Dodson, S.I. (1984). Predation of Heterocope septentrionalis on two species of Daphnia: Morphological defences and their cost. Ecology, Brooklyn. 65(4):1249-1257, figs. 1-7, tab. 1. (viii-1984).

84865

10.2307/1938331 [view]

Dodson, S.I.

1984

65(4):1249-1257, figs. 1-7, tab. 1. (viii-1984)

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Two herbivorous zooplanktonic species, Daphnia middendorffiana and D. Pulex have disjunct distributions in arctic ponds of the Alaskan north coastal plain. D. Middendorffiana co—occurs in ponds with the predaceous copepod Heterocope septentrionalis. Body size, tail spine length, and carapace strength of D. Middendorffiana are defenses against Heterocope predation. These defenses occur only in the developmental stages susceptible to predation. The morphology of Daphnia changes from generation to generation in response to the predator's annual life cycle. Daphnia pulex lacks morphological antipredator defenses and lives in the absence of Heterocope. Field samples suggest that D. Middendorffiana has a lower reproductive rate than D. Pulex. The lower rate may reflect the cost of producing morphological antipredator defenses, especially large offspring. D. Middendorffiana may be able to afford its morphological antipredator defenses only in the presence of Heterocope, which may keep the herbivore density lower and the food density higher than in D. Pulex ponds.

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