Mortality Rates of North American Bears

The age structures of 39 populations of three species of North American bears were analyzed. Estimated mortality rates of cubs in their first year were 30-40% for brown bears and 25-30% for black bears. Apparent subadult mortality rates derived from living animals (15-35% annually) were higher than those of adults. Apparent mean annual mortality rates of subadult and adult females combined were 17.2, 16.8, and 18.8% for black, brown, and polar bears respectively. Comparable values for males were 25.5, 23.0, and 22.6% annually. Because hunting appears to be the major mortality factor in most North American bear populations, interpretation of age structures is facilitated by explicitly incorporating the effects of hunting and its associated biases in the analyses. The simple model proposed to accommodate the hunter-bear interaction clarifies differences in age distributions between species and between sexes within species. Most of the differences in sex-specific mortality rates are a product of differential vulnerability related to home range size and method of hunting.Key words: age distribution, bears, mortality rates, North America, sex ratios, Ursus speciesMots clés: distribution d'âge, ours, taux de mortalité, Amérique du Nord, proportion par sexe, espèce Ursu

Preliminary studies on the gonadal enhancement of giant red sea urchins taken from barrens in British Columbia

We collected giant red sea urchins (Strongylocentrotus franciscanus) in barrens habitat with the intent of enhancing them for market. We placed the urchins in enclosures and provided them with giant kelp (Macrocystis integrifolia) for the 83-day period between 20 March 1998 and 12 June 1998. Sea urchins that were fed giant kelp had a final gonad index of 8.3, whereas the donor population had initial and final gonad indices of 2.9 and 3.5, respectively. In addition, the proportion of individuals displaying a state of starvation via dark brown gonads was significantly lower after feeding compared to the donor population at the end of the experiment (2% and 17%, respectively). These results suggest that food limitation is an important factor in the gonadal development of this urchin population. Moreover, the findings suggest that the urchin resource can be expanded to include barren habitats. Urchins taken from barrens can be quickly enhanced before being sent to market

Data from: The dominant detritus-feeding invertebrate in arctic peat soils derives its essential amino acids from gut symbionts

Supplementation of nutrients by symbionts enables consumers to thrive on resources that might otherwise be insufficient to meet nutritional demands. Such nutritional subsidies by intracellular symbionts has been well studied; however, supplementation of de novo synthesized nutrients to hosts by extracellular gut symbionts is poorly documented, especially for generalists with relatively undifferentiated intestinal tracts. Although gut symbionts facilitate degradation of resources that would otherwise remain inaccessible to the host, such digestive actions alone cannot make up for dietary insufficiencies of macronutrients such as essential amino acids (EAA). Documenting whether gut symbionts also function as partners for symbiotic EAA supplementation is important because the question of how some detritivores are able to subsist on nutritionally insufficient diets has remained unresolved. To answer this poorly-understood nutritional aspect of symbiont-host interactions, we studied the enchytraeid worm, a bulk soil feeder that thrives in arctic peatlands. In a combined field and laboratory study, we employed stable isotope fingerprinting of amino acids to identify the biosynthetic origins of amino acids to bacteria, fungi and plants in enchytraeids. Enchytraeids collected from arctic peatlands derived more than 80% of their EAA from bacteria. In a controlled feeding study with the enchytraeid Enchytraeus crypticus, EAA derived almost exclusively from gut bacteria when the worms fed on higher fiber diets, whereas most of the enchytraeids' EAA derived from dietary sources when fed on lower fiber diets. Our gene sequencing results of gut microbiota showed that the worms harbor several taxa in their gut lumen absent from their diets and substrates. Almost all gut taxa are candidates for EAA supplementation because almost all belong to clades capable of biosynthesizing EAA. Our study provides the first evidence of extensive symbiotic supplementation of EAA by microbial gut symbionts, and demonstrate that symbiotic bacteria in the gut lumen appear to function as partners for both symbiotic EAA supplementation as well as for digestion of insoluble plant fibers