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Experimental Estimates of Census Efficiency and Pseudoturnover on Islands: Error Trend and Between-Observer Variation when Recording Vascular Plants
I. N. Nilsson and S. G. Nilsson
Journal of Ecology
Vol. 73, No. 1 (Mar., 1985), pp. 65-70
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2259768
Page Count: 6
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(1) Vascular plant species on forty-one small islands in Lake Mockeln, southern Sweden were recorded in 1976, 1978, 1980 and 1982. In 1982 the counts were made by two independent teams. (2) Census time per island increased over time to more than 200 man-minutes ha-1 in 1982. Similarly, the number of species recorded per island increased with time. In 1982, both teams had similar census efficiency which was, at most, 79%. (3) Between-team pseudoturnover (i.e. sampling errors that increase species turnover estimates) was 11· 4%, with 95% C.L. of 10· 2-12· 6%. Within-team pseudoturnover was significantly lower. (4) Pseudoturnover was negatively correlated with island area. The implication of this result for tests of island biogeographic theory is discussed. (5) The number of species found on each island in at least one of the years 1976-80, but not in 1982, as a percentage of the total number found on that island in 1982 was about 5%. This percentage, which is a maximum estimate of local population extinction, was negatively correlated with island area. We suggest that, at most, 1% of the vascular plant species present on an island becomes extinct each year.
Journal of Ecology © 1985 British Ecological Society