Are invasive macaques reducing fruit availability to an Endangered bat species?
Invasive introduced species, are today the biggest threats to Mauritian biodiversity, including its unique forest ecosystems and associated wildlife.
While a quarter of the island is considered forested, only about 5% of the land area is actually composed of native forests, with the rest being plantations and scrublands.
Besides being highly fragmented, these remnants of natural forest are dominated by invasive plants such as the strawberry guava (locally known as ‘Goyaves de Chine’), which are effectively taking over and replacing native plants, and consequently the many animal species that depend on them.
Several studies on the impact of invasive plants currently provide essential information in the quest to successfully advocate for the uptake of non-lethal measures to mitigate local human-bat conflicts. Indeed, the removal of invasive plants not only contributes to increased fruit production by native trees but the Mauritian flying fox (Pteropus niger) is also known to forage more in managed forests.
Adding up new pieces of information, a recent study published in the Journal of Mammalogy investigated if the invasive long-tailed macaque (Macaca fascicularis) and the flying fox are competing for food.
For this, the researchers worked in five forest sites, comparing the diet of these two species, how and when they consume plant parts and also looked at factors that could influence their fruit consumption.
What does the study tell us?
Fruit production by the native trees studied was low and highly variable. For some species, the period of fruiting also differ across sites, an important feature indicating that flying fox could rely on these resources in time and space.
Out of 13,785 native fruits sampled, 15% was eaten by the flying fox, 4% by macaques, 39% was intact (though a percentage of those were probably dropped by macaques when walking on branches to reach for fruits) and the remaining 42% were eaten or parasitised by other animals like rats and moth larvae.
Even though only a small proportion of fruits were eaten by macaques, for some species, like ebony, almost all fruits were eaten (85 to 100%).
Flying foxes and the macaques fed on similar tree species, with an overlap of 62%, but their feeding behaviour are different. While the Mauritian flying fox, fed mostly on ripe fruits and left the seeds intact, macaques ate mostly unripe fruits and seeds.
How does the findings inform conservation decision-making?
The study’s findings lend support to the existing data that the Mauritian flying fox may, at times, feed outside the native forests due to lack of food, a consequence of the impact of both invasive plants and animals.
The importance of prioritising the removal of aliens species to conserve Mauritian native forests and the flying fox is also highlighted.
“These findings emphasize that an integrative approach to forest restoration, requiring both systematic weeding efforts to rid native remnant forests of invasive plants, and an understanding of seed predators and restoration of plant–disperser interactions, may be valuable to conservation of P. niger and its habitat.”- Reinegger, R. and co-authors, 2021.
As of 2020, official figures state that 672.6 ha of native vegetation are under some conservation management, which equates to a staggering 93 % of native habitats currently being degraded.
It is unclear how restoration and reforestation programmes by different organisations contribute to this figure, but while specific actions have been favoured to mitigate human-wildlife conflict (unsuccessfully), official targets for native forest conservation management, as set in the National Biodiversity Strategy and Action Plan, have been missed.
Now, only strong decisive and timely collaboration with local organisations (e.g. NGOs, and research institutions), with the right expertise and resources (here including private landowners) can contribute in removing limiting factors, currently preventing Mauritius from making important progress with regards to the effective and successful restoration of its native forests.
