Effect Of Different Habitats Research Articles

Influence of different habitats and mating on olfactory behavior of onion flies seeking ovipositional hosts

Using traps baited with natural and synthetic onion volatiles, we examined the effects of different habitats and mating on the olfactory behavior of laboratory-reared and wild onion flies. Rankings of olfactory treatments as host-finding stimuli for females were dependent on their mating status and the habitat in which they were foraging. In habitats devoid of hosts, traps baited with individual alkyl sulfides were as effective as 4-day-old chopped onions and more effective than 1-day-old onions in eliciting host-finding behavior in laboratory-reared unmated females (LUF) and laboratory-reared mated females (LMF). However, upwind dispersal and percent recapture were always significantly greater in LUF. In one experiment, Pr2S2 was 19 times more attractive to LMF in a fallow field, as than it was in an onion field. Reduced effectiveness of alkyl sulfides as host-finding stimuli in onion fields probably results in part because they are less findable, but more importantly because of a change in searching behavior after females have mated. Evidence to support the latter contention is that traps baited with alkyl sulfides and onions were equally findable by unmated females in both habitats. The behavior of LMF was identical to that of wild females, whereas the behavior of LUF was identical to wild males. The hypothesis that olfactory host-finding behavior in onion flies is modified by the resource level was upheld. Alkyl sulfides appear to be the primary, and possibly the only, chemical effectors of host-finding at the patch level of resource distribution, whereas the complex blend emitted by aged, chopped, or damaged onions appears to be acting at the final level of host-finding, while egg-laying females are moving between adjacent hosts in search of an optimal oviposition site.

Individual variation in winter foraging of black-capped chickadees

Wintering black-capped chickadees (Paridae: Parus atricapillus) in northwestern Massachusetts showed a high degree of individual variation in foraging behavior. After accounting for the effects of different habitats and weather conditions, individual differences comprised 6–17% of the total observed variation in four measures of foraging location and rate of feeding. Differences between age and sex groups were not significant and explained comparatively little variation (0.0–1.4%). The chickadees did not fall into a few distinct behavioral categories but instead showed continuous variation on all measures of foraging behavior. It appeared that some variation among individuals was a consequence of behavioral convergence within social groups, since birds that were observed together were more similar in their foraging than expected by chance, after taking habitat differences into account. Our results therefore do not support the interpretation that individual variation in feeding behavior serves to reduce exploitation competition within social groups.

Effect of Annual and Habitat Variations in Prey on the Growth and Productivity of Red-Tailed Hawks (Buteo jamaicensis)

The effects of different habitats, years and brood sizes on the growth rates, asymptotic body sizes, biomass fledged per nest and nestling mortality in red-tailed hawks are compared in this investigation. Habitats were categorized as crop, pasture or mixed. During three years of the study, drought and wet years occurred. Both male and female hawks showed similar growth rates and patterns of growth. Differences in habitat and brood size had no effect on the four parameters measured. Among years, there was a difference in biomass fledged per nest: more were fledged during 1982 than in previous years. This difference was taken to indicate larger clutches that year, given that rate of mortality was essentially similar among years. Prey availability affected the reproductive biology of red-tailed hawks before the eggs were laid rather than afterwards. Prey availability affects the reproductive biology of raptors in several ways. Limited prey availability can (1) decrease growth rates (Moss, 1979), (2) decrease weight at fledging (Cave, 1968; Moss, 1979), (3) increase nestling mortaltiy (Bechard, 1983; Mebs, 1964; Southern and Lowe, 1968) and (4) decrease size of clutch (Cave, 1968; Linkola and Myllymaki, 1969; McInvaille and Keith, 1974; Mebs, 1964; Smith et al., 1981; Southern and Lowe, 1968). The extent that prey availability affects each of these aspects of reproductive biology may vary among species of raptors. This study determined which aspects of the red-tailed hawk's (Buteo jamaicensis) reproductive biology responded to differences in available prey. Differences in available prey in the vicinity of a red-tailed hawk's nest were inferred rather than measured. The estimate of populations of two important prey species of red-tailed hawks (rabbits and snakes) is difficult (Fitch and Bare, 1978; Fitch et al., 1946). There is evidence that different Corresponding address: 2267 N. Yale, Wichita, Kansas 67220. This content downloaded from 157.55.39.112 on Wed, 07 Sep 2016 05:24:28 UTC All use subject to http://about.jstor.org/terms VOLUME 91, NUMBERS 3-4 97 habitats contain different amounts of available prey. Red-tailed hawks delivered more prey to nests located in certain habitats compared with others (Luttich et al., 1970; McInvaille and Keith, 1974). Nests of red-tailed hawks located near water or pasture habitats, which were presumed to have more prey, had larger clutches than those in other habitats (Adamcik et al., 1979; Howell et al., 1978). In Swainson's hawk (Buteo swainsoni), a congeneric species, the amount of searchable space available varies with habitat and so does the amount of prey and the development of the nestlings (Bechard, 1982, 1983). It was assumed that there were more prey available in a pasture than crop habitat. Weather conditions differed markedly for the three years of this study. A severe drought occurred during 1980 and much wetter conditions occurred during the next two years. An increase in microtine populations was reported in several areas of the state between 1980 and 1982 (Slade, pers. comm.; Terman, pers. comm.) and more microtine carcasses were found in the nests during 1982 than in either previous year (Cress, 1982). More prey were assumed available during 1982 than 1980. Growth rates, asymptotic body sizes, nestling mortality and biomass fledged per nest of red-tailed hawks reared in different habitats and during different years were compared to see which of these parameters responded to potentially different amounts of available prey.

A comparison of variability in size dimensions of intertidal and subtidal mussels (Mytilus edulis) (Mollusca: Bivahia)

Variability in size dimensions of bivalve species has previously been claimed (1) to decrease with size and (2) to be greater for individuals in an intertidal habitat than in a subtidal habitat. Results from this study showed that the decrease in variability with size was an artifact of the techniques previously used, and that variability was the same for all sizes of Mytilus edulis. The previous study utilized an interspecific comparison to examine the effects of habitat on variability, which is considered unacceptable because differences in variability are likely to be a consequence of species differences rather than the effects of different habitats. Results presented here from the intraspecific comparison of M. edulis showed that variability was the same for mussels from an intertidal habitat and from a subtidal habitat.