Island biology by Carlquist Sherwin John 1930-

Author:Carlquist, Sherwin John, 1930-
Language: eng
Format: epub
Tags: Island ecology
Publisher: New York, Columbia University Press
Published: 1974-03-14T16:00:00+00:00

Insular Woodiness

Euphorbia, for example. However, continental species of these genera are at least as arborescent as insular species and occur in open country in any case, not in closed stands.

Wallace (1878) claimed that woodiness of island plants connotes greater longevity, which permits repeated flowering and thereby a greater chance for cross-pollination in situations where paucity of pollinating insects would make cross-pollination of more ephemeral plant species less likely. He assumes that paucity of insular pollinating insects is a bottleneck. This assumption is dubious: plants may self-pollinate (see chapter 13), at least in a number of cases. Moreover, if conditions are suitable for an insect species with pollinating capabilities, population density of the insect should, if anything, be greater than in a mainland species (assuming the nature of insect faunas on islands is disharmonic), or else a suitable insect would be expected to be entirely absent—but rarely the intermediate condition Wallace predicates. If Wallace's assumption were true, more ephemeral species would be expected to evolve on islands as suitable insects became available, but ephemeral species are the exception on oceanic islands, as seen later in this chapter. Climatic factors, again, seem to be overriding in evolution of growth forms on islands. Less pronounced seasonality in flowering does occur in some insular plants, but this extension of flowering time appears to be the result of adjustment to less seasonal insular climates, not a factor for establishment of groups.

Measures of Selection and Adaptation

TRANSPLANT STATIONS

Thus far, no rigorously chosen and monitored transplant stations, such as those employed by the Carnegie Institute of Washington in the various studies by Clausen, Keck, and Hiesey, have been used for the study of insular plants and their tolerances. Cultivation of plants of Echium (Boraginaceae) from Macaronesia was described in chapter 5. Some insular species have been cultivated in the following California localities, however, and even though the results are crude, they may suggest the value of carefully performed studies:

1. San Francisco (Golden Gate Park, ca. 2 mi. inland from coast). Both Wilkesia (Asteraceae: from Kauai, 2000-3000 ft) and Lobelia

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