Distribution and environmental synchronization of the marine insect, Halobates robustus, in the Galapagos islands

Non-independence of individuals in a population of Drosophila melanogaster: effects on spatial distribution and dispersal

We used a simple quadrat analysis to globally categorise the spatial distribution of Drosophila melanogaster individuals. Individuals were spatially aggregated and this was not only due to sexual attraction. This aggregation seemed to be maintained during dispersal, hence explaining the great variability of this behaviour observed in our work and by other authors. Thus, individuals are expected to arrive as small groups into a new patch. This may induce costs through competition and benefits by ensuring the presence of reproductive mates and/or if there is a phenomenon of local resource enhancement by the presence of conspecifics, hence influencing the evolution of dispersal.

Feeding, predation and aggregation behaviour in a marine insect, Halobates robustus Barber (Hemiptera: Gerridae), in the Galapagos Islands

The flightless marine insect Halobates robustus Barber (Hemiptera : Gerridae) occurs on the surface of the coastal waters of the Galapagos archipelago, frequently aggregated close to mangrove and lava edges. Its food consists almost exclusively of dead insect prey floating on the sea. Feeding is carried out by solitary individuals which leave the non-feeding flotillas and adopt a characteristic hunting behaviour. Hunting occurs largely at high water, which, together with a tendency to remain close to mangrove edges during tidal flow away from the shore, reduces the possibility of the insects being swept into the open sea. Predation by fish, birds and a reptile is reduced by extremely effective avoidance behaviour by the flotillas.