关键词：
SLUGS
HILL PASTURES
LIFE CYCLES
POPULATION DYNAMICS
摘要：
Life cycles of the slugs Deroceras reticulatum and Arion intermedius were studied over a 2.5-year period in a sheep-grazed pasture in the Kaimai Range, New Zealand. D. reticulatum approximated a bivoltine phenology, with intervals between consecutive generations ranging from 4 to 7 months and maximum life span from 8 to 12 months. Egg laying occurred in autumn and spring-early summer. Periods of egg hatching were followed by a phase of juvenile growth characterised by linear increase in the logarithm of population mean body weights. This was followed by a phase of reproductive activity. A. intermedius had an annual life cycle. Eggs laid during late summer and autumn hatched during autumn-winter. Immature slugs were characterised by a period of low growth rate during winter followed by a period of rapid growth culminating in reproductive maturity. In both species, the phase of rapid growth rate was associated with enlargement of the hermaphrodite gland. The size of the hermaphrodite gland relative to body weight reached a maximum during the spermatozoon stage, generally coincident with maximum body weight. During the reproductive period of D. reticulatum and A. intermedius the body weight remained relatively stable but the hermaphrodite gland became progressively smaller as the slugs approached the post-reproductive stage. The albumen gland attained maximum weight at the oocyte stage of the hermaphrodite gland, at the onset of reproductive activity. The pasture, strongly dominated by grasses, was heterogenous in slope, vegetation and treading/grazing influences from sheep due to stratification of the habitat into contour tracks, associated with sheep movement around the slope contours, and intertrack areas. High population densities of D. reticulatum were associated with the track edges (kerbs) and the upper intertrack slopes, while densities of A. intermedius were highest for the intertrack slopes. Low densities of both species occurred on the tracks and at sheep ca
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