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Influence of driver ant swarm raids on earthworm prey densities in the Mount Kenya forest: implications for prey population dynamics and colony migrations

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Title Influence of driver ant swarm raids on earthworm prey densities in the Mount Kenya forest: implications for prey population dynamics and colony migrations
 
Creator Schöning, C.
Csuzdi, C.
Kinuthia, W.
Ogutu, Joseph O.
 
Description J. O. Ogutu is ILRI author
African driver ants are nomadic social mesopredators feeding on a highly diverse array of prey species at different trophic levels. Colonies of certain driver ant species have a biomass which can equal that of medium-sized mammalian carnivores and the ultimate cause of their nomadic life-style is thought to be local prey depletion. The impact of driver ant swarm raids is therefore expected to be strong but the degree to which they reduce prey populations has not been quantified and it is unknown whether these spectacular predators exert significant top-down effects. We examined the combined effect of driver ant (Dorylus molestus) and swarm-attending bird (Alethe poliocephala) predation on the population dynamics of earthworms, which constitute the ants’ main prey type in the montane forest of Mount Kenya. Pre-raid earthworm biomass densities in the soil layer down to a depth of 8 cm varied by a factor of 31. The immediate effect of swarm raids was a reduction in earthworm numbers in this layer, but 8 days later earthworm numbers had recovered to pre-raid levels. When earthworm biomass densities were compared, no significant effect of swarm raids was detected. The estimated proportion of earthworm prey biomass extracted from 0 to 8 cm layer by driver ants and birds together was about 2.2%. Although colony distribution was overdispersed as expected based on knowledge of D. molestus migratory behaviour, predation events were highly localized. Predation frequency was low (once every 62 days on average) and highly variable. These results indicate that earthworm prey is highly abundant but at the same time so difficult to harvest that swarm raids exert only a marginal influence on earthworm populations. Longer-term studies would be required to determine whether earthworm populations are limited by swarm raids. The small impacts of individual raids and rapid recovery of earthworm prey populations likely underlie the low frequency of migrations and short distances travelled by migrating colonies of D. molestus.
 
Date 2010-01-16T20:38:27Z
2010-01-16T20:38:27Z
2010-02-15
 
Type Journal Article
 
Identifier Schöning, C.; Csuzdi, C.; Kinuthia, W.; Ogutu, J.O. 2010. Influence of driver ant swarm raids on earthworm prey densities in the Mount Kenya forest: implications for prey population dynamics and colony migrations. Insectes Sociaux. 57(1): 73-82.
0020-1812
1420-9098
https://hdl.handle.net/10568/465
 
Language en
 
Source Insectes Sociaux