Graeme James Caughley - Significant Contributions

Significant Contributions

During 1966 Caughley presented methods by which to determine mortality patterns in mammals. He looked at mortality rate curves (qx) among ungulates, rats, voles, sheep, and man he found that they followed a common pattern. This "u" shaped pattern had a high juvenile mortality followed by a decrease and then a steady increase in mortality punctuated by a sharp increase with maturity. With this mortality pattern it was shown that although age of mortality differs among species as well as cause of death (disease, lack of food, predation) the trend that mammal species follow is similar. This is important in wildlife management since it shows that regardless of natural mortality factors populations tend to have high juvenile and mature deaths.

While working for the Forest Service and attending the University of Canterbury for his PhD Graeme modified Lotka and Fisher's equations for birth rates in populations to ones that applied to seasonally breeding populations. He wrote that most of the animal world had a season for breeding and that if births were treated as occurring at only one point in time then these equations could be used for seasonally breeding populations. This modification now gave a more accurate estimate of the reproductive value of a population without overestimating births by assuming year around reproduction.

Caughley and Birch (1971) published "Rate of Increase" to point out some of the misuses with this equation. Originally applied mainly to insects and humans they claim that the questions asked by entomologists are not necessarily those asked by mammalogists and vice versa. It is this difference in questions that caused misuse of particular equations in the realm of vertebrate studies. They point out that the rate of increase at a given density for a population of a stable age distribution (rs) is not obtainable when looking at mammals. This is because the assumptions used to make the age distributions (rs=0) when used to estimate rs cause it to be low.

The second argument is that the maximum rate at which a population with a stable age distribution increases in a given environment (rm= intrinsic rate of increase) can be calculated with the correct data. It had however, been used incorrectly by mammalogists who thought that vertebrate life table and fecundity data somehow paralleled those of caged insects held at low density. The correction was to infer what the rate of increase for a given population would be at both the initial density and at a higher density. In this way they corrected a misapplication of models so that those managing populations would use the right equation for the question that they were asking.

Not only did Graeme Caughley clarify methods so that they would be more applicable to population ecology, but he also condensed material that he thought was useful. In "Analysis of Vertebrate Populations" he distilled analyses that he thought were most relevant to the field and chose those that were also easy to understand. R. S. Millar stated in his review that until this book literature on analyses had been scattered and difficult to understand, but Graeme made topics more readable.

Caughley also co-published a book on Wildlife Ecology, Conservation, and Management: the first portion of the book covers an overview of population ecology while the second part is on applied ecology or management. His last publication Conservation Biology in Theory and Practice gives a history of prehistoric and historic extinctions as well as a collection of case studies. It contains chapters that look at the different ways population dynamics, risks, and legislation are approached. Perez claims that there is such a high volume of conservation textbooks today, but this one is more of a handbook on diagnosing and treating problems with populations. This diagnostic style is in part due to it being written by two field biologists, something that Clinchy and Krebs say took sixteen years in the making. That this is the first time that field biologists have written a book on conservation biology is a breakthrough in conservation biology. Before this, textbooks written by lab ecologists were used to teach field ecologists in a more abstract theoretical way.