Introductory Remarks

Abstract

These proceedings, like the meeting from which they sprang, bring together two topics of long-standing interest to ecologists: the regulation of individual species and the relative abundance of different species in a community. Indeed, the explicit quest for understanding population regulation can be traced to Gilbert White who, in 1778, queried why year after year there were always eight pairs of swifts in Selbourne. In view of the amount of study which has already been expended on these topics, one may ask ‘what is new?’ As is clear from this symposium, we are now more in a position to achieve a synthesis of these two topics. Another difference from the situation of some 40 years ago is the fact that plants are now being considered alongside animals and we are gaining new insights from their study. Coming to more recent history, from about 1920 until 1970 the emphasis was on the dynamics of singleand two-species population interactions. Several models were produced, of which the Lotka—Volterra and Nicholson—Bailey models have been the most enduring. Quite properly, ecologists searched for meaningful field tests of the theories which underlay these models. Such tests involved the measurement of populations in the field, to constructing precise life tables. This work was most straightforward in certain insects, where discrete generations imposed by the seasonal cycle enabled the complexities of overlapping generations and the problems of the determination of the precise age of an individual to be circumvented. Some of the leading work of that time was undertaken in Australia by Davidson & Andrewartha, in Canada by R. F. Morris and his colleagues, and in the United Kingdom by O. W. Richards, N. Waloff at Silwood Park and by G. C. Varley in Oxford. Many techniques were developed for enumerating populations and for analysing them, among the best known being key factor analysis. This technique was devised to detect the stage at which variations in survival contributed most to generation-to-generation fluctuations in popu­ lation size. As modified by Varley and Gradwell, the technique could also be used in the search for regulating factors, but there were many complications. Some of these factors were statistical arising from a lack of independence of data, but others were because of the sheer mechanical labour of analysing complicated sets of data when all one had at one’s disposal were handturned calculators, a situation that it is hard to envisage today. As this work progressed, two further insights added to the complications, though at the same time refocusing our questions in a more constructive way.