bluuebunny/crossref_metadata_2025 huggingface dataset:
Layered sexual selection: a comparative analysis of sexual behaviour within an assemblage of piophilid flies
Authors: Bonduriansky Russell
Published: June 2003

Although many theoretical and empirical studies have addressed the dynamics of sexual selection, little is known about the evolution of multiple sexual-selection mechanisms within the same system. I performed a qualitative comparative study of sexual behaviours in seven sympatric species of piophilid flies to identify and compare the apparent mechanisms of sexual selection operating in each system. In each of the seven species I observed several distinct types of malemale and malefemale interactions, potentially representing multiple mechanisms of sexual selection. Malemale interactions included scramble competition and, in some species, bouts of intense combat. Malefemale interactions exhibited two distinct patterns: (1) some form of premounting courtship followed by a simple copulatory sequence or (2) no premounting courtship but palpation behaviours during the copulatory sequence. Either pattern was combined with malefemale struggle in some species. In two species, male mating success also appeared to depend on the ability to overcome a "revealing obstacle", a female adaptation that exposed variation in male performance without direct assessment or struggle. In each species these mechanisms operated in a rough sequence and thus could be viewed as "layers" of sexual selection, with each layer potentially reducing the subset of individuals that have opportunities to compete in the next layer. A brief review of the literature suggests that layered sexual selection is the typical pattern in many animal groups and thus may have important evolutionary consequences.
Aggregative response of Harlequin Ducks to herring spawning in the Strait of Georgia, British Columbia
Authors: Rodway Michael S , Regehr Heidi M , Ashley John , Clarkson Peter V , Goudie R Ian , Hay Douglas E , Smith Cyndi M , Wright Kenneth G
Published: June 2003

We determined the scale of aggregative response of Harlequin Ducks (Histrionicus histrionicus) to seasonally and locally superabundant prey at Pacific herring (Clupea pallasi) spawning sites in the northern Strait of Georgia, British Columbia, in 19952002. Aggregations of 34005500 birds gathered at a small number of sites along the same 8-km stretch of shoreline each year that spawn was available there. Aggregations occurred in only a small fraction of the habitat area where spawn was available. Duration of stay at spawning sites averaged 23 weeks and many birds returned to their wintering grounds afterwards. Birds moving to spawning sites represented 5587% of the total wintering population. The proportion of local wintering populations that moved to spawning sites was negatively related to the distance they had to travel, and few birds travelled farther than 80 km. The decline in proportions moving with increasing distance suggests that more distant individuals may be constrained by a lack of information or that there are trade-offs between the benefits of exploiting spawn and the costs of movement. This raises a conservation concern because the temporal and geographic range of herring spawning in British Columbia is contracting and some wintering waterbird populations may be losing access to this important late-winter food.
Lungworm (Pharurus pallasii: Metastrongyloidea: Pseudaliidae) infection in the endangered St. Lawrence beluga whale (Delphinapterus leucas)
Authors: Houde Magali , Measures Lena N , Huot Jean
Published: June 2003

Eighty-eight percent of adult beluga whales, Delphinapterus leucas (age [Formula: see text]7 years; n = 32), and 72% of juveniles (1 year [Formula: see text] age < 7 years; n = 11) were infected with the cranial sinus nematode Pharurus pallasii. No fetuses or young of the year (age [Formula: see text]1 year; n = 9) were infected. The mean intensity of infection was 419 (range 22042) in adults and 179 (range 1500) in juveniles. There was no difference in mean intensity of infection between the sexes or between juvenile and adult beluga. The absence of P. pallasii in young of the year suggests that transmission is not transplacental or transmammary and that infections are acquired as young beluga begin to feed on infected prey. Pharurus pallasii were 3 times more numerous in the peribullar sinuses than in the frontal sinuses, but were equally distributed laterally. Male and female P. pallasii in heavily infected sinuses were significantly longer than those in lightly infected sinuses. No intensity-dependent effect on fecundity of gravid females was observed. No macroscopic lesions were observed in association with P. pallasii in fresh or frozen carcasses. Low numbers of adult P. pallasii in the lungs suggest that the cranial sinuses are the preferred site of infection. No relationship was found between intensity of infection and body condition of beluga.
Functional morphology and feeding strategy of the hydrothermal-vent polychaete Archinome rosacea (family Archinomidae)
Authors: Ward Megan E , Jenkins Cheryl D , Dover Cindy Lee Man
Published: June 2003

Polychaetes are a large component of deep-sea hydrothermal-vent invertebrate faunas, yet little is known about the trophic ecology of most species. In this study, the feeding mode of a common and widespread vent polychaete, Archinome rosacea (order Amphinomida), is investigated through morphological studies and gut-content analyses. The foregut of this polychaete is similar in structure to that of other shallow-water Amphinomida. Prey capture is facilitated by a ventral muscular eversible proboscis with two glandular lateral-lip structures. Extracellular digestion is suggested by packets of digestive enzymes observed to be discharged from the apical ends of the midgut epithelial cells into the lumen. Midgut tissues also contain inclusions resembling spherocrystals, possibly sites where toxic materials are sequestered. Gut-content analyses indicate a preference for mobile prey, including polychaetes and crustaceans. We propose that predation and scavenging are important trophic strategies for A. rosacea.
Does fungus consumption by the woodland jumping mouse vary with habitat type or the abundance of other small mammals?
Authors: Orrock John L , Farley Deborah , Pagels John F
Published: June 2003

Fungi are important in the diet of many small mammal species, but patterns of fungus consumption (mycophagy) in eastern forests of North America have received little attention. Examination of stomach contents of the woodland jumping mouse, Napaeozapus insignis, revealed that fungi were an important dietary component in both eastern hemlock and mixed mesophytic habitats. Jumping mice in both forest types consumed mostly Glomalean fungi (primarily from the genera Glomus and Endogone), in agreement with previous studies. Mice also consumed fungi from the genera Elaphomyces and Melanogaster, previously unreported in the literature. Fungi from the genus Hymenogaster were only found in mice from eastern hemlock habitats. Melanogaster spores occurred more frequently in jumping mice from sites in which deer mice, Peromyscus maniculatus, were abundant, whereas Glomalean fungi were less frequent in the diet of N. insignis when deer mice were abundant. Overall frequency of spores in the diet of jumping mice was negatively related to the abundance of deer mice, suggesting that interactions between species may shape patterns of mycophagy.
Temperature and ontogenetic effects on color change in the larval salamander species Ambystoma barbouri and Ambystoma texanum
Authors: Garcia T S , Straus R , Sih A
Published: June 2003

Temperature has been shown to affect body color in several species of amphibians. The interaction between color and temperature may also change over larval ontogeny, perhaps because of age-related or seasonal changes in selection pressures on color. We quantified the effects of temperature on the color of the salamander sister species Ambystoma barbouri and Ambystoma texanum over larval ontogeny. We found that early-stage larvae responded to cold temperatures with a dark color relative to that of the warm temperature response. Both species then exhibited an ontogenetic shift in larval color, with larvae becoming lighter with age. Interestingly, older larvae showed decreased plasticity in color change to temperature when compared with younger stages. Older A. barbouri larvae showed no color response to the two temperature treatments, whereas older A. texanum larvae exhibited a reversal in the direction of color change, with cold temperatures inducing a lighter color relative to warm temperatures. We suggest that the overall pattern of color change (a plastic color response to temperature for young larvae, a progressive lightening of larvae over development, and an apparent loss of color plasticity to temperature over ontogeny) can be plausibly explained by seasonal changes in environmental factors (temperature, ultraviolet radiation) selecting for body color.
Seasonal changes in the diving performance of the bimodally respiring freshwater turtleRheodytes leukopsin a natural setting
Authors: Gordos Matthew A , Franklin Craig E , Limpus Colin J
Published: June 2003

The objective of this study was to investigate how seasonally fluctuating environmental conditions influence the diving performance of the highly aquatic, bimodally respiring turtle Rheodytes leukops in a natural setting. Over four consecutive seasons (Austral autumn 2000 to summer 2001), the diving behaviour of adult turtles was recorded via pressure-sensitive timedepth recorders within Marlborough Creek, central Queensland, Australia. Short surfacing intervals recorded for R. leukops in winter suggest that the species utilizes aquatic respiration as an overwintering strategy to prevent the development of a metabolic acidosis during the long inactive dives observed during the season. As water temperature increases and aquatic PO2decreases, R. leukops switches from facultative to obligate air-breathing, presumably because of the increased metabolic cost associated with aquatic respiration under summer conditions. Increases in mean surfacing time from winter to spring and summer are attributed to seasonal changes in behaviour possibly associated with foraging rather than to the physiological state of the turtle, given that no difference in median surfacing time among seasons was observed.
The effects of habitat fragmentation on amphibian species richness of Prince Edward Island
Authors: Silva Marina , Hartling Leslie A , Field Sarah A , Teather Kevin
Published: June 2003

We surveyed 11 forest remnants and their adjacent ponds to assess the species richness of amphibians on Prince Edward Island, Canada. By combining aquatic and terrestrial sampling methods, we detected the presence of four urodeles and five anurans in our study sites. No significant difference in species richness was found between the sites located in Prince Edward Island National Park (n = 6) and those outside the park (n = 5). The most frequently captured species in forest remnants were blue-spotted salamanders (Ambystoma laterale) and American toads (Bufo americanus) with 35.1 and 29.8% of the captures, respectively. In ponds, the most abundant and widespread species was the green frog (Rana clamitans). Red-backed salamanders (Plethodon cinereus) were captured in one site only. Species richness was not significantly associated with either forest remnant area or perimeter length. There was a significant nonlinear relationship between amphibian abundance and the perimeter length of forest remnants. Although our findings suggest paucity in species composition of amphibian communities, we did not find evidence suggesting that amphibians have declined during the last 30 years on Prince Edward Island.
Effects of initial (larval) size and host body temperature on growth in trematodes
Authors: Poulin Robert , Latham A David M.
Published: June 2003

For ectotherms, temperature is an important correlate of variation in body size within species. Variation in body size among related species could also be attributable in part to temperature if the different species grow under different thermal regimes. The roles of both initial (larval) size and host body temperature on final (adult) size of parasitic trematodes were investigated in a comparative analysis. Trematodes are a good model group for such a study, with almost half of known species growing at high and constant temperatures in endothermic vertebrates and the rest at lower and fluctuating temperatures in ectothermic vertebrates. The relative growth of trematodes, i.e., their growth relative to the size of their larvae, varied greatly among species. Increases in body size from the cercarial larval stage to the adult stage averaged almost 40-fold (maximum 1300-fold), whereas increases in size from the metacercarial stage to the adult stage averaged 6-fold (maximum 110-fold). There were no differences between trematodes in ectothermic hosts and trematodes in endothermic hosts with respect to these measures of relative growth, however, which suggests that host type and the thermal regime provided by the host have no effect on the growth of trematodes from larval to adult stages. In contrast, the final (adult) body size of trematodes appears to be determined to some extent by their initial (larval) size, independently of the type of host in which they developed.
Salt and water balance of modern baleen whales: rate of urine production and food intake
Authors: Kjeld M
Published: June 2003

Whales, as pelagic marine mammals, are thought to have evolved from fresh-water-dependent terrestrial mammals. Baleen whales feed primarily on salty euphausiids (krill) and have no access to fresh water. How have these mammals adapted to lifelong habitation in a hyperosmotic medium? A new approach is proposed for studying this by using allometry (scaling) of endogenous creatinine clearance in mammals together with determinations of creatinine concentration in fresh postmortem blood and urine of fin whales (Balaenoptera physalus) and sei whales (Balaenoptera borealis). From the predicted mean creatinine-clearance values and the measured mean creatinine concentrations, a urine-production rates of 974 and 627 L/day for the fin and sei whales, respectively, were computed. Average daily krill ingestion of about 1300 and 835 L is predicted for the fin and sei whales, respectively. The whales seem to ingest about 30% more than earlier reported of a prey, which has about 50% of the salt concentration of seawater, thus maintaining the salt and water balance with a minimum of 12% seawater ingestion. The method used to estimate the above volumes could be a valuable tool in further studies of the water and salt balance of the large baleen whales, which may not have the same osmoregulatory control mechanisms as the smaller Odontoceti.
Matching productivity to resource availability in a small predator, the stoat (Mustela erminea)
Authors: King Carolyn M , White Piran C.L , Purdey Dan C , Lawrence Barry
Published: June 2003

Stoats (Mustela erminea), introduced to New Zealand in the late nineteenth century, are common in New Zealand beech (Nothofagus sp.) forests, where populations of feral house mice (Mus musculus) fluctuate between years much as voles do in the northern hemisphere. We present new field evidence and two models demonstrating (i) a strong correlation between density indices for young stoats in summer and for mice in the previous spring, and (ii) a significant linear relationship between productivity per female and spring density of mice up to 25 mice captures per 100 trap-nights. These models confirm that short-lived small mustelid predators dependent on fluctuating populations of prey have evolved means of matching their productivity to the prospects of success across a wide range, from total failure in rodent crash years to >12 independent young per female in rodent peak years. We suggest that the enhanced reproductive success of female stoats when rodents are abundant is due to a combination of critical improvements in both the reproductive physiology and the foraging behaviour of female stoats in rodent peak years. Conversely, a drastic shortage of rodents increases the mortality of embryos and nestlings, while the adult females are able to survive, and even remain relatively fat, on other foods.
Gray whale distribution relative to forage habitat in the northern Bering Sea: current conditions and retrospective summary
Authors: Moore Sue E , Grebmeier Jacqueline M , Davies Jeremy R
Published: June 2003

Hundreds of gray whales (Eschrichtius robustus) stranded dead along beaches from Mexico to Alaska in 1999 and 2000. The cause of the mortalities remains unknown, but starvation resulting from a reduction in prey, especially in the Chirikov Basin, was suggested as the cause. In the 1980s, the Chirikov Basin was considered a prime gray whale feeding area, but there has been no recent comprehensive assessment of whale or prey distribution and abundance. In 2002, a 5-day survey for gray whales revealed restricted distribution in the basin and a 3- to 17-fold decline in sighting rates. To put these data in context, a retrospective summary of gray whale and benthic fauna distribution and abundance was undertaken. During the 1980s, gray whale sighting rates in the Chirikov Basin were highly variable. Ampeliscid amphipods dominated the benthos where gray whale sighting rates were highest. Available measures of biomass suggest a downturn in amphipod productivity from 1983 to 2000, when estimates of gray whale population size were increasing, suggesting that the whales simply expanded their foraging range. We encourage long-term study of the Chirikov Basin as a location where predatorprey responses to changing ocean climate can be researched, because decadal time series data are available.
Metabolic fright responses of different-sized largemouth bass (Micropterus salmoides) to two avian predators show variations in nonlethal energetic costs
Authors: Cooke Steven J , Steinmetz Jeff , Degner Jacob F , Grant Emily C , Philipp David P
Published: June 2003

Recently, researchers have identified that nonlethal costs of predation may arise not only from lost energy intake but also potentially from increased energetic expenditure. During periods of heightened stress following unsuccessful predation attempts, organisms may remain in an altered physiological state with elevated metabolism for some time. Few studies have quantified these nonlethal energetic costs of predation. We monitored the cardiac response (cardiac output (Q), heart rate (fH), and stroke volume (SVH)) of largemouth bass, Micropterus salmoides, ranging in size from 200 to 425 mm, to simulated avian predation attempts by great blue heron, Ardea herodias, and osprey, Pandion haliaetus. Fear bradycardia during a 30-s predation attempt varied depending upon the size of the fish and the type of predator. The magnitude of the bradycardia decreased with increasing size of the fish; however, the disturbances were more extreme in response to osprey than to blue heron models. Maximal cardiac disturbance following simulated predation attempts by osprey were consistent among size classes of bass. However, the magnitude of the disturbance following heron predation attempts reduced as the size of the fish increased. Size-specific trends were even more extreme for cardiac-recovery durations. Largemouth bass of all sizes exposed to osprey predation attempts required ~40 min for Q and fH and ~30 min for SVH to return to predisturbance levels. Although small bass exposed to heron predation attempts required recovery times similar to fish exposed to osprey predation attempts, as the size of largemouth bass exposed to the heron model increased above ~300 mm, the recovery time decreased significantly. We conclude that the size-specific response of largemouth bass to different predators is reflective of their ability to assess the risk posed by different predators. In addition, the nonlethal costs of predation can be substantial and should be considered in future bioenergetics models.
Demography and viability analyses of a diamondback terrapin population
Authors: Mitro Matthew G
Published: June 2003

The diamondback terrapin, Malaclemys terrapin, is a long-lived species with special management requirements but quantitative analyses to support management are lacking. I analyzed markrecapture data and constructed an age-classified matrix population model to determine the status and viability of the only known diamondback terrapin population in Rhode Island. Female diamondback terrapins were captured, marked, and recaptured while nesting during 19902001. Population growth rate (λ) was 1.034 (95% confidence interval = 1.0121.056). For the preceding 5 years, however, abundance had been stable at about 188 breeding females. Adult apparent survival was high but declined slightly by 0.14% per year from 0.959 in 1990 to 0.944 in 2000. Recruitment of breeding females also decreased during the study period; therefore, survival was increasingly a greater component of population growth rate. Juvenile survival was 0.565 at λ = 1.034 and 0.446 at λ = 1. Both retrospective (markrecapture) and prospective (matrix population model) analyses showed a greater influence of survival versus reproduction on population growth. Population- model projections showed that capping nests to improve reproductive success could increase population growth rate, but the magnitude of increase was positively related to pre-reproductive survival, therefore negating nest capping as a remedy for declining populations or poor survival. Extinction attributable to demographic stochasticity is unlikely.
Influence of abundance of small-mammal burrows and conspecifics on the density and distribution of spotted salamanders (Ambystoma maculatum) in terrestrial habitats
Authors: Regosin Jonathan V , Windmiller Bryan S , Reed J Michael
Published: June 2003

Spotted salamander (Ambystoma maculatum) distributions were studied within eighteen 272-m2 field enclosures in upland deciduous forest adjacent to two breeding ponds. The enclosures were subsequently used in experiments involving (i) removal of small-mammal burrows to determine if burrow abundance influenced salamander density and (ii) manipulation of salamander densities to determine if increased density was associated with decreased growth, fecundity, or probability of re-emerging to breed. Mean density of salamanders wintering in enclosures <65 m from the breeding ponds was 1.0/100 m2 (SD = 1.1/100 m2, n = 17, range = 04.0/100 m2). Density declined as distance to the nearest breeding pond increased, and the sex ratio was skewed sharply toward males (8:1) wintering close (<65 m) to the pond but not farther from the pond (1:1). Males residing within the enclosures weighed more than males wintering farther from the breeding ponds. Migrating salamanders were over 3 times more likely to leave burrow-removal plots than control plots prior to the summer inactive period. Salamanders housed at high density (15/enclosure) were less likely to re-emerge to breed than were salamanders housed at low density (5/enclosure), but we observed no effects on growth or fecundity. Results suggest that conspecific distribution and burrow availability might affect the density of spotted salamanders within terrestrial habitats.
mRNA analysis in flattened fauna: obtaining gene-sequence information from road-kill and game-hunting samples
Authors: Doyon C , Trudeau V L , Hibbert B M , Howes L A , Moon T W
Published: June 2003

Whether gene-sequence information could be obtained using mRNA from road-kill and hunting samples was investigated. Adipose tissue was used to clone cDNA fragments of the hormone leptin and brain tissue was used for the enzyme glutamic acid decarboxylase (GAD). Tissues collected from road-killed animals were used to clone leptin from RNA samples of raccoon (Procyon lotor) and woodchuck (Marmota monax). We were able to extract RNA and clone GAD67 from samples of masked shrew (Sorex cinereus), although the time of death was unknown. We collaborated with hunters who provided tissues from which we cloned leptin and GAD isoforms from beaver (Castor canadensis), red squirrel (Tamiasciurus hudsonicus), black bear (Ursus americanus), and moose (Alces alces americana). Molecular phylogenetic analyses confirmed that the sequences obtained did not result from contamination. A time-course experiment showed that even 24 h after the death of rats, sufficient mRNA remains to amplify leptin from adipose tissue. These results suggest that road-kill and hunting samples could be used as a valuable source of gene-sequence information.
Dominance relations and agonistic behaviour of Tundra Swans (Cygnus columbianus columbianus) during fall and spring migration
Authors: Badzinski Shannon S
Published: June 2003

Social interactions and agonistic activities of Tundra Swans (Cygnus columbianus columbianus) were documented at Long Point, Ontario, to determine (i) dominance relations among social groups and (ii) the frequency and intensity of agonistic acts by swans. Families were involved in one-third as many interactions as were nonfamily groups. Nonfamily groups initiated interactions with other nonfamily groups more often than they did with family groups, but families initiated the same relative numbers of interactions with family and nonfamily groups. Further, families won nearly all conflicts with nonfamily groups, which suggests that they generally dominated nonfamily groups. Tundra Swans also showed a dominance hierarchy based largely on family or group size. To reduce conflict and energy expenditure, swans may use a simple "decision rule" during interactions: larger groups and initiators win. Two results supported this: (1) swans initiated interactions more often with smaller groups and (2) groups that initiated won interactions more often than did recipients. Swans used low-intensity agonistic acts more frequently than higher intensity ones when engaging members of other social groups, but intensity of aggression was independent of group status. Dominance based on the use of simple cues may be especially beneficial in unstable social environments at major staging areas.
Estimate of the Ipswich Sparrow population on Sable Island, Nova Scotia, in 1998, using a random-transect survey design
Authors: Smith Stephen J , Lucas Zoe , Stobo Wayne T
Published: June 2003

The Ipswich Sparrow (Passerculus sandwichensis princeps) population on Sable Island, Nova Scotia, has been designated as "vulnerable" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Previous surveys of this population during the nesting season have varied in coverage and the rigour of statistical-survey design. In 1998 we surveyed the population using a stratified random-transect design. Estimated total numbers (±SE) were obtained along with confidence intervals calculated using bootstrap methods. The precision of our survey estimates would permit detection of population differences on the order of 20%. Higher densities of birds were observed in areas with heath, grass (fescue), and beach grass and pea vegetation types than in areas with other vegetation types. However, densities within these favoured vegetation types were constant with increasing transect length, which appears to be contrary to patterns expected from using published models of the effects of breeding habitat patch size on bird population density. Topographical constraints characteristic of Sable Island may impose limits on the birds' territorial boundaries and constrain density, independently of patch size.
Foraging in the subterranean social Damaraland mole-rat,Cryptomys damarensis: an investigation into size-dependent geophyte utilization and foraging patterns
Authors: Barnett Mandy , Bennett Nigel C , Telford Steven R , Jarvis Jennifer U.M
Published: June 2003

The foraging behaviour of captive colonies of the Damaraland mole-rat, Cryptomys damarensis, was investigated in an artificial soil-filled burrow system provided with three tray patches that varied in bulb and corm (i.e., geophyte) density and size. Members of two founder colonies (comprising three and four mole-rats) were exposed to resource patches that varied in food profitability (both size and density of geophytes). There was no preference for excavating any of the patches with different densities or sizes of geophytes. The larger geophytes were preferentially stored and the smaller ones preferentially eaten both on encounter and within the food store. The duration of handling and rate of consumption of geophytes by 15 animals of various body sizes from three colonies were recorded. Handling time was related to the size of the geophytes. Small geophytes were less profitable to consume. It was concluded that the mole-rats generally followed the qualitative predictions of optimal foraging theory but fell short of being energy maximizers.
Using invertebrate and microbial communities to assess the condition of the hyporheic zone of a river subject to 80 years of contamination by chlorobenzenes
Authors: Williams D Dudley , Fulthorpe Roberta R
Published: June 2003

For over 80 years, chlorobenzenes were discharged into the Sebasticook River, Maine, from a woollen mill. Environmental conditions were assessed using invertebrate and bacterial techniques that were applied to river bed sediments at three contaminated and two reference sites. Invertebrate densities and species richness did not differ markedly among the impacted sites, one reference site, and data in the literature from clean waters. Paradoxically, the highest diversity and densities of invertebrates and their eggs occurred at the most contaminated site. Insect representation was low compared with other hyporheic zones. Although chlorobenzene concentrations were much greater than published limits for freshwater life, certain species (e.g., mayflies, caddisflies, and midges) were associated with high concentrations. The majority of variance in the faunal and microbial data was attributable to redox potential, ammonium levels, and downwelling, rather than to chlorobenzene. Genetic fingerprinting revealed a unique microbial community at the site most heavily contaminated with chlorobenzenes, but a high degree of similarity among the other two mill sites and the reference sites (although the latter proved subsequently to be contaminated with ketones and methyl chloride). There were no differences in taxonomic richness among sites.
Age-dependent fitness costs of alarm signaling in aphids
Authors: Mondor Edward B , Roitberg Bernard D
Published: June 2003

For an alarm signal to evolve, the benefits to the signaler must outweigh the costs of sending the signal. Research has largely focused on the benefits of alarm signaling, and the costs to an organism of sending an alarm signal are not well known. When attacked by a predator, aphids secrete cornicle droplets, containing an alarm pheromone, for individual protection and to warn clonemates. As aphid alarm pheromone is synthesized de novo in a feedback loop with juvenile hormone, we hypothesized that the secretion of cornicle droplets may result in a direct fitness cost to the emitter. We show that the secretion of a single cornicle droplet by pre-reproductive (third- and fourth-instar) pea aphids, Acyrthosiphon pisum, directly altered the timing and number of offspring produced. Third-instar pea aphids delayed offspring production but produced more offspring overall than non-secreting aphids, demonstrating a life-history shift but no significant fitness cost of droplet secretion. Fourth-instar pea aphids also delayed offspring production but produced the same number of offspring as non-secretors, resulting in a direct fitness cost of droplet secretion. Offspring production by adult, reproductive pea aphids that secreted a cornicle droplet did not differ from that of non-secretors. Thus, the fitness costs of secreting cornicle droplets containing an alarm signal are age-dependent.
Use of sulfur and nitrogen stable isotopes to determine the importance of whitebark pine nuts to Yellowstone grizzly bears
Authors: Felicetti Laura A , Schwartz Charles C , Rye Robert O , Haroldson Mark A , Gunther Kerry A , Phillips Donald L , Robbins Charles T
Published: June 2003

Whitebark pine (Pinus albicaulis) is a masting species that produces relatively large, fat- and protein-rich nuts that are consumed by grizzly bears (Ursus arctos horribilis). Trees produce abundant nut crops in some years and poor crops in other years. Grizzly bear survival in the Greater Yellowstone Ecosystem is strongly linked to variation in pine-nut availability. Because whitebark pine trees are infected with blister rust (Cronartium ribicola), an exotic fungus that has killed the species throughout much of its range in the northern Rocky Mountains, we used stable isotopes to quantify the importance of this food resource to Yellowstone grizzly bears while healthy populations of the trees still exist. Whitebark pine nuts have a sulfur-isotope signature (9.2 ± 1.3 (mean ± 1 SD)) that is distinctly different from those of all other grizzly bear foods (ranging from 1.9 ± 1.7 for all other plants to 3.1 ± 2.6 for ungulates). Feeding trials with captive grizzly bears were used to develop relationships between dietary sulfur-, carbon-, and nitrogen-isotope signatures and those of bear plasma. The sulfur and nitrogen relationships were used to estimate the importance of pine nuts to free-ranging grizzly bears from blood and hair samples collected between 1994 and 2001. During years of poor pine-nut availability, 72% of the bears made minimal use of pine nuts. During years of abundant cone availability, 8 ± 10% of the bears made minimal use of pine nuts, while 67 ± 19% derived over 51% of their assimilated sulfur and nitrogen (i.e., protein) from pine nuts. Pine nuts and meat are two critically important food resources for Yellowstone grizzly bears.
Daytime activity budgets of feral goats (Capra hircus) on the Isle of Rum: influence of season, age, and sex
Authors: Shi Jianbin , Dunbar R I.M , Buckland David , Miller David
Published: June 2003

The activity budgets of feral goats (Capra hircus) on the Isle of Rum, northwest Scotland, were studied from January to December in 1981 and from May to November in 2000. We investigated differences in activity patterns in relation to season, time of day, and agesex classes of goats, and their possible causes. Since the goats spent the night sleeping (or resting) in caves or other sheltered sites, only diurnal activity budgets were considered. Activity patterns were very similar between the two study periods (from May to November). All agesex classes of feral goats spent most of the daytime feeding in both years, especially during autumn and winter. Feral goats increased the percentage of daytime that they spent feeding and decreased their resting time from summer to autumnwinter in response to the decrease in available day length and, possibly, the decrease in forage quality and biomass. Feral goats on Rum had two or three daily peaks of feeding in summer, but showed no obvious daily feeding peaks in winter, although their percentage of feeding time remained relatively high throughout the daytime in winter. No significant differences in general activity budgets between adult males and females were found, but yearlings were found to spend more time feeding than adults and kids. Adult males spent more time in social activities than did other agesex classes, and adult males sharply decreased the percentage of daytime that they spent feeding during rutting periods, which may have contributed to their higher mortality over the subsequent autumn and winter.
Prolonged foraging bouts of a solitary gleaning/hawking bat, Myotis evotis
Authors: Chruszcz Bryan J , Barclay Robert M.R
Published: June 2003

We investigated the foraging behaviour of reproductive female long-eared bats, Myotis evotis, roosting solitarily in natural habitat in the badlands of the South Saskatchewan River valley, Alberta, Canada. Myotis evotis behaved differently than other temperate-zone insectivorous species studied previously. Individuals foraged all night, every night, regardless of ambient temperature or reproductive condition, and only spent a small proportion of the night roosting (less than 10% of the time spent out of the roost). A high daily energy demand and an energetically costly mode of flight may necessitate this behaviour. The ability to both aerial-hawk and glean prey from surfaces may make night-long foraging profitable for M. evotis, and for other flying nocturnal insectivores that can glean.
Are great tits (Parus major) really optimal foragers?
Authors: Berec Michal , Krivan Vlastimil , Berec Ludek
Published: June 2003

In this study, we test the classical prey model of optimal-foraging theory with great tits (Parus major) feeding on two types of mealworms presented on a conveyor belt. Contrary to the results of some previous experiments, prey types were given to birds in random order, therefore birds could not predict their next prey item. We tested birds' diet choices at four different prey-encounter rates. Our results show that in 95% of cases great tits consumed the more profitable prey type upon encounter. On the other hand, consumption of the less profitable prey type did not differ statistically from the "always-attack" strategy in 77% of cases when the rate of encounter with the more profitable prey was below a critical value, and did differ from that strategy in 67% of cases when the rate of encounter with the more profitable prey was above that critical value. Contrary to predictions of the classical prey model of optimal-foraging theory, our birds never completely excluded the less profitable prey type from their diet. We also estimated the functional responses of individual birds with respect to the more profitable prey type; birds' diet changes occurred too slowly to make these functional responses stabilizing.
Indirect estimates of wing-propulsion forces in horizontally diving Atlantic puffins (Fratercula arcticaL.)
Authors: Johansson L Christoffer
Published: June 2003

Instantaneous force production in wing-propelled diving Atlantic puffins (Fratercula arctica) was investigated using four birds for which instantaneous estimates of velocity and acceleration of the body were made. The quasi-steady resultant force acting on the body in the sagittal plane was calculated using acceleration reaction coefficients, buoyancy estimates, and drag coefficients taken from the literature and calculated, using two different methods, from a video sequence of a puffin gliding (CDw= 0.021 and 0.026, respectively). The forces calculated from the motion of the body coincide well with the wing-beat cycle, with a forward- and upward-directed force produced by the wings during the downstroke and a forward- and downward-directed force produced during the upstroke. The result suggests that a thrust force may also be produced during at least the lower-stroke reversal. This means either that there may exist some undescribed propulsive mechanism, possibly caused by an interaction of the wings beneath the body, or that the body drag coefficient may be overestimated. However, the body drag coefficient calculated in the study is close to the coefficients measured on dead birds. Furthermore, I conclude that the high reduced frequency (average 0.82) suggests a non-steady-state hydrodynamic mechanism of wing-propelled diving in puffins.
Mitochondrial DNA extracted from eastern North American wolves killed in the 1800s is not of gray wolf origin
Authors: Wilson P J , Grewal S , McFadden T , Chambers R C , White B N
Published: June 2003

We analysed the mitochondrial DNA (mtDNA) from two historical samples of eastern North American wolves: the last wolf reported to have been killed in northern New York State (ca. 1890s) and a wolf killed in Maine in the 1880s. These wolves represent eastern wolves, presently classified as the gray wolf (Canis lupus) subspecies Canis lupus lycaon, which were present well before the expansion of western coyotes (Canis latrans) into these regions. We show the absence of gray wolf mtDNA in these wolves. They both contain New World mtDNA, supporting previous findings of a North American evolution of the eastern timber wolf (originally classified as Canis lycaon) and red wolf (Canis rufus) independently of the gray wolf, which originated in Eurasia. The presence of a second wolf species in North America has important implications for the conservation and management of wolves. In the upper Great Lakes region, wolves of both species may exist in sympatry or interbreed with each other, which impacts the accuracy of estimates of numbers of wolves of each species within this geographic region. Furthermore, the historical distribution of the eastern timber wolf (C. lycaon), as revealed by these skin samples, has important implications for the reintroduction of wolves into the northeastern U.S. states, such as New York and Maine.
Testing models of biological scaling with mammalian population densities
Authors: Dobson F Stephen , Zinner Bertram , Silva Marina
Published: June 2003

Two hypotheses have been suggested to explain the form of interspecific scaling of organismal characteristics to body size, such as the well-known increase in total metabolism with body mass. A hypothesis based on simple Euclidean geometry suggests that the scaling of many biological variables to body size should have a scaling exponent of 2/3, or [Formula: see text]0.667. On the other hand, according to a hypothesis based on fractal dimensions, the relationship between biological variables and body mass should have a scaling exponent of 0.750. We conducted a power analysis of the predicted exponents of scaling under the Euclidean and fractal hypotheses, using average adult body masses and population densities collected from the published literature on mammalian species. The collected data reflect 987 mammal populations from a broad variety of terrestrial habitats. Using statistical methods we determined the sample sizes required to decide between the values of the scaling exponent of the density-to-mass relationship based on the Euclidean (0.667) and fractal (0.750) hypotheses. Non-linearities in the dataset and insufficient power plagued our tests of the predictions. We found that mammalian species weighing less than 100 kg had a linear scaling pattern, sufficient power to reveal a difference between the scaling coefficients 0.667 and 0.750, and an actual scaling coefficient of 0.719 (barely significantly different from 0.667 but not from 0.750). Thus, our results support the fractal hypothesis, though the support was not particularly strong, which suggests that the relationship between body mass and population density should have a scaling exponent of 0.750.
Terrestrial trophic dynamics in the Canadian Arctic
Authors: Krebs Charles J , Danell Kjell , Angerbjörn Anders , Agrell Jep , Berteaux Dominique , Bråthen Kari Anne , Danell Öje , Erlinge Sam , Fedorov Vadim , Fredga Karl , Hjältén Joakim , Högstedt Göran , Jónsdóttir Ingibjörg S , Kenney Alice J , Kjellén Nils , Nordin Torgny , Roininen Heikki , Svensson Mikael , Tannerfeldt Magnus , Wiklund Christer
Published: June 2003

The Swedish Tundra Northwest Expedition of 1999 visited 17 sites throughout the Canadian Arctic. At 12 sites that were intensively sampled we estimated the standing crop of plants and the densities of herbivores and predators with an array of trapping, visual surveys, and faecal-pellet transects. We developed a trophic-balance model using ECOPATH to integrate these observations and determine the fate of primary and secondary production in these tundra ecosystems, which spanned an 8-fold range of standing crop of plants. We estimated that about 13% of net primary production was consumed by herbivores, while over 70% of small-herbivore production was estimated to flow to predators. Only 9% of large-herbivore production was consumed by predators. Organization of Canadian Arctic ecosystems appears to be more top-down than bottom-up. Net primary production does not seem to be herbivore-limited at any site. This is the first attempt to integrate trophic dynamics over the entire Canadian Arctic.
The western screech-owl and habitat alteration in Baja California: a gradient from urban and rural landscapes to natural habitat
Authors: Rodríguez-Estrella Ricardo , Careaga Aleyda Peláez
Published: June 2003

We studied the western screech-owl (Otus kennicottii) in the desert of the southern Baja California peninsula to determine its status and habitat selection and whether it benefits from moderate human-caused habitat changes. Based on the response to tape-recorded call broadcasts, western screech-owls were more abundant in undisturbed vegetation than in human-altered habitat. In man-made environments, more owls responded in rural than in urban areas; indeed, they were practically absent in urban areas. In natural areas, a total of 1.6 owls/km was estimated in the nonbreeding season and 2.7 owls/km in the breeding season. The most important habitat features selected in natural areas were greater shrub cover in the strata containing shrubs 12 and 23 m high and greater canopy cover of trees >5 m high. In rural areas adjacent to cultivated areas, owls were present in areas with the greatest cover of shrubs 13 m high and a higher density of shrubs. The western screech-owl also occurs at lower densities in rural areas than in natural areas. Towns appear to be avoided in the arid desert of Baja California Sur. Western screech-owls may be still able to persist in rural areas that occupy an intermediate position on the gradient from a functional natural system (desert vegetation) to a completely altered ecological system, urbanized areas.
Migration chronology of Eastern-Population Tundra Swans
Authors: Petrie S A , Wilcox K L
Published: June 2003

We used satellite platform transmitting transmitters (PTTs) in 19982000 to track spring and fall migratory movements of Tundra Swans (Cygnus columbianus columbianus) captured at Long Point, Ontario. Migration corridors reported here corroborated those identified in previous studies using alphanumerically coded neck collars. However, PTTs provided additional information on duration of spring and fall migrations, duration of stay in different staging regions, time spent on breeding and wintering areas, and migration speed. Birds migrated between the Atlantic coast and northern prairies along a narrow geographic corridor through portions of the southern Great Lakes. From the northern prairies, swans followed 3 corridors to breeding areas on the west coast of Hudson Bay, central High Arctic, and Mackenzie River delta. While swans spent considerable time on Great Lakes (27% of spring migration) and northern prairie (40%) staging areas in spring, the northern boreal forest was an important fall staging area (48% of fall migration). Tundra Swans spent 20% of the annual cycle on wintering areas, 28% on spring staging areas, 29% on breeding areas, and 23% on fall staging areas. The long duration of migration and the fact that birds spend half their lives on staging areas underscore the importance of conserving Tundra Swan migratory habitats. Thirty-gram neck-collar-attached PTTs were more suitable than 95-g Teflon-harness-attached backpack PTTs for tracking Tundra Swans.