Fruit bat diet, foraging ecology and seed dispersal in the Vhembe Biosphere Reserve.

Ph.D. (Zoology)

Department of Biological Sciences

Agricultural intensification, and a rapid human population growth have resulted in increased human wildlife contact. In the case of fruit bats, conflict with commercial fruit farmers has been a leading contributor to a decline of bat species populations, despite the vital ecosystem service of seed dispersal provided by fruit bats. Conflict between fruit bats and fruit farmers often stems from perceived or actual damage to their crops, especially during the harvest season. Such conflict often leads to the persecution of fruit bats, either legally or illegally. Therefore, a proactive assessment of bats diet in agroecosystems is important. South Africa is one of the major producers of litchi and its litchi industry is well established and continues to grow. This study provides insight into the diet, foraging behavior, and ecosystem service of seed dispersal of fruit bat species in litchi orchards and natural habitats to advise on management strategies on how to reduce crop damage. It also assesses crop raiding by fruit bats and other crop raider animals, and their activity patterns in response to litchi abundance during the harvest season using camera traps. This study also used a vertebrate exclusion experiment to quantify the effect of excluding crop raiders on yield, as well as a questionnaire survey to quantify the perceived damage in litchi orchards. The study was conducted in the subtropical fruit growing area of Levubu and the natural habitats of the Soutpansberg, Limpopo province, South Africa. An introduction to the order Chiroptera and important fruit bats ecosystem service of seed dispersal as well as the disservice of crop depredation in agroecosystems is provided in Chapter One. Chapter Two, bats were captured with mist nest in both agricultural and natural habitats during the litchi pre-harvest and harvest seasons. We sampled the litchi orchards as well as natural habitats from February 2018 to November 2020 and used GIS and R (ggplot2, iNEXT, lme4) to analyse fruit bats diet, their effect on seeds germination and habitat use with respect to litchi fruit abundance. Results show that fruit bat diet was dominated by wild fruit species (95%) during the litchi harvest season (December) when fruit bats are perceived to be feeding on litchi fruits. Ficus (Ficus spp.) seeds collected as fruit bats spit-out seeds had significantly lower germination rates than regular seeds, but a significantly lower germination latency, and a similar pattern was also observed for quinine tree (Rauvolfia caffra). Our results suggested that fruit bats inhabiting litchi orchards and surrounding natural vegetation feed primarily on wild fruits due to the high percentage of natural vegetation in our study area, which support the importance of natural orchard edges in mitigating crop raiding. Chapter Three, we mounted 10 camera traps (from October 2019 to December 2020) on two litchi orchards for assessing fruit bats and other crop raider animal species richness and activity patterns in response to litchi abundance during litchi harvest season. Six time-triggered canopy camera traps were mounted (6m above the ground) to monitor the animals visiting litchi tree canopies during litchi pre-harvest (October/November) and harvest sessions (December). Additionally, four motion-triggered camera traps were mounted 30 cm above the ground to monitor animals visiting the litchi trees at the ground level. We used Digikam software to tag images and R (ggplot2, iNEXT, lme4, overlap, RSQLite) to analyse species richness, Relative abundance Index (RAI), and crop raider activity patterns. We recorded a significantly higher species richness index during the harvest season (December) compared to litchi pre-harvest season (October/November). Crop raider species richness was lower compared to incidentally observed species during the litchi harvest season. Fruit bats (which could not be assigned to either Epomophorus or Rousettus genus) recorded lower activity (RAI (of 2.49) compared to Dark-capped Bulbul (Pycnonotus tricolor; RAI (43.44)). Lastly, fruit bats did not show/exhibit any change in seasonal activity between the litchi pre-ripe and ripe seasons. As reported in Chapter Four, we collected the litchi yield data on both vertebrate exclusion trees (caged) and paired open control trees during the December/January harvest season between 2019 and 2020, to quantify the effect of excluding crop raider vertebrates, weather, and insect damage on yield. We constructed a total of six vertebrate exclusion cages on two litchi orchards, each enclosing one litchi tree and paired them with open control trees marked with a tapper. Additionally, a questionnaire survey was conducted in Chapter Four from both commercial and small-scale litchi farmers to quantify the perceived damage caused by crop raiders and later compared the results to the total yield for trees inside the exclusion cages and paired open control trees. Our litchi yield results show that open control trees produced significantly higher yield than caged trees, which is contrary to our hypothesis. There was also a weak but non-significant trend towards higher vertebrate damage on control trees compared to caged trees. Questionnaire survey results revealed that weather (sun/rain) and monkeys were the main cause of damage in litchi orchards, when compared to fruit bats, and there was a strong agreement among farmers that the damage varied by vertebrate groups. Farm type (commercial versus small-scale) also show statistically significant difference in the perceived damage caused by bats, birds, insects, monkeys, weather and wild pigs. The results of our study also show lower crop raiding incidence were reported for fruit bats. In summary, Chapter Five concludes that fruit bats prefer to feed on wild fruits over commercially cultivated fruits such as litchi, and potentially provide ecosystem service of seed dispersal, and that remnant natural vegetation at the orchard edges are important food sources, and assist in mitigating crop raiding, and need to be maintained or restored. The study also shows that fruit bats are not crop raiders of litchi fruits, and do not change their seasonal foraging activity in respond to litchi abundance during the litchi harvest season, as believed by farmers. However, further research on fruit bats crop raiding must be conducted in an area with known abundance of colonial species like Rousettus aegyptiacus, a known global pest of litchi crop. Additionally, the use of radio tracking should be considered, and could provide insight into fruit bats habitat use. Our study further revealed that vertebrate exclusions did not increase litchi yield, and that weather and monkeys were the main cause of damage when compared fruit bats. As a result, this study provides information to farmers on fruit bat`s important ecosystem service of seed dispersal and the benefit of maintaining natural orchard edges.

NRF