1,721,099 research outputs found
Within-sex density dependence and population dynamics of red squirrels Sciurus vulgaris
No full text1.
Social organization and dispersal of red squirrels (
Sciurus vulgaris
L.) differ between
sexes, and intrasexual competition is intense. Therefore, we predicted that demographic
parameters should be gender-specific: that is density-dependent factors will be more
strongly related to density of the same sex than to density of the opposite sex. We studied
the relative importance of within- and between-sex density-dependent factors and of
density-independent factors (habitat type, food abundance, winter temperature) on different
demographic parameters, in two populations in northern Belgium.
2.
Spring density of males was positively correlated with tree-seed abundance in the
previous year, but this was not the case for females. None of the population parameters
we measured differed between habitats, indicating that the same density-dependent and
density-independent mechanisms prevailed in coniferous and deciduous habitat.
3.
Within each sex, we found several demographic parameters that were dependent on
the densities of the same sex; however, none of these parameters was found to be
dependent on the density of the opposite sex.
4.
Reproductive rate increased with food abundance and decreased with female density.
Adult survival of females decreased with female density in autumn–winter, while survival
of adult males in spring–summer increased with the size of the previous year’s seed crop.
5.
Immigration rate of males was higher in spring than in autumn, and spring immigration
increased with food abundance. Male recruitment rate, in both seasons,
increased with food abundance, but was male density dependent. However, spring–
summer loss rates also increased when food supplies were good, suggesting that despite
high food availability, emigration of juvenile and subadult males increased when intrasexual
competition was intense. Recruitment rate of females decreased with increasing
female density. After a good seed crop, more subadult females dispersed, but their settlement
success (recruitment) was lower at high female density.
6.
Seed crop size positively affected red squirrel densities through increased reproduction,
immigration and adult survival of males, but density-dependent reproduction and withinsex
density-dependent recruitment of locally born juveniles and dispersing subadults limit
the fluctuations in numbers and regulate densities in winter–early spring, as well as in summer
Plasticity in the timing of detachment of an Eurasian-African songbird tick, Ixodes frontalis
No full textIn non-permanent parasites, host detachment should take place in an environment that ensures the continuation of their life cycle. Timing of detachment - in combination with the host's space use - affects dispersal and transmission success of the parasites and of the pathogens they vector. Before reaching the adult reproductive stage, ticks need to go through multiple immature developmental stages (larva and nymph), each feeding on host blood. In between the feeding bouts, they often remain in the off-host environment for considerable periods of time. With this study, we aimed to obtain more insight in Ixodes frontalis’ off-host habitat use by comparing its detachment pattern in different life stages with that of two habitat-specialized ticks also found on birds: the endophilic tree-hole tick (Ixodes arboricola) and the exophilic sheep tick (Ixodes ricinus), the latter living in humid understory vegetation of forests. For this, we artificially infested hole-roosting (great tits, Parus major) and open-roosting (blackbirds, Turdus merula) birds with ticks under laboratory conditions, and recorded whether detachment occurred during the day or the night. We hypothesize that nocturnal detachment improves off-host mating opportunities and host localization, whereas diurnal detachment optimizes tick dispersal. Ixodes frontalis nymphs detached during the night, especially when feeding on blackbirds. This behaviour was very similar to that of I. arboricola (larva and nymph) feeding on great tits. In contrast, I. frontalis larvae detached during the day, especially when feeding on great tits, which resembles that of I. ricinus’ feeding behaviour (larva and nymph). Ixodes frontalis left the host within seven days, immediately after completion of the blood meal. This is similar to both developmental stages of I. ricinus but contrasts with the very long (up to 20 days) feeding duration in I. arboricola. Thus I. frontalis shows strong plasticity, switching from dispersal-centered (larvae) to host-centered (nymphs) detachment behaviour. Findings are discussed with regard to the ticks’ habitat use, dispersal, life history and host specificity
Ancestral origins and invasion pathways in a globally invasive bird correlate with climate and influences from bird trade
Full text linkInvasive species present a major threat to global biodiversity. Understanding genetic patterns and evolutionary processes that reinforce successful establishment is para- mount for elucidating mechanisms underlying biological invasions. Among birds, the ring-necked parakeet (Psittacula krameri) is one of the most successful invasive spe- cies, established in over 35 countries. However, little is known about the evolutionary genetic origins of this species and what population genetic signatures tell us about patterns of invasion. We reveal the ancestral origins of populations across the invasive range and explore the potential influence of climate and propagule pressure from the pet trade on observed genetic patterns. Ring-necked parakeet samples representing the ancestral native range (n = 96) were collected from museum specimens, and modern samples from the invasive range (n = 855) were gathered from across Europe, Mauritius and Seychelles, and sequenced for two mitochondrial DNA markers comprising 868 bp of cytochrome b and control region, and genotyped at 10 microsatellite loci. Invasive populations comprise birds that originate predominantly from Pakistan and northern areas of India. Haplotypes associated with more northerly distribution limits in the ancestral native range were more prevalent in invasive populations in Europe, and the predominance of Asian haplotypes in Europe is consistent with the higher number of Asian birds transported by the pet trade outside the native range. Success- ful establishment of invasive species is likely to be underpinned by a combination of environmental and anthropogenic influences
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
Effects of spatio-temporal variation in food supply on red squirrel (Sciurus vulgaris) body size and body mass and its consequences for some fitness components
No full textFood availability is likely to influence body condition and, in turn, fitness. The intensity of this response may
vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6
Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and
body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also
investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female
reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed
between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females
were slightly heavier than males, but this difference was largely explained by mass gain of females during
reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between
habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass
between populations were partially explained by habitat-related differences in body size and variability of seedcrops,
suggesting differential selection for smaller squirrels in spruce-larch forests against selection for larger and
heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed
production. The probability of reproduction by females increased with body mass, but varied strongly between
habitats and years, with more females reproducing in years with rich seed-crops. In both sexes, body mass
positively affected probability of settlement and length of residency. Our results suggest that in temporally
variable environments that differ in overall amount of food resources, individual variation in body mass is
related to habitat type, and that having a relatively high body mass, within each population, positively affects
male and female settlement success and local survival, and female reproductive success
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