The Role Of Fruit Bat Eidolon Helvum And Avian Frugivores In Guava Seed Dispersal And Tree Establishment In Agricultural Landscapes In Vihiga, Western Kenya

Abstract

Seed dispersal by bats and avian frugivores is significant for plant regeneration in fragmented agricultural landscapes in tropical regions. This study was aimed at determining the role of the Eidolon helvum and other avian frugivores in guava seed dispersal and tree establishment in farmlands within Vihiga County. Its objectives were to: establish which frugivore assemblages are dispersing the seeds of Psidium guajava and their relative importance, determine the effects of gut treatment by E. helvum on germination of guava seeds and assess seed rain, seedling establishment, and tree density. Three study sites including two E. helvum roosting sites (Mbale and Ilwanda) and a non - roosting site (Chugi) were selected for study. In each site, 2 ha plots were defined where five transects measuring 100m long and 20m apart were established and 10 focal trees selected for sampling frugivores. Under, the crowns of the focal trees, data on seed rain was collected using 1m2 quadrats. Germination experiments were conducted to determine the effect of four treatments (manually extracted seeds, intact seeds, seeds from bat excreta and seeds obtained from spats) on the rate of germination of guava seeds. Data on seedling establishment were collected below the crowns of 20 selected trees in each study site by mapping seedlings in six randomly chosen 1m2 quadrats. In each site, one hectare plot was divided into 10 sampling plots measuring 10 m by 10m to collect data on tree density and diversity. Statistical analyses were performed using SPSS version 20.0 and STAT program software and were evaluated at p < 0.05 level of significance. A total of 4288 E. helvum fruit bats were recorded visiting guava trees in all the study sites. These were categorized as; Ilwanda (46%, n=1991), Mbale (34%, n=1446) and Chugi (20%, n=851). A total of 1,835 individual birds comprising of 61 species belonging to 21 families were observed visiting 30 P. guajava trees in all the three study sites. Visits by E. helvum fruit bats were significantly higher than avian frugivore visits in all the study sites (Z = - 4.78, p < 0.05). Germination distributions of seeds among the four treatments were not significantly different (Kruskal-Wallis Test, χ2 = 4.32, d.f. = 2, p > 0.05). The mean density of pellets (number of pellets/m2) containing guava seeds deposited by E. helvum under the crowns of P. guajava trees were significantly different among sites (F2, 27 = 10, p < 0.05). The mean density of seedlings (number of seedlings/m2) varied significantly among the (F2, 57 = 29.5, p < 0.05). The density of trees was highest in Ilwanda at 45.7 ± 1.3 trees/ha compared to Mbale at 38.1 ± 1.1trees/ha and Chugi at 30.9 ± 0.86 trees/ha. These findings clearly indicate that, the E. helvum is the most effective disperser of guava seeds and hence conservation of its roosting sites is critical to ensure plant regeneration in agricultural landscapes in Vihiga County.