Andrewartha became the most influential Australian ecologist, best known for attributing density-independent forces, such as weather, to be even more important than density-dependent factors in influencing population regulation. In 1933, Andrewartha began his studies on apple thrips, Thrips imagines, but later transitioned his studies to the plague grasshopper, Austroicetes, when he moved to Adelaide in 1935. This led to his first publication with his former student Charles Birch in 1941, "The influence of weather on grasshopper plagues in South Australia". In 1945, when his mentor James Davidson died, Andrewartha inherited 15 years of data collected on thrips population. After several years of statistical analysis of that data, Andrewartha and Birch demonstrated strong connections between thrips physiology, population levels, and other environment factors. This led to the publication of two major books, The Distribution and Abundance of Animals and The Ecological Web. Through this work, Andrewartha and Birch found a new school of population ecology, which emphasized the role of environmental controls as opposed to a community-dependent approach based on density-dependent factors. The joint work of Andrewartha and Birch earned them the "Eminent Ecologist Award" from the Ecological Society of America, which had never before been presented jointly to two persons The following timeline depicts the scope of his employment, responsibilities and publications throughout his career—
1962–1972 Professor of Zoology, University of Adelaide
1984 The ecological web : more on the distribution and abundance of animals published
Significant work
General theory of the distribution and abundance of animals
The ecology of Thrips imaginis
The ecology of Austroicetes cruciata
Diapause], period of suspended development in an invertebrate, or mammal embryo, especially during poor environmental conditions
The Queensland fruitfly Dacus tryoni
Honours and awards
Andrewartha received many prestigious awards including the Clarke Medal from the Royal Society of New South Wales, Verco Medal from the Royal Society of South Australia, and the Gold Medal from Australian Ecological Society in 1987. He was President of the Nature Conservation Society of South Australia and Chairman of the National Parks and Wildlife Advisory Council of South Australia.
1971: Introduction to the Study of Animal Populations, 2nd ed. Chicago: University of Chicago Press; London: Methuen & Co which includes additional information and adjustments.
1984: The Ecological Web. Chicago: University of Chicago Press
Retirement and death
Andrewartha retired in 1972. In 1975 he suffered a serious stroke, but continued writing his last book with Birch. He died on 27 January 1992 at the age of 84. He married Harriett Vevers Steele, herself a trained entomologist, in Melbourne in 1935. Predeceased by his wife, Andrewartha was survived by his son Graeme and daughter Susan Dutch.
Legacy
The HG Andrewartha Medal of the Royal Society of South Australia, was established to recognise outstanding research by an early-career, young Australian scientist.