Treefall gaps are through to contribute to the diversity of plants in tropical forests by providing opportunities for niche differentiation in modes of regeneration. To examine this hypothesis, we studied the survival, diameter growth, and recruitment of saplings in ≥100 species of woody plants in a 50—ha permanent plot of moist tropical forest on Barro Colorado Island, Panama, from 1982 to 1985. The performance of saplings in low—canopy sites (<10 m) was compared to that of saplings in high—canopy sites (°>10 m), and performance of common species was compared to that of rare species. Of the 108 species for which all three parameters of performance were measured, 104 fell into four response groups, each with characteristic patterns of survival, growth, recruitment, and response to canopy height. Pioneers (six species) survived poorly in both canopy—height categories, and survivors grew rapidly in low—canopy sites. Sapling recruitment was skewed toward low—canopy sites. Understory specialists (three species) survived well in high—canopy sites and poorly in low—canopy sites. They grew slowly and recruited poorly in both situations. Generalists (79 species) survived well and grew slowly in both canopy—height categories. Per—adult recruitment was usually low, and often skewed toward low—canopy sites. Poorly performing species (16 species) survived poorly, grew slowly, and recruited infrequently in both canopy—height categories. Most of the common (>10 saplings/ha) species appeared to be generalists. Many rare (<1 sapling/ha) or occasional (1—10 saplings/ha) species survived significantly (P ≤ .05) less well than the average survivorship of saplings, while many common species survived significantly better than average. Some rare or occasional species grew rapidly, either in low—canopy sites or in both canopy—height categories, while most common species grew slowly in both situations. Rare and occasional species had significantly more recruits per adult than did common species, but often this did not balance their higher mortality. Large differences in survival, growth, and recruitment between canopy—height categories were found only among rare and occasional species.

Papers and panel discussions given during a 1992 symposium on bioenergetics models are summarized. Bioenergetics models have been applied to a variety of research and management questions relating to fish stocks, populations, food webs, and ecosystems. Applications include estimates of the intensity and dynamics of predator–prey interactions, nutrient cycling within aquatic food webs of varying trophic structure, and food requirements of single animals, whole populations, and communities of fishes. As tools in food web and ecosystem applications, bioenergetics models have been used to compare forage consumption by salmonid predators across the Laurentian Great Lakes for single populations and whole communities, and to estimate the growth potential of pelagic predators in Chesapeake Bay and Lake Ontario. Some critics say that bioenergetics models lack sufficient detail to produce reliable results in such field applications, whereas others say that the models are too complex to be useful tools for fishery managers. Nevertheless, bioenergetics models have achieved notable predictive successes. Improved estimates are needed for model parameters such as metabolic costs of activity, and more complete studies are needed of the bioenergetics of larval and juvenile fishes. Future research on bioenergetics should include laboratory and field measurements of key model parameters such as weight‐dependent maximum consumption, respiration and activity, and thermal habitats actually occupied by fish. Future applications of bioenergetics models to fish populations also depend on accurate estimates of population sizes and survival rates.

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We extended a bioenergetics model of growth for the average individual alewife Alosa pseudoharengus to the Lake Michigan population of this species in the mid‐1970s. We used the model to estimate patterns of total consumption of zooplankton by alewives. About 10% of total annual zooplankton consumption by Lake Michigan alewives could be attributed to larval fish feeding during the first 40 d of life. Young‐of‐year and larval fish together accounted for 50% of total annual consumption by alewives. Typical adult (age‐3 and older) fish accounted for only 21% of total consumption. We evaluated the sensitivity of estimates of consumption by alewife larvae by using upper and lower bounds on metabolic rate and energy density of larvae. Total consumption estimates based on the low and high metabolic rates differed by a factor of 3. Consumption was relatively insensitive to energy density. Modeling a 29‐d, normally distributed spawning period versus a single‐day spawning period resulted in a 9% increase in total consumption from first‐feeding larvae to fall young of the year. Predation by the alewife population was strongly seasonal: 45% of total annual consumption occurred in August and September, and 73% occurred during July through October. The mean daily population consumption (for each month), expressed as a percent of crustacean zooplankton biomass, peaked in August and September at about 8% of biomass per day. Similar estimates for the mid‐1980s alewife population were greatest in August at 2.3% of zooplankton biomass consumed per day. We estimated potential consumption by the peak 1966 alewife population (ifsevere mortality had not occurred that year) at 20% of zooplankton biomass per day, which suggested that food limitation was one cause of the severe mortality that year.

We examined relationships between angling and spearing catch rates (catch/h) and walleye population density (number/acre) in 118 northern Wisconsin lakes to determine if walleye catchability in these fisheries was density dependent. The densities of both adult and total walleye populations were unrelated to lake surface area. Similarly, the catchability of walleyes in angling and spearing fisheries was unrelated to lake surface area. Angling catch rates of walleyes were linearly related to total walleye population density, whereas spearing catch rates of walleyes were exponentially related to adult walleye population density. Walleye catchability in the angling fishery was not significantly related to population density, whereas walleye catchability in the spearing fishery was inversely related to population density. We conclude that walleye angling is density independent and is therefore self-regulating, whereas walleye spearing is density dependent and is therefore not self-regulating.