Ecology and behaviour of the Seychelles giant millipede.

Abstract

On certain islands in the Seychelles archipelago a large and abundant animal is the Seychelles giant millipede, Seychelleptus seychellamm (Desjardins, 1834). This study quantifies the ecological role of this species in litter breakdown on Cousine Island, Seychelles. Observations on various ecological aspects and surface behaviour of this millipede were also made. The population of the Seychelles giant millipede on Cousine Island consists mostly of mature females, with few mature males and immatures. Apparent millipede density was higher at night (i.e. 4.44 ind.m⁻²) than during the day (i.e. 0.19 ind.m⁻²). Millipede biomass was 1.95 tons.ha¯¹. Millipedes were observed feeding on eight food types, with the most common food types being leaf litter and fallen fruit. Predation and scavenging on the Seychelles giant millipede was rarely seen, with only a total of 18 observations being made. The giant ghost crab was the only predator observed killing a millipede. The most common scavenger on dead millipedes was the Seychelles magpie robin. Mean litter ingested by the Seychelles giant millipede was 157 ± 28.1 mg.day¯¹ (n = 45) and mean faecal production was 111 ± 12.8 mg.day¯¹ (n = 45). On Cousine Island, the Seychelles giant millipede consumed daily, approximately 4.6 % of the total litter standing crop and approximately 17.2 % of the daily litter fall. Daily faecal production by the Seychelles giant millipede on Cousine Island was equivalent to approximately 2.9 % of the litter standing crop and to approximately 11.0 % of the daily litter fall. The implications of these results for nutrient dynamics and soil fertility on Cousine Island are discussed. Seven types of surface behaviour were observed being performed by the millipede. More behavioural types were observed at night than during the day, with burrowing and grooming being exclusively nocturnal behaviours. The most commonly observed behaviours were walking and feeding. Movement was more evident in the males and immatures, whilst feeding was more apparent in the females. Less behavioural types were observed in areas of low vegetational heterogeneity and complexity. Vegetation disturbance also had an inhibitory effect on millipede behaviour. Possible explanations for these differences in behaviour are discussed. The implications of these results for the conservation of the Seychelles giant millipede and Cousine Island are also discussed.