Artificial nest and seed predation experiments in tropical lowland rainforest remnants of Singapore

Abstract

Tropical lowland rainforests of Southeast Asia are continually being fragmented and lost at an alarming rate. Little is known about the consequences of this large-scale habitat modification. Using artificial nest and seed experiments, we determined predation rates in forest remnants (2.5-1100 ha in area) of Singapore and Pulau Ubin. Singapore (641 km2) is highly urbanised with only 5% of the native forest cover remaining, whereas Pulau Ubin (11 km2) is relatively less developed with about 60% of the native forest cover remaining. We specifically determined if predation rates varied in relation to: (i) distance from edge, (ii) forest types, (iii) forest areas, (iv) isolation, (v) edge to area ratio, (vi) canopy closure, and/or (vii) area (Singapore vs Pulau Ubin). Overall, 80.5% (n = 328) of artificial ground nests were depredated, of which 55.3% were predated by small mammals. For seeds, 98.2% (n = 219) experimental stations were predated. Generally, the predation rate did not vary significantly in relation to the distance from the edge, though a primary forest remnant had lower artificial nest and seed predation rates than the other remnants. Pulau Ubin remnants were found to have lower predation rates than remnants on Singapore island. No significant correlations were found between predation rates and remnant area, isolation from other remnants, or the edge/area ratio, or canopy density. Relatively high predation rates in some tropical secondary and primary forest remnants may greatly influence plant regeneration and bird community structure.