. Animal Ecology. Animal ecology. ^_ 2 1915 I 1925 1935 | 1945 1920 1930 1940 1950 YEARS FIG. 101 Dispersal of the European starling in North Ame between 1918 and 1949 (compiled trom Kessel 1953). acclimatize to new climatic conditions, and acquire new behavior patterns. Manner and means of dispersal Animals find suitable habitats and niches in various ways. In a uniform environment, dispersal movements radiate in all directions from the home area. The greater the density of individuals in the home area, the more quickly distant areas are invaded, and the farther away do individuals
. Animal Ecology. Animal ecology. ^_ 2 1915 I 1925 1935 | 1945 1920 1930 1940 1950 YEARS FIG. 101 Dispersal of the European starling in North Ame between 1918 and 1949 (compiled trom Kessel 1953). acclimatize to new climatic conditions, and acquire new behavior patterns. Manner and means of dispersal Animals find suitable habitats and niches in various ways. In a uniform environment, dispersal movements radiate in all directions from the home area. The greater the density of individuals in the home area, the more quickly distant areas are invaded, and the farther away do individuals SOUTH FIG. 10-2 Relation of breeding localities to birthplaces among robins. Numerals on concentric circles are distances from the origin in miles (I mile = kilometers). Data points beyond the 200-mIle radius are not placed to scale (Farner 1945). A common method of achieving dispersal is the broadcasting of enormous numbers of eggs, spores, encysted stages, or young so that they scatter into a wide variety of places in a more or less random man- ner. Those that come by chance into suitable environ- ments persist and become established ; those that enter into unfavorable locations are destroyed or never de- velop. Broadcasting is a wasteful procedure; it is especially characteristic of aquatic species. The fresh- water clam annually produces hundreds, perhaps thousands, of eggs. Only two fertilized eggs need ma- ture that the two parents be numerically replaced when they die, and thus the population of the species be maintained at a constant level. Contrastingly, in those forms, such as birds and mammals, that have developed a high degree of parental care, the number of eggs or young annually produced is commonly a half-dozen or less, and the offspring exercise con- siderable discrimination in their choice of suitable habitat. Although the dispersal of broadcast offspring is not under the control of the parents or the young, it is not often truly random. Water and wind cur
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Keywords: ., bookcentury1900, bookcollectionbiodive, booksubjectanimalecology
