1,721,012 research outputs found
Gurnell, J. — The Natural History of Squirrels. Christopher Helm, London, 1987
No full textBourlière François. Gurnell, J. — The Natural History of Squirrels. Christopher Helm, London, 1987. In: Revue d'Écologie (La Terre et La Vie), tome 43, n°3, 1988. p. 326
Interspecific competition in tree squirrels: do introduced grey squirrels (Sciurus carolinensis) deplete tree seeds hoarded by red squirrels (S-vulgaris)?
No full text
Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur?
No full textIn heterogeneous environments, differential niche selection by two competing species will result in niche partitioning so that individuals of each species can maximise their fitness under different sets of environmental variables. Thus, niche partitioning is considered essential to allow co-existence of ecologically related species. To assess whether niche partitioning was occurring between native red squirrels and alien grey squirrels living together in a 13-ha high-quality mixed deciduous woodland in north Italy, we investigated temporal and spatial patterns in their activity and foraging behaviour between 1996 and 1998. We used live trapping and radio-tracking to study numbers, distribution and behaviour of squirrels. Daily and seasonal temporal activity patterns, and activity on the ground and in the trees, were similar in the two species. However, grey squirrels were more tree specialists and had a narrower tree-species niche width than red squirrels, in particular making greater use of oak. Other studies of red and grey squirrels in allopatry show that the two species differ in the extent they utilise oak. Overall, tree-species niche overlap was about 70%. Grey squirrels had larger home ranges than red squirrels. Home ranges and core areas of both species were larger in males than females. Also, intraspecific home range and core-area overlap patterns were similar to those found in allopatric populations of these species. Overall, there was no evidence that the use of space of one species was affected by the other. Our results show that there was no niche partitioning of activity or foraging behaviour in time or space during the study. This suggests that, at moderate grey-squirrel densities, red squirrels are unable to avoid competition with grey squirrels, and that competition for food and/or space will occur when these resources become limiting
Effects of spatial variation in food availability on spacing behaviour and demography of Eurasian red squirrel
No full textIn heterogeneous habitats with limited resources, spacing behaviour will affect individual variation in breeding success and density of populations, and is thus of general interest to ecologists. We investigated how red squirrels Sciurus vulgaris adapt their social organisation to fine-grained heterogeneity in habitat quality, studying spacing behaviour, habitat use and population dynamics in a forest in north Italy, characterised by a mosaic of high-quality (chestnut-pine) and poor-quality patches. We compared the data with those from more homogeneous broadleaf and mixed woodlands with similar overall tree seed abundance ("stable" habitats). Squirrels lived at lower densities (pre-breeding density 0.39-0.58 ha-1) than in "stable" habitats, although breeding rate was not reduced. Female breeding success was related to being primiparous as yearlings, and increased with body mass and proportion high-quality habitat in the home range. Persistency rate of females was as in stable habitats. It was higher than male persistency, but immigration and recruitment rates were male biased, resulting in even sex-ratio. All residents occupied high-quality patches, and no subadults established a permanent home range in poor-quality habitat. Home range and core-area size was typically larger in males than in females and a male's core-area overlapped those of other males and of females. Female core-areas were overlapped by males but not, or very little, by other females (intrasexual territoriality). Home ranges, or core-areas, were not smaller than in "stable" habitats, nor did we find a higher degree of core-area overlap. We conclude that in patchy habitats dominant, resident red squirrels exclude dispersing animals from preferred, high-quality habitat, producing a spacing pattern referred to as ideal despotic distribution, and that poor patches were only used temporarily by transient individuals, resulting in a reduction of density in comparison to populations in "stable" habitats
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
Spacing behaviour, kinship, and population dynamics of grey squirrels in a newly colonized broadleaf woodland in Italy
No full text Eastern grey squirrels, Sciurus carolinensis, introduced to Britain and northern Italy are replacing the native Eurasian red squirrel, Sciurus vulgaris. We studied the pattern of colonization of a high-quality broadleaf woodland by grey squirrels by means of livetrapping and radio-tracking. The studies started in July 1996, when six grey squirrels (four males, two females) first colonized the woodland, and lasted until November 1998, when densities exceeded those of the local red squirrel population. Grey squirrel colonization was rapid, with a high proportion of adult and yearling females breeding. Juvenile recruitment was also higher than in stable populations in Britain. Adult survival was better in 1997 (83%) than in 1998 (47%), with predation accounting for 67% of losses in 1998. This indicates the effects of local predator communities on the colonization process. Densities of grey squirrels were moderate in 1998, with a maximum of 1.9 squirrels/ha and we expect density to increase further. Adult home range sizes were three to four times larger than those of subadults, and male ranges were larger than those of females. Body mass was positively correlated with both total home range size and core-area size. Core-area size for adults was inversely correlated with food availability. Juvenile female grey squirrels were philopatric, forming female kin groups, while most juvenile males settled outside the mother's home range. </jats:p
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
- …
