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A tree hole is any tree cavity, produced through the action of extrinsic factors, that is in direct contact with the external environment at some point in its development. Tree holes have received relatively little attention from ecologists. Recently (Park, Auerbach, and Corley 1950) tree holes were classified; physical and biotic factors important in the origin and development of such habitat niches discussed; the tree-hole microsere concept developed; and a start made in a study of the tree-hole food web and pyramid of numbers. In this initial paper the research emphasis was on the populations of beetles of the family Pselaphidae that inhabit tree holes. The present report is another small step in the accumulation of data and ideas concerning this relatively small, delimited habitat niche. Such biotopes are more easily studied than, say, the floor stratum of a forest, although the tree hole may be thought of as a discontinuous extension of the forest floor (Allee, Emerson, Park, Park, and Schmidt 1949, p. 486). It has a population of log mold animals if it be in the terrestrial phase of the microsere, and this population tends to increase in size and taxonomic diversity as its walls soften, and the cavity begins to fill with litter. This makes for increase in ecological complexity as well. The tree hole also has its particular type of microclimate, vet one that is correlated with the more fluctuating microclimate of the whole forest community. In such tree-hole populations the oribatid mites and the collembolans usually are the most numerous arthropods, again, in parallel with the abundance of these two groups in forest floor leaf mold and log mold. All of these organisms are inextricably involved in the Darwinian web-oflife of the major community. |
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