Spatial patterns at different scales for beetle predators and aphid prey.
Perry, Joe*,1, Alexander, Colin1, Holland, John2, Winder, Linton3, Griffiths, Georgianne2, 1 Rothamsted Research, AL5 2JQ, United Kingdom, email@example.com Game Conservancy Trust, Fordingbridge, Hampshire, UK3 University of Plymouth, Newton Abbott, Devon, UK
ABSTRACT- We studied interactions between the generalist predator carabid Pterostichus cupreus, an aphid prey species Metopolophium dirhodum and the crop density of winter wheat at the field scale. Spatial pattern was measured using the SADIE technique. Large-scale spatial dissociation between predator and prey populations early in the season, when generalist predators are considered to have control potential, suggested that P. cupreus activity-density delayed M. dirhodum population development and reduced its achieved maximum density. By contrast, whilst crop density had no large-scale spatial pattern, its small-scale variability was consistent with an influence on the time at which M. dirhodum achieved its maximum density. In sampling, groups of sample units may be aggregated in different schemes to optimize efficiency of population estimates. The relation between the shape and dimensions of the group and the spatial pattern of the sampled organism affects the difference between the actual and estimated population density (the bias), and the variability of that estimate (the precision). We use spatially-explicit ecological field data on beetles and aphids to compare simulations of common sampling scemes. Existing knowledge of spatial pattern may be used to inform the choice of sampling scheme and provide considerable improvements in accuracy (Alexander et al., in press). Reference Alexander, C.J., Holland, J.M., Winder, L., Wooley, C. & Perry, J.N. (2005) Performance of sampling strategies in the presence of known spatial patterns. Annals of Applied Biology (in press).
Key words: spatial pattern, spatial association, SADIE, scale
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