How resources and encounters affect the distribution of foraging activity in a seed-harvesting ant

We examined how the foraging ecology of the seed-harvesting ant Messor andrei depends upon the distribution of resources and the presence of conspecifics. Bait experiments showed that colonies can recruit to high-density patches of seeds. However, at the seasonal scale, natural resource distribution did not affect the distribution of foraging activity. We conducted the study in years of high rainfall and thus seed availability may not have been a limiting factor. Colonies always preferred to forage in areas closer to their nest, which may reduce travel time between the nest and foraging sites. On a day-to-day scale, encounters between neighboring colonies at a site increased the probability that colonies would return to forage at that site; this was true both for natural and experimental encounters. In the summer, this resulted in colonies foraging at the sites of intraspecific encounters on more days than in areas where no encounter had occurred. Encounters between colonies included fighting, and there was little overlap between the foraging areas of neighboring colonies: both results suggest that one function of encounters is to defend foraging space. The high probability of return to the site of an encounter between colonies suggests that encounters may have a second function: to indicate the presence of resources. Received: 28 June 1999 / Received in revised form: 12 October 1999 / Accepted: 16 October 1999     

Foraging strategies and prey encounter rate of free-ranging Little Penguins

There is little information on the effort put into foraging by seabirds, even though it is fundamental to many issues in behavioural ecology. Recent researchers have used changes in the underwater cruising speed of penguins to allude to prey ingestion since accelerations are thought to reflect the encounter and pursuit of prey. In this study, we attached minute accelerometers, to determine flipper beat frequency as a proxy for prey pursuit, to Little Penguins Eudyptula minor foraging in shallow waters in Western Australia. During diving, Little Penguins flapped continuously and at a regular pace of 3.16 Hz while descending the water column and throughout the bottom phase of most dives. However, the frequency and amplitude of wingbeats increased transitorily, reaching 3.5–5.5 Hz, during some dives indicating prey pursuit. Pursuit phases lasted a mean of 2.9±3.3 s and occurred principally during the bottom phases of dives (75.4%). Most dives in all birds (86%) had a clear square-shaped depth profile indicating feeding activity near the seabed in the shallow waters of the bays. Hourly maximum depth, time spent underwater, percentage of dives with pursuit events and catch per unit effort showed an overall increase from zero at ca. 0500 h to a maximum during the hours around mid-day before decreasing to zero by 1900 h. During pursuit phases, Little Penguins headed predominantly downward, probably using the seabed to assist them in trapping their prey. In the light of our results, we discuss depth use by Little Penguins and their allocation of foraging effort and prey capture success as a function of environmental conditions.     

Oceanographic characteristics of areas used by Cory’s shearwaters during short and long foraging trips in the North Atlantic

Many breeding seabird species are central-place foragers and constrained to find productive prey patches within their foraging ranges. We assessed how different populations of a pelagic seabird species, the Cory’s shearwater Calonectris diomedea, breeding in oceanic and neritic conditions, cope with these constraints in the North Atlantic, during both incubation and chick-rearing periods. We analysed 237 foraging trips to study the movements and oceanographic characteristics of foraging habitats of seven different populations of Cory’s shearwaters. Generally, oceanic populations exhibited higher foraging effort, by travelling more time and to more distant areas, and larger home ranges and feeding areas, than the neritic population (i.e. breeding on an island within the Portuguese continental platform). On their short trips (i.e. ≤4 days), birds from the different populations fed mostly in shallower waters around the colony. During long trips (i.e. ≥5 days), feeding areas of both oceanic and neritic populations were characterized by high concentration values of chlorophyll-a, low sea-surface temperature and shallower habitats, with oceanic populations of the Azores exploiting areas north of the islands over known seamounts and frontal regions. Birds from other oceanic population (Selvagens) also exploited the African continental shelf system on their long trips. The home ranges of the different populations overlapped widely, but there was a general spatial segregation in terms of the core feeding areas at the population level. Core feeding areas and areas of foraging overlap between different populations should be important to inform conservation management measures, such as the definition of Marine Important Bird Areas for seabirds over the North Atlantic.     

Competitive organization of the soft-bottom macrobenthic communities of southern California lagoons

The sandy-bottom macrobenthic community of Mugu Lagoon, a relatively pristine southern California (USA) marine lagoon, demonstrated (1) nearly constant community composition over 37 months of observation, (2) relatively little temporal variability in the population densities of the most abundant species over 37 months, and (3) a pattern of depth stratification in which very little vertical overlap existed among the six most abundant species. The only two species whose vertical distributions overlapped broadly showed horizontal spatial segregation, each abundant in different areas within the sand habitat. These community characteristics imply the importance of biological factors in structuring the sand benthos. The relatively large volume required for living space by these macrofauna suggests that competition for space may be the biological factor most important in determining the observed temporal and spatial abundance patterns. The muddy-sand community and the mud community of Mugu Lagoon also revealed similar patterns of stratification: new abundant species replaced species at the same sedimentary level while not greatly affecting species populations at other non-overlapping levels. In the sand community of Tijuana Slough, two of the abundant species of Mugu Lagoon's sand community were nearly absent as an apparent result of human over-exploitation. Probably in response, densities of species living at the sedimentary levels normally occupied by the missing species were much higher than would be predicted if competition for space were unimportant. In field experiments, removal of the deposit feeder Callianassa californiensis resulted in high recruitment of Sanguinolaria nuttallii, whereas control areas showed no S. nuttallii recruitment. Experiments also suggest that negative intraspecific interactions between Cryptomya californica individuals may explain the observed rapid emigration from areas of artificially high density. Perhaps the relatively great environmental predictability of southern California lagoons has permitted competitive interactions to play a singnificant role in determining the temporal and spatial abundance patterns of the soft-bottom macrobenthos.     

Chinstrap penguins alter foraging and diving behavior in response to the size of their principle prey, Antarctic krill

Penguins may exhibit plasticity in their diving and foraging behaviors in response to changes in prey availability. Chinstrap penguins are dependent predators of Antarctic krill in the Scotia Sea region, but krill populations have fluctuated in recent years. We examined the diet of chinstrap penguins at Livingston Island, South Shetland Islands, in relation to their diving and foraging behavior using time-depth recorders over six breeding seasons: 2002–2007. When krill were smaller, more chinstrap penguins consumed fish. In these years, chinstrap penguins often exhibited a shift to deep dives after sundown, and then resumed a shallower pattern at sunrise. These night dives were unexpectedly deep (up to 110 m) and mean night dive depths sometimes exceeded those from the daytime. The average size of krill in each year was negatively correlated to mean night dive depths and the proportion of foraging trips taken overnight. Based on these patterns, we suggest that when krill were small, penguins increasingly targeted myctophid fish. The average krill size was negatively correlated to the time chinstrap penguins spent foraging which suggests that foraging on smaller krill and fish incurred a cost: more time was spent at sea foraging.     

Plasticity in foraging strategies of inshore birds: how Little Penguins maintain body reserves while feeding offspring

Breeding animals face important time and energy constraints when caring for themselves and their offspring. For long-lived species, life-history theory predicts that parents should favor survival over current reproductive attempts, thus investing more into their own maintenance than the provisioning of their young. In seabirds, provisioning strategies may additionally be influenced by the distance between breeding sites and foraging areas, and offshore and inshore species should thus exhibit different strategies. Here, we examine the provisioning strategies of an inshore seabird using a long-term data set on more than 200 Little Penguins, Eudyptula minor. They alternated between two consecutive long and several short foraging trips all along chick rearing, a strategy almost never observed for inshore animals. Short trips allowed for regular provisioning of the chicks (high feeding frequency and larger meals), whereas long trips were performed when parent body mass was low and enabled them to rebuild their reserves, suggesting that adult body condition may be a key factor in initiating long trips. Inshore seabirds do use dual strategies of alternating short and long trips, but from our data, on a simpler and less flexible way than for offshore birds.     

Development of food preferences: social learning by Belding's ground squirrels Spermophilus beldingi

Summary The mechanisms by which food selection behavior develops may constrain the evolution of optimal foraging, yet these mechanisms have received relatively little attention in recent optimal foraging studies. We used cafeteria-style feeding trials to examine the role of social learning in the development of food preferences by a generalist mammalian herbivore, Spermophilus beldingi. Naive young spent relatively little time feeding and showed no preferences among five plant species offered in their feeding trials. This random pattern persisted for one set of young during two subsequent trials in the absence of their mother. A second group of young squirrels was tested initially alone, once with their mothers, and then once more alone. These squirrels fed more than those in the control group during their final trials, and showed significant preferences among plant species. These paralleled the preferences of their mothers. These results suggest that social learning may be important in the development of feeding behavior in ground squirrels, and provide a possible mechanism for cultural differences in food preferences among populations.     

Individual trophic specialisation and niche segregation explain the contrasting population trends of two sympatric otariids

Individual specialisation is increasingly recognised to be an ecological and evolutionary process having important consequences for population dynamics of vertebrates. The South American fur seal (SAFS) and the South American sea lion (SASL) are two otariid species with similar ecology that coexist in sympatry in the Uruguayan coast. These two species have contrasting trends and widely different population sizes. The underlying reasons for these population trends, unique in their geographical ranges, remain unknown. We studied the foraging ecology of these otariid species over 2 years at the individual- and population levels using the isotopic ratios (δ¹³C–δ¹⁵N) in whiskers of both sexes. We compared the isotope ratios between species and sexes and used several metrics to characterise the degree of overlap and distinctiveness in the use of isotopic niche space at the individual- and population levels. Interspecific trophic niche overlap was minimal, thus ruling out interspecific competition as the cause for the contrasting population trends of both species. At the intraspecific level, both species had sexual segregation in their foraging areas, but each species had a large overlap in the isotopic niches between sexes. While SAFS had a wider niche and generalist individuals, SASL had the narrower niche with a higher degree of individual specialisation. Behavioural constraints during the breeding season, intraspecific competition and a major dependence on resources of the Uruguayan coastal shelf may explain why SASL had a higher trophic individual specialisation and a larger vulnerability in a heavily exploited habitat by fisheries and, by consequence, a locally declining population trend.     

Food availability and diet composition of three coexisting Mediterranean limpets (Patella spp.)

The gut contents of three intertidal patellid limpets were analysed by collecting foraging specimens on a breakwater on the Tyrrhenian coast (central Italy) between May 1988 and October 1989. The three species coexist there showing a different, but partially overlapping zonation: Patella aspera dominates the infralittoral fringe; the majority of P. caerulea inhabits the lower midlittoral, while P. rustica is most abundant in the upper midlittoral. The algae present on slivers of substratum over which each limpet collected was moving were identified. Moreover, floristic surveys were made along the shore in order to characterize the algal cover of the different zonal belts. The floristic study revealed that the basic elements of algal communities typical of western Mediterranean rocky shores are present in the study area. The algae found on the slivers under the foraging limpets were generally representative of the algal community typical of the same zone. There was a marked difference between the diets of P. rustica and P. aspera due to the fact that the first species forages on a few low lying epilithic and endolithic Cyanophyceae, while P. aspera feeds on a large number of species belonging to all the main algal classes and life forms considered, including frondose epilithics and epiphytics. The diet of P. caerulea resembles that of P. aspera in algal heterogeneity, but is dominated by Cyanophyceae as in P. rustica. A detailed analysis of the differences between gut contents of each limpet species and the relative slivers showed an obvious general correspondence, but revealed also that the diets of the three species do not completely reflect the availability of algae. These findings suggest that the basic diet segregation mechanism between the three populations is their zonal separation. However, the difference in gut contents of heterospecific limpets foraging in the same zone suggests the existence of supplementary morphy-functional or behavioural mechanisms for diet segregation between the three species.     

海南岛及邻近陆地拟细鲫的种群遗传分化和亲缘地理过程

为了解海南岛及邻近陆地拟细鲫(Aphyocypris normalis)的遗传分化和亲缘地理过程,采用线粒体细胞色素b(Cyt b)对9个种群共124个个体的遗传多样性和遗传分化进行评估,并探讨这一物种的亲缘地理结构及演化历史.结果显示,在1 140 bp的序列中,共检测到87个核苷酸变异位点,定义了34个单倍型.基于...     

Prey dynamics affect foraging by a pelagic predator (Stenella longirostris) over a range of spatial and temporal scales

Studies have shown that pelagic predators do not overlap with their prey at small scales. However, we hypothesized that spinner dolphin foraging would be affected by the spatio-temporal dynamics of their prey at both small and large scales. A modified echosounder was used to simultaneously measure the abundance of dolphins and their prey as a function of space and time off three Hawaiian islands. Spinner dolphin abundance closely matched the abundance patterns in the boundary community both horizontally and vertically. As hypothesized, spinner dolphins followed the diel horizontal migration of their prey, rather than feeding offshore the entire night. Spinner dolphins also followed the vertical migrations of their prey and exploited the vertical areas within the boundary layer that had the highest prey density. Cooperative foraging by pairs of dolphins within large groups was evident. The geometric and density characteristics of prey patches containing dolphins indicate that dolphins may alter the characteristics of prey patches through this cooperative foraging. The overlap of Hawaiian spinner dolphins and their prey at many temporal and spatial scales, ranging from several minutes to an entire night and 20 m to several kilometers, indicates that the availability of truly synoptic data may fundamentally alter our conclusions about pelagic predator-prey interactions.     

Use of the superpopulation approach to estimate breeding population size: an example in asynchronously breeding birds

Many populations of animals are fluid in both space and time, making estimation of numbers difficult. Much attention has been devoted to estimation of bias in detection of animals that are present at the time of survey. However, an equally important problem is estimation of population size when all animals are not present on all survey occasions. Here, we showcase use of the superpopulation approach to capture-recapture modeling for estimating populations where group membership is asynchronous, and where considerable overlap in group membership among sampling occasions may occur. We estimate total population size of long-legged wading bird (Great Egret and White Ibis) breeding colonies from aerial observations of individually identifiable nests at various times in the nesting season. Initiation and termination of nests were analogous to entry and departure from a population. Estimates using the superpopulation approach were 47-382% larger than peak aerial counts of the same colonies. Our results indicate that the use of the superpopulation approach to model nesting asynchrony provides a considerably less biased and more efficient estimate of nesting activity than traditional methods. We suggest that this approach may also be used to derive population estimates in a variety of situations where group membership is fluid.     

Fitness costs of neighborhood disruption in translocations of a solitary mammal

Translocation is used to reestablish wild populations of animals, but translocation projects often do not meet their objectives because postrelease mortality of animals is high. One reason for translocation failure is that the behavioral or ecological requirements of released animals are unmet. Maintaining founder-group social relationships during release can affect reestablishment of social species. Solitary territorial species with stable neighbors (restricted dispersal and lifetime occupation of a home range) of the same species may also benefit from the maintenance of these social relationships during translocation. We translocated Stephens' kangaroo rats (Dipodomys stephensi), a solitary species listed as endangered under the U.S. Endangered Species Act, with and without neighboring kangaroo rats. We compared the settlement (establishment of a stable home range) decisions and fitness of kangaroo rats between the 2 treatments. Kangaroo rats translocated with neighbors traveled shorter distances before establishing territories, had higher survival rates, and had significantly higher reproductive success than kangaroo rats translocated without neighbors. Number of offspring was 24-fold higher for kangaroo rats translocated with neighbors than those translocated without neighbors. Differences in behavior following release may partially explain differences in survival between the 2 groups. Immediately following release, animals translocated with neighbors fought less and spent significantly more time foraging and digging burrows than animals translocated without neighbors. Our results indicate that even for solitary species, maintaining relationships among members of a translocated group of animals can influence translocation success. This study is the first empirical demonstration of the fitness consequences of disrupting social relationships among territorial neighbors.     

Antipredator defenses along a latitudinal gradient in Rana temporaria

Antipredator defenses are expected to decrease toward higher latitudes because predation rates are predicted to decrease with latitude. However, latitudinal variation in predator avoidance and defense mechanisms has seldom been studied. We studied tadpole antipredator defenses in seven Rana temporaria populations collected along a 1500-km latitudinal gradient across Sweden, along which previous studies have found increasing tadpole growth and development rates. In a laboratory common garden experiment, we measured behavioral and morphological defenses by raising tadpoles in the presence and absence of a predator (Aeshna dragonfly larva) in two temperature treatments. We also estimated tadpole survival in the presence of free-ranging predators and compared predator densities between R. temporaria breeding ponds situated at low and high latitudes. Activity and foraging were generally positively correlated with latitude in the common garden experiment. While all populations responded to predator presence by decreasing activity and foraging, high-latitude populations maintained higher activity levels in the presence of the predator. All populations exhibited defensive morphology in body and tail shape. However, whereas tail depth tended to increase with latitude in the presence of predator, it did not change with latitude in the absence of the predator. Predator presence generally increased larval period and decreased growth rate. In the southern populations, predator presence tended to have a negative effect on metamorphic size, whereas in the northern populations predators had little or a positive effect on size. Latitude of origin had a strong effect on survival in the presence of a free-ranging predator, with high-latitude tadpoles experiencing higher mortality than those from the low latitudes. In the wild, predator densities were significantly lower in high-latitude than in mid-latitude breeding ponds. Although the higher activity level in the northern populations seems to confer a significant survival disadvantage under predation risk, it is probably needed to maintain the high growth and development rates. However, the occurrence of R. temporaria at high latitudes may be facilitated by the lower predator densities in the north.     

Are penguins and seals in competition for Antarctic krill at South Georgia?

The Antarctic fur seal (Arctocephalus gazella) and macaroni penguin (Eudyptes chrysolophus) are sympatric top predators that occur in the Southern Ocean around South Georgia where they are, respectively, the main mammal and bird consumers of Antarctic krill (Euphausia superba). In recent years the population of fur seals has increased, whereas that of macaroni penguins has declined. Both species feed on krill of similar size ranges, dive to similar depths and are restricted in their foraging range at least while provisioning their offspring. In this study we test the hypothesis that the increased fur seal population at South Georgia may have resulted in greater competition for the prey of macaroni penguins, leading to the decline in their population. We used: (1) satellite-tracking data to investigate the spatial separation of the Bird Island populations of these two species whilst at sea during the breeding seasons of 1999 and 2000 and (2) diet data to assess potential changes in their trophic niches between 1989 and 2000. Foraging ranges of the two species showed considerable overlap in both years, but the concentrations of foraging activity were significantly segregated spatially. The size of krill taken by both species was very similar, but over the last 12 years the prevalence of krill in their diets has diverged, with nowadays less krill in the diet of macaroni penguins than in that of Antarctic fur seals. Despite a significant degree of segregation in spatial resource use by the study populations, it is likely that the South Georgia populations of Antarctic fur seal and macaroni penguin exploit the same krill population during their breeding season. For explaining the opposing population trends of the two species, the relative contributions of independent differential response to interannual variation in krill availability and of interspecies competition cannot be resolved with available evidence. The likely competitive advantage of Antarctic fur seals will be enhanced as their population continues to increase, particularly in years of krill scarcity.     

Contrasting home-range size and spatial partitioning in cryptic and sympatric pipistrelle bats

The extent of spatial partitioning in insectivorous bats, whose prey is patchily distributed and transient in nature, remains a contentious issue. The recent separation of a common Palaearctic bat, the pipistrelle, into Pipistrellus pipistrellus and Pipistrellus pygmaeus, which are morphologically similar and sympatric, provides an opportunity to examine this question. The present study used radio telemetry to address the spatial distribution and foraging characteristics of P. pipistrellus and P. pygmaeus in northeast Scotland, to test the hypothesis that coexistence between these species is facilitated through spatial segregation. We reveal large and significant differences in the spatial distribution and foraging characteristics of these two cryptic species. Individual P. pipistrellus home ranges were on average three times as large as that of P. pygmaeus, and they foraged for approximately an hour longer each night. Inter-specific spatial overlap was minimal (<5%) and core foraging areas of either species were essentially mutually exclusive despite the proximity of the two roosts. Inter-specific differences in range size were associated with the spatial dispersion of productive foraging sites within individual foraging ranges. P. pipistrellus foraging sites were highly dispersed, necessitating larger ranges. It is predicted that the spatial segregation revealed by the present study is a result of selection favouring the avoidance of competition in these species through differential habitat use.     

毛竹混交林主要种群多维生态位特征

应用生态位空间分割法，分别考虑资源利用率与否测定毛竹混交林多维资源空间中主要种群多维生态位宽度及多维生态位重叠，结果表明：考虑资源利用率与否对多维生态位宽度的测定有较大的影响，毛竹混交林中主要种群的多维生态位宽度与物种的生物学特性及竞争力密切相关，同一生境中物种的多维生态位重叠可通过生态位分化而减少竞争，研究毛竹混交林主要种群多维生态位特征对毛竹混交林营造具有指导作用．表8参24．     

Higher trophic level prey does not represent a higher quality diet in a threatened seabird: implications for relating population dynamics to diet shifts inferred from stable isotopes

Diet quality is a key determinant of population dynamics. If a higher trophic level, more fish-based diet is of higher quality for marine predators, then individuals with a higher trophic level diet should have a greater body mass than those feeding at a lower trophic level. We examined this hypothesis using stable isotope analysis to infer dietary trophic level and foraging habitat over three years in eastern rockhopper penguins Eudyptes chrysocome filholi on sub-Antarctic Campbell Island, New Zealand. Rockhopper penguins are ‘Vulnerable’ to extinction because of widespread and dramatic population declines, perhaps related to nutritional stress caused by a climate-induced shift to a lower trophic level, lower quality diet. We related the stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotope values of blood from 70 chicks, 55 adult females, and 55 adult males to their body masses in the 2010, 2011, and 2012 breeding seasons and examined year, stage, age, and sex differences. Opposite to predictions, heavier males consumed a lower trophic level diet during incubation in 2011, and average chick mass was heavier in 2011 when chicks were fed a more zooplankton-based, pelagic/offshore diet than in 2012. Contrary to the suggested importance of a fish-based diet, our results support the alternative hypothesis that rockhopper penguin populations are likely to be most successful when abundant zooplankton prey are available. We caution that historic shifts to lower trophic level prey should not be assumed to reflect nutritional stress and a cause of population declines.     

Neighboring groups and habitat edges modulate range use in Phayre’s leaf monkeys (<Emphasis Type="Italic">Trachypithecus phayrei crepusculus</Emphasis>)

An animal’s use of space may be strongly influenced by habitat edges and neighboring conspecifics encountered in and around its home range. Habitat edges are known to affect species density and distribution, but their impact on home range use is largely unknown. Additionally, among large animals, interactions with neighbors become particularly important as increasing home range size leads to decreasing exclusivity of resource use, but the effect of neighbors on home range use remains poorly understood. Here, we examine the influence of neighbors and habitat edges on the ranging patterns of three groups of Phayre’s leaf monkeys (Trachypithecus phayrei crepusculus) in northeast Thailand over a period of more than 2 years. The study animals occupied dry evergreen forest, and adjacent patches of dry dipterocarp forest created a habitat edge and formed barriers between some groups. We found that the use of home range interiors was 50–90% higher than the border areas, indicating concentrated use of resources within the home range. The use of peripheral areas was influenced by social organization, the presence of neighboring groups, and forest edges. While one multimale group showed no particular habitat preference, two single-male groups preferred areas bordering dry dipterocarp habitat and avoided areas bordering neighboring groups, suggesting that the threat of neighbors mediated border presence. Additionally, groups may have been attracted to the forest edge, where conspecific competitors are absent and increased sunlight may increase resource abundance and/or quality. This study revealed that the use of border areas can be modulated by neighboring groups and habitat edges, thereby adding to our understanding of home range use among territorial species in heterogeneous habitats.