The world’s tropical forests are threatened by deforestation due to agricultural, industrial and urban expansion; as well as by drought, fire, and disease, all worsened by climate change. Human reforestation efforts are limited by budget and capacity, so the restoration of degraded habitats by means of animal seed dispersal is essential to the future of global forests.
Fruit-eating bats are vital to tropical reforestation due to their ability to disperse seeds to degraded areas. A new study published in mongabay.org’s open-access journal Tropical Conservation Science explores the use of commercial fruits as attraction agents in increasing plant seed dispersal to deforested areas in Southern Mexico. “Fruit-eating bats play a fundamental role in animal seed dispersal and should be considered key actors in tropical forest restoration,” write the researchers.
Bats play a fundamental role in seed dispersal due to their exceptional species diversity, abundance, and a variety of canopy and understory feeding habits. “Bats disperse a larger amount of seeds per species than birds, increasing the probability of seed establishment,” write the study authors. As importantly, bat foraging habits take them from remnant rainforest fragments or riparian vegetation into perturbed areas, with the “seed-rain” that bats produce composed mainly of forest pioneer plant species.
The study compared species richness and abundance of fruit-eating bats in perturbed areas with and without the lure of commercial tropical fruits, and sought to determine the importance of bats as seed dispersers, to identify the plant species they disperse, and to evaluate the seed-rain that they produce.
Sowell’s Short-tailed bat (Carollia sowelli). Photo credit: Anna Horváth.
Fruit-eating bats locate mature fruit by smell, explain the scientists. However, there is a shortage of fruit-producing plants in degraded landscapes, so bats visit these areas less often, and so disperse fewer seeds for reforestation there. Some researchers have used essential oils extracted from chiropterochoric fruits to draw bats into perturbed areas and improve dispersal. The new study replaced these bat-attracting oils with local commercially grown fruits which are cheaper and readily available year-round.
“Our hypothesis,” write the researchers, “is that commercial tropical fruits such as banana (Musa paradisiaca) and mango (Mangifera indica), chosen by their year-round availability, low price, and allure for bats, can act as olfactory attractants and increase bat species richness and abundance, which in turn increase seed-rain, promote seed establishment, and may accelerate the regeneration process in perturbed areas.”
The study took place in an area impacted by forest fires in the state of Chiapas in Southern Mexico. The team placed ripe mangos and bananas in the degraded area to attract bats. No commercial fruits were placed at a control site. Bats were then captured at both locations and the team extracted seeds from their feces for analysis. Bat and bat-dispersed plant species richness and abundance were evaluated, and the importance of each bat species as a disperser was determined. Additionally, germination boxes were set up to evaluate the growth of seeds found in bat feces.
The study revealed that the most important disperser at both the treated and control sites was the Sowell’s Short-tailed bat, followed by the Jamaican Fruit-eating and Toltec Fruit-eating bat, and that “the germination percentage was greater than 50 percent, suggesting that the use of fruits to attract bats can be a feasible wildlife management activity to encourage the [forest] succession process.”
More specifically, the results of the site collection analysis produced 724 individuals of 16 frugivorous bat species – 15 subspecies in treated sites and 12 subspecies in control sites. Importantly, the diets of the bats also confirmed that a higher percentage of pioneer species were consumed and dispersed.
The researchers conclude that “the use of commercial tropical fruits may multiply the effectiveness of frugivorous bats as seed dispersers in neotropical perturbed areas. The attraction of an important seed-dispersing bat species such as C. sowelli to perturbed areas can allow the germination of such pioneer and persistent plant species as Solanum erianthumm [potato tree] and Psychotria sp. [including around 1,800 species] which in turn generate microclimates for the short-term establishment of other plant species and encourage the [forest] succession process.”
The scientists recommend the creation of bat feeding roosts stocked with banana and mangos in degraded areas lacking tree cover as “a feasible, low-cost and functional technique for promoting seed dispersion into fire-affected zones,” and “to initiate a restoration strategy that may include the planting of later successional tree species as well.”
- Preciado-Benítez, O., Gómez y Gómez, B., Navarrete-Gutiérrez, D. A. and Horváth. A. (2015) The use of commercial fruits as attraction agents may increase the seed dispersal by bats to degraded areas in Southern Mexico . Tropical Conservation Science Vol.8 (2): 301-317.