SREL Reprint #1859

Effect of Gambusia holbrooki on a similar-sized, syntopic Poeciliid, Heterandria formosa: competitor or predator?

Mark C. Belk1,2 and Charles Lydeard1,3

1University of Georgia's Savannah River Ecology Laboratory, Drawer E, Aiken, South Carolina, 29802
2University of Georgia, Department of Zoology, Athens, Georgia 30602
3Auburn University, Department of Zoology and Wildlife Science, Auburn, Alabama 36849-5414

Abstract: We examined the effect of eastern mosquitofish, Gambusia holbrooki, on least killifish, Heterandria formosa, two similar-sized members of the family Poeciliidae, to determine which form of interaction was most important—competition or predation. Experimental populations were established in replicate mesocosms (wading pools), and growth and demographic characteristics of H. formosa populations were examined in the presence and absence of G. holbrooki. In pools with G. holbrooki, populations of H. formosa were small and significantly skewed toward large-bodied females, and relative abundance of males and juveniles was reduced. In populations of H. formosa alone, sex ratios and adult to juvenile ratios were about 1:1, individual adult female body sizes were smaller, and populations were large. This combination of population characteristics coincides with those predicted by a strong predator-prey model. We suggest that, even though these species are similar in adult size, diet, and habitat use, the dominant interaction between them, rather than competition, is size-selective predation by large G. holbrooki on small H. formosa. However, in natural populations, predation on G. holbrooki by other species may ameliorate the strong effects on H. formosa observed in this study.

SREL Reprint #1859

Belk, M.C. and C. Lydeard. 1994. Effect of Gambusia holbrooki on a similar-sized, syntopic Poeciliid, Heterandria formosa: competitor or predator? Copeia 1994:296-302. 

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).