Chapter 7 - Relative Methods of Population Measurement and the Derivation of Absolute Estimates

Most relative methods require comparatively simple equipment and, as they often serve to concentrate the animals, they provide impressive collections of data from situations where few animals will be found by absolute methods. This makes them particularly appropriate for initial faunal surveys and from a statistical viewpoint, plentiful data will appear to be preferable to the hard-won, often scanty, information obtained from unit area sampling. Most traps will collect specimens continuously, providing a relatively large return for the amount of time spent working with them; the cost of the data is low. With all these apparent advantages it is hardly surprising that these methods have been extensively used and developed. There are probably more accounts of their design and use in the literature than references to all the other topics in this book (therefore the list at the end of this chapter is highly selective).

7.1 Factors affecting the size of relative estimates 7.1.1 The 'phase' of the animal 7.1.2 The activity of the animal 7.1.3 Differences in the response between species, sexes and individuals 7.1.4 The efficiency of the trap or searching method 7.2 The uses of relative methods 7.2.1 Measures of the availability 7.2.2 Indices of absolute population 7.2.3 Estimates of absolute population 7.2.4 Collecting 7.3 Relative methods - catch per unit effort 7.3.1 Observation by radar 7.3.2 Hydroacoustic methods 7.3.3 Fish counters 7.3.4 Electric fishing 7.3.5 Aural detection 7.3.6 Exposure by plough 7.3.7 Collecting with a net or similar device 7.3.8 Visual searching and pooting 7.4 Relative methods - trapping 7.4.1 Interception traps 7.4.2 Flight traps combining interception and attraction 7.4.3 Light and other visual traps 7.4.4 The Pennsylvanian and Texas traps 7.5 Traps that attract the animals by some natural stimulus or a substitute 7.5.1 Shelter traps 7.5.2 Trap host plants 7.5.3 Baited traps 7.5.4 The use of vertebrate hosts or substitutes as bait for insects 7.6 Using Sound