Quantitative methods for detecting invertebrate predation occurring in the field.

Abstract

1.  Brief descriptions are given of methods that can be used either to determine the mortality caused by a complex of predators to a single target prey species or to quantify the diet of a single target predator species.
2. The following methods can be used quantitatively; direct observation, field caging, recovery of labelled prey, electrophoresis, single radial immunodiffusion, rocket immunoelectrophoresis, enzyme-linked immunosorbent assay.
3. The following methods have potential for quantitative use; faecal analysis, gut dissection, tube precipitin test, ring test, Oakley-Fulthorpe test, crossed immunoelectrophoresis, crossover immunoelectrophoresis, fluorescence immunoassays.
4. The following tests are likely to remain qualitative; chromatography, double-diffusion, immunofixation, standard immunoelectrophoresis, latex agglutination, passive haemagglutination inhibition assay, complement fixation test.
5. Examples are given of the use of these tests in predation studies.
6. Precautions associated with the use of these methods are described.
7. Various equations are reviewed for estimating predation rates using data on predator density, proportion positive and detection period in post-mortem tests.
8. There are limitations to the use of all current methods. Direct observation and field caging are of restricted application and often involve disturbance to the system being studied. Faecal analysis and post-mortem methods can confuse scavenging and secondary consumption with predation and they measure biomass ingested rather than number of prey killed or injured. Recovery of labelled prey has the faults of all these methods.
9. Potential new techniques are described for determining, from an examination of its gut contents, what a predator has eaten, when it ate it and in what quantity.