produces relatively more domatia compared to the tiered, open crowns typical of mature

C. alliodora trees. This counterintuitive pattern of domatia production may be an artifact

of the planting design in the Huertos Project: because there was little competition for

light among young C. alliodora plants, they displayed thick, bushy growth prior to

dramatic increases in height accompanied by shedding of the lower branches as

competition for light increased (J.J. Ewel, pers. comm.).

 Regardless of the generality of C. alliodora crown geometry as the plants age, in

this study the abundance of available nesting space in 2-yr-old trees may largely explain

why ant species richness was highest at this age. The changes in crown structure may

also partially explain why many of the generalist ant species found in the 2-yr-old plants

were not present in the 5-yr-old trees. If interspecific competition for nest sites limits

species coexistence as the plants age, then the presence of more unoccupied domatia in

the 2-yr-old plants may have promoted species diversity at this stage of plant

development. This could be particularly true when the ant colonies were small and

unable to wage territorial wars typical of arboreal ant communities (Holldobler and

Lumsden 1980). Tillberg (2003) showed that the lower branches of 2-yr-old plants were

inhabited by a diversity of generalist ants, which presumably did not recolonize after

these branches senesced as the plants developed the crown structure typical of mature

trees. Additionally, since many of the species found on 2-yr-old trees were generalist

live-stem nesters, they may have been only opportunistic inhabitants of the younger C.

alliodora plants and either died or moved as the plants aged and competition for nest sites

increased (Alonso 1998, Longino 1996, Palmer et al. 2000).