Variation in predation pressure as a mechanism underlying differences in numerical abundance between populations of the poeciliid fish Heterandria formosa |
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Authors: | Jean M L Richardson Margaret S Gunzburger Joseph Travis |
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Institution: | (1) Department of Biological Science, Florida State University, Tallahassee, FL 32306-4340, USA;(2) Department of Biological Sciences, Brock University, 500 Glenridge Ave., L2S 3A1 St. Catharines, ON, Canada;(3) Present address: United States Geological Survey, Florida Integrated Science Center, 7920 NW 71st St., Mexico, FL 32653-3701, USA |
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Abstract: | We explored whether a variation in predation and habitat complexity between conspecific populations can drive qualitatively
different numerical dynamics in those populations. We considered two disjunct populations of the least killifish, Heterandria formosa, that exhibit long-term differences in density, top fish predator species, and dominant aquatic vegetation. Monthly censuses
over a 3-year period found that in the higher density population, changes in H. formosa density exhibited a strong negative autocorrelation structure: increases (decreases) at one census tended to be followed
by decreases (increases) at the next one. However, no such correlation was present in the lower density population. Monthly
census data also revealed that predators, especially Lepomis sp., were considerably more abundant at the site with lower H. formosa densities. Experimental studies showed that the predation by Lepomis gulosus occurred at a much higher rate than predation by two other fish and two dragonfly species, although L. gulosus and L. punctatus had similar predation rates when the amount of vegetative cover was high. The most effective predator, L. gulosus, did not discriminate among life stages (males, females, and juveniles) of H. formosa. Increased predation rates by L. gulosus could keep H. formosa low in one population, thereby eliminating strong negative density-dependent regulation. In support of this, changes in H. formosa density were positively correlated with changes in vegetative cover for the population with a history of lower density, but
not for the population with a history of higher density. Our results are consistent with the hypothesis that the observed
differences among natural populations in numerical abundance and dynamics are caused in part by the differences in habitat
complexity and the predator community. |
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Keywords: | Density Habitat complexity Population dynamics Population limitation Species-specific predation |
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