Population dynamics of small mammals in relation to production of cones in four types of forests in the northern Sierra Nevada, California

摘要

We studied assemblages of small mammals in four types of coniferous forest (white fir, red fir, mixed-fir, and pine-cedar) in the Sierra Nevada of California for 2 field seasons (2003-2004). We assessed production of cones by dominant species of conifers in both years. Production of cones was greater overall in autumn 2003, but varied within type of forest and between species of conifers. Parallel to this, mean maximum densities of North American deermice (Peromyscus maniculatus) increased in 2004 (from 0.7-7.3 individuals/ha to 65.7-112.7 individuals/ha). Size of populations of golden-mantled ground squirrels (Spermophilus lateralis) were similar in both years; typical of hibernating species, this taxon occurred at low densities in May (6.6 +/- 0.2), peak densities were in September (24.5-32.5 individuals/ha), and their populations declined in October (9.2 +/- 4.8). Long-eared chipmunks (Tamias quadrimaculatus) reached higher densities in red fir (48.2 +/- 13.4 individuals/ha) and mixed-fir forests (36.0 +/- 13.5 individuals/ha) than in white fir forests (7.6 +/- 2.7 individuals/ha), and all populations peaked in September. Shadow chipmunks (Tamias senex) remained at lower densities than T. quadrimaculatus except during September 2004, when they reached high densities (54.6 +/- 26.8 individuals/ha). Survival of P. maniculatus was dependant on an interaction between type of forest and month, with additive effects of over-winter survival and mean production of cones in autumn 2003. Survival of S. lateralis varied by month, whereas survival in both species of Tamias varied with the interaction of type of forest and month, plus additional effects of over-winter survival and mean, p production of cones for T. quadrimaculatus. Dusky-footed woodrats (Neotoma fuscipes) were present at lower elevations and reached greatest densities in pine-cedar forests. Northern flying squirrels (Glaucomys sabrinus) were not captured commonly, and they occurred predominantly in red fir forests.