Comparative Life History Tactics of the Sphaeriid Clam, Musculium partumeium (Say), from a Permanent and a Temporary Pond

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Abstract
A population of the sphaeriid clam, M. partumeium, in an ephemeral pond, exhibits a semelparous univoltine life cycle (life-span 13 mo.). The population in a permanent pond has an interoparous bivoltine life cycle (life-spans of both generations 13 mo.). Both populations exhibit a type III survivorship curve. Population differences are discussed in terms of life history tactics. Clams in the permanent pond mimic the life-cycle pattern of the population in the temporary pond by exhibiting dormancy over the summer when the ephemeral pond is dry. For the population of the permanent pond, neither temperature, dissolved O2 nor suspended organics (food) can be invoked as controls for the initiation of growth.