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1.
Genetic influence on caste in the ant Camponotus consobrinus 总被引:6,自引:0,他引:6
V. S. Fraser B. Kaufmann B. P. Oldroyd R. H. Crozier 《Behavioral ecology and sociobiology》2000,48(3):188-194
Genetic influences on polyethism within social insect colonies are well known, suggesting that the determination of caste
(soldiers and minor workers) may also be genetically mediated. The Australian sugar ant Camponotus consobrinus is suitable for such a study, having soldiers and minor workers that follow a complex allometry. Further, although most C. consobrinus colonies are monogynous, 13 of 42 surveyed using microsatellites were found to be polygynous. Thus, although a minority of
colonies were polygynous, the great majority of queens live in polygynous colonies. From the 29 monogynous colonies studied,
we inferred that the queens are monandrous. Ants from four polygynous colonies were assigned to families on the basis of microsatellite
genotypes, after measurements had been taken of head width and scape length. These measurements reflect a complex allometry
interpretable as soldier and minor worker growth curves with a large changeover zone. Genetic influence on caste determination
was examined by testing for differences between families within colonies in the distribution of scape lengths, residuals from
the overall colony allometric curve, and proportions of soldiers and minor workers (as determined by head width falling above
or below the inflection point of the overall colony allometric curve). Families in all four colonies differed significantly
in caste proportions and in head-width distributions, and three of the four colonies showed significant differences between
families in residuals from the overall colony growth curve. Nested ANOVAs using head widths and scape-length residuals showed
that when the effect of family is removed, intercolony differences in allometry are negligible. This evidence indicates genetic
rather than environmental causes for the observed differences between families. We speculate that this variation may reflect
some selective advantage to within-colony heterogeneity between families or that selective differences are few between a wide
array of family growth patterns.
Received: 16 June 1999 / Received after revision: 13 September 1999 / Accepted: 25 September 1999 相似文献
2.
The allocation to growth, defense and reproduction varies in social insects within a species' life cycle and between species. A life cycle model (Oster and Wilson 1978) generally failed to predict caste allocation in small litter-nesting colonies of Neotropical Pheidole. Two of its assumptions were often invalid: food was unlikely to be limiting in four of five populations, and sexual biomass production accelerated, not decelerated, with colony size in three of five populations. One of five Pheidole populations studied had higher caste ratios (soldiers /workers) in reproductive colonies as predicted, and in no species did caste functions conform to predictions. We also adapted three models from plant defense theory to study between-species patterns of caste allocation. Among 12 litter Pheidole the amount of sterile biomass devoted to soldiers varied from 18 to 62%. Queen size, growth rate, and soldier investment positively covaried. Only one model, the cost of replacement hypothesis (McKey 1979), correctly predicted that species with costly female alates invest more in defense. The two hypotheses linking apparency to defense may also be valid if fast-growing colonies are more likely to attract the attention of predators. 相似文献
3.
Comparisons of forager distributions from matched honey bee colonies in suburban environments 总被引:4,自引:0,他引:4
Keith D. Waddington Thomas J. Herbert P. Kirk Visscher Monica Raveret Richter 《Behavioral ecology and sociobiology》1994,35(6):423-429
We conducted experiments designed to examine the distribution of foraging honey bees (Apis mellifera) in suburban environments with rich floras and to compare spatial patterns of foraging sites used by colonies located in the same environment. The patterns we observed in resource visitation suggest a reduced role of the recruitment system as part of the overall colony foraging strategy in habitats with abundant, small patches of flowers. We simultaneously sampled recruitment dances of bees inside observation hives in two colonies over 4 days in Miami, Florida (1989) and from two other colonies over five days in Riverside, California (1991). Information encoded in the dance was used to determine the distance and direction that bees flew from the hive for pollen and nectar and to construct foraging maps for each colony. The foraging maps showed that bees from the two colonies in each location usually foraged at different sites, but occasionally they visited the same patches of flowers. Each colony shifted foraging effort among sites on different days. In both locations, the mean flight distances differed between colonies and among days within colonies. The flight distances observed in our study are generally shorter than those reported in a similar study conducted in a temperate deciduous forest where resources were less dense and floral patches were smaller. 相似文献
4.
Thomas D. Seeley 《Behavioral ecology and sociobiology》1982,11(4):287-293
Summary The adaptive origins of the honeybee's age polyethism schedule were studied by testing whether the schedule for labor inside the nest reflects a compromise between efficiency in locating tasks and efficiency in performing tasks. I checked two predictions of this hypothesis: (1) at each age a worker handles a set of tasks (rather than one task), and (2) the elements of each age's task-set co-occur spatially in the nest (rather than being spatially segregated). Most observations match these predictions, once workers reach the age of 2 days. The unpredicted specialization of 0 to 2-day-old workers on the single task of cell cleaning may reflect an unusual ease in locating work sites for this particular task. There are 5 female castes in honeybee colonies: the queen (reproductive caste), plus 4 age subcastes among the workers (cell cleaning caste, broodnest caste, food storage caste, and forager caste). 相似文献
5.
Larval and post-larval crab distribution was surveyed in three different habitats in Kachemak Bay, Alaska to determine temporal
and spatial variability. Distribution varied temporally and spatially from June 2005 to September 2006. Nine sites of varying
habitat complexity were surveyed monthly using scuba surveys and light traps to measure habitat variables and quantify crab
zoeae and megalopae. A total of 10,016 crabs belonging to seven families were identified. Four species comprised the majority
(97%) of the total crab assemblages and included Cancer oregonensis, Fabia subquadrata, Telmessus cheiragonus, and Pugettia gracilis. Peak abundances occurred in summer but varied on small temporal scales with species. No single bay-wide variable determined
the appearance of all species. Depending on species, appearance may be influenced by seasonality of environmental variables.
Spatially, highest abundances occurred in habitats with less structural complexity. Spatial differences in crab abundance
may have resulted from variability on large scale physical transport mechanisms and not kelp-mediated flow alterations. 相似文献
6.
We monitored the reproductive cycle of Strongylocentrotus droebachiensis (OF Müller) between April 1993 and August 1995 in kelp beds, barren grounds and grazing fronts at both a wave-exposed and
a sheltered site along the Atlantic coast of Nova Scotia. Gonad index and histological analyses showed that S. droebachiensis has an annual reproductive cycle that is synchronous across sites and habitats, and between females and males. Spawning occurs
in March/April of each year but a small proportion of sea urchins in the study populations also spawned in fall 1995. During
most of the year, sea urchins in kelp beds and grazing fronts have a higher gonad index than those in barren grounds. Gonad
indices also tended to be higher at the wave-exposed than the sheltered site. Interannual variability in peak gonad index
was significant in the barren grounds at the wave-exposed site and in the grazing front at the sheltered site. The gametogenic
cycle is characterized by six stages based on the abundance of nutritive and germinal/gametic cells. Nutritive phagocytes
are abundant after spawning and replaced by increasing numbers of germinal and gametic cells as the gametogenic cycle progresses.
The temporal patterns of abundance of each cell type were similar among habitats indicating that the gonads were qualitatively
similar despite large differences in gonadal mass. The quantity of gut contents (ratio of food volume to body volume) was
similar among habitats, but the quality (percentage of organic material) tended to be higher in kelp beds and grazing fronts
than in barren grounds suggesting that differences in gonad index of S. droebachiensis in different habitats are related to differences in diet. The high density of sea urchins in grazing fronts combined with
their high fecundity suggests that they make the greatest contribution, per unit area, to the overall larval pool.
Received: 20 May 1997 / Accepted: 21 January 1998 相似文献
7.
Blaine J. Cole 《Behavioral ecology and sociobiology》1992,31(3):181-187
Summary This paper examines the characteristics of the spontaneous acivity levels of individual worker ants of Leptothorax allardycei and explores the influence of spontaneous worker activity on colony activity patterns. While there are substantial differences among workers in the characteristics of their spontaneous activity, all of the variation occurs within the colony. There are virtually no differences in the levels of spontaneous activity between colonies. Variation among workers is due to age; workers decline exponentially in their probability of becoming active, p
a
,at a rate of -0.02 per day. I built computer models under four different sets of assumptions about the spontaneous activity patterns of workers, and performed simulations to test the ability of colonies of simulated workers to synchronize their movement activity. The most realistic results are obtained with models in which workers already have an underlying propensity to oscillate and which interact with one another to produce Type 1 phase resetting. The simulations generate predictions concerning the ability of colonies to synchronize, the most significant of which is that the average age of workers in a colony is very important in determining the extent of colony synchrony, while the distribution of ages is not. 相似文献
8.
Sections of brood from colonies of the Cape honeybee ( Apis mellifera capensis), the African honeybee ( A. m. scutellata), and hybrid bees of the two races were exchanged between colonies to study the effect of different brood-origin/nurse-bee combinations on development of caste characters. When Cape larvae were raised by African workers the amount of food provided almost doubled in comparison with Cape larvae reared by their own workers. In contrast, African larvae raised by Cape workers were provided with only half the amount they received from their own workers. After the bees emerged, we found a large degree of plasticity in characters related to caste differentiation, which corresponded closely to the amount of food provided. Super-fed Cape bees had enlarged spermathecae, were heavier than normal workers and developed more rapidly, and had reduced pollen combs, all typical for a more queen-like condition. Ovariole numbers did not appear to be enhanced by additional feeding. Cape bees that behave as social parasites in African bee colonies were most queen-like in the characters studied, albeit within the range that was found for Cape bees from normal colonies, suggesting within-colony selection for characters that enhance reproduction.Communicated by R. Page 相似文献
9.
J. Cnaani G. E. Robinson G. Bloch D. Borst A. Hefetz 《Behavioral ecology and sociobiology》2000,47(5):346-352
Endocrine analyses were used to investigate the well-known association between queen production and the onset of worker reproduction
(termed the competition phase, CPh) in Bombus terrestris. Larvae that reached the age of 5 days before the CPh had a worker-like profile: low juvenile hormone (JH) biosynthesis rates
and low JH hemolymph titers. In contrast, larvae that reached the age of 5 days during the CPh had a queen-like profile: high
JH biosynthesis rates and high hemolymph JH levels. Larval fate could be manipulated by transplanting egg cells into host
colonies with different social structures. There was a steep rise in JH production in larvae transplanted into colonies near
or during the CPh. This indicates that during colony development, larvae switch from the ”worker developmental pathway” to
the ”queen developmental pathway,” and that the switch is socially regulated. In small rearing groups, larvae reared with
queens before the CPh developed into workers, whereas those reared with queens after the CPh developed into queens. Variation
in worker type (naive or experienced) did not affect caste determination. Therefore, we hypothesize that queens produce a
pheromone that directly inhibits queen differentiation by larvae. We also present two alternative scenarios that explain the
timing of gyne production in B. terrestris, one based on ecological constraints and the other based on queen-worker competition.
Received: 20 October 1999 / Received in revised form: 18 December 1999 / Accepted: 23 January 2000 相似文献
10.
The selection of breeding sites in heterogeneous habitats should ideally be based on cues closely reflecting habitat quality and thus predicting realized individual fitness. Using long-term population data and data on territory establishment of male Northern Wheatears (Oenanthe oenanthe), we examined whether territory characteristics linked to individual fitness (reproductive performance and survival) also were linked to territory preference. Breeding territories varied in their physical characteristics and their potential effects on reproductive performance, and this variation among territories was correlated from one year to the next. Of all measured territory characteristics (from the focal and the previous year) only territory field layer height predicted individual fitness, i.e., reproductive performance was higher in territories with permanently short rather than growing field layers. Territory preference, instead, was only linked to the size of territory aggregations, i.e., males settled earlier at territory sites sharing borders with several adjacent sites than at those with few or no adjacent sites. This mismatch between territory characteristics linked to fitness and those linked to territory preference was not explained by site fidelity or compensated for by the different fitness components measured. Because the results were not in agreement with an ecological trap scenario, where poor habitats are preferred over high-quality habitats, our results suggest a more general case of nonideal habitat selection. Whereas nonideal selection with respect to territory field layer height may be explained by its poor temporal predictability within the breeding season, the preference for territory aggregations is still open to alternative adaptive explanations. Our study suggests that nonideal habitat selection should be investigated by direct estimates of preferences (e.g., order of territory establishment) and their links to habitat characteristics and fitness components. Furthermore, we suggest that the probability of establishing a territory needs to be included as a factor influencing patterns of habitat selection. 相似文献
11.
Brian R. Johnson 《Behavioral ecology and sociobiology》2005,58(3):219-226
Caste theory predicts that social insect colonies are organized into stable groups of workers specialized on particular task sets. Alternative concepts of organization of work suggest that colonies are composed of extremely flexible workers able to perform any task as demand necessitates. I explored the flexibility of workers in temporal castes of the honey bee Apis mellifera by determining the ability of colonies to reorganize labor after a major demographic disturbance. I evaluated the flexibility of temporal castes by comparing the foraging rates of colonies having just lost their foragers with colonies having also lost their foragers but having been given a week to reorganize. The population sizes and contents of the colonies in each group were equalized and foraging rates were recorded for one week. Colonies given a weeks initial recovery time after the loss of their foragers were found to forage at significantly higher rates than those colonies given no initial recovery time. This result was consistent for nectar and pollen foraging. These results suggest that honeybee workers lack sufficient flexibility to reorganize labor without compromising foraging. This finding is consistent with the caste concept model of organization of work in insect societies. 相似文献
12.
This study aimed to gain insight on patterns of spatial variability of seagrass epiphytes of both leaves and of rhizomes in
three different habitats, continental coasts, offshore banks and islands. Moreover, we tried to discriminate between habitat-dependant
variability and scale-dependant variability of Posidonia oceanica epiphytic assemblages. Results showed the absence of significant differences in the structure of assemblages of epiphytes
both on leaves and on rhizomes among continental coasts, offshore banks and islands, even if the patterns of spatial variability
changed among habitats. In fact, although a high variability at small scales appeared a constant pattern in epiphytic assemblages,
large-scale variability resulted higher in continental coasts and offshore banks than in islands. In conclusion, epiphytic
assemblages of Posidonia oceanica appear homogeneous among habitats, showing a similar structure and species composition in the same geographic area. On the
contrary, differences between meadows appeared linked to local differences in environmental factors that are more evident
in habitats influenced by human disturbance.
An erratum to this article can be found at 相似文献
13.
Hany Alonso José P. Granadeiro Vitor H. Paiva Ana S. Dias Jaime A. Ramos Paulo Catry 《Marine Biology》2012,159(6):1197-1207
In pelagic seabirds, who often explore distant food resources, information is usually scarce on the level of trophic segregation
between parents and their offspring. To investigate this issue, we used GPS tracking, stable isotopes and dietary information
of Cory’s shearwaters Calonectris diomedea breeding in contrasting environments. Foraging trips at Selvagem Grande (an oceanic island) mainly targeted the distant African
coast, while at Berlenga island (located on the continental shelf), shearwaters foraged mainly over nearby shelf waters. The
degree of isotopic segregation between adults and chicks, based on δ13C, differed markedly between the two sites, indicating that adult birds at Selvagem fed their chicks with a mixture of shelf
and offshore pelagic prey but assimilated more prey captured on coastal shelf waters. Isotopic differences between age classes
at Berlenga were much smaller and may have resulted from limited dietary segregation or from age-related metabolic differences.
The diet of shearwaters was also very different between the two colonies, with offshore pelagic prey only being detected at
Selvagem Grande. Our findings suggest that spatial foraging constraints influence resource partitioning between pelagic seabirds
and their offspring and can lead to a parent–offspring dietary segregation. 相似文献
14.
Sebastian Pohl Volker Witte Susanne Foitzik 《Behavioral ecology and sociobiology》2011,65(11):2029-2036
In social insect societies, division of labor, i.e., workers of a colony specializing in different tasks, is thought to improve
colony performance. Workers of social parasitic slave-making ants focus on a single task, searching for and raiding host colonies
to replenish their slave workforce. However, in the North American slavemaker Protomognathus americanus, some workers do not partake in raids but remain inside the colony. We analyzed raid participation, fertility, and cuticular
hydrocarbon profiles of slavemaker workers and slaves to understand these behavioral differences and the regulation of division
of labor in slavemaker colonies. Raid observations showed that some workers were repeatedly involved in raiding activities
(exterior workers), whereas others stayed inside the nest (interior workers). Exterior workers were always infertile, while
half of the interior workers were fertile. Analysis of cuticular hydrocarbons demonstrated differences between the groups.
We also detected chemical differences between interior and exterior slaves, indicating an influence of the individuals’ tasks
on their cuticular profiles. Task- and fertility-related profiles may allow selective nestmate recruiting. Division of labor
should also adapt to varying conditions. Since slave raids are dangerous, they should only be initiated when the colony needs
additional slaves. Exclusively fed by their slaves, slavemaker workers could determine this need via their nutritional status.
In an experiment with various feeding regimes, colonies subjected to a lower food provisioning rate showed increased proportions
of slavemaker workers searching for host colonies. Division of labor in slave-making ants, therefore, might be flexible and
can change depending on the colonies’ needs. 相似文献
15.
The relationship between densities of Achoerodus viridis (Pisces: Labridae) and reef habitats at various localities within New South Wales (NSW), Australia was examined. Types of
habitats were quantified at inner, mid and outer estuarine locations in each of two estuaries (Botany Bay and Port Jackson)
to determine whether purported patterns of movement from estuaries could be related to differences in habitat. Although the
same types of habitat were generally found at all locations, differences in the proportion of habitat types were found between
shallow and deep reefs and among inner, mid and outer estuarine locations for both estuaries. Shallow habitats were usually
dominated by Ecklonia radiata, turf and/or fringe habitat in Botany Bay, whereas deep sites were generally dominated by urchin-grazed barrens habitat and,
sometimes, sponge- and ascidian-dominated deep reef. Shallow sites in Port Jackson were dominated by a mixture of habitats,
as were deep reefs at mid-estuarine locations. Other deep reefs in Port Jackson were dominated by E. radiata (inner estuarine) or barrens (outer estuarine) habitat. Thus, patterns of habitat cover were not consistent between estuaries
and numbers of fish could not be related to proportional representation of habitat on reefs along estuarine gradients. Univariate
and multivariate analyses showed that there was little evidence that any size class of fish was correlated with the proportional
representation of a particular habitat or group of habitats. Counts of fish that focused on barrens and E. radiata forest habitats over a period of 10 yr showed that similar numbers and all sizes of fish were found in the two types of habitat.
Greater numbers of small fish were, however, found in the E. radiata forest habitat than in the barrens habitat. Estimates of abundance along the coast of NSW (100s to 1000 km) in a range of
habitats (e.g. ascidian-dominated reef, kelp forest, urchin-grazed barrens) showed that there was no indication that a particular
habitat consistently had greater numbers of A. viridis than other habitats. Therefore, A. viridis of a range of sizes appears to be flexible in its use of habitats on reefs.
Received: 24 December 1997 / Accepted: 23 June 1998 相似文献
16.
Thermal environment is often regarded as a key determinant of distribution limits in marine invertebrates and hence may represent one of the most important barriers to invasion by non-indigenous species. For the first time in the subarctic northwestern Atlantic, we investigated variation in the timing and magnitude of settlement, recruitment, and colony cover of the recently (early 2000s) introduced bryozoan Membranipora membranacea on the kelp Saccharina longicruris and how this variation relates to changes in sea temperature (thermal histories) across eight sites spanning a 450-km latitudinal range between southwestern Newfoundland and southeastern Labrador, Canada. We show that (1) up to 61 % of the variation in settlement, recruitment, and colony cover was explained by sea temperature alone, with highest and lowest abundances at warmest and coldest sites, respectively; (2) between-site differences in rates of sea cooling explained 85 % of the variation in settler abundance; (3) varying the temporal window over which data were aggregated increased the explanatory power of sea temperature to as much as 98 % for settlement and recruitment, and 86 % for colony cover; (4) exposure to waves and surface area of colonies improved relationships between sea temperature and settlement and recruitment by up to 11 %; and (5) recruit abundance was a strong predictor of colony cover, explaining as much as 89 % of the variation. Consistently low abundances of settlers and recruits at the northern tip of Newfoundland and southern tip of Labrador suggest that M. membranacea is nearing its northern distribution limit in the northwestern Atlantic. Our findings extend knowledge of population dynamics of M. membranacea in the northwestern Atlantic, while highlighting the complexity of the interactions between physical and biological factors and processes that affect population dynamics in invertebrates with planktonic larvae in predominantly cold marine habitats. 相似文献
17.
Piotr Minias 《Behavioral ecology and sociobiology》2014,68(5):851-859
It has long been suggested that habitat structure affects how colonial birds are distributed within their nesting aggregations, but this hypothesis has never been formally tested. The aim of this study was to test for a correlated evolution between habitat heterogeneity and within-colony distributions of Ciconiiformes by using Pagel’s general method of comparative analysis for discrete variables. The analysis indicated that central-periphery gradients of distribution (high-quality individuals occupying central nesting locations) prevail in species breeding in homogeneous habitats. These were mainly ground-nesting larids and spheniscids, where clear central-periphery patterns were recorded in ca. 80 % of the taxa. Since homogeneous habitats provide little variation in the physical quality of nest sites, central nesting locations should be largely preferred because they give better protection against predators by means of more efficient predator detection and deterrence. By contrast, central-periphery gradients tended to be disrupted in heterogeneous habitats, where 75 % of colonial Ciconiiform species showed uniform patterns of distribution. Under this model of distribution, edge nest sites of high physical quality confer higher fitness benefits in comparison to low-quality central sites, and thus, high-quality pairs are likely to choose nest sites irrespectively of their within-colony location. Breeding in homogeneous habitats and uniform distribution patterns were identified as probable ancestral states in Ciconiiformes, but there was a significant transition rate from uniform to central-periphery distributions in species occupying homogeneous habitats. 相似文献
18.
Spatial and temporal genetic homogeneity in the Arctic surfclam (<Emphasis Type="Italic">Mactromeris polynyma</Emphasis>) 总被引:1,自引:0,他引:1
Commercially harvested marine bivalve populations show a broad range of population-genetic patterns that may be driven by
planktonic larval dispersal (gene flow) or by historical (genetic drift) and ecological processes (selection). We characterized
microsatellite genetic variation among populations and year classes of the commercially harvested Arctic surfclam, Mactromeris polynyma, in order to test the relative significance of gene flow and drift on three spatial scales: within commercially harvested
populations in the northwest Atlantic; among Atlantic populations; and between the Atlantic and Pacific oceans. We found small
nonsignificant genetic subdivision among eight populations from the northwest Atlantic (F
ST = 0.002). All of these Atlantic populations were highly significantly differentiated from a northeast Pacific population
(F
ST = 0.087); all populations showed high inbreeding coefficients (F
IS = 0.432). We tested one likely source of heterozygote deficits by aging individual clams and exploring genetic variation
among age classes within populations (a temporal Wahlund effect). Populations showed strikingly different patterns of age
structure, but we found little differentiation among age classes. In one case, we were able to analyze genetic diversity between
age classes older or younger than the advent of intensive commercial harvesting. The results generally suggest spatially broad
and temporally persistent genetic homogeneity of these bivalves. We discuss the implications of the results for the biology
and management of surfclam populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
19.
Little is known in general about how group size or ectoparasitism affect survival in colonial animals. We estimated daily within-season survival probabilities for nesting adult and recently fledged juvenile cliff swallows (Petrochelidon pyrrhonota) at 239 colonies from 1983 to 2003 in southwestern Nebraska, USA. Some colonies had been fumigated to remove ectoparasites. We conducted mark-recapture at each colony site to estimate daily survival. There were no systematic differences between males and females in daily survival. Adults and juveniles occupying parasite-free colonies had, on average, 4.4% and 62.2% greater daily survival, respectively, than their counterparts in naturally infested colonies. Daily survival of all birds increased with colony size for both parasite-free colonies and those under natural conditions, although the effect was stronger for adults at fumigated sites and for juveniles. Average daily survival probability for adults tended to increase during warmer and drier summers. Although daily survival varied at some sites over the course of the nesting cycle, there were no strongly consistent within-year temporal effects on survival. Even small differences in daily survival probability can translate into large effects on mean lifespan. The deleterious effects of ectoparasites on daily survival within the season represent a previously unknown cost of ectoparasitism. The increase in within-season survival with colony size reflects the net effects of many costs and benefits associated with colony size. Ectoparasitism is probably the most important cost that tends to partly balance the positive effects of large colonies. The greater survival of cliff swallows in the larger colonies is a previously unknown advantage of colonial nesting.Communicated by P. Heeb 相似文献
20.
Sexual dimorphism, reproductive strategy, and human activities determine resource use by brown bears
Despite significant sexual dimorphism and differing reproductive strategies in carnivores, sexual segregation is rarely studied and is often overlooked in the management of wild populations. Potential nutritional constraints imposed by sexual dimorphism and differing reproductive strategies between the sexes have important implications, particularly when combined with differential effects of human activities on sex and age classes. We examined the effects of sexual dimorphism, reproductive strategies, and human activities (bear-viewing and hunting) on resource use by different sex and age classes of brown bears (Ursus arctos). Sexual segregation of habitat use and effects of experimental bear-viewing were quantified at a single site in south-central Alaska, U.S.A., by capturing, collaring, and observing brown bears at a salt marsh and salmon stream. Effects of salmon capture rate, availability of alternative salmon runs, harvest pressure, and numbers of annual visitors on sex and age class use were examined from data collected or previously published from 13 other sites. Bear-viewing sites on salmon streams where salmon capture rates were low (<4 salmon/hour) resulted in low use by adult males (<10% of all bears), except for sites with falls. However, maximum male use of viewing areas also depended on the availability of alternative salmon streams and harvest pressure. Use of habitats by females with dependent young was significantly related to the prevalence of adult males at the site. Thus, both sexual dimorphism and differing reproductive strategies led to sexual segregation in habitat use by bears. As a result of infanticide, females with young appear to prioritize avoidance of male bears over avoidance of humans when choosing habitats, in contrast to responses documented in herbivores. Because carnivores often exhibit both sexual dimorphism and infanticide, selection for sexual segregation is likely to be high. In these cases, the nutritional demands of large adult males, balanced with responses to human activity, drive dynamic temporal and spatial distributions of individuals in the population. 相似文献