. Animal Ecology. Animal ecology. TABLE 16 3 Roproductivlty of the grain weevil Grain Weevil Weevils per gram of grain 0. Number o( grains per weevil 100 50 PopulaUon size after 64 days 69 95 Progeny per weevil 11. at different densities (MecUgan 1932). Density 50 1 2 4 8 16 32 25 138 167 192 77 51 29 8 8. 6 stages induced liy intraspecific competition, preda- tion, and conditioning of the habitat becomes exten- sive w'nh. overcrowding and is usually much more important. Prcttation It is well known that variations in the popula- tion level
. Animal Ecology. Animal ecology. TABLE 16 3 Roproductivlty of the grain weevil Grain Weevil Weevils per gram of grain 0. Number o( grains per weevil 100 50 PopulaUon size after 64 days 69 95 Progeny per weevil 11. at different densities (MecUgan 1932). Density 50 1 2 4 8 16 32 25 138 167 192 77 51 29 8 8. 6 stages induced liy intraspecific competition, preda- tion, and conditioning of the habitat becomes exten- sive w'nh. overcrowding and is usually much more important. Prcttation It is well known that variations in the popula- tion level of predators coincide or often follow closely after variations in the population of prey species, but it is not always certain whether the number of preda- tors depends simply on the abundance of prey serving as food, or whether the predators by their feeding regulate the number of prey animals. Experimental studies amply demonstrate that under certain condi- tions, at least, both true predators and parasitoids greatly affect the numbers of the species on which they feed, and hence similar relationships may be looked for under natural conditions. .?\ study made in California shows clearly that while the long-tailed mealybug increases rapidly on the citrus trees from March through May, their populations are reduced by June or July by the ac- tion of three insect predators, two lacewings and a lady beetle. The predator populations are low com- pared with the prev, but each predator destroys many mealybugs (DeBach 1949). Quantitative determination of the significance of predation in controlling vertebrate populations under natural conditions is difficult to make, since it re- quires accurate measurement of the number of prey per unit area, the number of predators in the same area, and the number of prey taken by the predators. In one of the best such studies (Errington 1937a), carried on in Wisconsin and Iowa between 1930 and 1935, the population of the prey, the bobwhite quail.
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