Evol Ecol Res 4: 1033-1048 (2002)     Full PDF if your library subscribes.

The long-term temporal variability and spectral colour of animal populations

Pablo Inchausti1* and John Halley2

1Centre for Population Biology, Imperial College at Silwood Park, Ascot, Berks SL5 7PY, UK and 2Department of Ecology, School of Biology, Aristotle University, UP Box 119, 54006 Thessaloniki, Greece

Address all correspondence to Pablo Inchausti, Laboratoire d’Ecologie, Ecole Normale Supérieure, 46 rue d’Ulm, Paris 75005, France.
e-mail: inchausti@biologie.ens.fr


We analysed the temporal variability and the spectral colour of 544 natural populations of 123 species that have been censused for more than 30 years. We compared the tendency for variability to increase with time (equivalent to spectral reddening) using three basic measures: an exponent of increasing variance, the 30 year temporal variability and the spectral exponent. For each, we considered the main ecological correlates: taxon, trophic level, latitude, and habitat type and body size. Our results confirm previous findings that population variability increases over time, and those ecological populations have reddened spectra. This effect is universally prevalent, being similar for populations of different taxa, having different body sizes, belonging to different trophic levels, living at different latitudes and exhibiting different types of population dynamics. Generally, the amount of reddening appears to be greater than that expected from environmental forcing alone. Also, there is no evidence that ecological variability tends towards a finite limit, although the increase of variability does decelerate. Our results suggest that widely used measures of population variability, such as the coefficient of variation or standard deviation of the logarithm of abundance, should be supplemented by measures of either spectral reddening or the rate of increase of the population variance.

Keywords: autocorrelation, conservation, extinction, fractal, noise, spectral colour, temporal variability.

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