Habitat distribution and body size in rain-pool dwellers

Rain-pools differ from oceanic islands, essentially, in being ephemeral. Ability to disperse and reproduce is therefore a special priority among inhabitants.
Pupal exuviae of a principal inhabitant, Chironomus imicola , were collected from pools in tropical Africa. Length of pupal skin is positively related both to flight duration and ovule number in adult chironomids. Hence length of pupal skin can be related to fitness in this temporary pool dweller.
Predictably, therefore, remote pools are inhabited by large individuals while those in clusters have more small forms.
That duration of the habitat also influences body size is demonstrated by Polypedilum vanderplanki. These larvae are able to survive dry periods and therefore experience the habitat as permanent. In contrast to C. imicola, P. vanderplanki responds to isolation with a disproportionate number of small flies.
In addition to these differences in average size, variance in body size is affected by isolation of the habitat. Comparison with progeny of a single female shows increased variability to be determined not only by habitat location but also to be an inherent characteristic of animals perceiving the habitats as ephemeral.