Former authors claimed that, due to parasites' aggregated distribution, small samples underestimate the true population mean abundance. Here we show that this claim is false or true, depending on what is meant by 'underestimate' or, mathematically speaking, how we define 'bias'. The 'how often' and 'on average' views lead to different conclusions because sample mean abundance itself exhibits an aggregated distribution: most often it falls slightly below the true population mean, while sometimes greatly exceeds it. Since the several small negative deviations are compensated by a few greater positive ones, the average of sample means approximates the true population mean., Jenő Reiczigel, Lajos Rózsa., and Obsahuje bibliografii
Quantitative community-wide moth surveys frequently employ flight-interception traps equipped with UV-light emitting sources as attractants. It has long been known that moth species differ in their responsiveness to light traps. We studied how the settling behaviour of moths at a light trap may further contribute to sampling bias. We observed the behaviour of 1426 moths at a light tower. Moths were classified as either, settling and remaining still after arrival, or continually moving on the gauze for extended periods of time. Moths that did not move after settling may not end up in the sampling container of the light trap and therefore are under-represented in automated trap samples relative to their true proportions in the community. Our analyses revealed highly significant behavioural differences between moths that differed in body size. Small moths were more likely to remain stationary after settling. As a corollary, representatives of three taxa, which in Europe are predominantly small species (Nolidae, Geometridae: Eupitheciini, Erebidae: Lithosiini), usually settled down immediately, whereas most other moths remained active on or flying around the trap for some time. Moth behaviour was also modulated by ambient temperature. At high temperatures, they were less likely to settle down immediately, but this behavioural difference was most strongly apparent among medium-sized moths. These results indicate the likely extent of the sampling bias when analysing and interpreting automated light-trap samples. Furthermore, to control for temperature modulated sampling bias temperature should always be recorded when sampling moths using flight-interception traps. and Mirko Wölfling, Mira C. Becker, Britta Uhl, Anja Traub, Konrad Fiedler.