Common blossom bats ( Syconycteris australis) as pollinators in fragmented Australian tropical rainforest

Abstract

The effectiveness of the common blossom bat ( Syconycteris australis) as a pollinator of the rainforest tree Syzygium cormiflorum was assessed by comparing movements, pollen loads, and visitation frequency, with those of birds. The study was carried out in a fragmented rainforest landscape in north Queensland and movements were determined by radio-telemetry. Bats carried 6 times more pollen than birds, but were less frequent visitors to S. cormiflorum, suggesting that the quantity of pollen distributed by the two groups may not differ greatly. However, pollen quality (the geographic/genetic distance moved) may be a more important factor in determining pollinator effectiveness. Bats were very mobile in the fragmented landscape, with home ranges varying from 12 to 1796 ha and often encompassing more than one forest fragment. Bats usually moved along strips of vegetation, but were found to fly up to 5.8 km (mean=1 km) across cleared land. This mobility led to similar numbers of S. australis being caught in small (<50 ha) forest fragments and continuous forest. At the scale of individual trees, bats fed for an average of 1.2 min per tree, compared to 5.0 min for birds. Short foraging times per tree and frequent movements of >200 m should increase the opportunity for movement of pollen between individual trees. Collectively, these observations suggest that S. australis carry pollen of high quality. Although they fly across cleared land, fragmentation may impact bat populations by allowing increased owl predation in open country and by increasing the reliance of bats on flower resources in the agricultural matrix. On the Atherton Tablelands, the latter is provided mostly by cultivated bananas ( Musa sp.), which produce nectar but not pollen.