Showing papers on "Flying squirrel published in 1997"

Landscape characteristics associated with the occurrence of the flying squirrel Pteromys volans in old-growth forests of northern Finland

Abstract: We investigated whether the occurrence of the flying squirrel, a declined virgin forest species, was accounted for by the structure of the landscape in northeastern Finland. We sampled 20 forest areas (1-77 km 2 in size) in 1995 for the occurrence of the species using a sampling plot method. Landscape structure around occupied and unoccupied areas were compared using seven different radii ranging from 100 m to 10 km. Classified satellite images were analyzed with Geographic Information System (GIS). Ten areas could be determined to be occupied by the flying squirrel. Results showed that occupied areas did not deviate from unoccupied ones in total area. In unoccupied areas there were more mature pine-spruce forests, and less matrix habitat, at the home range scale (100 m and 200 m radii) than in occupied areas. Furthermore, in unoccupied forest areas open habitats (clear-cuts, open fens) were more common than in occupied ones at distances between 200 m and 2 km around sampling plots. These differences resulted from both larger mean patch size of and smaller mean nearest neighbor distance between open habitat patches in unoccupied than in occupied forest areas. According to a logistic regression analysis, information on the amount of open habitat within 1 km radius alone correctly classified 75% of the areas into occupied and unoccupied ones. The probability of the presence of flying squirrel decreases with the increasing amount of open habitat within 1 km. The results suggest that increasing the amount of open habitats (e.g. clear-cutting) at the local scale has a negative impact on the flying squirrel. It is obvious that in the present situation where the population has severely declined and its optimal habitat is still diminishing, every patch suitable for the species - whether occupied or not - may be important for the population persistence.

Scaling of the mandible in squirrels.

Abstract: We compared the shape of the mandible among New World tree squirrels and selected outgroup taxa using linear measurements and areas defined by the median axis and conventional anatomical landmarks. We modified the median axis technique to define novel measurements, which proved complementary to those obtained from conventional landmarks. Allometric analyses showed that the scaling of the mandible among the New World tree squirrels is generally isometric (as has been observed in other groups of mamimals), but diverges from isometry in a tendency in smaller animals for the masseteric ridge to be displaced anteriorly, the condylar process and posterior portion of the ascending ramus to be relatively elongated, and the coronoid process to be shortened. Allometric analyses also revealed the ways and extent that outgroup taxa deviated from the scaling pattern observed for the New World tree squirrels. A flying squirrel (subfamily Pteromyinae), a moderate-sized callosciurine squirrel, and three species of pygmy tree squirrels from Asia and Africa show mandibular proportions very similar to those predicted for New World tree squirrels of corresponding size. Ground squirrels (tribe Marmotini) and successively more distant relatives such as Aplodontia, two myomorph rodents, and a rabbit show greater differences from the New World tree squirrels in their mandibular proportions. Combining the use of median-axis and conventional measurements makes it possible to examine changing relationships between locations of anatomically homologous landmarks and the geometry of the form. J Morphol 232:107–132, 1997. © 1997 Wiley-Liss, Inc.