| Summary: | Significant differences in morphology, vertical distribution, aggressiveness, and feeding habits were found between limnetic and benthic forms of the threespine stickleback
(Gasterosteus aculeatus) in a small coastal British Columbian lake.
In deep laboratory aquaria, simulating lake pelagic and benthic regions, the benthic form was aggressive, solitary, and attracted to bottom cover, in which it remained. The limnetic form, in contrast, was gregarious, non-aggressive, attracted to surface cover, and seldom found near the bottom. In shallow aquaria, representing littoral lake regions, limnetic stickleback were aggressive and non-gregarious until cover was added, whereafter most individuals established residence in it and became significantly less aggressive. Benthic stickleback put into shallow aquaria huddled in small groups until cover was added, after which they spaced themselves
out. These results were consistent with differences in the behavior of the two forms of stickleback in the field.
The limnetic form fed heavily on zooplankton in the lake, while the benthic form mostly ate macro-benthos, Gammarus being its principal prey. Laboratory studies compared the feeding rates of both phenotypes; that of the limnetic form was highest on plankton, while that of the benthic form was highest on araphipods.
The extensive dissimilarities demonstrated in social behavior and feeding ability of the two forms of stickleback indicate that their spatial and trophic segregation In Paxton Lake are due mainly to innate behavioral differences, rather than interaction. === Science, Faculty of === Zoology, Department of === Graduate
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