Niche Partitioning

The food niche relationships of a lizard community of an arid zone in the State of Sonora, NW Mexico, were studied during 1982, 1983 and 1984. The species with highly specialized diets showed little variation in food habits during those years, while the opposite occurred with more eclectic predators. The expected correlation between the size of the predator and the size of its prey can also be biased by food specialization. Food niche overlaps, based on analysis of the volume and the taxonomic status of the prey at a family level, were persistently low. The role that food niche partitioning could play in determining the organization of this lizard guild is discussed.

1. In relatively fertile ecosystems, such as the tallgrass prairie, local species diversity is largely controlled by the competitive effects of community dominants. Despite the relative importance of soil resources in shaping competitive outcomes, we have a limited understanding of the ways by which plants partition below-ground space and resources while competing, and thus, how these interactions feedback to affect local diversity. 2. We experimentally tested whether potential rooting depth affected plant species diversity and composition by seeding 36 tallgrass prairie species into replicated, bare-ground plots in which soil depth was manipulated to produce shallow-(20 cm), medium-(42 cm) and deep-soil treatments all within one soil type. Because root architecture and foraging strategies differ among species, we hypothesized that soil depth alone could affect plant richness, diversity and community composition. 3. After 3 years, richness (S) significantly increased with soil depth (P < 0.0001), but there was no significant change in species diversity (P > 0.1) or composition (multi-response permutation procedure, P > 0.2). The lack of a depth effect upon diversity resulted from the opposing effect of increasing soil depth enhancing S, but decreasing evenness. 4. Species presence among depth treatments was strongly nested, with species found in shallow soils reflecting a subset of the species found in the medium-depth treatment, and the species found within the medium-depth treatment reflecting a subset of those found in the deepest soils. 5. All depth treatments contained the same dominant grasses, thus differences in S resulted from the nested loss of forbs. Conversely, increasing soil depth added sets of new species, but the specific identity of the species present appeared interchangeable among replicates of a given depth. 6. Synthesis. Our results provide the first field-based experimental evidence that altering soil depth alters species occurrence and diversity in predictable ways in seeded tallgrass prairie. Our results have important theoretical implications for understanding the processes promoting plant co-occurrence in grasslands, and generate testable hypotheses concerning the conditions under which root-niche partitioning is probably important for maintaining local richness in grasslands. Future work is needed to elucidate the generality and mechanistic basis of our results.

Obtaining adequate dietary information for many shark and chimaera species has long been a challenge for ecosystem managers, largely due to logistical difficulties in the collection of large sample sizes required for stomach content analyses. Here, we use multivariate analysis of signature fatty acid (FA) profiles as a complementary method to examine the diet composition of 16 demersal shark and chimaera species, collected off south eastern Australia. Comparative results of FA profiles of potential prey and chondrichthyan species mostly agree with the stomach content data. Multivariate analysis correctly classified chimaeras as prominent low-order and benthic consumers, medium-sized dogfish as predators of mid-trophic fish and squid, catsharks as dominant cephalopod consumers, and larger and deeper dwelling dogfish as feeders of bathypelagic fish, squid and feeding on higher order species (cetaceans and seals). Our results demonstrate that signature FA analysis can be applied in dietary studies of sharks and chimaeras to (1) distinguish interspecific differences in general resource (diet and habitat) use patterns; (2) identify degrees of dietary specialisation; and (3) detect niche partitioning of resources by co-occurring species. The FA profiling approach is particularly valuable where sample numbers are likely to be low, such as for these deep-sea and threatened organisms.

3 Departamento de Geología y Paleontología, Instituto Argentino de Nivología, Glaciología, y Ciencias Ambientales, Centro Regional de Investigaciones Científicas y Técnicas, Consejo Nacional de Investigaciones Científicas y Técnicas, Avda. Ruiz Leal s/n, 5500 ...

Species belonging to the same guild (i.e. sharing the same resources) can reduce the negative effects of resource competition through niche partitioning. Coexisting species may differ in their resource exploitation and in the associated allocation of nutrients, depending on their resource niche. Trade-offs in nutrient allocation, such as between reproduction and survival, or between early and late reproduction, are moderated by the abundance and distribution of resources. In this study we investigate differences in larval resource exploitation and adult reproductive strategy of two sympatric aphid parasitoids sharing a common host. The habitat specialist Aphidius rhopalosiphi and the generalist Aphidius avenae occur in cereal crops of Western Europe, where both species attack the major host resource: the grain aphid Sitobion avenae. For this purpose, we measured their acquisition of capital lipid resources, their age-specific fecundity and reproductive effort, their life span and their metabolic rate. We found that these species do not differ neither in larval lipid accumulation nor in the number of eggs at emergence and the timing of egg production, but diverge in other adult reproductive strategies. The rate of adult egg production was higher in A. rhopalosiphi than A. avenae, but at the expense of producing smaller eggs. Throughout adult life, reproductive effort was higher in A. avenae, perhaps facilitated by its higher metabolic rate than A. rhopalosiphi. The divergence between species in life history syndromes likely reflects their adaptations to their resource niche. A high egg production probably allows the specialist A. rhopalosiphi to exploit more S. avenae individuals in cereal crops, while the generalist A. avenae because of its variety of hosts, maximizes the investment per egg but at the expense of a lower lifespan. Our results suggest that differential resource allocation may be a more common pattern that promotes coexistence of species within a guild.

Carnivores have been used as a model to understand the effects of competition in community structure. Behavioral mechanisms that facilitate species coexistence have been poorly explored and may explain the lack of community-wide morphological character displacement in some carnivore assemblages. We use the results of large-scale and intensive camera-trap surveys conducted in the Atlantic Forest of NE Argentina between 2003 and 2008 to describe the spatial patterns of detection and the daily pattern of records of the six wild cat species present in the region (jaguar Panthera onca, puma Puma concolor, ocelot Leopardus pardalis, jaguarundi Puma yagouaroundi, margay Leopardus wiedii, and oncilla Leopardus tigrinus). We use these patterns to generate hypotheses about behavioral differences that may facilitate species coexistence. The larger species were more frequently recorded in the better-protected areas, probably as a result of anthropogenic effects (poaching of cats and their prey). Competitive release from ocelots and jaguarundis may explain why the oncilla and the margay showed the opposite pattern. Morphologically similar species had the most contrasting activity patterns: the margay was exclusively nocturnal and the jaguarundi diurnal. The other species were cathemeral, but alternated their peaks of activity in relation to the relative order of their body weights. The contrasting temporal patterns observed and the ability of pumas and oncillas to adjust their activity patterns to local conditions may facilitate the coexistence of these cat species and explain the lack of character displacement in this assemblage.

Feeding preferences of nectarivorous ants for sugars and amino acids were studied in an Australian tropical rain forest using artificial nectar solutions. Fifty-one ant species were recorded feeding on the solutions. 2. Preferences among carbohydrates were principally concordant between ant species. In paired tests, sucrose was often preferred over fructose, glucose, maltose, melezitose, raffinose and xylose, respectively. Attractiveness of sucrose baits increased with concentration. 3. Many ant species preferred sugar solutions containing mixtures of amino acids over pure sugar solutions. However, preferences among seven pairs of single amino acids in sugar solutions differed substantially between ant species, including several cases where different ant species displayed significant opposite choices. 4. Ant selectivity between solutions was significantly reduced when different ant species co-occurred on the same bait. Preferences for single amino acids were also reduced when colonies fed extensively on the same compound prior to the experiment for 2 days.

Many species of Pseudomonas have the ability to use a variety of resources and habitats, and as a result Pseudomonas are often characterized as having broad fundamental niches. We questioned whether actual habitat use by Pseudomonas species is equally broad. To do this, we sampled extensively to describe the biogeography of Pseudomonas within the human home, which presents a wide variety of habitats for microbes that live in close proximity to humans but are not part of the human flora, and for microbes that are opportunistic pathogens, such as Pseudomonas aeruginosa. From 960 samples taken in 20 homes, we obtained 163 Pseudomonas isolates. The most prevalent based on identification using the SepsiTest BLAST analysis of 16S rRNA (http://www.sepsitest-blast.de) were Pseudomonas monteilii (42 isolates), Pseudomonas plecoglossicida, Pseudomonas fulva, and P. aeruginosa (approximately 25 each). Of these, all but P. fulva differed in recovery rates among evaluated habitat types (drains, soils, water, internal vertebrate sites, vertebrate skin, inanimate surfaces, and garbage/compost) and all four species also differed in recovery rates among subcategories of habitat types (e.g., types of soils or drains). We also found that at both levels of habitat resolution, each of these six most common species (the four above plus Pseudomonas putida and Pseudomonas oryzihabitans) were over- or under-represented in some habitats relative to their contributions to the total Pseudomonas collected across all habitats. This pattern is consistent with niche partitioning. These results suggest that, whereas Pseudomonas are often characterized as generalists with broad fundamental niches, these species in fact have more restricted realized niches. Furthermore, niche partitioning driven by competition among Pseudomonas species may be contributing to the observed variability in habitat use by Pseudomonas in this system.

The picocyanobacterial genus Synechococcus occurs over wide oceanic expanses, having colonized most available niches in the photic zone. Large scale distribution patterns of the different Synechococcus clades (based on 16S rRNA gene markers) suggest the occurrence of two major lifestyles ('opportunists'/'specialists'), corresponding to two distinct broad habitats ('coastal'/'open ocean'). Yet, the genetic basis of niche partitioning is still poorly understood in this ecologically important group.

1. Neoecology and paleoecology both seek to answer the same questions, albeit using different material, at different time scales and with different limitations. Nevertheless, too often, neoecologists neglect paleoecology, and paleoecologists only use neoecology as a baseline for actualism. One reason for this is the lack of tools that can be applied to both fields. 2. This is a review of the contributions to both neoecology and paleoecology of three-dimensional (3D) dental microwear texture analysis (DMTA), a method that can act as a bridge between these fields. 3. DMTA studies can be grouped according to the type of ecological questions researchers seek to answer: specific ecology, intra-specific ecology, niche partitioning and dietary overlap, and ecology over time. The first question has been the main focus of research; the other three were only superficially studied. 4. In this review, selected examples will be presented to demonstrate that DMTA, as one of the few tools that can be applied to both modern and fossil samples, has been used to address key ecological questions in mammalian neoecology and paleoecology. 5. With the wide range of neoecological and paleoecological questions that DMTA can answer, it is clear that this methodology will be used increasingly in the future, possibly in combination with other ecological proxies.

Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA. We collected individuals at five ponds throughout summer 2005, weighed them in the field, and calculated wing loading (N·m -2 ) and wing aspect ratios from digital photographs. We measured the perch-height preferences of these species in 'low perch' (10, 20, 30, and 40 cm) and 'high perch' (20, 40, 60 and 80 cm) experiments. Flywheel anemometers recorded wind speeds at each perch height. Species differed significantly in mean body mass, spanning nearly an order of magnitude from Perithemis tenera (67 mg) to Libellula vibrans (633 mg). There were also significant differences in wing morphology that correlated with mean mass; larger species had greater wing loadings and greater wing aspect ratios that smaller species. Species also differed significantly in their perch-height preferences in both experiments, in a manner correlating with body mass and hindwing aspect ratios. Erythemis simplicicollis and P. tenera preferred short perches, Celithemis fasciata, Pachydiplax longipennis and Plathemis lydia used perches of intermediate height, and Libellula auripennis, L. cyanea, L. incesta, L. luctuosa, and L. vibrans preferred the tallest perches. Because mean wind speed and maximum wind speed also increased with perch height, larger species may prefer taller perches to experience greater wind speed and generate more compensatory lift to offset their larger wing loadings. However, it is also possible that correlations between body mass and perch height are the result of large species competitively restricting smaller species to lower perches.

To elucidate whether dipterocarp species, dominant late-successional species of tropical forests in Southeast Asia, actually have a disadvantage when planted on open site in terms of their photosynthetic characteristics, we investigated photosynthesis in dipterocarp seedlings planted in the open on degraded sandy soils in southern Thailand. These species were compared with seedlings of Acacia mangium Willd., a fast-growing tropical leguminous tree, which is often planted on degraded open site in Southeast Asia. The dipterocarp seedlings had an irradiance-saturated net photosynthetic rate (P N ), stomatal conductance (g s ), carboxylation efficiency, and photosynthetic capacity comparable to or superior to those of A. mangium. In particular, seedlings of Dipterocarpus obtusifolius Teijsm. ex Miq. showed an irradiance-saturated P N of 21 µmol m -2 s -1 , a value higher than any previously reported for a dipterocarp species, accompanied by high g s (0.7 mol m -2 s -1 ) and high photosynthetic capacity. Thus dipterocarp species do not necessarily have a disadvantage in terms of their photosynthetic characteristics on open sites with degraded sandy soils. Abbrevations: C i -internal CO 2 concentration; Chl -chlorophyll; g s -stomatal conductance; P N -net photosynthetic rate; PPFDphotosynthetic photon flux density; PS2 -photosystem 2; R D -dark respiration rate.

The paleodietary ecology of Late Pleistocene ungulate faunas of the Mammoth Steppe ecosystem was investigated at Fairbanks (Alaska) and Brown Bank (North Sea) through dental mesowear and microwear analysis. The purpose of the study is to address questions concerning the paleoecology of the Mammoth Steppe, an ecosystem that has no extant analog. Dental wear patterns indicate that the niche partitioning at Brown Bank (BB) region was consistent with ecosystem dynamics found in diverse ungulate faunas in recent time. In contrast, despite the lower numbers of extinct taxa, the Fairbanks (FB) fauna is ecologically bizarre. In general, the microwear of this fauna includes excessive numbers of very (narrow) fine scratches that are atypical for extant mixed feeders and grazers. Moreover, the mesowear signal suggests unusual paleodiets (niche dynamics), where low-crowned mixed-feeding cervids, Rangifer and Cervus, adopted diets that are similar to Equus in terms of mesowear (abrasion) and much more abrasive than the diets of either Bison or Ovis. We suggest that the anomalies may relate to unique, possibly disharmonious, ecosystem dynamics during the Pleistocene-Holocene transition. In addition to these findings, it was discovered (found) that dental wear patterns, particularly microwear variables such as scratch frequency and scratch width are strongly affected by geographic region, irrespective of species-specific dietary preferences.

Many species of Pseudomonas have the ability to use a variety of resources and habitats, and as a result Pseudomonas are often characterized as having broad fundamental niches. We questioned whether actual habitat use by Pseudomonas species is equally broad. To do this, we sampled extensively to describe the biogeography of Pseudomonas within the human home, which presents a wide variety of habitats for microbes that live in close proximity to humans but are not part of the human flora, and for microbes that are opportunistic pathogens, such as Pseudomonas aeruginosa. From 960 samples taken in 20 homes, we obtained 163 Pseudomonas isolates. The most prevalent based on identification using the SepsiTest BLAST analysis of 16S rRNA (http://www.sepsitest-blast.de) were Pseudomonas monteilii (42 isolates), Pseudomonas plecoglossicida, Pseudomonas fulva, and P. aeruginosa (approximately 25 each). Of these, all but P. fulva differed in recovery rates among evaluated habitat types (drains, soils, water, internal vertebrate sites, vertebrate skin, inanimate surfaces, and garbage/compost) and all four species also differed in recovery rates among subcategories of habitat types (e.g., types of soils or drains). We also found that at both levels of habitat resolution, each of these six most common species (the four above plus Pseudomonas putida and Pseudomonas oryzihabitans) were over-or underrepresented in some habitats relative to their contributions to the total Pseudomonas collected across all habitats. This pattern is consistent with niche partitioning. These results suggest that, whereas Pseudomonas are often characterized as generalists with broad fundamental niches, these species in fact have more restricted realized niches. Furthermore, niche partitioning driven by competition among Pseudomonas species may be contributing to the observed variability in habitat use by Pseudomonas in this system.

Geographical areas historically characterized by a lower risk of diurnal avian predation should in theory allow bats to be active in daytime too, especially to forage. Oceanic islands are ideal for studying temporal niche shifts in bats since they often feature depauperate avian assemblages with fewer birds of prey. We report on the second case of diurnal activity known for an insular insectivorous bat, Hipposideros ruber on the island of São Tomé (Gulf of Guinea). We present observations of daylight flights made at several sites on the island in six months (from July to November and in January). We also carried out daytime (09h00–16h00) emergence counts at three roosts. In this time interval, bats were continuously active, although activity rates changed: bats tended to return to roosts in early afternoon and, at two sites, to decrease emergence rate under intense light probably to reduce the risk of hyperthermia. At one roost, we observed that heavy rain caused abrupt daytime returns of large numbers of bats. In daytime bats did forage and kept echolocating. Social interactions (chases) were also frequently observed. In daytime adult males were significantly more frequent than females, while the opposite was noticed at night, an intersexual segregation possibly leading to temporal niche partitioning.

The trophic niche characteristics of an amphibian assemblage were studied at a pond locality in Canale Monterano, province of roma, Central Italy. The assemblage consisted of six species, four anurans (Bufo bufo, Hyla intermedia, rana dalmatina, Pelophylax skl. esculentus), and two salamanders (triturus carnifex, triturus vulgaris). Food contents were obtained by stomach flushing. Stomach vacuity index varied substantially among species, and the species spending longer timespan within the reproductive site were also those with lower vacuity index values. Correspondence analysis discriminated two groups of species: one feeding mainly on terrestrial prey and the other on aquatic prey. Pseudo-community analysis revealed that the terrestrial guild of species was non-randomly structured when analysed by rA2 algorithm for volume of prey but neither for number of prey, nor for both number and volume of prey analysed by rA3. The aquatic subset of species appeared to be randomly assembled according to both rA2 and rA3 algorithms, either for number or for volume of prey. These results indicate that for terrestrial species, micro-habitat resource partitioning and body size discrepancy among species could be the factors influencing dietary patterns and facilitating species coexistence, whereas for aquatic species the observed high overlap in diet spectrum is mainly due to both generalist feeding habits of newts and the superabundance of food resources occurring at the study pond.

Data on 220 sampling units from the Lower Cambrian section of the Siberian Platform (78), Mongolia (74), and some other regions (68) yielded qualitative and quantitative information on reef faunal composition and facies. This data set served to find out the diversity components of the Early Cambrian radiation within reefal communities. Additionally, dynamics of the development of faunal regions and of total archaeocyathan species diversity were computed. The plotting of all these data sets indicated that the Early Cambrian global species diversity was mostly the factor of two variables. Those variables were beta and gamma diversity, expressing taxonomic differentiation between communities and the overall taxonomic differentiation between geographic regions, respectively. Alpha diversity showing the richness of taxa within a single community was significant during short episodes of the very initiation of Cambrian reef-building and of recovery that followed mass extinctions. Thus, specialisation, which was the function of restriction of species to peculiar communities, and degree of endemicity were the principal factors of taxonomic diversity in the earliest Phanerozoic reefal palaeocommunities, while the significance of niche partitioning was restricted to peculiar intervals. Endemicity itself was the factor of both geographic isolation and community differentiation leading to ecological specialisation. The early evolution of Phanerozoic reefal communities was expansive and not intense.

The introduced and highly toxic cane toad (Bufo marinus) is rapidly spreading across northern Australia where it may affect populations of large terrestrial vertebrate predators. The ecological impact of cane toads will depend upon the diets, foraging modes and habitat use of native predators, and their feeding responses to cane toads. However, intraspecific niche partitioning may influence the degree of vulnerability of predators to toxic prey, as well as the time course of the impact of alien invaders on native species. We studied the diet of the northern death adder Acanthophis praelongus and their feeding responses to cane toads. In the laboratory, death adders from all size classes and sexes readily consumed frogs and cane toads. Diets of free ranging A. praelongus from the Adelaide River floodplain were more heterogeneous. Juvenile snakes ate mainly frogs (39% of prey items) and small scincid lizards (43%). Both sexes displayed an ontogenetic dietary shift from lizards to mammals, but adult males fed on frogs (49%) and mammals (39%) whereas adult females (which grew larger than males) fed mainly on mammals (91%) and occasionally, frogs (9%). Feeding rates and body condition of adult snakes varied temporally and tracked fluctuations in prey availability. These results suggest that cane toads may negatively affect populations of northern death adders in the Darwin region. However, we predict that different size and sex classes of A. praelongus will experience differential mortality rates over different timescales. The initial invasion of large toads may affect adult males, but juveniles may be unaffected until juvenile toads appear the following year, and major affects on adult female death adders may be delayed until annual rainfall fluctuations reduce the availability of alternative (rodent) prey.

The food niche relationships of a lizard community of an arid zone in the State of Sonora, NW Mexico, were studied during 1982, 1983 and 1984. The species with highly specialized diets showed little variation in food habits during those years, while the opposite occurred with more eclectic predators. The expected correlation between the size of the predator and the size of its prey can also be biased by food specialization. Food niche overlaps, based on analysis of the volume and the taxonomic status of the prey at a family level, were persistently low. The role that food niche partitioning could play in determining the organization of this lizard guild is discussed.

Ephemeral pools are widespread in (semi-)arid regions, where they form unique, mostly isolated habitats in an otherwise dry landscape matrix. They are characterized by extremely variable conditions, the most important stress factors being (1) frequent and fast desiccation and rehydration, (2) long dry seasons, (3) intensive solar irradiation and high temperatures during the dry season, (4) large diurnal oscillations of O 2 and CO 2 concentration and pH in the pool water, (5) extreme nutrient shortage, especially nitrogen. One functional plant type being highly adapted to these stressful conditions are aquatic resurrection plants, i. e. poikilohydric cormophytes like Chamaegigas intrepidus (Scrophulariaceae). This species grows endemically in ephemeral rock pools on granite outcrops in Central Namibia. Ch. intrepidus shows a number of anatomical, biochemical and physiological adaptations to the complex of extreme habitat conditions such as contractive xylem, velamen radicum, accumulation of abscisic acid, dehydrins and carbohydrates during desiccation. Nitrogen deficiency is partly avoided by acquisition of amino acids and an efficient utilisation of urea. Chamaegigas populations on single inselbergs are genetically very highly isolated, whereas gene flow between sub-populations from different pools on one inselberg is rather high. In accordance with the predominantly outcrossing breeding behaviour, most genetic diversity is found within a pool. A habitat model showed clear niche partitioning between Ch. intrepidus and the less desiccationtolerant species Limosella grandiflora with respect to depth of the pools. The specific constitutive dehydration tolerance mechanisms displayed by Ch. intrepidus are discussed as a vital adaptation to the low predictability of the occurrence and duration of periods favourable for growth and reproduction.

The paleodietary ecology of Late Pleistocene ungulate faunas of the Mammoth Steppe ecosystem was investigated at Fairbanks (Alaska) and Brown Bank (North Sea) through dental mesowear and microwear analysis. The purpose of the study is to address questions concerning the paleoecology of the Mammoth Steppe, an ecosystem that has no extant analog. Dental wear patterns indicate that the niche partitioning at Brown Bank (BB) region was consistent with ecosystem dynamics found in diverse ungulate faunas in recent time. In contrast, despite the lower numbers of extinct taxa, the Fairbanks (FB) fauna is ecologically bizarre. In general, the microwear of this fauna includes excessive numbers of very (narrow) fine scratches that are
atypical for extant mixed feeders and grazers. Moreover, the mesowear signal suggests unusual paleodiets (niche dynamics), where low-crowned mixed-feeding cervids, Rangifer and Cervus, adopted diets that are
similar to Equus in terms of mesowear (abrasion) and much more abrasive than the diets of either Bison or Ovis. We suggest that the anomalies may relate to unique, possibly disharmonious, ecosystem dynamics
during the Pleistocene–Holocene transition. In addition to these findings, it was discovered (found) that dental wear patterns, particularly microwear variables such as scratch frequency and scratch width are strongly affected by geographic region, irrespective of species-specific dietary preferences.

The Common Five-Lined Skink (Plestiodon fasciatus), Southeastern Five-Lined Skink (P. inexpectatus), and Broadheaded Skink (P. laticeps) are all found in forested ecosystems of the southeastern United States and occur in apparent sympatry. No aspect of their ecology has been quantitatively shown to be different. Differences in their natural history, such as northern extent of geographic range, observations of differences in habitat preference, and differing physiological responses to temperature, implicate the thermal environment as a potential niche dimension by which these organisms partition resources.

Competition often occurs between sympatric species that exploit similar ecological niches. Among canids, competition may be reduced by partitioning resources such as food, time, and habitat, but the mechanisms of coexistence remain poorly understood, particularly among fox species. We described the food habits of two foxes that live sympatrically across northern and central Asia, the corsac fox (Vulpes corsac) and red fox (V. vulpes), by analyzing scats collected during a field study in Mongolia. We analyzed 829 corsac and 995 red fox scats collected from April 2005 to August 2007 and tested the extent to which food partitioning occurred. The diets of both species consisted mainly of insects followed by rodents, but also included birds, reptiles, large mammal remains (carrion), plant material (including fruits and seeds), and garbage. Despite high overlap in the proportion of food items consumed, differences existed between species in overall diet with corsacs more frequently consuming beetles, but proportionally fewer crickets and large mammal remains than red foxes. We detected interspecific differences during the pup rearing and dispersal seasons, when prey was abundant, but not during the breeding season, when prey was scarce and diet overlap highest. Each species' diet also differed seasonally and exhibited moderate overall breadth. Corsacs consumed proportionally more beetles and rodents during pup rearing and crickets during dispersal relative to other seasons, whereas red foxes consumed proportionally more crickets during pup rearing and dispersal and more rodents and large mammals during pup rearing and breeding relative to other seasons. Our results suggest that partitioning of food resources during most of the year facilitates coexistence, and that the potential for competition is highest during winter months.

For most organisms, patterns of natural enemy-mediated mortality change over the course of development. Shifts in enemy pressure are particularly relevant for organisms that exhibit exponential growth during development, such as juvenile insects that increase their mass by several orders of magnitude. As one of the dominant groups of insect herbivores in most terrestrial plant communities, larval lepidopterans (caterpillars) are host to a diverse array of parasitoids. Previous research has described how the frequency of herbivore parasitism varies among host plants or habitats, but much less is known about how parasitism pressure changes during host development. To test whether the two major parasitoid taxa, wasps and flies, differentially attack shared hosts based on host developmental stage, we simultaneously exposed early-and late-instar Euclea delphinii Boisduval (Lepidoptera: Limacodidae) caterpillars to parasitism in the field. We found strong evidence that parasitoids partition hosts by size; adult female wasps preferentially parasitized small caterpillars, whereas adult female flies preferred to attack large caterpillars. Our results demonstrate that host ontogeny is a major determinant of parasitoid host selection. Documenting how shifts in enemy pressure vary with development is important to understanding both the population biology and evolutionary ecology of prey species and their enemies.

The paleodietary ecology of Late Pleistocene ungulate faunas of the Mammoth Steppe ecosystem was investigated at Fairbanks (Alaska) and Brown Bank (North Sea) through dental mesowear and microwear analysis. The purpose of the study is to address questions concerning the paleoecology of the Mammoth Steppe, an ecosystem that has no extant analog. Dental wear patterns indicate that the niche partitioning at Brown Bank (BB) region was consistent with ecosystem dynamics found in diverse ungulate faunas in recent time. In contrast, despite the lower numbers of extinct taxa, the Fairbanks (FB) fauna is ecologically bizarre. In general, the microwear of this fauna includes excessive numbers of very (narrow) fine scratches that are atypical for extant mixed feeders and grazers. Moreover, the mesowear signal suggests unusual paleodiets (niche dynamics), where low-crowned mixed-feeding cervids, Rangifer and Cervus, adopted diets that are similar to Equus in terms of mesowear (abrasion) and much more abrasive than the diets of either Bison or Ovis. We suggest that the anomalies may relate to unique, possibly disharmonious, ecosystem dynamics during the Pleistocene-Holocene transition. In addition to these findings, it was discovered (found) that dental wear patterns, particularly microwear variables such as scratch frequency and scratch width are strongly affected by geographic region, irrespective of species-specific dietary preferences.

Reef-building corals are fundamental to the most diverse marine ecosystems, yet a detailed understanding of the processes involved in the establishment, persistence and ecology of the coral-dinoflagellate association remains largely unknown. This study explores symbiont diversity in relation to habitat by employing a broad-scale sampling regime using ITS2 and denaturing gradient gel electrophoresis. Samples from Pocillopora damicornis, Stylophora pistillata and Seriatopora hystrix all harboured host-specific clade C symbiont types at Heron Island (Great Barrier Reef, Australia). While Ser. hystrix associated with a single symbiont profile along its entire depth distribution, both P. damicornis and Sty. pistillata associated with multiple symbiont profiles that showed a strong zonation with depth. It is shown that, with an increased sampling effort, previously identified &#x27;rare&#x27; symbiont types within this group of host species are in fact environmental specialists. A multiva...

When habitats are declining, niche segregation by demographic groups, such as the two sexes, can have a profound impact on the extinction risk of a species as a whole. Thus, differences in the requirements of demographic groups are of importance in conservation. We combined behavioural and genetic data to investigate whether the sexually segregated parti-colored bat (Vespertilio murinus) exhibits sex-specific niche partitioning. We use our data to evaluate implications for conservation of this potentially vulnerable species in Switzerland, the western boundary of its range. Using radio-telemetry, we found sex-specific differences in habitat use. Foraging females strongly relied on lakes while foraging males displayed more flexibility in their habitat use. Moreover, males covered significantly larger foraging areas than females. Sequencing 341 base pairs of the mitochondrial D-loop of 247 individuals revealed sex-specific differences in the genetic structure of colonies, but no such difference was observed for three nuclear micro-satellite markers. We found high mtDNA diversity in two Swiss male colonies and one German female colony, but low mtDNA diversity in two Swiss female colonies. Our genetic data suggest that considerable gene flow occurs via male dispersal and mating. At the same time immigration of females into the existing female colonies in Switzerland is rare compared to the immigration of new males into male colonies. Since we found the sexes in Vespertilio murinus to differ markedly in their ecology, population genetics, and behaviour, we conclude that sex-specific conservation plans are required to protect this species efficiently.

The wet tropical forests in Madagascar have endemic dung beetles that have radiated for tens of millions of years using a limited range of resources produced by the species-poor mammalian fauna. Beetles were trapped in two wet-forest localities over 4 years (6407 trap nights, 18,869 individuals). More limited data for six other local communities were used to check the generality of the results. Local communities are relatively species poor (around 30 species) in comparison with wet-forest-inhabiting dung beetle communities elsewhere in the tropics (typically 50 or more species). The species belong to only two tribes, Canthonini and Helictopleurina (Oniticellini), which have evolved, exceptionally for dung beetle tribes, completely nocturnal versus diurnal diel activities, respectively. Patterns in the elevational occurrence, body size and resource use suggest that interspecific competition restricts the numbers of locally coexisting species exploiting the limited range of resources that are available. On the other hand, regional turnover in the species composition is exceptionally high due to a large number of species with small geographical ranges, yielding a very large total fauna of dung beetles in Madagascar (>250 species). Apart from exceptionally low local (alpha) diversity and high beta diversity, the Malagasy dung beetle communities are ecologically distinctive from comparable communities in other tropical regions in having high numerical dominance of the most abundant species, small average body size and low degree of resource specialization.

It has been hypothesized that niche partitioning of the light resource by tree seedlings helps maintain species diversity in tropical forests. This paper describes a study where three co-occurring Entandrophragma spp. were grown under simulated light environments to test for a shift in species rank that would support the niche partitioning hypothesis. The species described represent some of the highest value and most heavily exploited timber species in central Africa and data on seedling light requirements has direct application to silviculture. Results showed that Entandrophragma cylindricum and E. utile performed as well as E. angolense under conditions simulating the light environment of small forest gaps. E. angolense out-performed congeners under intermediate light conditions and all three species performed poorly under full sunlight. The results provide some support for the niche partitioning hypothesis but additional studies that include understory light conditions are necessary. The growth performance results of E. utile under low light are particularly important given its extremely poor performance under a variety of fertility-moisture combinations in recent studies. These results suggest that the best way to favor recruitment of Entandrophragma spp. seedlings in natural forest would be through a series of small to intermediate sized gaps.

Most attempts to identify the processes that structure natural communities have focused on conspicuous macroorganisms whereas the processes responsible for structuring microbial communities remain relatively unknown. Two main theories explaining these processes have emerged; niche theory, which highlights the importance of deterministic processes, and neutral theory, which focuses on stochastic processes. We examined whether neutral or niche-based mechanisms best explain the composition and structure of communities of a functionally important soil microbe, the arbuscular mycorrhizal (AM) fungi. Using molecular techniques, we surveyed AM fungi from 425 individual plants of 28 plant species along a soil pH gradient. There was evidence that both niche and neutral processes structured this community. Species abundances fitted the zerosum multinomial distribution and there was evidence of dispersal limitation, both indicators of neutral processes. However, we found stronger support that niche differentiation based on abiotic soil factors, primarily pH, was structuring the AM fungal community. Host plant species affected AM fungal community composition negligibly compared to soil pH. We conclude that although niche partitioning was the primary mechanism regulating the composition and diversity of natural AM fungal communities, these communities are also influenced by stochastic-neutral processes. This study represents one of the most comprehensive investigations of community-level processes acting on soil microbes; revealing a community that although influenced by stochastic processes, still responded in a predictable manner to a major abiotic niche axis, soil pH. The strong response to environmental factors of this community highlights the susceptibility of soil microbes to environmental change.

Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at o 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation.

Niche partitioning has been examined in breeding bird communities and in winter quarters, but has received less attention when comparing a resident breeder and migrants during spring. Here, such an assemblage of species of the same genus (Oenanthe) and guild were analysed on the Mediterranean island of Cyprus. Northern Wheatear O. oenanthe and Eastern Black-Eared Wheatear O. hispanica melanoleuca were migrants, while Cyprus Wheatear O. cypriaca was resident. Migrant wheatears were more common in open habitats without trees, with a lower proportion of vegetation in the 10 cm layer, less tree and bush cover, a higher proportion of herbaceous layer, and a higher amount of bare areas. By using a discriminant function, we found that O. oenanthe was least tolerant towards a high proportion of bush/tree cover, and O. cypriaca was most tolerant, with O. h. melanoleuca in between. Also, O. oenanthe tolerated the least proportion of vegetation in the lowest layer, and O. h. melanoleuca the highest. O. oenanthe hunted more often by hop-and-peck and O. cypriaca more often used sallying and perch-and-pounce. O. oenanthe was the most ground-dwelling species with low perch heights and highest number of hops per minute and hops per movement, while O. cypriaca was the most arboreal species with the highest perches. Mean foraging rate did not differ between the species. A principal component analysis followed by a discriminant function showed that O. cypriaca has a high amount of aerial sallying and perch-pounce hunting behaviour with fewer hops, while O. oenanthe represents the contrary with hop-and-peck movements on the ground and with fewer flights. The data further indicate a clearer separation between O. oenanthe and O. cypriaca while O. h. melanoleuca lies in between utilising both foraging modes.

The coexistence of multiple species of short-tailed fruit bats (Phyllostomidae: Carollia) is common throughout the range of the genus. Previous studies of fecal and stomach contents have documented differences in dietary breadth and in habitat use as mechanisms by which these species may partition dietary niches. By comparing values of d15N and d13C across species of Carollia from 17 sites in Central and South America, we show that co-occurring Carollia frequently differ in dietary breadth, foraging habitats, and level of insectivory. Values of d15N, which tended to be enriched in C. castanea, depleted in C. perspicillata, and intermediate in C. brevicauda and C. sowelli, indicate trophic stratification. Values of d13C followed the opposite trend, tending to be enriched in C. perspicillata and depleted in C. castanea, suggesting interspecific differences in breadth of the foraging area. Isotopic comparisons among Carollia, other bat species, and potential food items at 5 of our sites illustrate that populations of Carollia tend to be trophically intermediate between strictly phytophagous and strictly insectivorous organisms, and, contrary to the paucity of insect remains found in fecal samples, indicate that the consumption of insects by Carollia is more common and potentially more important than previously was thought.

1 A height-light trajectory (HLT, a fitted curve relating canopy exposure to tree height) was determined for populations of individuals of each of 47 tree species in a Liberian lowland rainforest. The HLTs were compared and related to tree allometry and adult stature. Crown exposure was measured for 7460 trees and related to tree height using a multinomial regression analysis. Individual trees were followed for 2.8-9.8 years.

The Australo-Papuan Meliphaga honeyeaters have diversiWed over a wide range of habitats and elevational zones and are one of the few regionally known cryptic avian radiations. Using a combined 1580 bp of mitochondrial and nuclear DNA we investigate the species limits, systematic aYnities and biogeographic history of Meliphaga. We also investigate the role of spatial sorting mechanisms, including altitudinal replacement and niche partitioning, as mechanisms underlying the adaptive radiation of this group. Phylogenetic analysis indicates that the genus Meliphaga comprises at least 16 species, three more than recognized in current classiWcations. The genus divides into two clades; the species-poor lewinii group, and the larger analoga group that has diversiWed into a wider range of vertical, vegetational and elevational niches. The basal division of each clade into an Australian and New Guinean assemblage was likely induced by the formation of the Arafura Sea during the early Pliocene (»4 MYA) with a single reinvasion of Australia by the open forest species M. gracilis during the early Pleistocene (1.2-1.5 MYA) via intermittent land bridges or island hopping. Most recent sister species were found to replace each other geographically within the same ecological and elevational zone conforming to the classical allopatric mode of speciation. In contrast, M. orientalis (650-1950 m) and M. analoga (0-1100 m) were found to replace each other altitudinally across ecological zones providing empirical support for altitudinal speciation as a mechanism of diversiWcation in a montane avifauna. We Wnd no evidence of sympatric speciation (co-existing sister lineages) and suggest that spatial segregation within the habitat (niche partitioning) is primarily a mechanism enabling more divergent species to coexist.

Differentiation of species distributions along environmental gradients and phenotypic specialization help explain the co-presence of 17 oak species that might otherwise be expected to competitively exclude one another. In an effort to understand the role of niche differentiation in the co-presence of these congeneric species in north-central Florida, we examined the community structure of oak-dominated forests in this region in relation to environmental variables and a suite of life history and physiological traits. Landscape distribution patterns of oaks and other woody species were determined from randomly established plots in three state parks. Soil moisture, nutrient availability, and fire regime were found to be critical factors influencing community structure, and the distribution of oak species was strongly correlated with these gradients. Detrended correspondence analysis of species' distributions supported the grouping of oak species into three major community types: (1) hammock, (2) sandhill, and scrub. Principal components of multiple traits also supported differentiation of oak species into these three groups.

The distribution and spatial pattern of plants in tropical forests have important implications for how species interact with each other and their environments. In this article we use a large-scale permanent census plot to address if the coexistence of 16 co-occurring species of Myristicaceae is aided by topographic and light gradient niche partitioning. We used a second order spatial pattern analysis based on Ripley's K function to describe species' distributions and associations among species, and a torus translation procedure to test for associations with three topographically defined habitats. A majority of species displayed spatial aggregation and over half had one or more significant habitat associations. Four species were associated with the ridge habitat, four species with slope habitat, and two with valley habitat. Seven other species showed no habitat association. Within each habitat group, species exhibited a variety of distributions in relation to light availability. However, habitat associations were largely unexplained by differential rates of mortality, growth or recruitment over a 5-year interval. We conclude that although in principle partitioning of the topographic and light environments may double or treble the number of species able to coexist, there is no evidence that partitioning of physical habitats can explain the coexistence of all 16 of these closely related species.

Patterns of community structure in the marine environment are strongly influenced by population relationships to biotic and physical gradients. The aim of this work is to explore the relationships of tropical rocky reef fish assemblages to wave exposure and benthic coverage in a gradient of distance from the coast. The study was conducted on the Guarapari Islands, southeastern Brazilian coast. Fish were sampled by underwater visual census (166 transects) and benthic cover was estimated with quadrats (223 replicates). Two main kinds of habitats were found to be derived from the close interrelation between exposure and benthic coverage: (1) exposed areas subjected to major hydrodynamic forcing, and (2) sheltered or moderately exposed areas. The first group is associated with mid-water schooling species like planktivorous labrids and Chromis, piscivorous Caranx, as well as gregarious omnivores like Abudefduf and Diplodus. In terms of benthic composition, macroalgae and encrusting calcareous algae prevail in this highenergy habitat. The second group is characterized by site-attached and reef associated species like territorial pomacentrids, invertebrate feeders such as Halichoeres poeyi and Chaetodon striatus, and small cryptobenthic fishes (e.g. blenniids and labrisomids). Turf algae, zoanthids and massive corals dominate this environment. Environmental plasticity is also common with some genera showing high abundances in all habitats (e.g. Holocentrus, Haemulon, Acanthurus). Examples of the coupling of food availability and fish abundance were found. Planktivores, territorial herbivores, macroalgae browsers and spongivores were positively related with the abundance of their preferred food items along the exposure gradient. Within-family analyses of Pomacentridae and Labridae showed that niche partitioning is likely occurring and seems to be mediated by swimming 'ability' and associated feeding performance.

A large data set of over 4,700 records of avian mercury (Hg) levels in northeastern North America was compiled and evaluated. As Hg emissions remain poorly regulated in the United States and Canada, atmospheric deposition patterns and associated ecological responses continue to elicit interest by landscape managers, conservation biologists, policy makers, and the general public. How avian Hg exposure is interpreted greatly influences decision-making practices. The geographic extent and size of this data set is valuable in understanding the factors that affect the exposure of Hg to birds. Featured are differences found among tissues, major aquatic habitats and geographic areas, between age class and gender, and among species. While Hg concentrations in egg and blood reflect short-term Hg exposure, Hg concentrations in liver and feather provide insight into long-term Hg exposure. Blood is a particularly important matrix for relating site-specific exposure to methylmercury (MeHg). The level of MeHg is generally 5-10x greater in adults compared to nestlings. Age also influences MeHg bioaccumulation, particularly for individuals where MeHg intake exceeds elimination. Gender is of interpretive concern when evaluating Hg exposure for species exhibiting sexual dimorphism and niche partitioning. Based on two indicator species, the belted kingfisher (Ceryle alcyon) and bald eagle (Haliaeetus leucocephalus), we found MeHg availability increased from marine, to estuarine and riverine systems, and was greatest in lake habitats. A large sample of >1,800 blood and egg Hg levels from the common loon (Gavia immer) facilitated a suitable comparison of geographic differences. Although some clusters of highly elevated Hg exposure (i.e., blood levels >3.0 lg/g, ww and egg levels >1.3 lg/g, ww) were associated with hydrological and biogeochemical factors known to increase MeHg production and availability, others were not. Geographic areas without a relationship between Hg exposure and biogeochemical processes were associated with emission or waterborne point sources. Differences in Hg exposure among species are primarily correlated with trophic position and availability of MeHg. Although piscivorous species were repeatedly shown to have some of the highest MeHg levels of the 38 species analyzed, insectivorous birds in both aquatic and terrestrial habitats (such as montane areas) were also found with elevated MeHg levels. A better understanding of the factors confounding interpretation of Hg exposure provides an effective basis for choice of indicator species and tissues according to 12 selected scenarios. This and the national need for spatiotemporal monitoring of MeHg availability require careful consideration of indicator species choice. Only then will local, regional, continental, and even global monitoring efforts be effective.

The discovery of genetically distinct Erysiphe necator groups (A or B), with high phenotypic similarities, raises important questions about their coexistence. For plant pathogens, niche partitioning, allowing the coexistence on the same host (i.e. the same resource), might result from separation in space and/or time. We used a landscape genetic approach to study the geographic distribution of genetic groups of E. necator (distinguished by a SNP in the β-tubulin gene) at the spatial scale of the Languedoc-Roussillon region (southern France) and to assess the temporal succession of groups along the course of the 2007 epidemic. Spatial distribution revealed a high heterogeneity between vineyards: from 100% B to 100% A, with 62% and 38% of vineyards showing a majority of A and B isolates, respectively. Temporal isolation seems to be the major mechanism in the coexistence of the two genetic groups: all isolates collected towards the end of the epidemic belonged to group B, whatever the initial frequency of genetic groups. Our results confirm that both A or B isolates can lead to flag-shoot symptoms, and showed that group A isolates tend to disappear during the course of the epidemic, whereas group B isolates may be active during the entire epidemic and involved in further production of cleistothecia, when recombination takes place. For the first time, the relationship between the frequency of genetic groups and disease levels on leaves and clusters at the end of the epidemic was evaluated. We showed a strong relationship between the disease severity and the genetic composition of E. necator populations: the damage was more important when the epidemic was initiated by B isolates.

In bird migration systems, the question of coexistence and competition of migrants with residents in the nonbreeding season and their role in shaping the evolution of present avian communities is much debated. However, conclusions are often drawn in a speculative way. In the Palearctic-African bird migration system, many studies have addressed the question of coexistence of Palearctic breeding birds with Afrotropical species in the former's wintering grounds. These studies have led to some generalizations concerning habitat selection and foraging ecology about the traits that might enable migrants to coexist with residents. Migrants were therefore assumed to forage in more open habitats, in more peripheral parts of the vegetation and with a higher foraging speed than residents. Furthermore, they were also assumed to be more flexible in foraging behavior by using a wider range of foraging tactics, but some studies revealed contradicting results. We studied the ecology of Palearctic migrants in Comoé National Park, Ivory Coast, West Africa, during three successive winters to explore the factors of niche partitioning between migrants and residents and to test the hypothesis of whether there are common behavioral traits in migrants. Therefore, we compared the ecology of two Palearctic breeding species: pied flycatcher, Ficedula hypoleuca, and willow warbler, Phylloscopus trochilus, with resident members of the respective guilds. With respect to use of microhabitat, foraging speed, and intake rates, we could not confirm the above-mentioned generalizations, showing that care has to be taken into account when drawing conclusions from few studies for a whole migration system on a huge continent. However, both migrating species were more flexible in foraging behavior than were their Afrotropical counterparts. As there are hints that this is also the case when migrants are compared with residents on their breeding grounds, we suggest that this flexibility enables migrants to partition resources with residents and, therefore, coexist with Afrotropical species. We discuss, however, whether this flexibility is an adaptation to migratory behavior or a prerequisite for the evolution of migration. The role that competition plays in present communities cannot be solved with a few observational studies because of the following problems. First, it is difficult to detect competition in the field. Second, there are constraints of performing field experiments that have not previously been performed in Africa, and third, there are several possible hypothetical scenarios about the role of competition in shaping present communities, including factors that might have been important in the past and are therefore impossible to detect at present.