[An error in determining the number of migrants during the trapping of small mammals with weighted lines].
The number of residential animals in daily samples is diminishing regularly during prolonged catching. It might diminish according to exponential law if: (1) the probability to be captured for each animal living on the sampling territory does not alter in the course of trapping; (2) all animals have the same possibility to be captured. The number of captured non-residential (migrating) animals stays the same during he whole period of trapping, thus increasing the number of animal captured at the end of trapping vs. one expected according exponential law. It is not correct however to consider the presence of migrants to be the only reason of the deviation from exponential decrease, because it is observed also in residential animals. (1) Home ranges of some animals overlap the trap line only by their edge. The possibility to capture such animals is 2-3 times lower than animals with central position of home ranges on the trap line. (2) The removal of peculiar demographic groups is not equal. Adult females are captured with highest intensity; young animals, on the opposite, stay uncaptured longer. It may be registered as increasing of proportion of young and subadult animals per an adult female with each day of removal. (3) Reproduction is intensive in summer. Young animals (up to age of 20 days) does not visit traps. Some of them become active in the middle and the end of trapping period when a great share of older animals (including their parents) is already captured. Because of these reasons disturbed exponential removal exists even in residential animals, and we can not differ the real proportion of migrants even in cases when the disturbance of exponential decrease per se is proved properly.
Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Science, Ekaterinburg, Russia.
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VS
Smirnov
D000818:Animals; D016009:Chi-Square Distribution; D017753:Ecosystem; D005260:Female; D008297:Male; D008722:Methods; D011156:Population Density; D012377:Rodentia; D013997:Time Factors
Oshibka v opredelenii chisla migrantov pri otlove melkikh mlekopitaiushchikh liniiami davilok.