Measure Of Niche Breadth Research Articles

Ecología trófica de Brycon henni (Pisces: Bryconidae) en afluentes de los Ríos Nare y Guatapé, cuenca del río Magdalena, Colombia

Understanding the trophic ecology of fish and how they use resources in space and time is important to support conservation and management actions. The trophic ecology of Brycon henni in the Nare and Guatapé rivers, Magdalena river basin, Colombia was determined. Five field samplings were carried out between October 2007 and January 2010, in rainy, dry, and dry-to-rainy transition periods. Stomachs of 262 specimens were collected. A Kruskall-Wallis analysis and a Mann-Whitney pairwise comparison test was performed to detect differences in the alimentary importance index of each food category between sex, size class, hydrological period and basins (Nare vs Guatapé). The Levin’s Measure of Niche Breadth and the Morisita’s Diet Overlapping Index were calculated to establish differences between size class in the different hydrological periods. Vegetable material was the most important food item, followed by Insecta, and fish. Individuals from Guatapé basin consumed more plant material and fish and fewer insects. We observed increased consumption of plant material and fish in ontogeny. Levin's niche breadth was lower and diet overlapping between individuals of length classes was higher during rainy period because the diet was mainly based on plant material. The diet of B. henni was composed mainly of plant material and Insects, and to a lesser extent from other groups such as fish, crustaceans and arachnids.

Niche breadth and overlap of spotted deer and domestic cattle with swamp deer in tropical region of Nepal

BackgroundKnowledge about the niche overlap among wild species and domestic cattle is helpful to conserve and manage wildlife. We assessed the habitat niche breadth and overlap of sympatrically living spotted deer (Axis axis) and domestic cattle with swamp deer (Cervus duvaucelii) in Shuklaphanta National Park, Nepal during the dry season to explore the possibility of interspecific competition by studying the habitat use by these species. The assumption was made that the presence of pellets is proof of habitat used by species.MethodsGrids of 2 km × 2 km have four subgrids, each with four sample plots, making a total of 16 plots (20 m × 20 m) in each grid. The size of each sub-grid was 200 m × 200 m and they were placed randomly inside the grid but at least 1 km apart from one another. The data was collected in a 96 plots in total. Levin’s niche breadth and Morisita’s overlap index were calculated to determine the niche breadth and the habitat overlap, respectively.ResultsThe Levin’s measure of niche breadth suggested that spotted deer had the highest acclimatization with an index value of 0.94, followed by domestic cattle at 0.50, and swamp deer at 0.33 in our study area. Thus, our findings supported the evidence that spotted deer are habitat generalists, whereas swamp deer are habitat specialists. The swamp deer had lower niche breadth and more overlap with domestic cattle.ConclusionOur study showed the least niche breadth of swamp deer in comparison to spotted deer and domestic cattle. The domestic cattle had the highest and least niche overlap with spotted deer and swamp deer, respectively, in terms of habitat use. Our study suggests that domestic cattle grazing should be stopped, and grassland management should be carried out for the benefit of ungulates. Similar studies should be conducted, including different seasons and places, prior to appropriate habitat management. In addition, further studies are needed to quantify the extent of interspecific competition by incorporating more species.

Stable isotopes as measure of niche breadth of nesting green turtles (Chelonia mydas) on Rocas Atoll, Brazil

The study analysed the niche breadth of nesting green turtles, Chelonia mydas, on Rocas Atoll, Brazil, through stable isotopes (δ15N and δ13C), comparing samplings of egg yolk and carapace collected from two nesting groups (2017 and 2019). The mean δ15N values in egg yolk and carapace were 7.1‰ (2017) and 6.8‰ (2019), and 7.8‰ (2017) and 7.3‰ (2019), respectively. For δ13C, the mean values were -17.4‰ (2017) and -17.5‰ (2019) in egg yolk, and -18.4‰ (2017) and -17.9‰ (2019) in carapace. The results suggest herbivory in coastal-benthic environments as the main feeding pattern in this nesting population. The niche breadth was similar between 2017 and 2019 in both tissues. In general, the trophic diversity (NR, CR, CD and SEA) was comparable between years as well as the trophic redundancy (MNND and SDNND), which was overall high. The niche metrics pointed to a homogeneous feeding pattern in the two nesting groups (2017 and 2019). This study adds a piece to solve the puzzle of adult green turtle trophic ecology.

Microhabitat analyses support relationships between niche breadth and range size when spatial autocorrelation is strong

Multiple evidence of positive relationships between nice breadth and range size (NB–RS) suggested that this can be a general ecological pattern. However, correlations between niche breadth and range size can emerge as a by‐product of strong spatial structure of environmental variables. This can be problematic because niche breadth is often assessed using broad‐scale macroclimatic variables, which suffer heavy spatial autocorrelation. Microhabitat measurements provide accurate information on species tolerance, and show limited autocorrelation. The aim of this study was to combine macroclimate and microhabitat data to assess NB–RS relationships in European plethodontid salamanders (Hydromantes), and to test whether microhabitat variables with weak autocorrelation can provide less biased NB–RS estimates across species. To measure macroclimatic niche, we gathered comprehensive information on the distribution of all Hydromantes species, and combined them with broad‐scale climatic layers. To measure microhabitat, we recorded salamander occurrence across > 350 caves and measured microhabitat features influencing their distribution: humidity, temperature and light. We assessed NB–RS relationships through phylogenetic regression; spatial null‐models were used to test whether the observed relationships are a by‐product of autocorrelation. We observed positive relationships between niche breadth and range size at both the macro‐ and microhabitat scale. At the macroclimatic scale, strong autocorrelation heavily inflated the possibility to observe positive NB–RS. Spatial autocorrelation was weaker for microhabitat variables. At the microhabitat level, the observed NB–RS was not a by‐product of spatial structure of variables. Our study shows that heavy autocorrelation of variables artificially increases the possibility to detect positive relationships between bioclimatic niche and range size, while fine‐scale data of microhabitat provide more direct measure of conditions selected by ectotherms, and enable less biased measures of niche breadth. Combining analyses performed at multiple scales and datasets with different spatial structure provides more complete niche information and effectively tests the generality of niche breadth–range size relationships.

Niche breadth and species richness: Correlation strength, scale and mechanisms

AbstractAimIt is often assumed that species in richer sites are more specialized, but empirical studies show conflicting results. In the present study, we quantify the correlation between community‐level niche breadth and richness. We contrast three mechanisms for gradients in niche breadth: climate, community assembly and nested interactions. First, the climatic stability within the tropics enables species to specialize, resulting in high richness. Under this scenario, we predict stronger richness–niche breadth correlations over larger latitudinal extents and when using environmental niche breadth measures (e.g., habitat). Second, in species‐rich areas, biotic interactions drive species to specialize. This may yield richness–niche breadth correlations regardless of the latitudinal extent and the type of niche breadth measure examined, whether environmental or functional (e.g., diet). Third, increased richness intensifies interactions between extreme specialists and generalists. Here, we predict stronger richness–niche breadth correlations when using functional niche breadth measures.LocationGlobal.Time period1973–2018.Major taxa studiedMany taxa.MethodsWe conducted a meta‐analysis, with the effect size estimated as the correlation between richness and community‐averaged niche breadth extracted from each study. We also examined how these correlations depend on the niche breadth measure used (environmental or functional), scale (grain and latitudinal extent), ecosystem and taxa.ResultsWe found a strong negative correlation between richness and niche breadth, and overall, a non‐significant correlation between latitude and niche breadth. The richness–niche breadth correlation was independent of the niche breadth measure used (environmental or functional). Scale, ecosystem and taxa had little effect on the strength of the correlation.Main conclusionsWe confirm that species in richer sites, but not necessarily in the tropics, are more specialized. This finding is not dependent on scale or on the type of niche breadth measure used. These results suggest that high richness drives community‐level specialization, and thus community assembly is likely to be the major driver of niche breadth rather than climatic gradients shaping both niche breadth and richness.

Spatial autocorrelation inflates niche breadth–range size relationships

AbstractAimSpecies with broader environmental tolerances are expected to be more widely distributed than specialist species, implying a positive correlation between niche breadth and geographic range size. When this relationship is evaluated using data derived from broad‐scale geographic distributions of species, spatial autocorrelation of species distribution data and environments may inflate niche breadth–range size relationships, bringing into question the causal relationship between environmental tolerance and range size. Using null models, we quantify the contribution of spatial autocorrelation to the frequently reported relationship between species’ range size and niche breadth.LocationSouth Africa.Time periodCurrent.Major taxa studiedEighty species in the genus Pelargonium.MethodsUsing phylogenetic least squares regression, we examined the extent to which variation in range size of Pelargonium species is related to temperature and precipitation niche breadths. We developed null models that randomized the spatial distribution of the climatic variables, but retained their broad spatial autocorrelation structure. We tested whether observed niche breadth–range size relationships were stronger than expected, given spatial autocorrelation of climatic variables.ResultsWe found the expected positive relationships between measures of niche breadth and range size, but these were no stronger than expected based on our spatial null models. Including spatial structure in simulations reduced expected niche breadths compared to simulations based on fully randomized environmental variables, resulting in steeper slopes for the simulated niche breadth–range size relationships.Main conclusionOur results indicate that spatial autocorrelation may positively bias niche breadth–range size relationships. This bias suggests that previously reported relationships between range size and niche breadth based on broad‐scale distributional data may be, at least in part, artefactual. Future studies need to explicitly account for spatial autocorrelation, and inferences on the role of environmental tolerance in driving patterns of species range size variation should be derived in conjunction with laboratory and field‐based experiments.

Space Partitioning among Two Sympatric Species, Sand Cat (Felis margarita) and Rüppell's Fox (Vulpes rueppellii), in a Desert Landscape in Central Iran

This study evaluates and compares habitat preferences and spatial niche breadth and overlap between two sympatrically occurring species, the sand cat (Felis margarita) and Ruppell's fox (Vulpes rueppellii), in a desert landscape of central Iran. A field survey from 2014 to 2016 was conducted to collect occurrence points for the two species as well as to identify their structural characteristics of used habitats in the occurrences points. Jacobs' index as a measure of habitat preference, Shannon and Levins' indices as measures of niche breadth, MacArthur, Levins and Pianka's indices as measures of niche overlap were calculated and interpreted. The results of this study showed that the sand cats are specifically restricted to sand dune and sabulous habitat type, whereas Ruppell's foxes have wider ecological amplitude. Sand cats only prefers sand dunes while Ruppell's foxes were found to prefer foothills, badlands, and sand dunes. Ruppell's foxes therefore had a wider niche breadth compared to the sand cats. The asymmetric MacArthur and Levins indices yielded a higher value of niche overlap for the sand cats compared to Ruppell's foxes, while the symmetric Pianka's measure of niche overlap was relatively high for both species. Such habitat preference and niche segregation between the two species may be a result of their feeding habits or the physical protective structure of their habitats attributes.

Human activity reduces niche partitioning among three widespread mesocarnivores

Anthropogenic disturbances can constrain the realized niche space of wildlife by inducing avoidance behaviors and altering community dynamics. Human activity might contribute to reduced partitioning of niche space by carnivores that consume similar resources, both by promoting tolerant species while also altering behavior of species (e.g. activity patterns). We investigated the influence of anthropogenic disturbance on habitat and dietary niche breadth and overlap among competing carnivores, and explored if altered resource partitioning could be explained by human‐induced activity shifts. To describe the diets of coyotes, bobcat, and gray foxes, we designed a citizen science program to collect carnivore scat samples in low‐ (‘wildland’) and high‐ (‘interface’) human‐use open space preserves, and obtained diet estimates using a DNA metabarcoding approach. Habitat use was determined at scat locations. We found that coyotes expanded habitat and dietary niche breadth in interface preserves, whereas bobcats and foxes narrowed both niche breadth measures. High human use was related to increased dietary niche overlap among all mesocarnivore pairs, increased coyote habitat overlap with bobcats and foxes, and a small reduction in habitat overlap between bobcats and foxes. The strongest increase in diet overlap was among coyotes and foxes, which was smaller in magnitude than their habitat overlap increase. Finally, coyote scats were more likely to contain nocturnal prey in interface preserves, whereas foxes appeared to reduce consumption of nocturnal prey. Our results suggest that dominant and generalist mesocarnivores may encroach on the niche space of subordinate mesocarnivores in areas with high human activity, and that patterns in resource use may be related to human‐induced activity shifts.

Intraspecific and interspecific competition induces density-dependent habitat niche shifts in an endangered steppe bird.

Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.

Niche segregation between Sciurus aureogaster and S. oculatus in a disturbed forest in central Mexico

Niche segregation has been proposed as the driving factor facilitating species coexistence by reducing interspecific competition. Nonetheless, although niche segregation has been widely studied, few studies have examined it in disturbed environments. Because of their dependence on mature forests, arboreal squirrels are model organisms for studying how sympatric species coexist in disturbed habitats. We examined niche segregation between Sciurus aureogaster and S. oculatus in an oak-pine forest of Pinal de Amoles, Queretaro, Mexico, disturbed by insect infestation and deforestation. We were interested in the degree of niche overlap in activity patterns, space and tree use, and feeding behavior. Because S. aureogaster has a greater geographic distribution and occurs in a wider range of habitats, we predicted that it would show wider niche values, and would be more tolerant to disturbance compared to S. oculatus. We also predicted that nests would be situated in areas with low deforestation pressure. We searched for squirrels, nests, and tree stumps while walking along dirt roads and trails, and through the dense part of the forest. Levin's measure of niche breadth and Pianka's measure of niche overlap were used to evaluate how both species segregate across resource dimensions. Number of stumps was used to evaluate deforestation pressure around nests and squirrels within 30-m-radius circles. S. aureogaster showed slightly narrower niche breath values in 5 out of 7 dimensions compared to S. oculatus. We found high niche overlap values in all dimensions examined. Both squirrel species strongly relied on pine (Pinus) trees for feeding, traveling, and nesting. S. aureogaster and S. oculatus were observed in areas with similar disturbance, and nests were situated in areas with medium deforestation pressure. Pine trees were mostly logged illegally and for forest sanitation, posing a serious threat to the persistence of arboreal squirrels within the study area.

Diet and feeding in the Cape Cobra, Naja nivea

It is widely reported that African cobras (genus Naja) are generalist predators, but examination of formal literature yields relatively little evidence of this for most species. Here, we review the diet of cape cobras (Naja nivea) based on examination of museum specimens, an extensive literature review, and social media reported natural history observations. We quantify dietary niche breadth and test the hypothesis that cape cobras are generalist predators. Additionally, we test the hypotheses that diet varies significantly (1) across biomes, and (2) across winter, summer and year-round rainfall regions. We gathered 101 feeding records for cape cobras and based on family-level prey frequencies calculated Levins’ measure of niche breadth as B = 6.57, which we standardised to BA = 0.29. We found no association between prey classes and biomes or rainfall region. Our data indicate that cape cobras consume a wide range of vertebrate prey from all four tetrapod classes, including a large number and diversity of snakes. Our findings suggest that cape cobras may be involved in several important ecological processes. Moreover, our study demonstrates the utility and value of collating natural history observations reported on social media platforms.

Alpha richness and niche breadth of a widespread group of aquatic insects in Nearctic and Neotropical streams

Summary The increase in species richness from the poles to the equator is one of the most consistent biogeographical patterns of species distributions. Using a globally distributed group of stream insects–black flies (Diptera: Simuliidae)–we addressed two questions: (i) How does α‐richness vary among streams of the New World? (ii) Does niche width, as measured by a proxy based on stream‐habitat conditions, differ between the Nearctic and Neotropical regions? In our analyses of α‐richness, we consider the potential effects of area, elevation, sample size and season. Examining 296 streams in 12 regional collections, we found that α‐richness differed little among New World streams. Using stream variables to delineate a measure of niche breadth, we also found no difference in the mean niche breadth of species between North and South America. Our results are consistent with niche conservatism. In other words, as black flies expanded into the tropics, their mean niche breadth did not contract relative to that of their northern counterparts.

Niche-breadth of freshwater macrophytes occurring in tropical southern African rivers predicts species global latitudinal range

The study tested the hypothesis that measurement, using multivariate Principal Components Analysis (PCA), of the niche-breadth of river macrophyte species in southern tropical Africa, may predict their larger-scale biogeographical range. Two measures of niche-breadth were calculated for 44 riverine macrophyte species, from 20 families commonly occurring in Zambia, using an approach based on PCA ordination with 16 bio-physico-chemical input variables. These included altitude, stream order, stream flow, pH, conductivity and soluble reactive phosphate concentration (SRP). In the absence of additional chemical water quality data for Zambian rivers, invertebrate-based measures of general water quality were also used. These were benthic macroinvertebrate Average Score per Taxon (ASPT), and individual abundance of nine macroinvertebrate families with differing water quality tolerance, indicated by their Sensitivity Weightings within the Zambian Invertebrate Scoring System (ZISS). Macrophyte large-scale latitudinal range was derived from world geopositional records held by online databases, and additional records held by the authors. The two niche-breadth metrics divided the species into narrow-niche and intermediate/broad-niche categories, showing significant variation (from one or both of correlation and ANOVA test outcomes) in altitude, stream flow, conductivity, SRP, pH and ASPT, but not stream order. Macrophyte alpha-diversity (as a measure of number of individual niches co-existing per habitat) showed no significant relationship with individual species niche-breadth. Narrow-niche species included a higher proportion of Afrotropical endemics than did species with broader niche size. There were significant predictive relationships between macrophyte niche-breadth and latitudinal range of the target species at global and Afrotropical scales, but not for the Neotropics.

Fine-Scale Habitat Segregation between Two Ecologically Similar Top Predators.

Similar, coexisting species often segregate along the spatial ecological axis. Here, we examine if two top predators (jaguars and pumas) present different fine-scale habitat use in areas of coexistence, and discuss if the observed pattern can be explained by the risk of interference competition between them. Interference competition theory predicts that pumas should avoid habitats or areas used by jaguars (the dominant species), and as a consequence should present more variability of niche parameters across study areas. We used non-invasive genetic sampling of faeces in 12 different areas and sensor satellite fine-scale habitat indices to answer these questions. Meta-analysis confirmed differences in fine-scale habitat use between jaguars and pumas. Furthermore, average marginality of the realized niches of pumas was more variable than those of jaguars, and tolerance (a measure of niche breadth) was on average 2.2 times higher in pumas than in jaguars, as expected under the interference competition risk hypothesis. The use of sensor satellite fine-scale habitat indices allowed the detection of subtle differences in the environmental characteristics of the habitats used by these two similar top predators, which, as a rule, until now were recorded using the same general habitat types. The detection of fine spatial segregation between these two top predators was scale-dependent.

Discrimination of grasshopper (Orthoptera: Acrididae) diet and niche overlap using next-generation sequencing of gut contents.

Species of grasshopper have been divided into three diet classifications based on mandible morphology: forbivorous (specialist on forbs), graminivorous (specialist on grasses), and mixed feeding (broad-scale generalists). For example, Melanoplus bivittatus and Dissosteira carolina are presumed to be broad-scale generalists, Chortophaga viridifasciata is a specialist on grasses, and Melanoplus femurrubrum is a specialist on forbs. These classifications, however, have not been verified in the wild. Multiple specimens of these four species were collected, and diet analysis was performed using DNA metabarcoding of the gut contents. The rbcLa gene region was amplified and sequenced using Illumina MiSeq sequencing. Levins’ measure and the Shannon–Wiener measure of niche breadth were calculated using family-level identifications and Morisita’s measure of niche overlap was calculated using operational taxonomic units (OTUs). Gut contents confirm both D. carolina and M. bivittatus as generalists and C. viridifasciata as a specialist on grasses. For M. femurrubrum, a high niche breadth was observed and species of grasses were identified in the gut as well as forbs. Niche overlap values did not follow predicted patterns, however, the low values suggest low competition between these species.

Metabolic Flexibility as a Major Predictor of Spatial Distribution in Microbial Communities

A better understand the ecology of microbes and their role in the global ecosystem could be achieved if traditional ecological theories can be applied to microbes. In ecology organisms are defined as specialists or generalists according to the breadth of their niche. Spatial distribution is often used as a proxy measure of niche breadth; generalists have broad niches and a wide spatial distribution and specialists a narrow niche and spatial distribution. Previous studies suggest that microbial distribution patterns are contrary to this idea; a microbial generalist genus (Desulfobulbus) has a limited spatial distribution while a specialist genus (Methanosaeta) has a cosmopolitan distribution. Therefore, we hypothesise that this counter-intuitive distribution within generalist and specialist microbial genera is a common microbial characteristic. Using molecular fingerprinting the distribution of four microbial genera, two generalists, Desulfobulbus and the methanogenic archaea Methanosarcina, and two specialists, Methanosaeta and the sulfate-reducing bacteria Desulfobacter were analysed in sediment samples from along a UK estuary. Detected genotypes of both generalist genera showed a distinct spatial distribution, significantly correlated with geographic distance between sites. Genotypes of both specialist genera showed no significant differential spatial distribution. These data support the hypothesis that the spatial distribution of specialist and generalist microbes does not match that seen with specialist and generalist large organisms. It may be that generalist microbes, while having a wider potential niche, are constrained, possibly by intrageneric competition, to exploit only a small part of that potential niche while specialists, with far fewer constraints to their niche, are more capable of filling their potential niche more effectively, perhaps by avoiding intrageneric competition. We suggest that these counter-intuitive distribution patterns may be a common feature of microbes in general and represent a distinct microbial principle in ecology, which is a real challenge if we are to develop a truly inclusive ecology.

Niche Breadth and Overlap Measures of Sarcosaprophagous Flies Exploiting Human Settlements

Sarcosaprophagous flies, filth-inhabiting dipterans, were caught in carrion bait trap from 12 study sites covering township, village and uninhabited places having various sanitary conditions for 3 years covering three seasons per year. Data were analyzed for three measures of niche breadth and five measures of niche overlap. The results show that human settlements provide various habitats to these carrion flies that compete each other to utilize food resource and exploit unhygienic condition of human settlements. It is found that measurement of niche breadth and niche overlap against the resource gradient is necessary in assessing the nature of species packing. It is commented that the degree of overlap among the synanthropic species is quite close than those of asynanthropic species, i.e., nature of resource partitioning is different. Among the niche breadth analyses, plotted graph of Levins’ B is helpful in visualizing the niche breadth. All the niche overlap measures, presented in this article, show more or less similar trend of overlap and point towards intense interspecific competition. Cluster analysis and Pearson correlation analyses approve the above outcome. This one-dimensional niche study explained that although intra-generic and inter-generic competition among the fly species is intense they exhibit unique species packing due to resource continuum.

Using fine-scale GIS data to assess the relationship between intra-annual environmental niche variability and population density in a local stream fish assemblage

Summary 1. Geographic information systems (GIS) have recently proved useful for estimating the environmental niche of species across broad geographic regions. However, the application of these niche-based GIS techniques has yet to be extensively applied to local systems. The assumptions of the methods are transferable across scales: species exist across a range of habitats, and these habitats represent a gradient of suitability that can be characterized using multivariate environmental data in association with known species occurrences. 2. Habitat availability and species’ niche characteristics are often considered to be important predictors of population density. However, seasonal habitat variability and stochastic events have been hypothesized to limit interactions among species and confound the relationship between available habitat, species niche characteristics and community structure. This research examines the relationship between environmental niche breadth and niche position and population density among species of stream fishes in a seasonally variable environment using a novel application of fine-scale GIS data. 3. Niche breadth and niche position were estimated for 11 species in a local assemblage using five fine-scale (0·5 m) GIS-based environmental data sets collected during four different times of the year (July, October, January, April). We compared niche measures to variation in population density among species to determine whether environmental niche characteristics, in the context of available habitat, explain variation in numbers of individuals among species. 4. Variation in population density among species in the October sample was predicted by niche breadth measures (R2 = 0·752), while variation in population density among species in the January sample was predicted by a model incorporating measures of both niche breadth and niche position (R2 = 0·953). Measures of niche breadth and niche position were not correlated with variation in population density in the July and April samples. 5. Species presence and local abundance are often assumed to be predictable based on the availability of suitable habitat. However, little effort has been directed at understanding the influence of both niche breadth and niche position on local abundance. Our results suggest that the amount and distribution of available habitat can be a strong predictor of interspecific variation in population density, even in seasonally variable environments.

Scale‐invariance of niche breadth in fleas parasitic on small mammals

The resource specialization or niche breadth of a species is not fixed across populations, but instead varies over geographical space. A species may be a local specialist but a regional generalist, if it uses locally few resources that are substitutable across locations. In contrast, a species is a local generalist and a regional specialist if it uses locally many resources that cannot be substituted from 1 location to the next. Scale‐dependence can thus be a major factor in estimation of niche breadth. Here, we test for relationships between local and global estimates of host specificity (a measure of niche breadth for parasites) in fleas (Siphonaptera) parasitic on small mammals from 49 different regions within the Holarctic. Across all fleas, we found a strong, positive relationship between the number of host species that a flea uses in 1 locality and the number of different host species that can serve as the flea's principal host (i.e. the one supporting the most fleas in a region) among all regions. Also, we observed a strong positive relationship between the taxonomic distinctness of the host species used in 1 locality and that of all known principal hosts among all localities. These relationships held after correcting for potentially confounding phylogenetic influences. We discuss the implications of scale‐independent host specificity and its association with geographical range size and species‐specific patterns of host use.

Bacterial carbon processing by generalist species in the coastal ocean

The assimilation and mineralization of dissolved organic carbon (DOC) by marine bacterioplankton is a major process in the ocean carbon cycle. However, little information exists on the specific metabolic functions of participating bacteria and on whether individual taxa specialize on particular components of the marine DOC pool. Here we use experimental metagenomics to show that coastal communities are populated by taxa capable of metabolizing a wide variety of organic carbon compounds. Genomic DNA captured from bacterial community subsets metabolizing a single model component of the DOC pool (either dimethylsulphoniopropionate or vanillate) showed substantial overlap in gene composition as well as a diversity of carbon-processing capabilities beyond the selected phenotypes. Our direct measure of niche breadth for bacterial functional assemblages indicates that, in accordance with ecological theory, heterogeneity in the composition and supply of organic carbon to coastal oceans may favour generalist bacteria. In the important interplay between microbial community structure and biogeochemical cycling, coastal heterotrophic communities may be controlled less by transient changes in the carbon reservoir that they process and more by factors such as trophic interactions and physical conditions.