Image from page 248 of “Animal Ecology” (1961)
Title: Animal Ecology
Year: 1961 (1960s)
Authors: Kendeigh, S. Charles (Samuel Charles), 1904-
Subjects: Animal ecology
Publisher: Englewood Cliffs, N. J. , Prentice-Hall
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library
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FIG. 17-1 Onset and subsidence of an outbreak of chinch bugs in Illinois during the 1930’$. Areas supporting the densest popu- lations are indicated by the darker pattern (Shelford and Flint 1943). come an important crop or fruit pest in the United States, investigators are sent to its place of origin, to discover its natural parasitoid or predator enemies and introduce them into the area of infestation. On the whole, this procedure has been successful (Sweet- man 1958). About the turn of the century several attempts were made in Europe, especially in France, to sup- press plagues of meadow voles by starting epizootics of typhoid. This bacterium was found present in dying voles, was cultured and distributed through the fields on food that the voles would eat. The success of the various attempts was always controversial, and when it was appreciated that the disease was also dangerous to man, these procedures were generally abandoned (Elton 1942). Considerable study is be- ing made at the present time of the use of bacteria and other micro-organisms in the biological control of insects (Steinhaus 1960). Myxomatosis has been used for the suppression of the rabbit population in Australia. Caused by a filter- able virus, it is highly contagious among the intro- duced European rabbits, but apparently not trans- missible to man or other animals. The virus is carried between rabbits principally by mosquitoes in Aus- tralia, and by fleas in England. Death occurs about 15 days after exposure. In 1950, extensive field trials with the myxoma virus were undertaken in eastern Australia, and by the end of the year mortalities locally as high as 99.8 per cent occurred. Epizootics have continued in later years but with somewhat lower virulence. The virus was introduced into France in 1952, where it spread rapidly; it reached England in 1953. The prognosis of the disease is un- certain. In some regions of Australia, rabbits have recovered from less virulent strains of the virus, or there has been selection of genetically more resistant individuals, so it is possible that some degree of im- munization may arise. The disease, however, may be successful in keeping the population at a low level (Bourlicre 1956). Irruptions may occur with almost any kind of animal in any habitat. Irruptions of the bean clam occurred several times between 1894 and 1955 in the intertidal zone at La Jolla, California. The abrupt decline of the last outbreak in 1951-52 was the result of an epizootic associated with a minute unicellular organism of uncertain identity, found in the tissues of the clam (Coe 1955). CATASTROPHES Catastrophes occur at more or less widely spaced intervals and bring marked depressions in the population level of a species. Figure 17.2 shows an- nual populations of the house wren over 41 years, first in Ohio, then in Illinois. Decidedly low points Irruptions, catastrophes, and cycles 235
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