How large size affects overwinter growth and survival of age-0 fish may vary as a function of food, predation, and energetic condition. During two winters in Ohio, we assessed how these factors affected growth and survival of varying sizes of age-0 largemouth bass (Micropterus salmoides) by combining a field survey (N = 2 reservoirs) with multiscale experiments (reservoirs, ponds, outdoor pools). In our survey, more small (< 100 mm total length) individuals died by spring in one reservoir than in the other. Similarly, when we stocked two reservoirs with marked age-0 largemouth bass in fall, mortality of small individuals was higher in one system overwinter, potentially due to differences in predation intensity. In ponds during two winters, size-selective mortality of small largemouth bass occurred in only two of eight ponds, potentially as a function of cannibalism. Varying ration in pools (starved, 0.5× maintenance, or 1.5× maintenance) did not affect survival, even though starved individuals lost substantial wet weight and energy content. Only when predators were present did small individuals die at high rates, although energy depletion may have contributed to predatory mortality. To increase the probability of overwinter survival, managers should seek to improve first-summer growth, reduce winter predation, and increase winter forage.

Winter severity (temperature, duration, and photocycle), geographic origin, food availability, and initial body size likely influence growth, survival, and, therefore, recruitment of age-0 largemouth bass Micropterus salmoides. We collected age-0 largemouth bass (70-160 mm total length) from low (33ЊN), intermediate (40ЊN), and high (45ЊN) latitudes throughout their natural range (origin), and we subjected all three groups of fish to three experimental winters that mimicked these latitudes (N ϭ 9 largemouth bass per treatment). Within each winter and origin, one-half of the largemouth bass were fed fish prey, whereas the remaining one-half were starved. Winter strongly influenced survival; overall survival rates in the high-, intermediate-, and low-latitude winters were 34.9, 59.4, and 61.1%, respectively (2 test, P Ͻ 0.05). Largemouth bass from 33ЊN suffered high mortality in the high-latitude winter. Across all winters, more fed fish (64.5%) survived than did starved fish (38.1%) (2 test, P Ͻ 0.05). Pooling fish into small (Ͻ100 mm) and large (Ն100 mm) size classes revealed that more small fish died than did large fish in the low-and high-latitude winters, but this was not the case in the middle-latitude winter. Wet weights (g) of fed largemouth bass increased, remained constant, and declined in the low-, intermediate-, and high-latitude winters, respectively. Wet weights and total energy content (kJ) of fed individuals were consistently higher than those of their starved counterparts in all winters. However, energy density (kJ/g) of fed individuals often declined to levels similar to those of starved largemouth bass. Winter temperature combined with duration likely dictate the northern limit of largemouth bass by reducing growth, even when food is abundant. Because survival of individuals from the low latitude was poor in higher latitude winters, stocking southern largemouth bass in northern systems may translate to high mortality and perhaps to degradation of physiological tolerances of local populations through hybridization.

Parameters of a phosphorus cycling model were estimated for two configurations of a lake ecosystem. The piscivore-dominated configuration had one more trophic level than the planktivore-dominated configuration. We derived four main conclusions from analysis of the model. (1) Results support the argument of DeAngelis et al. that turnover rate of a limiting nutrient is directly related to ecosystem resilience. (2) Results support the hypothesis of Pimm and Lawton that longer food chains are less resilient. (3) Inputs of phosphorus to the pelagic system derived from inshore feeding by fishes were a large flux, which is comparable to inputs from physical-chemical fluxes. (4) Algal (seston) standing crops, unlike all other compartments, were less sensitive to phosphorus inputs in the piscivore-dominated system. Consistent with the trophic cascade hypothesis, the piscivore-dominated system had higher herbivore standing crops and lower algal standing crops than the planktivore-dominated system. Changes in trophic structure that derive from trophic cascades can be viewed as changes in the phosphorus cycle driven by fishes.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract. We designed a field experiment to examine predator interactions-in particular, the effect of each predator on the growth and survival of the other, and to examine the effects of predation on prey assemblages-in particular, predation effects by each predator alone as well as together. Blue crabs (Callinectes sapidus) and the fish, spot (Leiostomus xanthurus), co-occur in Southeastern estuaries of the USA, and share many prey taxa and habitat types. We predicted that the blue crabs and spot would suffer both interference and exploitation competition when held together in enclosures. We also predicted that, as a consequence of the competitive interactions, their joint impact on prey assemblages would be different from that predicted based on the impact when held alone.We installed mesh enclosures in an existing earthen pond after allowing it to be filled with water from Bogue Sound, North Carolina, and to be colonized by the naturally occurring species assemblage. A factorial design was used to allow us to test for nonadditive effects of the two predators on their prey assemblage. Contrary to our predictions, we found that spot survival was enhanced in the presence of blue crabs. This enhancement was probably effected by removal of the alga Enteromorpha intestinalis by the crabs. The alga was positively affected by spot. The positive effect of spot on Enteromorpha, and the negative effect of crabs, was probably responsible for differences in densities and distributions of prey taxa within the enclosures. Significant interaction terms in our analysis suggest that community response to either predator is not independent of the other. Our data suggest that we cannot expect to explain adequately the effects of multi-species predator assemblages on their prey by combining information obtained through single-predator experiments.