The Interpretation of Mortality Data in Studies on Population Dynamics

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Abstract
Biologists in general, and entomologists in particular, have published many data of the ‘percentage mortality’ type. It appears to be a natural tendency in the ecological study of an insect to attempt to measure the degree of mortality caused bv difierent factors. Early publications listed many figures on ‘percentage age parasitism’ because it was one of the easiest mortalities to measure. More recently, as betrcr techniques were developed for population sampling and mortality assessment, it has been possible to derive mortality data for other factors. Notable progress has even been made with such difficult problems as measuring the mortality caused by avian, mammalian, and invertebrate predators. Despite these developments, life tables generally show some residual mortality that cannot be attributed to a specific factor. Frequent population measurement can establish the exact time of such mortality, however, while concomitant work on behaviour, physical ecology, and inherent factors can provide very useful clues as to what intrinsic or extrinsic factors it may be related. Fairly complete life tables are already available for natural populations of a few species, and will no doubt become available for additional species from time to time.