Patterns of reproductive effort in male and female shrubs of Oemleria cerasiformis: a 6-year study

1 We monitored flowering and fruiting of individual male and female plants of Oemleria cerasiformis over a 6-year period in a population in western Canada, and calculated fruit set (percentage of pistils maturing) and reproductive effort (RE) (gram of reproductive tissue per gram of leaf).
2 Over 6 years, male O. cerasiformis had on average much lower total RE, but much higher RE at flowering, than females.
3 In males, strong correlations between RE and light suggested that investment in reproduction was largely determined by light levels. There were strong positive correlations of RE between years, with no evidence of periodic fluctuations.
4 In females, in contrast to males, RE at flowering was not related to light. However, fruit set was strongly correlated with light. Flowering RE and fruit set were uncorrelated in females, indicating that these are affected by different factors.
5 Correlations of RE between years in females, although often significant, were lower than in males, indicating that RE fluctuates more between years in females than in males and may respond to past levels of RE. Flowering may reflect adjustments in response to past reproduction, or may be controlled by resources other than light. Fruit set was not significantly related to previous RE.
6 The greater total RE of females and their limited ability to adjust fruit set are probably major factors contributing to the greater mortality rates of females and the male-biased sex ratios in O. cerasiformis .     

Habitat and sex specific differences in the dioecious weed Acetosella vulgaris (Polygonaceae)

Abstract Patterns of resource allocation, numbers of reproductive structures and sex ratios of flowering populations of the dioecious weed Acetosella vulgaris (Fourr.) were examined in the Kosciuszko alpine region of Australia. Specifically, the sex‐specific response of ramets was compared between a disturbed alpine habitat, in which weeds such as A. vulgaris are common (disturbed roadside/path‐edge), and a native alpine habitat in which weeds appear to have a limited capacity to germinate, grow and reproduce (undisturbed tall alpine herbfield). The disturbed habitat was generally more favourable for growth of A. vulgaris. Ramets of both sexes had greater total and vegetative biomass than ramets in native habitats. Although reproductive biomass was also greater in disturbed habitats, females had less reproductive biomass than males, which was not as predicted. Reproductive effort was not affected by habitat or gender. The disturbed habitat also favoured increased numbers of inflorescences per ramet and flowers per ramet, as expected. Whereas the gender of the ramet also influenced numbers of reproductive structures, again, this was not as predicted. Females had more flowers per ramet and more flowers per inflorescence than males. This may be because of factors associated with wind pollination. Females were taller in native habitats but there was no difference between the sexes in disturbed habitats. Sex ratios varied from all male populations to nearly all female populations among the 25 sites sampled irrespective of habitat. Factors such as time since last disturbance may have contributed to variation in the sex ratios of alpine populations of A. vulgaris in Australia.     

Population structure and spatial pattern in the dioecious shrub Ceratiola ericoides

Abstract. The dioecious shrub Ceratiola ericoides (Florida rosemary) dominates xeric, infrequently burned Florida scrub vegetation, often to the near-exclusion of other woody species. We studied the spatial pattern, age, sex and size structure of four populations in Florida, USA: two coastal scrub populations subject to recurrent local disturbances due to sand movement, and two inland scrub populations in sites periodically burned by stand-replacing fires. The age structure of individual genets was estimated from node counts and used to describe the age structure of the populations. The sex ratio of males to females was not significantly different from 1:1, except within a female-biased coastal population subject to frequent sand movement. Node counts indicated that the mean age for reproductive individuals was 15 - 16 yr for the inland populations and 13 - 16 yr for the coastal populations. In all sites, there was no difference in mean age between males and females. Vegetative reproduction was uncommon except for the least-disturbed coastal population where 72 % of the reproductive individuals originated through layering. Individuals were generally randomly dispersed at the coastal sites, whereas significant aggregation of males and females occurred in the inland sites where the populations were initiated following fire. Seedling recruitment was continuous in the disturbed coastal scrub site, where 35% of the individuals were juveniles. Most juveniles were dispersed from 0.5 to 0.75 m around females. At one of the inland sites, where juveniles comprised 11% of the population, juveniles were clustered at 0.25 to 5.75 m around females. Coastal populations were all-aged, while inland populations were uneven-aged. Recruitment appears to follow periods of disturbance; infrequent fire in the inland populations and continuous sand movement on the coast are factors initiating recruitment.     

Epipactis helleborine shows strong mycorrhizal preference towards ectomycorrhizal fungi with contrasting geographic distributions in Japan

Epipactis helleborine (L.) Crantz, one of the most widespread orchid species, occurs in a broad range of habitats. This orchid is fully myco-heterotrophic in the germination stage and partially myco-heterotrophic in the adult stage, suggesting that a mycorrhizal partner is one of the key factors that determines whether E. helleborine successfully colonizes a specific environment. We focused on the coastal habitat of Japanese E. helleborine and surveyed the mycorrhizal fungi from geographically different coastal populations that grow in Japanese black pine (Pinus thunbergii Parl.) forests of coastal sand dunes. Mycorrhizal fungi and plant haplotypes were then compared with those from inland populations. Molecular phylogenetic analysis of large subunit rRNA sequences of fungi from its roots revealed that E. helleborine is mainly associated with several ectomycorrhizal taxa of the Pezizales, such as Wilcoxina, Tuber, and Hydnotrya. All individuals from coastal dunes were exclusively associated with a pezizalean fungus, Wilcoxina, which is ectomycorrhizal with pine trees growing on coastal dunes. Wilcoxina was not detected in inland forests. Coastal populations were indistinguishable from inland populations based on plant trnL intron haplotypes. Our results indicate that mycorrhizal association with geographically restricted pezizalean ectomycorrhizal fungi is a key control upon this orchid species' distribution across widely different forest habitats.     

Evidence for Environmental Sex Determination in the American eel, Anguilla rostrata

Males have predominated among migrating silver eels in the Annaquatucket River, Rhode Island, for at least two decades, with no significant variation in mean total length in either sex. Because the species is panmictic (random breeding), this consistency suggests environmental sex determination (ESD). Most yellow (feeding phase) eels <300mm total length in the Annaquatucket are sexually undifferentiated, and in contrast to all other published sex ratios, males greatly outnumber females (3:1) among differentiated yellow eels. Estimates of yellow eel population densities are 4–10 times greater than published values for other habitats. We propose that this crowding results in a long period of undifferentiation and the suppression of femaleness. Published field and experimental evidence indicates that high population density results in high proportions of males in Atlantic Anguilla, and that low population density results in the predominance of females. This ESD may be adaptive, resulting in vast numbers of small males in coastal habitats, relatively close to the spawing area, and much larger and more fecund females that occupy most of the available eel habitat.     

Reproductive allocation between the sexes,across natural and novel habitats,and its impact on genetic diversity

Allocation to reproductive mode (sexual and asexual) can vary depending on environmental conditions but is often examined at the population level, whereas selection acts upon the individual. We examined individual variation in reproductive mode to identify how the interaction of sex and the environment affect population genetic diversity. Using the plant Marchantia inflexa, we tested whether reproductive allocation pattern varies consistently between males and females and among plants collected from different environments, and determined if morphological responses were the result of individual plasticity or genetic differences. We then quantified genetic variability between the different environments and between the sexes. Male and female plants were collected from two strikingly different habitats within the same region: along natural sites (rivers) and along novel human-modified sites (roadsides). Using a common garden approach, we found a strong sex by habitat interaction: male and female responses differed significantly by their source habitat. For females, relative to river-collected, road-collected plants had higher growth and asexual reproduction, while the pattern was reversed, although not significant, for males. Genetic differentiation was significant between the two habitats with no evidence of individual differences in plasticity for growth, but there was a genotype effect for asexual propagule production. Males and females did not differ genetically; but river-collected plants with lower sexual potential were more diverse than roadside-collected plants, possibly the result of founder events. These results show that individual variation in reproduction is controlled by the interaction of both the environment and genetics. Due to different selection pressures between natural and novel habitats, there are observable differences in life history traits with an associated evolutionary response to the novel habitat.     

Gender, season and habitat: Patterns of variation in photosynthetic activity, growth and fecundity in Thymelaea velutina

Changes in the ecophysiological performance of a plant species due to different environmental conditions generally reflect adaptations to the habitat where the plant grows and are often related to its survival capacity in a particular place. We examined this with the dioecious shrub Thymelaea velutina, in two contrasting populations representing the extremes of the altitudinal gradient where the species lives (coastal dunes and mountain habitats over 1000 m). We measured net photosynthetic rates and stomatal conductance, estimated the level of plant stress by chlorophyll fluorescence, and assessed their correlations with growth rate, plant size, flower production and fruit set. We hypothesized that plants at high altitude were more photosynthetically stressed than at sea level and expected a gender × habitat interaction in performance as females need more resources than males. Plants in the mountain experienced chronic photoinhibition during winter and a reduced photosynthetic performance both in winter and spring compared to plants in coastal dunes. However, there was no association between any of the fluorescence variables and either plant growth or fecundity, suggesting that other factors are involved determining performance. Mountain plants showed also an apparent lower capacity of heat dissipation to excessive radiation than dune plants. In the dunes, the greater leaf area and mass can lead to a higher photosynthetic carbon gain by whole individuals compared to plants in the mountain. No effect of gender was detected on the ecophysiological performance of this species, which we partly attribute to the small size of fruits of the female plants.     

Ecological reproductive isolation of coast and inland races of Mimulus guttatus

Adaptive divergence due to habitat differences is thought to play a major role in formation of new species. However it is rarely clear the extent to which individual reproductive isolating barriers related to habitat differentiation contribute to total isolation. Furthermore, it is often difficult to determine the specific environmental variables that drive the evolution of those ecological barriers, and the geographic scale at which habitat-mediated speciation occurs. Here, we address these questions through an analysis of the population structure and reproductive isolation between coastal perennial and inland annual forms of the yellow monkeyflower, Mimulus guttatus. We found substantial morphological and molecular genetic divergence among populations derived from coast and inland habitats. Reciprocal transplant experiments revealed nearly complete reproductive isolation between coast and inland populations mediated by selection against immigrants and flowering time differences, but not postzygotic isolation. Our results suggest that selection against immigrants is a function of adaptations to seasonal drought in inland habitat and to year round soil moisture and salt spray in coastal habitat. We conclude that the coast and inland populations collectively comprise distinct ecological races. Overall, this study suggests that adaptations to widespread habitats can lead to the formation of reproductively isolated species.     

Saline stress tolerance partly matches with habitat preference in ground‐living wolf spiders

Salinity interacts with many physiological functions and therefore probably influences the distribution of terrestrial fauna in tidal flooded salt marshes. The present study tests the hypothesis that the physiological tolerance of stenotopic wolf spiders for saline conditions at least partially determines their occurrence throughout salt‐marsh and nonsaline habitats. The duration of survival of three stenotopic wolf spider species (Araneae: Lycosidae) with different habitat preferences is compared in a controlled laboratory experiment. The forest‐dwelling Pardosa saltans, the salt‐marsh resident Pardosa purbeckensis and its sister species the inland‐living Pardosa agrestis are exposed to experimental conditions with different levels of salinity. Individuals (45 males and 20–45 females per treatment) are placed in individual air‐tight boxes filled with water‐saturated sand. Three levels of salinity are tested: nonsaline (0‰), medium saline (33–35‰) and highly saline (66–70‰). Contents of carbon, hydrogen and nitrogen and the molar ration carbon/nitrogen remain constant over time and do not differ among salinity treatments, indicating that starvation effects on survival, if any, are similar for all treatments. Conversely, body water significantly decreases over time and differs among salinity treatments, in accordance with patterns of survival. Conforming to their habitat preference, the survival of P. saltans and P. agrestis decreases quickly under highly saline conditions. Pardosa purbeckensis, however, has a high survival under both saline and nonsaline conditions. The duration of survival of females is significantly lower than that of males of P. saltans and P. purbeckensis. Durations of survival of ground‐living wolf spiders exposed to salinity partly match their habitat distribution but do not explain the restriction of salt‐marsh species to saline habitats.     

Soil water content and patterns of allocation to below- and above-ground biomass in the sexes of the subdioecious plant Honckenya peploides

Background and aims Dioecious plants often show sex-specific differences in growth and biomass allocation. These differences have been explained as a consequence of the different reproductive functions performed by the sexes. Empirical evidence strongly supports a greater reproductive investment in females. Sex differences in allocation may determine the performance of each sex in different habitats and therefore might explain the spatial segregation of the sexes described in many dimorphic plants. Here, an investigation was made of the sexual dimorphism in seasonal patterns of biomass allocation in the subdioecious perennial herb Honckenya peploides, a species that grows in embryo dunes (i.e. the youngest coastal dune formation) and displays spatial segregation of the sexes at the studied site. The water content in the soil of the male- and female-plant habitats at different times throughout the season was also examined. Methods The seasonal patterns of soil-water availability and biomass allocation were compared in two consecutive years in male and female H. peploides plants by collecting soil and plant samples in natural populations. Vertical profiles of below-ground biomass and water content were studied by sampling soil in male- and female-plant habitats at different soil depths. Key Results The sexes of H. peploides differed in their seasonal patterns of biomass allocation to reproduction. Males invested twice as much in reproduction than females early in the season, but sexual differences became reversed as the season progressed. No differences were found in above-ground biomass between the sexes, but the allocation of biomass to below-ground structures varied differently in depth for males and females, with females usually having greater below-ground biomass than males. In addition, male and female plants of H. peploides had different water-content profiles in the soil where they were growing and, when differences existed (usually in the upper layers of the soil), the water content of the soil was higher for the female plants had than for the male plants. Conclusions Sex-differential timing of investment in reproduction and differential availability and use of resources from the soil (particularly water) are factors that probably offset the costs of reproduction in the above-ground growth in males and females of H. peploides. The results suggest that the patterns of spatial segregation of the sexes observed in H. peploides may contribute to maximize each sex's growth and reproduction.     

The vegetation of the Farasān Islands,Red Sea,Saudi Arabia

Abstract. Classification of the vegetation of the Farasān Islands using TWINSPAN technique resulted in the recognition of seven community types associated with seven different habitat types: silty runnels, palm orchards, rocky plains, rocky plateau crevices, coastal sand dunes, sand plains, and mangroves. These communities were dominated or co-dominated by 13 perennial species; 87 associate species were recorded in the study area with chamaephytes dominating the life-form spectrum. Canonical Correspondence Analysis (CCA) indicated that organic carbon, soil moisture, silt, electrical conductivity and calcium carbonate were the major edaphic gradients controlling the distribution of the plant communities on the Farasān Islands. Higher species richness was recorded in the plant communities inhabiting the palm orchards, the crevices of the rocky plateau, silty runnels, rocky plains and rocky plateau, while those of the mangrove and sand formations (dunes and plains) showed a lower species richness. Soil texture and organic matter are the main factors promoting species diversity in the more diversified habitats, while high salinity and calcium carbonate are the main factors associated with lower species diversity in the less diversified habitats of the study area.     

Life history and habitat use of Norwegian brown trout (Salmo trutta)

SUMMARY. 1. Brown trout ( Salmo trutta) life history and habitat use were studied in two Norwegian rivers: the Vosso river system, western Norway, and the Søre Osa, eastern Norway.
2. Age-groups were partly segregated in feeding habitats, the youngest fish living mainly in running water and in the littoral zone of lakes, the older fish also exploiting pelagic waters and deeper epibenthic habitats. In a population with free access to and from the sea, some individuals smoltified and became sea-run migrants, performing yearly migrations to the coastal sea, whereas others stayed as freshwater residents throughout their entire life span.
3. Within local populations, females were larger and less variable in size than males. This was partly because females matured at an older age than males, partly because the sexes tended to exploit feeding habitats with different food and growth Conditions. Within age-groups, females were more pelagic and migrated more than males, whereas males were more confined to running water and epibenthic areas than females. In the pelagic zone, males were more abundant in near-surface water, and females more abundant in deeper areas. When exploiting the same feeding areas, the two sexes grew at the same rate. There therefore appears to be a connection between feeding habitat and the reproductive ecology of brown trout.     

Habitat Use of American Alligators in East Texas

ABSTRACT The American alligator (Alligator mississippiensis) has made a remarkable recovery throughout its range during the last half-century. In Texas, USA, current inland alligator population and harvest management strategies rely on generalized and often site-specific habitat and population data generated from coastal populations, because it is assumed that habitat and demographic similarities exist between inland and coastal populations. These assumptions have not been verified, however, and no studies have specifically examined inland alligator habitat use in Texas. We quantified alligator habitat use in East Texas during 2003–2004 to address this information gap and to facilitate development of regionally specific management strategies. Although habitat was variable among study areas, alligators used habitats with >50% open water, substantial floating vegetation, and emergent vegetation close (<12 m) to dry ground and cover. Adults used habitats further from dry ground and cover, in open water (75–85%), with less floating vegetation (6–22%) than did subadults, which used habitats that were closer to dry ground and cover, with less open water (52–68%), and more floating vegetation (8–40%). Although habitat use mirrored coastal patterns, we estimated alligator densities to be 3–5 times lower than reported in coastal Texas, likely a result of inland habitat deviations from optimal coastal alligator habitat, particularly in the preponderance of open water and floating vegetation. Our findings that 1) inland habitats varied among sites and did not exactly match assumed optimal coastal habitats, 2) alligators used these inland habitats slightly differently than coastal areas, and 3) inland alligator densities were lower than coastal populations, all highlight the need for regionally specific management approaches. Because alligator populations are influenced by habitat quality and availability, any deviations from assumed optimal habitat may magnify harvest impacts upon inland populations.     

An elasmobranch maternity ward: female round stingrays Urobatis halleri use warm, restored estuarine habitat during gestation

The habitat use and movements of the round stingray Urobatis halleri were compared between shallow restored and natural habitats of the Anaheim Bay Estuary (CA, U.S.A.) in relation to water temperature. Restored habitat remained significantly warmer than natural habitat from spring through to autumn. Strong sexual segregation occurred in the restored habitat with mature female U. halleri forming large unisex aggregations in summer, during months of peak seasonal water temperatures, and males only present during spring. Most mature females collected from restored habitat during months of high abundance were determined to be pregnant using non-invasive field ultrasonography. Tagged females typically spent <14 days in the restored habitat, using the habitat less as seasonal water temperatures decreased. Females tended to emigrate from the estuary by mid-August, coinciding with the time of year for parturition. The elevated water temperatures of the restored habitat may confer an energetic cost to male U. halleri, but females (particularly pregnant females) may derive a thermal reproductive benefit by using warm, shallow habitats for short periods of time during months of peak water temperatures. These findings have management implications for the design of coastal habitat restoration projects and marine protected areas that incorporate thermal environments preferred by aggregating female elasmobranchs.     

Climate‐dependent costs of reproduction: Survival and fecundity costs decline with length of the growing season and summer temperature

Costs of reproduction are expected to vary with environmental conditions thus influencing selection on life‐history traits. Yet, the effects of habitat conditions and climate on trade‐offs among fitness components remain poorly understood. For 2–5 years, we quantified costs of experimentally increased reproduction in two populations (coastal long‐season vs. inland short‐season) of two long‐lived orchids that differ in natural reproductive effort (RE; 30 vs. 75% fruit set). In both species, survival costs were found only at the short‐season site, whereas growth and fecundity costs were evident at both sites, and both survival and fecundity costs declined with increasing growing season length and/or summer temperature. The results suggest that the expression of costs of reproduction depend on the local climate, and that climate warming could result in selection favouring increased RE in both study species.     

Sexual segregation by Masai giraffes at two spatial scales

In this paper alternative explanations for observed patterns of sexual segregation by giraffes are examined at two spatial scales: within-habitats and within-landscape. Habitats are defined as recognizable plant associations and the landscape as the collection of all available habitat types. The study was conducted in Mikumi National Park, Tanzania. At the within-landscape level, all sex and age classes of giraffes exhibited high degrees of preference for riverine habitats. Sex differences in habitat selection were mostly due to females with young, who tended to select open floodplain habitats in which their vigilance time was lowest. Males, and females without young, preferred more heavily-wooded habitat. Habitat preferences were not related to observed habitat-specific forage intake rates for either males or females. Within habitats, male and female giraffes selected different feeding heights, males feeding higher in the canopy than females. Females showed a strong tendency to generalize with respect to feeding height. It is suggested that a sexual dimorphism–body size hypothesis provides a parsimonious explanation for the observed feeding height selection patterns, whereas a reproductive strategy hypothesis can explain sex-differences in habitat selection patterns within the landscape.     

Reduced flight capability in British Virgin Island populations of a wing-dimorphic insect: the role of habitat isolation, persistence, and structure

1. The effects of habitat isolation, persistence, and host‐plant structure on the incidence of dispersal capability (per cent macroptery) in populations of the delphacid planthopper Toya venilia were examined throughout the British Virgin Islands. The host plant of this delphacid is salt grass Sporobolus virginicus, which grows either in undisturbed habitats (large expanses on intertidal salt flats and around the margins of salt ponds, or small patches of sparse vegetation on sand dunes along the shore), or in less persistent, disturbed habitats (managed lawns). 2. Both sexes of T. venilia were significantly more macropterous in disturbed habitats (77.1% in males, 12.5% in females) than in more persistent, undisturbed habitats (19.2% in males, < 1% in females). 3. Males exhibited significantly higher levels of macroptery (26.9 ± 7.6%) than did females (2.0 ± 1.7%), and per cent macroptery was positively density dependent for both sexes in field populations. 4. There was no evidence that the low incidence of female macroptery in a subset of island populations inhabiting natural habitats (1.7 ± 1.2%) was attributable to the effects of isolation on oceanic islands. The incidence of macroptery in British Virgin Island populations of T. venilia was not different from that observed in mainland delphacid species existing in habitats of similar duration. 5. Rather, the persistence of most salt grass habitats throughout the British Virgin Islands best explains the evolution of flight reduction in females of this island‐inhabiting delphacid. 6. Males were significantly more macropterous in populations occupying dune vegetation (37.6 ± 9.8%) than in populations occupying salt flat–pond margin habitats (7.6 ± 5.6%). By contrast, females exhibited low levels of macroptery in both dune (0%) and salt flat–pond margin (< 1%) habitats. Variation in salt‐grass structure probably underlies this habitat‐related difference in macroptery because flight‐capable males of planthoppers are better able to locate females in the sparse‐structured grass growing on dunes. This habitat‐related difference in male macroptery accounted for the generally higher level of macroptery observed in males than in females throughout the islands. 7. The importance of habitat persistence and structure in explaining the incidence of dispersal capability in T. venilia is probably indicative of the key role these two factors play in shaping the dispersal strategies of many insects.     

Environmental and genetic determinants of reproduction in the house sparrow: a transplant experiment

A transplant experiment was carried out to examine whether genetic differentiation can explain geographical variation in the reproductive strategies of house sparrows Passer domesticus. Individuals from an inland and a coastal population in Central Norway were released on a small island, near the coastal area. No directional selection was found on any of the morphological characters from the release to the onset of breeding, but the proportion of the inland males that remained to start breeding on the island was smaller than that of the coastal males. The new environment influenced the time of egg laying which was, relative to the source populations, more delayed among the introduced inland females than among the coastal females. In 1992, chicks raised by inland females grew faster and were fed more frequently than chicks raised by coastal females. No difference was found between birds of inland and coastal origins in their breeding success and their relative number of surviving recruits. Transplanted parents from the inland fed their offspring more frequently than transplanted parents from the coastal area. This experiment shows that the plasticity of reproductive traits in combination with stochastic factors in the environment may lead to an establishment of introduced genes in small populations.     

Using body mass dynamics to examine long-term habitat shifts of arctic-molting geese: evidence for ecological change

From 1976 onward, molting brant geese (Branta bernicla) within the Teshekpuk Lake Special Area, Alaska, shifted from inland, freshwater lakes toward coastal wetlands. Two hypotheses explained this redistribution: (1) ecological change: redistribution of molting brant reflects improvements in coastal foraging habitats, which have undergone a succession toward salt-tolerant plants due to increased coastal erosion and saltwater intrusion as induced by climate change or (2) interspecific competition: greater white-fronted geese (Anser albifrons) populations increased 12-fold at inland lakes, limiting food availability and forcing brant into coastal habitats. Both hypotheses presume that brant redistributions were driven by food availability; thus, body mass dynamics may provide insight into the relevance of these hypotheses. We compared body mass dynamics of molting brant across decades (1978, 1987–1992, 2005–2007) and, during 2005–2007, across habitats (coastal vs. inland). Brant lost body mass during molt in all three decades. At inland habitats, rates of mass loss progressively decreased by decade despite the increased number of greater white-fronted geese. These results do not support an interspecific competition hypothesis, instead suggesting that ecological change enhanced foraging habitats for brant. During 2005–2007, rates of mass loss did not vary by habitat. Thus, while habitats have improved from earlier decades, our results cannot distinguish between ecological changes at inland versus coastal habitats. However, we speculate that coastal forage quality has improved beyond that of inland habitats and that the body mass benefits of these higher quality foods are offset by the disproportionate number of brant now molting coastally.     

Sexual segregation in western grey kangaroos: testing alternative evolutionary hypotheses

In sexually dimorphic ungulates, sexual segregation is hypothesized to have evolved because of sex-specific differences in body size and/or reproductive strategies. We tested these alternative hypotheses in kangaroos, which are ecological analogues of ungulates. Kangaroos exhibit a wide range of body sizes, particularly among mature males, and so the effects of body size and sex can be distinguished. We tested predictions derived from these hypotheses by comparing the distribution of three sex–sex size classes of western grey kangaroos Macropus fuliginosus , in different habitats, and the composition of groups of kangaroos, across seasons. In accordance with the predation risk-reproductive strategy hypothesis, during the non-breeding season, females, which were more susceptible to predation than larger males, and were accompanied by vulnerable young-at-foot, were over-represented in secure habitats. Large males, which were essentially immune to predation, occurred more often than expected in nutrient-rich habitat, and small males, which faced competing demands of predator avoidance and feeding, were intermediate between females and large males in their distribution across habitats. During the breeding season, females continued to be over-represented in secure habitats when their newly emerged pouch young were most vulnerable to predation. All males occupied these same habitats to maximize their chances of securing mates. Consistent with the social hypotheses, groups composed of individuals of the same sex, irrespective of body size, were over-represented in the population during the non-breeding season, while during the breeding season all males sought females so that mixed-sex groups predominated. These results indicate that body size and reproductive strategies are both important, yet independent, factors influencing segregation in western grey kangaroos.