Introduced non-hominid primates impact biodiversity and livelihoods: management priorities

Foraging Strategies of Invasive Macaca fascicularis may Promote Plant Invasion in Mauritius

The effectiveness of seed dispersal by frugivorous primates may vary between seasons and plant species, depending on foraging strategies. We investigated how foraging strategies of an invasive frugivorous primate (the long-tailed macaque, Macaca fascicularis) affect seed dispersal effectiveness (SDE) between native and invasive plants in Mauritius’ native remnant forests. By collecting behavioural data on a group of partially habituated macaques via scan sampling from December 2019 until December 2020 (mean 19.2 ± SD 7.3 hours per month), we investigated seasonal patterns in diet, home range, and fruit availability to identify foraging strategies and determine fruit preference. We simultaneously assessed SDE for invasive vs native plants by quantifying native and invasive fruits consumed or dropped intact by macaques during feeding bouts (n = 114). Macaques fed increasingly on ripe invasive fruits and less on other food items as fruit availability increased, due to preference for invasive fruits and disproportionate availability of invasive vs native fruits. When fruit became scarcer, macaques had larger home ranges, increasingly fed on scarce unripe native and invasive fruits, and expanded their diet by eating orchard crops, indicating use of energy-maximizing strategies. Macaques consumed more native than invasive fruits when unripe and commonly destroyed seeds of native fruits, indicating higher SDE for invasive vs native plants. Higher discard rates of unripe compared to ripe fruits further reinforced these differences in SDE. Our results highlight potential facilitation of plant invasion by an invasive primate, due to foraging strategies shaped by the availability of invasive fruits.

First come, first served: fruit availability to keystone bat species is potentially reduced by invasive macaques

Bats provide important pollination and seed-dispersal services to native angiosperms. However, many bat species are increasingly threatened by human disturbance, including the Mauritian flying fox (Pteropus niger), an endemic, keystone seed disperser. Native forests are scarce and P. niger frequently feeds in commercial plantations, where it now is considered a pest and subjected to frequent culling, thereby hindering conservation efforts. The invasive long-tailed macaque (Primates: Cercopithecidae, Macaca fascicularis) potentially competes with P. niger for scarce native fruits. We investigated the extent of dietary overlap between M. fascicularis and P. niger on Mauritius by sampling fruit drop for 17 tree species and identifying additional food species along line transects. Fruits of 13 of 17 species were eaten by animals and fruit production across tree replicates generally was low but highly variable. Although M. fascicularis ate only 4% of fruit overall, they consumed 20–100% of the fruits of seven species. Approximately 39% of dropped fruits were intact; based on field observations, most probably were dropped by M. fascicularis. Unlike P. niger, M. fascicularis ate mostly unripe fruit and depleted all fruit of certain species at an unripe stage. Hence, M. fascicularis may restrict P. niger’s diet and potentially disrupt seed dispersal of some tree species. Furthermore, small trees are more prone to fruit depletion at an unripe stage by macaques. In addition, asynchronous fruiting phenology across forest fragments may modulate the provision of native fruits to P. niger throughout the year. Although competition can be demonstrated only by controlled experimental studies that are logistically impossible in our scenario, our results highlight potential detrimental consequences that introduced frugivores may have on keystone seed dispersers. Finally, our results suggest that a more integrative and island-wide approach to forest restoration may be valuable for the conservation of P. niger.