1,721,006 research outputs found
Ecological and evolutionary causes and consequences of intra-population variability in foraging niche: predator and prey in a marine archipelago
Full text linkThe niche concept, which provides a tractable measure of the environment encountered by organisms, figures prominently in ecological and evolutionary theory. Although neglected, valuable information may be gained by examining niche variation at hierarchies nested within its historical roots at the species level. Herein I examine intrapopulation variation in foraging niche - at the sub-population, social group, and individual levels - and investigate its ecological causes and evolutionary consequences in a predator-prey system within a marine archipelago.
I used two analytical techniques. My primary tool, stable isotope analysis of δ13C and δ15N, coalesces the multiple dimensions of the foraging niche into two dimensions. Variation in prey remains identified in faeces served as an independent data set.
I examined how different levels of resource availability over space and time as well as competition could account for observed intrapopulation niche variation in a terrestrial carnivore (wolf, Canis lupus). Major shifts in resource use were associated with biogeographic region, from dominance of in situ terrestrial resources (deer, Odocoileus hemionus) on the mainland to prevalence of allochthonous (marine) resources
islands. The probability of deer remains in wolf faeces declines as a function of island isolation. Correspondingly, marine enrichment in isotopic signatures of wolves increases with isolation. Estimates of marine biomass assimilation vary from roughly 25 to 50 to 75% among mainland, inner, and outer island sub-populations respectively
How animals select resources also can contribute to intrapopulation variability in niche. A `resource selection' approach indicated that, when available, wolves select spawning salmon (Oncorhynchus spp.) over deer. Although only available during autumn, salmon contribute up to 25% of biomass assimilation in wolves over the 6 month period for which it was estimated. Moreover, previously undocumented salmon hunting by wolves I report identifies them as among a few primary biological vectors that transfer salmon from marine into adjacent terrestrial ecosystems.
I also ask whether intrapopulation variation exists at finer scales, and specifically at the individual level. Approximately 40% of total variation in `isotopic niche' exists within social groups, likely a function of strong intraspecific (i.e. intra-pack) competition in this social carnivore. Moreover, the magnitude of inter-individual variation was significantly higher on inner islands compared with the mainland and outer islands, likely because of differences in prey species richness and interspecific competition, which likewise vary among biogeographic regions.
On a smaller spatial scale, 1 examined the niches of deer to ask whether microspatial variation in vegetation patterns also create conditions suitable for inter-individual niche divergence. Such variation presents a potentially central object on which natural selection can act. Using intra-generational comparisons of deer that had either survived or perished from wolf predation, I detected resource-specific fitness. Individuals with isotopic signatures that suggested they foraged in nutritionally-rich forest stands were more likely to be killed by wolves, suggesting a trade-off between predation risk and nutritional benefit. Moreover, non-survivors diverged more than survivors from median isotopic niches, suggesting selection against foraging specialization. Both selection against specialization and proposed trade-offs would maintain observed variation in niche, and possibly also traits associated with the niche. Stable isotope analysis in an evolutionary framework provides novel opportunity to integrate the ecological and selective landscapes to identify underlying ecological mechanisms of selection and provide insight into the maintenance of variability.
Variability in intrapopulation niche can be predicted by ecological and evolutionary conditions and processes in the environment. Specifically, niche variability is largely a Function of habitat variability, which large and varied protected areas would best provide. Moreover, management that aims to safeguard an 'average niche' for a population may not adequately protect diverse populations and the processes underlying such readily observed variability
The salmon-forest
No full textCross-habitat subsidies of nutrients and prey can structure community processes in receiving ecosystems. Every autumn throughout the northern Pacific region, anadromous salmon (Oncorhynchus spp.) return to their natal watersheds to spawn and die. a landward migration that imports marine protein to estuarine, freshwater and terrestrial habitats. Spawning salmon regulate the population dynamics of many wildlife species and fertilize aquatic and terrestrial systems with their nutrients and carcasses. When salmon spawn at high densities, vertebrate predators such as bears (Ursus spp.) selectively forage on energy-rich components of the salmon and transfer partially-consumed carcasses to adjacent forests.
Herein. I examine the ecosystem-level consequences of the salmon subsidy in forest food webs, with a primary focus on the role of terrestrial invertebrates in the consumption, distribution and cycling of salmon nutrients and energy in terrestrial habitats. Study watersheds occur throughout coastal British Columbia, with most comparisons from two productive systems on the central coast. Both have high-density salmon spawning and 5-10m waterfalls 1-2km from the estuary that block further upstream salmon migration.
Using stable isotope analysis of 615N and 613C I find that there are two principal pathways in which salmon nutrients enter forest food webs: 1) direct consumption of salmon tissue and/or salmon consumers (enrichment in 615N and 613C); or 2) marine-nitrogen fertilization of soil and vegetation N pools (enrichment in 615N hut not &3C).
There is a diverse community of terrestrial invertebrates (>60 species) directly associated with the decay of salmon carrion, although from a biomass perspective this is dominated by the terrestrial Diptera. I estimate that from 134-360g of Calliphora (Calliphoridae) maggots per meter of spawning length (or 3.5-9 million individuals in whole watershed) were generated from carcass transfer on the Clatse and Neekas, with the majority produced from the large-bodied chum (O. keta) relative to pink (O. gorbuscha). Processes of competition and predation on salmon-carrion produce temporal dietary shifts in higher-level consumers, and species-specific adaptations, including
communal breeding in burying beetles (Nicrophorus spp.). Overall, the insect niche generated by the input of salmon carcasses directly increases the diversity, carrying capacity and food-chain length of riparian food webs.
The bottom-up effects of salmon nutrient fertilization favours plants that are competitive in nutrient-rich soils and structures a community of macro-detritivores as the primary decomposers. Salmon-nutrient fertilization is detectable in multiple trophic guilds in riparian foodwebs, with estimates of %marine-derived nitrogen (%MDN) ranging as high as 78%. Across multiple watersheds, the pattern of %MDN enrichment is most strongly predicted by chum spawning density (kg/m), including the legacy of spawning density from the past. High a'5N and %MDN values can be used as indicators for intact ecosystem processes including the presence of wildlife transfer vectors, sufficient spawning densities to facilitate selective foraging, and the further distribution of salmon nutrients and energy by terrestrial insects.
Ongoing declines in salmon escapement throughout the Pacific Rim have far greater ecological context in riparian food webs that previously recognized. The salmon-forest interaction highlights the evolutionary interdependence between marine and terrestrial ecosystems in the North Pacific, and the need for ecosystem-level conservation that includes salmon, their riparian habitats, and their vertebrate and invertebrate scavengers
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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