Community ecology seeks to explain why patterns of species composition and food web dynamics vary among systems. When these factors are dictated by a particular species, acting as a strong interactor, its relative abundance should underlie variability in its effects across communities. Unlike north temperate lakes, where strong interactors are top predators, Ohio reservoirs contain gizzard shad (Dorosoma cepedianum), a strong interactor in the middle of the food web, which can strongly affect adjacent species
(age-0 sportfish competitors with zooplanktivorous larvae), as well as species in trophic levels above (age-0 sportfish predators) and below (zooplankton) it. The specific effects of gizzard shad on age-0 sportfish vary across reservoirs, depending on juvenile gizzard shad size, which determines their vulnerability to age-0 predators, and abundance, which influences total consumption of zooplankton.

We explored the generality of reservoir community regulation by juvenile gizzard shad, by determining to what extent (and why) larval gizzard shad growth and survival dictate juvenile size and abundance and their subsequent effects on sportfish recruitment. First, we experimentally quantified effects of zooplankton size and density on larval gizzard shad foraging, growth, and survival. High densities (>200/L) of small zooplankton
(< 0.40 mm) promoted larval gizzard shad foraging and survival.

We sampled 12 reservoirs during May -June, 1993 to evaluate the hypothesis that larval gizzard shad survival increases with reservoir productivity, reflecting postive effects of small zooplankton on larval gizzard shad success. Larval gizzard shad hatch abundance and survival positively correlated with reservoir productivity; however, crustacean zooplankton availability could not explain larval success.

Finally (1994), via upstream and downstream sampling of four reservoirs, we evaluated if available zooplankton could explain larval success at finer spatial and temporal scales. Abundant juveniles were only produced when high larval hatch coincided with abundant small zooplankton in upstream areas. Juvenile gizzard shad abundance increased with reservoir productivity. Juvenile size decreased with increasing abundance across mesotrophic to eutrophic conditions, but increased with abundance across eutrophic to hypereutrophic conditions. By classifying reservoirs according to their level of gizzard shad recruitment, managers can develop broadscale strategies specific to anticipated effects of gizzard shad on sportfish recruitment.