For a small mammal, the cocker spaniel-sized fossa, which is endemic to Madagascar, has a mightily big reputation as a cunning and ferocious predator. And, like all successful carnivores, the fossa is a master at evading detection – so much so that relatively little is known about the predator.
But now researchers working in the Betampona Natural Reserve in the north-east of the country have discovered something new about the species: it has been making predation attempts on diademed sifaka lemurs.
What makes this discovery so significant and a conundrum for conservationists, is that both animals are either vulnerable (fossa) or critically endangered (diademed sifaka lemur) and in urgent need of protection.
So, what do conservationists do when one threatened species attacks another?
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Madagascar's predator-prey dilemma
“We were conducting our daily behavioural observations (of diademed sifaka lemurs) when we came across a very unusual sight, a predation attempt by a fossa,” says researcher Giovanna Bonadonna from Washington University in St. Louis in the US.
“What we saw was very rare,” continues Bondadonna.
“There are other small carnivores in Madagascar, but they are not big enough to be able to prey upon an adult diademed sifaka because they are among the biggest lemurs. There are not so many predators that could actually get them.”
With slender bodies and long tails, fossae have many cat-like features and, being great climbers, they are sometimes compared to small cougars, though they're actually part of the weasel family.
Around 90% of Madagascar's forests have been destroyed and, as a result, virtually all of the country's 111 species of lemur are now endangered. Whilst less is known about the population of the fossa, it's recognised that its numbers are under increasing pressure too.
Betampona was the first protected park in Madagascar and is made up of 22 km2 of rainforest that's surrounded by farmland and is totally isolated from larger forest corridors – the nearest forest is over 20km away.
The result is that both the diademed sifaka and fossa are in effect trapped in the reserve and the concern is that there's a high risk of them disappearing from the forest altogether.
Consequently, Betampona is now acting as one vast open-air laboratory for understanding the predator–prey dynamics between these two species, the outcome of which could have a bearing on Madagascar's beleaguered wildlife.
“Although Betampona is one of the best protected reserves in Madagascar, its isolation from other viable forests with lemur populations has created a predicament in which the critically endangered lemurs cannot engage in typical dispersal patterns, leading to genetic and demographic isolation,” says Lisa Kelley, executive director of the Saint Louis Zoo Wildcare Institute.
“It is an incredible scenario in which you have a vulnerable species potentially over-predating on several critically endangered species,” observes Kelley.
The population of diademed sifakas was already in bad shape at Betampona, says Bonadonna, adding that “there is a huge predation pressure that was underestimated until we did this behavioural study. We were able to highlight inbreeding and other factors that may be behind the fact that this population cannot thrive at Betampona.”
Bonadonna is also quick to defend the fossa:
“It’s not that the fossa is the bad guy, it’s also in need of conservation.” says Bonadonna.
Researchers say that the study highlights how complicated the situation is with human activities leading to changes in dynamics within ecosystems, which in turn has cascading effects beyond the current understanding of conservationists.
“Despite the effort to conserve one species, it’s really the ecosystem and the balance of that ecosystem that is at stake once the habitat is compromised,” says Bonadonna.
Researchers are now hoping to undertake a census of the fossa population within the park and see if the density is very high.
“This may lead park authorities to take actions such as translocation into consideration” adds Bonadonna.
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