SYNOPSIS. On behavioral, hormonal, and physiological grounds, mammalian reproduction can be compartmentalized into the following continuous sequence of events: mating (courtship, estrous), gestation, parturition, lactation, post-lactational parental care, and maternal recovery. We point out that comparing the relative allocation of energy for these events across mammals is difficult because of life history variability (e.g., litter size, birth weight), allometry, phylogeny, and individual variation. We review the empirical and theoretical literature on each of these events with respect to: different methodologies in measuring energy use; broad patterns of energy consumption across diverse mammalian taxa; and, identification of particular reproductive characteristics {e.g., birthing, parental care) which may be costly but have yet to receive energetic measurements. Although most studies have considered gestation and lactation the critical reproductive events for energy expenditure, variation in these events is substantial and almost certainly is a function of relative allocation of time to gestation vs. lactation as well as the presumed energetic costs of mating, birthing and parental care. In addition, repeated observations show that behavioral compensation is an extremely important strategy for minimizing energy requirements during reproduction. From this review, we argue that more complete analyses will come from (1) incorporating energetic measurements in studies of mammalian behavior and (2) including mechanisms of behavioral compensation into physiological studies.

Direct observations of free—living individuals were employed to quantify foraging behavior in Dipodomys deserti, D. merriami, and Perognathus longimembris in two Mojave Desert communities. D. merriami and P. longimembris do not partition shrub and open microhabitats, and all three species concentrate their foraging efforts (>75%) near or beneath the canopies of desert shrubs. Results of livetrapping assessments of microhabitat usage (conducted concurrently with foraging observations) resemble those of earlier studies but differ greatly from observational data; trapping may not produce accurate representations of spatial utilization. P. longimembris avoids open areas and utilizes shrubs in a relatively coarse—grained fashion. D. merriami and D. deserti frequently traverse open areas at high speeds and hence utilize shrubs in a relatively fine—grained manner. Beneath shrubs, D. merriami and D. deserti are more active and discrete in their foraging than is P. longimembris; both Dipodomys apparently search for large clumps of seeds, while P. longimembris forages slowly and continuously, taking individual seeds from scattered dispersions. The distinctive morphology of Dipodomys is interpreted as an adaptation that allows fine—grained use of desert shrubs in the face of high predation risk during intershrub transits. Differences in heteromyid body sizes may also reflect two foraging strategies: small size would reduce energy demands, and thus lower the need to move between shrubs and reduce the need for predator avoidance; larger size would permit year—round activity (avoidance of torpor), reduce susceptibility to starvation (B. K. McNab, personal communication), increase the range of thermal tolerance, and generally increase abilities to cope with variations in environmental parameters (Boyce 1978). It is concluded that the morphological and behavioral differences between Dipodomys and Perognathus reflect divergent foraging strategies which may reflect equivalent but alternative strategies for exploitation of desert seeds.

The high level of RR(50) values to imidacloprid and thiamethoxam suggest an unstable decline in the susceptibility of B. tabaci to imidacloprid and thiamethoxam, with possible cross-resistance or predisposition for dual resistance selection.