Barriers to adaptive reasoning in community ecology.

Recent high-profile calls for a more trait-focused approach to community ecology have the potential to open up novel research areas, generate new insights and to transform community ecology into a more predictive science. However, a renewed emphasis on function and phenotype also requires a fundamental shift in approach and research philosophy within community ecology to more fully embrace evolutionary reasoning. Such a subject-wise transformation will be difficult due to at least four factors: (1) the historical development of the academic discipline of ecology and its roots as a descriptive science; (2) the dominating role of the ecosystem concept in the driving of contemporary ecological thought; (3) the practical difficulties associated with defining and identifying (phenotypic) adaptations, and; (4) scaling effects in ecology; the difficulty of teasing apart the overlapping and shifting hierarchical processes that generate the observed environment-trait correlations in nature. We argue that the ability to predict future ecological conditions through a sufficient understanding of ecological processes will not be achieved without the placement of the concept of adaptation at the centre of ecology, with influence radiating outwards through all the related (and rapidly specializing) sub-disciplines.

The evolutionary ecology of detritus feeding in the larvae of freshwater Diptera.

Detritus (dead organic matter), largely of terrestrial origin, is superabundant in inland waters but because of its indigestible nature, would appear to be a poor food source for animals. Yet this unpromising material is widely used as food and indeed can be viewed as a defining characteristic of the freshwater environment. We here explore the relationships among animals, detritus and its associated micro-organism decomposers, taking a functional approach. We pose questions about interrelationships and attempt to arrive at new insights by disentangling them from an adaptive point of view. To do this we have been careful in selecting the habitats for detailed consideration. Rain pools on rock surfaces in tropical Africa and pools on peat moorland in the UK were chosen. Both examples have a relatively simple community structure and hence offer the prospect of achieving our aim. As model organisms for study we focus principally on the aquatic stages of selected holometabolous insects; that is, selected genera of the universally common midges, Ceratopogonidae and Chironomidae. We approach these case studies from an evolutionary ecology perspective and see detritus as a simple template upon which a beautiful complex of adaptations can evolve.

Mating in a viscous universe: the race is to the agile, not to the swift.

Charles Darwin's theory of natural selection has at its focal point the mating success of organisms. Among male animals, large body size is widely seen as the principal determinant of mating success. However, where mating takes place in a three-dimensional arena such as water, the arboreal habitat or air, small size with its concomitant aerobatic advantages might be advantageous. Despite considerable interest, the relationship between aerobatic ability and mating success has not yet been demonstrated in a single animal species. Here, we test the hypothesis that the known mating success of small male midges is due to their greater aerobatic ability. To do this, male midges collected from leks in the wild were flown and their flight paths in free flight were recorded on high-speed cameras in the laboratory. Four flight parameters that would seem relevant to male mate acquisition in flight, i.e. acceleration, maximum speed, tortuosity and turn-rate, were analysed with respect to body size. We show that, while in terms of maximum speed there was no detectable difference between small and large males, small males outperformed larger ones with respect to acceleration, tortuosity and turn-rate. We conclude that the hypothesis that small males gain their mating advantage through aerobatic superiority is consistent with the observations reported here.

Are females selected against in ephemeral habitats? The case of a holometabolous insect (Chironomus pulcher).

Adults of the rain-pool dwelling midge Chironomus pulcher are sexually dimorphic with females larger than males. This difference is achieved by females remaining in the growing larval stage for longer. When food is scarce, as under crowded conditions, the average size of both sexes is reduced, but the difference between them is maintained. However, more females perish, presumably because they are unable to achieve a minimum female size. Under conditions of crowding, there is thus a switch in favour of males. Since crowding due to a diminishing habitat is a frequent event in rain-pools, males seem fitter than females in C. pulcher. This paradox is discussed.