The activity of subnivean invertebrates in southern Manitoba

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Aitchison, Caroline Williams.
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Snow cover affects the activity of invertebrates and determines which invertebrates are winter-active. Snow cover varied between 40 and 60 cm in all habitats in the first winter that was slightly colder than average. Subnivean temperatures ranged between 0o and -8oC, depending on the ambient air temperature: dips in the former occurred just after sudden drops of the latter. Snow cover for the second winter was established six weeks later than the previous year due to unusually warm weather: snow thickness varied between 30 and 50 cm. Subnivean temperatures ranged between 0o and -10.5oC. Snow density also affected the subnivean temperature... The activity of Araneae was positively correlated with subnivean temperature during the first winter, but was negatively correlated in the second winter. Both adults and immatures in most families overwintered. Forty-nine species were active throughout the year, with the exception of eleven species which occurred only in summer and autumn. Hence, no "winter species" were present, only winter-active ones. Many species of spiders were taken the second winter. Six of the 49 species had holarctic distributions. Coleopterans, mainly staphylinids, were extremely abundant in October and November, but ceased activity in winter, spring and much of the summer...