. Current topics in forest entomology : selected papers from the XVth International Congress of Entomology, Washington, , 1976. Forest insects Congresses. 1956 '60 64 '68 '72 year Figure 4.—Trends in Neodiprion swainei egg populations in seven localities in Quebec, 1956 to 1974. I know of no statistical averaging techniques which would permit the replication either of the discontinuities, or of the trajectories following perturbation of the observed populations. Instead, I shall presume cause, measure the effects in a simulation model, and compare the results with the observed world. These
. Current topics in forest entomology : selected papers from the XVth International Congress of Entomology, Washington, , 1976. Forest insects Congresses. 1956 '60 64 '68 '72 year Figure 4.—Trends in Neodiprion swainei egg populations in seven localities in Quebec, 1956 to 1974. I know of no statistical averaging techniques which would permit the replication either of the discontinuities, or of the trajectories following perturbation of the observed populations. Instead, I shall presume cause, measure the effects in a simulation model, and compare the results with the observed world. These presumed causes are: 1. competition among groups of animals at different trophic levels for a common limiting resource; 2. a "Type III" (Holling 1965) density response of a group of predators which saturates at an extremely low sawfly density: In the sawfly life system, these are insectivorous birds, feeding on larvae and adults (fig. 1); 3. a second group of predators exhibiting a Type III response saturating at high prey densities, just below the level at which food begins to be limiting to the sawfly: these are cinereus shrews (fig. 1); 4. an upper equilibrium set by foliage: this equilibrium is stable on the insect plane but conditionally unstable on the forest plane (Jones 1975, 1977; Holling et al. 1978), if the replacement rate of foliage is not fast enough to prevent widespread killing of trees as the sawfly reaches this 73. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original International Congress of Entomology (15th : 1976 : Washington, D. C. ). Washington : United States Dept. of Agriculture, Forest Service
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