Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-26T17:46:21.973Z Has data issue: false hasContentIssue false
  • English
  • Français

Qualitative Changes in Populations in Unstable Environments1

Published online by Cambridge University Press:  31 May 2012

W. G. Wellington
W. G. Wellington
Affiliation:
Forest Entomology and Pathology Laboratory, Victoria, B.C.
Get access Rights & Permissions [Opens in a new window]

Abstract

Inactive moths of Malacosoma pluviale (Dyar) oviposit near their birthplaces, and most of their offspring also are inactive. More active moths can travel farther before they oviposit, and always have a higher proportion of vigorous individuals among their progeny.

Such polymorphism allows the insect to cope with environmental diversity; e.g., inactive residents exploit favourable habitats, and active migrants colonize more severe habitats, or replenish the vigour of other populations.

Because the most active moths usually export the most vigorous progeny, the population left behind becomes less vigorous during successive generations. This steadily decreasing vitality eliminates local populations that are not replenished by vigorous immigrants.

Qualitative changes in Malacosoma populations follow this basic pattern, but the rate of deterioration is affected by the habitat. Departing migrants fly too high to be stopped by small trees in farmland, bur many are stopped near their source by tall trees in forests. Deterioration therefore is slower in forests. Forests also delay return migration to nearby farmlands, and thus allow some farmland populations to deteriorate unchecked.

In a fluctuating climate, the size of the area tolerable for the species varies annually. When it begins to expand, the vigorous progeny of active moths can take immediate advantage of slight local improvements. Consequently, they are the first to exploit each marginal habitat that becomes tolerable. But while better climate persists, some less active descendants of these pioneers appear in all occupied habitats.

When the regional climate deteriorates, the tolerable area contracts, and most marginal populations are totally destroyed. Moreover, even within the contracted tolerable area, the harsher climate becomes intolerable for any deteriorated stock. In the next generation, therefore, the only regional survivors are vigorous colonies deposited in the tolerable area by some of the few migrants that escaped the widespread destruction of the preceding generation in the margins. Their descendants recolonize depopulated sections of the refuge, and so preserve the species in the region while the climate remains severe.

Type
Articles
Information
The Canadian Entomologist , Volume 96 , Issue 1-2 , February 1964 , pp. 436 - 451
Copyright
Copyright © Entomological Society of Canada 1964

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Andrewartha, H. G. 1961. Introduction to the study of animal populations. University of Chicago Press, Chicago.Google Scholar
Andrewartha, H. G., and Birch, L. C.. 1954. The distribution and abundance of animals. University of Chicago Press, Chicago.Google Scholar
Birch, L. C. 1957. The role of weather in determining the distribution and abundance of animals. Cold Spr. Harb. Symp. quant. Biol. 22: 203–218.Google Scholar
Birch, L. C. 1962. Stability and instability in natural populations. N.Z. Sci. Rev. 20: 9–14.Google Scholar
Campbell, I. M. 1962. Reproductive capacity in the genus Choristoneura Led. (Lepidoptera: Tortricidae). I. Quantitative inheritance and genes as controllers of rates. Canad. J. Genet. Cytol. 4: 272–288.CrossRefGoogle Scholar
Chiang, H. C. 1961. Fringe populations of the European corn borer, Pyrausta nubilalis: their characteristics and problems. Ann. ent. Soc. Amer. 54: 378–387.CrossRefGoogle Scholar
Chitty, D. 1960. Population processes in the vole and their relevance to general theory. Canad. J. Zool. 38: 99–113.Google Scholar
Johnson, C. G. 1960. A basis for a general system of insect migration and dispersal by flight. Nature, Lond. 186: 348–350.Google Scholar
Kennedy, J. S. 1961. A turning point in the study of insect migration. Nature, Lond. 189: 785–791.CrossRefGoogle Scholar
Laux, W. 1962. Individuelle Unterschiede in Verhalten und Leistung des Ringelspinners, Malacosoma neustria (L.). Z. angew. Ent. 49: 465–524.Google Scholar
Laux, W., and Franz, J. M.. 1962. Über das Auftreten von Individualunterschieden beim Ringelspinner, Malacosoma neustria (L.). Z. angew. Ent. 50: 105–109.Google Scholar
Milne, A. 1962. On a theory of natural control of insect population. J. theoret. Biol. 3: 19–50.Google Scholar
Orians, G. H. 1962. Natural selection and ecological theory. Amer. Nat. 96: 257–263.Google Scholar
Southwood, T. R. E. 1962. Migration of terrestrial arthropods in relation to habitat. Biol. Rev. 37: 171–214.Google Scholar
Wellington, W. G. 1954. Atmospheric circulation processes and insect ecology. Canad. Ent. 86: 312–333.Google Scholar
Wellington, W. G. 1957a. The synoptic approach to studies of insects and climate. Annu. Rev. Ent. 2: 143–162.Google Scholar
Wellington, W. G. 1957b. Individual differences as a factor in population dynamics: the development of a problem. Canad. J. Zool. 35: 293–323.CrossRefGoogle Scholar
Wellington, W. G. 1958. Meteorology in population dynamics. Int. J. Bioclim. Biomet. 2 (Pt. III, Sect. B).Google Scholar
Wellington, W. G. 1959. Individual differences in larvae and egg masses of the western tent caterpillar. Can. Dep. Agric. For. Biol. Div. Bi-m. Prog. Rep. 15: 3–4.Google Scholar
Wellington, W. G. 1960. Qualitative changes in natural populations during changes in abundance. Canad. J. Zool. 38: 289–314.CrossRefGoogle Scholar
Wellington, W. G. 1962. Population quality and the maintenance of nuclear polyhedrosis between outbreaks of Malacosoma pluviale (Dyar). J. Ins. Pathol. 4: 285–305.Google Scholar