for food, and find out if there is a tipping point.
The research is published in the journal Biological Conservation.