. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage. Zoogeography -- Geographical distribution; Animal ecology. 82 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY The starfishes of the genus Pentaceraster, ranging through the entire Indian and Pacific oceans, present a great variety of form, but so many transitional and intermediate types are present that from a conservative standpoint they all belong to a single species, P. mami- The same phenomenon is true for some sponges, whose vagility is slight and for the most part confined
. Ecological animal geography; an authorized, rewritten edition based on Tiergeographie auf ockologischer grundlage. Zoogeography -- Geographical distribution; Animal ecology. 82 ECOLOGICAL FOUNDATIONS OF ZOOGEOGRAPHY The starfishes of the genus Pentaceraster, ranging through the entire Indian and Pacific oceans, present a great variety of form, but so many transitional and intermediate types are present that from a conservative standpoint they all belong to a single species, P. mami- The same phenomenon is true for some sponges, whose vagility is slight and for the most part confined to a short larval period. Thus thirty-two supposed species of Spirastrella, a widespread genus in the Atlantic, Pacific, and Indian oceans, have been united into a single protean species by the demonstration of transitional Reef. Fig. 5.—Outline, average size, and shell thickness (heavy contour = thick shell) of five forms of Anodonta cygnea at their centers of distribution: a, forma typica; b, ; c, ; d, ; e, After Buchner. corals are famous for their diversification and adaptability, and their environmental conditions have such great variation that each indi- vidual branch may be subject to special conditions, and there are almost as many modifications as Geographic isolation in inland waters.—Geographic isolation of small areas is especially characteristic of inland waters. A lake, a pond, a swamp, or a pool is surrounded by land as an island is by water. The great majority of inland lakes are small; less than 30 exceed 1000 sq. km. in extent, and many are very small. Rivers are separated by land at their sources, by the sea at their mouths, equally effective barriers for their fresh-water inhabitants. The environmental conditions, especially in standing waters, are extremely variable: the daily and seasonal temperature range; the dissolved substances, or- ganic and inorganic; the kind of bottom; t
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