. Research methods in ecology. Plant ecology. INVASION 235 hand, since a species may often be carried far from its geographical area, it is frequently of great significance in distribution. 283. Complete and partial invasion. When the movement of invaders into a formation is so great that the original occupants arc finally driven out, the invasion may be termed complete. Such invasion is found regularly in the case of many ruderal formations, and is typical of the later stages of many successions. It is ordinarily the result of continuous invasion. If. m Fig. 59. Continuous invasion into a new


. Research methods in ecology. Plant ecology. INVASION 235 hand, since a species may often be carried far from its geographical area, it is frequently of great significance in distribution. 283. Complete and partial invasion. When the movement of invaders into a formation is so great that the original occupants arc finally driven out, the invasion may be termed complete. Such invasion is found regularly in the case of many ruderal formations, and is typical of the later stages of many successions. It is ordinarily the result of continuous invasion. If. m Fig. 59. Continuous invasion into a new area; mats of Arenaria sajanensis. Silcne acaulis and Sieversia turbinata invading an aJpine gravel slide. the number of invaders is sufficiently small that they may be adopted into the formation without radically changing the latter, the invasion is partial. This is doubtless true of the greater munber of invasions, though these are regularly much less striking and important than instances of complete invasion. 284. Permanent and temporary invasion. The permanence of invasion depends upon the success attending ecesis, and upon the stability of the formation. It has already been noticed that under certain conditions plants may germinate and grovi^, and if they are perennials, even become 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 Clements, Frederic E. (Frederic Edward), 1874-1945. Lincoln, Neb. , University Pub. Co.


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