© 1986 by The Society for Integrative and Comparative Biology
Competition and Coexistence Among Four Estuarine Species of Fundulus1
Martin Marietta Environmental System 9200 Rumsey Road, Columbia, Maryland 21045
Four sympatric species of Fundulus (F. heteroclitus, F. majalis, F. diaphanus, and F. luciae) are distributed along tidal height and salinity gradients such that F. heteroclitus co-occurs with each species, while the remaining species rarely occur together. Feeding habitats of all the species are similar, and food has been shown to limit population size of F. heteroclitus. This paper examines whether competition is an important structuring force within this guild by addressing two questions: 1) is the spatial separation exhibited by three of the species due to physiological barriers or due to competitive exlusion? and 2) when F. heteroclitus occurs with other Fundulus species does competition for resources take place?
Laboratory studies indicate that all four species are tolerant of a wide range of environmental conditions; available evidence suggests that physiological barriers are an unlikely explanation for spatial segregation among some members of this guild. Competitive exclusion seems a likely alternate explanation, but is supported only by studies of diet overlap. Similarly, only inference from diet overlap is available to answer the second question. A field experiment is presented here in which F. heteroclitus and F. majalis were placed in enclosures separately and together. Competition between these species appears to be important, and similar field experiments are recommended to investigate competitive interactions among other species pairs within the genus