Walker, R.D. (1978). The effects of predation by threadfin shad, Dorosoma petenense, and competition on body length of Diaptomus in Piedmont North Carolina lakes. M.A. Thesis, University of North Carolina – Greensboro, Greensboro, North Carolina, USA. vi + 51 pp.

562371

Walker, R.D.

1978

vi + 51 pp.

Publication

http://libres.uncg.edu/ir/listing.aspx?styp=ti&id=29011

Available for editors   [request]

The species diversity of diaptomid copepods in piedmont North Carolina lakes has increased since these lakes were surveyed by McKee and Coker in 1940. This has been due, in large part, to the introduction of the vertebrate predator threadfin shad (Dorosoma petenense) and its effect on the only two diaptomid copepods present at that time, Diaptomus birgei and Diaptomus reighardi. These two copepods were never found together at the time of McKee and Coker*s survey, one or the other occupying the entire "Diaptomus niche" in any given lake. Ecological maturation of these lakes coupled with predation by Dorosoma petenense has enabled ether diaptomid copepods such as p_. pallidus and J). mississippiensis to enter these lakes and also has allowed the coexistence of p_. birgei and p_. reighardi. Study of seasonal fluctuations in copepod population densities has shown that in shad-inhabited lakes the larger species tend to be dominant during times of low shad predation and the smaller species become dominant when shad activity is high (Beavers and Stavn 1975) . To test the degree of size selectivity of prey by shad, measurements were made of a single species (p_. reighardi) over a one-year period in two lakes, one lake with and the other lake without shad. Seasonal variation in mean length was found to be similar in the two lakes during winter and early spring; however, from late spring through fall mean length of D. reighardi dropped below the yearly average to a greater degree in the shad-inhabited lake. This latter time period corresponded to the time of the year when shad were active in the shadinhabited lake. To establish what effect competition has on the size variability of diaptomid copepods, measurements were made of a species (D. pallidus) present in four lakes, each lake differing in the number of other diaptomid copepods present and, hence, in the degree of competition which this species experienced. It was found that variance of body length of this species was very much reduced in situations where a significant degree of competition with other diaptomid copepods existed. This was considered evidence that the size of diaptomid copepods is related to their ability to partition limiting resources and avoid direct competition.

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