科研之友
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摘要
Exploitative competition for food resources is one of the crucial biological interactions in nature. However, few studies have experimentally tested if competitive ability of consumer species changes depending on elemental contents of the food, although it has been suggested by the theories of resource ratio for competition and ecological stoichiometry. To verify if competitive superiority actually changes according to elemental contents of the food, competition experiments were conducted using high and low P algal food and three Daphnia species (D. galeata, D. pulicaria, and D. tanakai) with different threshold levels of carbon (TFC) and phosphorus (TFP) necessary for individual growth. Since the TFCs of D. tanakai and D. pulicaria were similar to each other but lower than that of D. galeata, we specifically predicted that when fed high P food (i.e., limited by C), D. tanakai and D. pulicaria would be competitively equal to each other but superior to D. galeata. We also predicted from their TFPs that when fed low P food, D. pulicaria would outcompete D. tanakai and D. galeata, while neither of the latter two would be competitively superior to the other. The results showed that when one of the two competitors was predicted to be competitively superior, the food level under competition was similar to the TFC (or TFP) of the superior species but lower than that of the other inferior species, and that the biomass of the former was much less affected by the competition. Also, when the two competing species were predicted to be competitively equal, the food levels under competition were generally similar to the TFC (or TFP) of both species and their biomasses decreased by the same magnitude. The results thus accorded well with the predictions from the TFC and TFP, and indicate that competitive superiority between the same two Daphnia species changes depending on P: C ratio of algal food. This study provides firm evidence for the first time that resource ratio theory can be applied to competition between animal consumers for essential substances packaged within a single food resource.
- 出版日期2012-1
