Canadian Journal of Zoology

Adult yellow perch, Perca flavescens, when offered equal numbers of small (52 – 59 mm total length) and large (66 – 73 mm total length) conspecifics, selected more small than large prey in 9 of 11 laboratory feeding trials. The small and large groups were selected from the smallest 40% and largest 15% of a natural length–frequency distribution of young-of-the-year yellow perch captured in the fall of 1985 from Dickie Lake, Ontario. The adult yellow perch predators ranged in size from 23.2 to 26.8 cm total length. Our experiment suggests that smaller individuals of a juvenile yellow perch cohort have a greater risk of mortality owing to size-selective predation than do larger individuals. Factors that affect the growth rate of juvenile yellow perch may therefore influence recruitment by modifying the extent of size-dependent predation mortality.

One of the performance features that is generally considered crucial to increasing the potential prey spectrum of lizards is bite capacity. In this study we tested whether bite forces may serve as a basis for diet selection in two syntopically occurring lacertid lizards. We did so by measuring bite forces in vivo for a large sample of lizards of the species Podarcis muralis and Lacerta vivipara. To assess the ecological relevance of the bite forces, we tested the hardness of a number of natural prey items of both species. The results of our study support the predictions of biomechanical models of biting in lizards and indicate that both larger animals and larger headed ones bite harder. Surprisingly, head shape is an excellent predictor of bite performance in the species studied. Moreover, it is demonstrated that bite capacity is a potentially important ecological variable that could be used as a factor in explaining patterns of food-resource use, ontogenetic dietary shifts, and sexual dimorphism in diet.

Experimental infections in rodents with Echinococcus multilocularis sibiricensis, Echinococcus granulosus canadensis, and Echinococcus granulosus (Lebanon origin) both by ingestion of onchospheres and by parenteral injection are recorded. The microscopic anatomy of the larval parasite and of the host reaction are discussed and illustrated in detail. Voles and cotton rats display little resistance to the development of the cyst of E. m. sibiricensis and ultimately destroy the host, while collared lemmings and golden hamsters overcome the cyst and destroy it. Muskrats and certain white mice are intermediate in their effects. In all cases, however, some degree of degeneration of the parasite into the alveolar form is shown. White rats, guinea pigs, and rabbits could not be infected with this parasite. E. g. canadensis was developing in the lung of one AKR strain mouse while in the chinchilla the parasite commenced to develop in the lung but was overcome at an early stage. No development took place in the other species of hosts. E. granulosus (Lebanon) appeared to be developing successfully in some cotton rats and white mice fed on onchospheres.

Larvae of nine species of black flies were exposed to synthetic particles in the laboratory. Sizes and concentrations of particles were chosen to simulate natural conditions. Smaller particles (diameter 5–10 μm) were offered at a rate of 50–100/cephalic fan area per second, and larger ones (diameter approximately 150 μm) at 0.3–1.0/cephalic fan area per second. Experiments were conducted at water velocities of 30, 50, and 70 cm/s.In all the laboratory experiments, only a small percentage of the particles passing through an area equal to that of the cephalic fans of a single larva were ingested. Particles larger than the spacing between the fan rays were ingested more efficiently than smaller ones. At 50 cm/s, the mean percentage ingested for all species was 1.6% (0.14–8.3%) of particles 150 μm in diameter and 0.094% (0.0026–0.76%) of particles 5–10 μm in diameter. The percentage of material ingested decreased at higher concentrations and water velocities. There were significant differences among the species.Experiments were done with one of the species in the field with similar results.Based on this work, an individual black fly larva in nature probably ingests 1–10% by weight of the material passing through its cephalic fans.

Field experiments were conducted to investigate the responses of benthic macroinvertebrate communities to experimental additions of fine sediments into riffles having a flow with either low tractive force so the sediments were deposited or sufficient tractive force to transport the added sediments. Sediment deposition had no measurable impact on most taxa, the only negative effects being significantly higher drift rates and lower benthic densities for Paraleptophlebia. Sediment transport by saltation created a physical disturbance that reduced total benthic densities by >50% in 24 h and significantly influenced macroinvertebrate community composition. Changes in the benthic community were the result of catastrophic drift, and distinct immediate and delayed responses of diurnal drift to the saltating sediments were evident. Taxa with the immediate drift response resided predominantly at the substrate surface and were instantaneously exposed to scouring as sediments were added. Macroinvertebrates showing the delayed response initially avoided the saltating sediments because of their deeper distribution, but an apparent diel shift in vertical distribution exposed these taxa to saltating sediments 6–9 h after sediment additions. Thus, even when tractive forces were insufficient to suspend fine sediments, catastrophic drift was initiated by fine sediments that slid and bounced along the surface of the stony substrate. Sediment saltation, therefore, has the potential to act as a community-level disturbance early in the storm hydrograph or at lower discharge magnitudes than required to suspend sediments.

Remote time–depth recorders (TDR) were deployed on six gravid leatherbacks nesting on Sandy Point, St. Croix. Dive behavior was monitored continuously for each turtle during internesting intervals ranging from 9 to 11 days. Dive duration averaged 9.9 min/dive (SD = 5.3, n = 5096); mean depth was 61.6 m (SD = 59.1, n = 5096). One turtle dived twice beyond the range of her TDR to depths we estimate >1000 m. Postdive surfacing intervals averaged 4.9 min/dive (SD = 13.1, n = 5090). Differences in mean dive depth, dive duration, and surface intervals among turtles were not attributable to differences in body size (length or mass). Distinct diel periodicity was observed in dive behavior; submergence intervals were longest at dawn, declined throughout the day, and were shortest at dusk. Night dives (19:00–04:59) were shorter, shallower, and more frequent than day dives (05:00–18:59). Dive depth was less variable at night than during the day. The dive pattern suggests nocturnal foraging within the deep scattering layer, a hypothesis that is corroborated by seasonal weight loss data.

During two winters we studied agonistic behavior of foraging mountain goats (Oreamnos americanus) in both natural and manipulated conditions. By maintaining food pellets at bait site we tested two hypotheses: (i) dominant goats will have primary access to the food, and (ii) kids of dominant nannies will have access to the food with their mothers. At the bait site, average group size was larger and goats in each sex–age class were more aggressive compared with those away from the site. The dominance order among sex–age classes at the bait was similar to that reported at mineral licks, except that 2-year-old males dominated adult females. When goats fed at the bait site, adult females with kids were very aggressive and nanny–kid distances decreased. At the bait, an orphan kid received much aggression, while kids with their mothers received few threats. At the bait site, dominant goats had primary, but not exclusive, access to the bait and kids fed with their mothers, which supported our hypotheses.

Evidence from several species of mammals suggests that the observed increase in female aggressiveness during lactation is aimed at protecting offspring from conspecifics. Whereas in rodents maternal aggression seems to constitute a deterrent against infanticidal behavior by adult males and females, in pinnipeds and primates its most likely function is to protect infants from general harassment by other individuals. Maternal aggression may also be involved in mate selection and function as a spacing mechanism. As an offspring defence behavior, maternal aggression can be considered a form of parental investment. As such, predictions can be made about its intensity in relation to the net effects it has on parental fitness. The functional aspects of maternal aggression suggest that this behavior should be analyzed in relation to other patterns of maternal care and investment in the offspring.

During a 5-year study of a marked population of mountain goats (Oreamnos americanus) in west-central Alberta, 5 of 17 females produced their first kid at 4 years of age, while most females did not reproduce until 5 years of age. Twinning accounted for 2% of births. Survival of kids to 1 year averaged 60%, and survival of females from 1 to 4 years of age was 52%. Most deaths of kids occurred in September–November and appeared due to predation by wolves (Canis lupus), cougars (Felis concolor), and grizzly bears (Ursus arctos). At least half of the yearlings lost from the population were preyed upon, but losses of 2-year-olds were concentrated in the summer, suggesting emigration. Survival rates of young goats were not different according to sex. We suggest that nutrient availability limits the reproductive performance of the goats by retarding their growth, while predation on young goats is a major source of mortality.