Abstract - Hydrobiologia, 1997b


The purpose of this study was to determine the affects of pond duration on the life history characters of the clam shrimp, Eulimnadia texana. This crustacean inhabits ephemeral ponds in southwestern North America. Since the shrimp live in temporary habitats, it is thought that there should be high selection pressure on life history characteristics associated with quick development, and lower selection on increased longevity. The characteristics emphasized in this study were age at maturity, longevity, fecundity, and growth. Shrimp that live in ponds that dry quickly (have a high s/v ratio) should have an earlier age at maturity, shorter longevity, lower fecundity, and faster growth. Therefore, if they inhabit a fast drying pond their life history characteristics may be accelerated compared to individuals from slower drying ponds (low s/v ratio). Pond size was measured and a surface to volume ratio calculated. The surface to volume ratio was used as an estimate of the drying rate of the ponds. Five replicates of clam shrimp were raised in a common garden experiment. Daily measurements of growth and egg production were taken. Ages at maturity and death were also recorded. Pond drying was not found to have an affect on the life history characteristics of the clam shrimp: although there were significant differences in age at maturity, longevity, fecundity, and growth between populations, these characteristics did not sort out in a pattern consistent with the s/v ratios of the ponds. Three possible interpretations of these results are discussed: (a) pond duration was incorrectly estimated, (b) complicating factors (e.g., inbreeding depression and community composition) may influence the life history characteristics of the populations, or (c) pond duration does not affect life history traits in expected directions.



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