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Resource Heterogeneity Fosters Coexistence of a Mite and a Midge in Pitcher Plants
Author(s) -
Naeem Shahid
Publication year - 1988
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/2937026
Subject(s) - midge , interspecific competition , competition (biology) , biology , ecology , abundance (ecology) , larva , resource (disambiguation) , computer network , computer science
Resource heterogeneity promotes coexistence between two competing species, Sarraceniopus darlingtoniae, a slime mite, and larvae of Metriocnemus edwardsi, a midge, which live together in pitchers of Darlingtonia californica, the California pitcher plant. Both species depend on resources derived from the decomposing insects captured by the pitchers. Experimentation revealed that midge larvae consumed resources at a greater rate than mites and that the densities of the two species are negatively correlated. These results indicate that M. edwardsi is a potential dominant competitor with S. darlingtoniae. Competition theory predicts that the presence of midge larvae should lead to the competitive exclusion of mites, yet these species coexist in field populations. This seeming paradox can be explained by temporal and spatial heterogeneity in resources. Midge larval density is generally associated with expected resource levels of pitchers, whereas mites are found in greatest abundance in pitchers whose resources differ from expected. This pattern suggests that the effects of competition vary and are strongest when actual resource levels equal expected resource levels. When resource levels are above expected levels, coexistence occurs. These results support Levins' (1979) model for coexistence of two species on a single resource. The implications of this study to the general debate over the role of interspecific competition in structuring communities are discussed.