100 150 200
Body size (cm)
this core for temporary stays in a much larger 'dispersal' area (1-3 km2), and juveniles permanently disperse within this range (Section 6.7 dealt with within-population variation in dispersal). Reunanen et al. (2000) compared the landscape structure around
Figure 7.11 Historic distribution of four locally extinct skates in the northwest and northeast Atlantic: (a) barndoor skate Dipturus laevis, (b) common skate D. batis, (c) white skate Rostroraja alba and (d) long-nose skate D. oxyrhinchus. e, area of local extinction; e?, possible local extinction; p, present in recent fisheries surveys; ?, no knowledge of status; scale bar represents 150 km. (e) Frequency distribution of skate body size - the four locally extinct species are dark orange. (After Dulvy & Reynolds, 2002.)
known flying squirrel home ranges (63 sites) with randomly chosen areas (96 sites) to determine the forest patterns that favor the squirrels. They first established that landscape patch types could be divided into optimal breeding habitat (mixed spruce-
Figure 7.12 Variation in physical and biotic variables in the Santuit River, USA during the migratory period of river herrings: (a) discharge, (b) temperature, (c) Secchi disc depth (low values indicate poor light transmission because of high turbidity), (d) rainfall, (e) lunar cycle and (f) Bosmina density. P denotes 'peak' periods of migration (>1000 fish week-1), P and A (>30 fish week-1) together denote 'all' periods of migration. (After Yako et al., 2002.)
deciduous forests), dispersal habitat (pine and young forests) and unsuitable habitat (young sapling stands, open habitats, water). Figure 7.13 shows the amount and spatial arrangement of the breeding habitat and dispersal habitat for examples of a typical flying squirrel site and a random forest site. Overall, flying squirrel landscapes contained three times more suitable breeding habitat within a 1 km radius than random landscapes. Squirrel landscapes also contained about 23% more dispersal habitat than random landscapes but, more significantly, squirrel dispersal habitat was much better connected (fewer fragments per unit area) than random landscapes. Reunanen et al. (2000) recommend that forest managers should restore and maintain a deciduous mixture, particularly in spruce-dominated forests, for optimal breeding habitat. But of particular significance in the context of dispersal behavior, they need to ensure good physical connectivity between the optimal squirrel breeding and dispersal habitats.
Was this article helpful?