Beyond BACI: Experimental designs for detecting human environmental impacts on temporal variations in natural populations

Biological effects of environmental impacts are usually defined simplistically in terms of changes in the mean of some biological variable. Many types of impact do not necessarily change long-run mean abundances. Here, designs for detection of environmental impact are reviewed and some of their shortcomings noted. New sampling designs to detect impacts that cause changes in temporal variance in abundance of populations, rather than their means, are described. These designs are effective at distinguishing pulse and press episodes of disturbance and could be used for other variables of interest (size, reproductive state, rate of growth, number of species, etc.) for monitoring. The designs require sampling different time-scales before and after a proposed development that might cause impact. Cases are discussed in which there is a single control location. Inadequacies of this approach for detection of environmental impact are mentioned, with some discussion of the consequences for management of impacts that cause temporal change rather than alterations of the mean abundance of a population.