Previous ecological studies of Thamnophis sirtalis in the Interlake region of Manitoba have concentrated on the spring and fall phases of the annual cycle. This study is an investigation of two aspects of the summer activity of these populations: summer dispersal and feeding habits. Summer dispersal in these animals is highly directional; snakes move south in spring and return north to their hibernation sites in late summer and fall. Large distances are also involved; movements of as much as 17.7 km have been recorded. No explanation of this pattern of dispersal is apparent. Feeding takes place in the summer range only, during June, July, and August. The wood frog (Rana sylvatica) is the most frequently eaten prey species. It is suggested that the short feeding period is the result of a life history strategy which maximizes the efficiency of reproductive activities at the expense of non-reproductive activities.
Vertical stratification samplers were developed for sampling the grave-sand substrate of a Brazos River, Texas riffle. Fifteen of 25 species recovered, occurred below Io cm. Mean percentages of total organisms recovered were 66.4%, 20%, 6.1% and 7.5% per lo cm level, respectively, from the surface down. Dominant insects were Neochoroterpes mexicanas naiads and chironomid, Simulium, Cheumatopsyche and Stenelmis larvae. Seasonal population peaks of these five groups in the top o cm correspond with observed emergence peaks. The smaller size classes were generally predominant in the o-Io cm level. Larvae of Stenelmis were the most evenly distributed among the various to cm levels in all size classes. A movement of Cheumatopsvche and Neochoroterpes to lower levels was observed following a large flood, suggesting an escape response to increased silt load and scouring.Dissolved oxygen ranged from saturation at the surface down to 0.4-0.7 ppm at 30-40 cm, indicating that it was possibly limiting at lower levels. Maximum temperature difference between io cm levels was only 3 C. Flow was negligible below Io cm.The vertical stratification sampler recovered significantly greater populations in the surface 20 cm, but not in the total 40 cm. than a modified Hess sq. ft. sampler.
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