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One final, important general point is that these asymmetries tend to reinforce the regulatory powers of intraspecific competition, in much the same way as exactly‐compensating or ‘contest’ competition (Section 5.3) gives rise to the most tightly regulated populations. This can be seen especially in a much longer term study that will almost certainly never be repeated, where a population of the herbaceous perennial, Anemone hepatica, in Sweden was visited and revisited every year from 1943 to 1956, with each plant being tracked individually (Figure 5.30; Tamm, 1956). Crops of seedlings entered the population each year between 1943 and 1952, but nonetheless, the most important factor determining which individuals survived to 1956 was whether or not they were established in 1943. Of the 30 individuals that were already of a large or intermediate size in 1943, 28 survived until 1956, and some of these had branched. By contrast, of the 112 plants that were either small in 1943 or appeared as seedlings subsequently, only 26 survived to 1956, and not one of these was sufficiently well established to have flowered. Tamm’s established plants were successful competitors – winners in a contest – year after year, but his small plants and seedlings were repeatedly unsuccessful. This guaranteed a near constancy in the number of established, winning plants between 1943 and 1956, accompanied by a variable number of ‘losers’ that not only failed to grow, but usually, in due course, died. Similar patterns can be observed in tree populations. The survival rates, the birth rates and thus the fitnesses of the few established adults are high; those of the many seedlings and saplings are low.

Figure 5.30 Asymmetric competition enhances population size regulation in an anemone. Space pre‐emption in a perennial, Anemone hepatica, in a Swedish forest. Each line represents one individual: straight for unramified ones, branched where the plant has ramified (i.e. produced new plants by vegetative growth), bold where the plant flowered and broken where the plant was not seen that year. Group A were alive and large in 1943, group B alive and small in 1943, group C appeared first in 1944, group D in 1945 and group E thereafter, presumably from seedlings.

Source: After Tamm (1956).