A formula giving the instantaneous birth rate is derived for egg bearing species or species which bear their young. It is shown that the instantaneous birth rate can be calculated when the egg ratio or pregnancy rate and the development time are known. The new method is compared with earlier ones by Edmondson and Caswell: the latter applies incorrectly an earlier formula by Leslie while Edmondson’s formula gives biased results, the bias depending on the length of the development time.

The purpose of this study was to examine the effect of the spatial arrangement of host—plant patches on local abundance of the cabbage butterfly (Piers rapae). By considering the movement behavior of adult females, we developed a detailed simulation model of P. rapae in patchy habitats. The model was then used to predict effects of cabbage patch spatial arrangement on P. rapae egg densities for a specific spatial arrangement of cabbage patches. Field studies confirmed the predictions. The results of this study are discussed in the context of the effects of dispersal behavior on relationships between aptch spatial arrangement and local abundance. The findings are consistent with general simulation results of L. Fahrig and J. E. Paloheimo (personal observation) that suggest large dispersal distances decrease the effect of the spatial arrangement of habitat patches on local population size.

In an earlier paper we described the growth of fishes, ΔW/Δt, in relation to the experimentally measurable variables, body weight (W), food intake (R), and total metabolism (T). Here we review experimental evidence of the nature of the relation between T and W, and its dependence on R and temperature. Making use of the basic energy equation, pR = T + ΔW/Δt, where p is the term for correction from injested to utilizable energy, we calculate T as the difference between the energy equivalents of R and ΔW/Δt, for comparison with results of oxygen consumption studies. Application to a number of published experimental results suggests that with constant food availability, this index of total metabolism, T, derived from feeding experiments, shows the same rate of change with body weight, W, as has been found by oxygen consumption studies under standard conditions. That is, the two sources of data provide estimates of a common γ in the relation[Formula: see text]where α and γ are the fitted parameters for the curve.When fish are fed on a "maintenance" diet, the value of α calculated from the food-growth difference (the growth change is rarely nil in a given experimental observation period), appears to correspond with that characterizing the "routine" metabolic level in oxygen consumption studies. Higher α levels result from higher levels of food availability, and at ad libitum feeding α appears to approach the levels known in oxygen consumption studies as "active" metabolic levels. Temperature effects in the experiments were estimated from multiple regression analyses and showed an elevation of α with increasing temperature. The long-term effect of temperature on α was comparable with that predicted by the Krogh correction at ad libitum feeding, but was significantly lower when food was limited, as at "maintenance" feeding.From a survey of effects of different designs of feeding experiments on these metabolic parameters, it appeared that apparently aberrant values of the weight exponent γ may instead be mistaken interpretations of changes in the level of metabolism α. That is, within the limiting conditions of standard or active metabolism, changes in temperature during experiments or manipulations of the availability of food by the experimenter, sometimes unintentionally, elicit adaptative responses in the level of metabolism, α. These show up in the results as effects on γ when the changes in conditions are gradual, hence confounded with body-size changes during growth.The ability to make distinctions between effects of various factors on these two metabolic parameters appears to depend upon a distinction between experiments conducted with a view to learning what fish do under particular circumstances, and experiments designed to explore what fish are capable of doing. The former type reveal a remarkable conservatism in the basic relation between metabolism and body size, γ. Results from the latter reflect possibilities of metabolic adaptation to environmental circumstances. The apparent predictability of the response of the total metabolism to various conditions of food energy supply and dissipation suggests that the remainder of the energy system, represented by the growth, may be similarly predictable. If this is true outside the laboratory, measurements of the metabolic parameters, α and γ, already familiar in physiological and behavioural research, could be directly used as indices of the (relative) positions of various sizes and species of fish in natural production systems.

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Data from experiments on feeding, assimilation, and reproduction of Daphnia pulex grown in different cell concentrations of Chlamydomonas reinhardtii formed the basis for an individual growth model for D. pulex. The model predictions of both the somatic growth and reproduction agree with subsequent experimental results. Contrary to many higher organisms, the assimilation efficiency increases with increasing body size. This may be, at least in part, the reason why larger body-sized zooplankton tend to dominate in aquatic ecosystems when not controlled by predators. The uptake rate per body weight as a function of cell concentration can be described by Michaelis–Menten type equations, but not the assimilation rate. Contrast between the feeding and assimilation rates suggest that as the nutrient level increases, a higher proportion of uptake is channeled by Daphnia into the detritus/bacterial compartment.Key words: Daphnia pulex, feeding, energetics, assimilation, growth model, nutrient level