Life‐cycle and feeding strategies of freshwater triclads: a synthesis

A relationship is discovered between feeding and life‐cycle strategies in triclads which explains why closely related and coexisting species may either be semelparous (annual) or iteroparous (perennial). Semelparous species feed on active food and in so doing adopt a sit and wait feeding strategy whereas iteroparous species feed on sluggish food and have to seek it out. The semelparous species therefore tend, because of their lower metabolic costs in foraging, to be more efficient converters of food to tissue than the iteroparous species. This efficiency, which allows more rapid growth rates and some immunity to disturbances in food supply, means that in the field semelparous juveniles are likely to have better survival chances (relative to parents) than iteroparous juveniles. Hence sit and wait feeders can “afford” to invest more in reproduction and usually have more to invest than seek‐out feeders.