SHUFFLING THE OFFSPRING - UNCOUPLING AND SPATIAL DISCORDANCE OF MULTIPLE STAGES IN VERTEBRATE SEED DISPERSAL

Recruitment of vertebrate-dispersed plants may be divided into a serie s of sequential stages including fruit removal by frugivores, seed del ivery to the ground, post-dispersal seed survival, seedling emergence, and seedling establishment. The particular processes operating at dif ferent stages may be independent of each other (''uncoupled''), and pe culiarities in the configuration of the interrelationships between sta ges (sign and magnitude of uncoupling) may lead to high site-specifici ty of the eventual outcome (''spatial discordance''). This conceptual framework is illustrated in this paper using recruitment data for the bird-dispersed tree Phillyrea latifolia (Oleaceae) from two southeaste rn Spanish localities (forest and scrubland habitats). Between-habitat differences in P. latifolia recruitment are best understood by consid ering that patterns of uncoupling among recruitment stages depend stro ngly on local conditions, particularly on the thoroughness of fruit cr op removal by frugivorous birds. The interaction of P. latifolia with frugivores has implications at every subsequent stage in recruitment, and proper understanding of the constraints operating on recruitment r equires recognition of the multiplicity of stages involved. Uncoupling of stages was found to originate fine-scale discordances in patterns of regeneration in the two habitats studied. We use a structural equat ion model to quantify the direct and indirect effects of the various r ecruitment stages on spatial variation in number of 2nd-year seedlings recruited. Variation among microhabitats in recruitment was due to va riation in seed rain intensity and seed survivorship in scrubland, whi le post-germination events limiting seedling emergence played a major role in forest recruitment. Results of this study highlight the need o f considering the multi-staged nature of recruitment in vertebrate-dis persed plants.