Foraging behaviour as a mechanism for trophic niche separation in a millipede community of southern Vietnam

Abstract

Trophic differentiation is one of the mechanisms for species coexisting in the communities of soil arthropods. Even in saprophagous animals having a generalized diet, separation of the trophic niches can be achieved by using different behavioural foraging strategies. We examined the foraging behaviour and time budget use in two millipede species, Thyropygus carli and Orthomorpha sp., which share the same habitat and have similar diet, in a lowland monsoon forest in southern Vietnam. We performed field observations of the millipedes’ behaviour with 1 min resolution time. For both species, observations covered full day and night with ten replications (240 h for each species). Species differed in their time budget use. T. carli spent most time in searching for food and much less time feeding and resting. Orthomorpha sp. usually spent the middle of the day resting and night time eating. The midday rest and relatively short periods of searching in Orthomorpha sp. are most likely caused by avoiding heat and dryness, whereas T. carli has no circadian rhythm, which is facilitated by a large body size, high mobility and a relative independence of abiotic conditions. We conclude that T. carli behaviour is related to an energy maximising foraging strategy, whereas Orthomorpha sp. realises time minimising strategy. Thus, behavioural differentiations and different use of time budget contribute to the trophic niche separation among coexisting millipede species.