The Biodemography of an Intertidal Snail Population

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<jats:p>Numbers, deaths and growth rates were observed for three years in a delimited population of Acmaea digitalis whose members had been individually marked. The zone of vertical distribution of the species is determined by the behavior of these snails. In the fall and winter they ascend in the intertidal, and descend a smaller distance in the spring. This leads to a differential distribution of size classes. The oldest and largest animals are found highest in the intertidal zone. That the vertical movements are adaptive is suggested by death rates which are highest in the upper portions in summer, but rise in the lowest zone in winter. Probability of survival improves with age. Growth rate was remarkably consistent during the period of observation. It was fastest in the fall and winter months. During the month of July, and in part of June and August growth ceased, at least as measured by a change in shell length. Crowding decreased growth slightly but significantly. Growth rates in different areas suggest that time available for feeding may be a significant variable. Experimental manipulation of density indicates that emigration rates are density—dependent. The mechanism of density regulation is postulated as operating even at low overall densities because of the behavior pattern of the species.</jats:p>

収録刊行物

  • Ecology

    Ecology 46 (6), 831-844, 1965-11

    Wiley

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