The Feeding Ecology of Hydra and Possible Implications in the Structuring of Pond Zooplankton Communities

Although most invertebrate predators are size-selective, two species of Hydra, H. oligactis and H. pseudoligactis, are not. A marked preference for Daphnia pulex over Simocephalus vetulus, similarly sized prey items, is observed in feeding trials. S. vetulus is virtually ignored and swims among the...

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Bibliographic Details
Published in:The Biological bulletin (Lancaster) 1983-02, Vol.164 (1), p.136-142
Main Authors: Schwartz, Steven S., Hann, Brenda J., Paul D. N. Hebert
Format: Article
Language:English
Subjects:
Community structure
Daphnia pulex
Freshwater
Freshwater ecology
Hydra oligactis
Hydra pseudoligactis
Invertebrates
Marine ecology
Ponds
Population ecology
Predation
Predators
Simocephalus vetulus
Species
Zooplankton
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Summary:Although most invertebrate predators are size-selective, two species of Hydra, H. oligactis and H. pseudoligactis, are not. A marked preference for Daphnia pulex over Simocephalus vetulus, similarly sized prey items, is observed in feeding trials. S. vetulus is virtually ignored and swims among the tentacles of Hydra, whereas D. pulex is rapidly attacked and captured. However, normal feeding responses are induced in the presence of homogenates of both Daphnia and Simocephalus. This suggests that the lack of response to live Simocephalus as prey items may be due to defense mechanisms evolved during the course of long-term coexistence in the shallow, weedy littoral zone of lakes and ponds. Such mechanisms could involve reduced activation of nematocysts, immunity to the toxin, or lack of penetration of nematocysts through the carapace of Simocephalus. The impact on the structure of the zooplankton community of this differential susceptibility to predation by Hydra is discussed.
ISSN:0006-3185
1939-8697
DOI:10.2307/1541196