Journal of Animal Ecology 2004 73, 996– 1006 © 2004 British Ecological Society Blackwell Publishing, Ltd. Stage-structured harvesting and its effects: an empirical investigation using soil mites T. C. CAMERON* and T. G. BENTON School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK Summary 1. Population dynamics results from an interplay between the environmental state and population density. With many organisms there is structure to the life history, and this structure has important consequences for the population’s density dependence and its interaction with environmental noise, and therefore its population dynamics. Perturb- ing population structure, such as through harvesting, may therefore affect the way that the populations respond to stochastic environmental variation. 2. We conducted three experiments on populations of soil mites kept under controlled conditions and harvested a constant proportion of eggs, juveniles or adults. The exper- iments (a) minimized environmental variability, (b) created environmental variability by randomizing food supplies, and (c) provided excess food and repeatedly subdivided the populations to maintain them below carrying capacity. 3. We find that harvesting different stages has marked effects on stage structure, which differ between constant and variable environments. For example, harvesting adults decreases the number of adults, harvesting eggs increases the number of adults and harvesting juveniles has no effect under near constant conditions, whereas in a variable environment harvesting adults and juveniles reduces adult numbers, but harvesting eggs has no effect. 4. As well as changing the mean age structure, harvesting can change the variance of the different stages. For example, in a constant environment harvesting juveniles does not change the variability in juvenile numbers or population size, but in a variable environ- ment harvesting juveniles increases the variability in the size of the juvenile class and hence the total population variability. 5. For populations that are kept at one-third to one-half carrying capacity (approxim- ately where the maximum sustainable yield should result) harvesting of the different age classes has marked positive effects on the population growth rates. Harvesting dif- ferent age classes causes changes in the density dependence, which explains the way in which the population parameters respond. 6. In conclusion, the population response to harvesting depends on the stage/age structure and the way it changes with harvesting and environmental conditions. Managing economically important populations, subject to harvesting, should consider structured life histories. Key-words: age structure, density dependence, environmental stochasticity, perturba- tion, population growth rate. Journal of Animal Ecology (2004) 73, 996–1006 Introduction In the simplest case (a closed population, no predators, uniform environment, etc.), the number of organisms largely depends on the amount of resources available and the way those resources are partitioned between members of the population. The interplay between the Correspondence and present address: T. G. Benton, School of Biological Sciences, Zoology Building, University of Aberdeen, Aberdeen, AB24 2TZ, UK. Tel: 01224 272399; E-mail: t.benton@abdn.ac.uk *Present address: Earth and Biosphere Institute, School of Biology, University of Leeds, Leeds LS2 9JT, UK. E-mail: bgytcc@leeds.ac.uk