1. An automated video-analysis method to study the foraging behaviour of polyphagous carabid predators for spatially heterogeneous populations of aphid prey
- Author
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King, Nigel
- Subjects
621.3994 ,Population ecology of insects - Abstract
A system was developed to automate the analysis of video images of polyphagous carabid predators searching for aphid prey. The system uses the following novel techniques: 1. large-scale foraging by predators across an arena of area in excess of 3 m squared. 2. automated collection of data on the movements of predators while searching within any sub-area of the arena (patch). An HVS VP112 tracking unit is used to analyse video images in real-time. A software system ('Predtrack') was developed on the BBC `B' micro-computer to analyse data generated by the tracker after storage, and has the capability to be entirely automatic. Predators are video-filmed as they search within a patch of prey centered in the arena. The output of the analysis programs is a set of means and standard errors for the following parameters of predator `tracks' (the trace of a single predator as it crosses the cameras field of view): 1. Duration of each track 2. Length of each track 3. Time spent moving per track 4. Time spent stopped per track 5. Number of stops per track 6. Average speed per track 7. Total angle turned through per track 8. Average rate of angle turned per unit distance per track 9. Average rate of angle turned per unit time per track The analysis method firstly isolates and identifies data belonging to each track in experimental data files and then uses a regression technique to convert this raw data into a set of representative lines from which angles of turn can be measured. Sample points are then taken along each line and timed relative to the raw data from which they are based. Statistics of movement as described above can be generated for any sub-period of an experiment. The system was used to investigate the response to spatial heterogeneity in populations of the aphid prey species Acyrthosiphon pisum, by the carabid predator Agonum dorsale. Preliminary results show that A. dorsale has the ability to aggregate to regions of high prey density, although the total response curve estimated for A. dorsale suggests that it cannot act in a regulatory manner upon populations of this prey species. Future experiments using two patches of different prey species at varying ratio's of each of their patch populations should be performed to investigate the possibility that, through the mechanism of prey switching, the total response of A. dorsale to aphid prey in the field could be such that a regulatory role is likely.
- Published
- 1990