Consequences of seed dispersal for gap-dependent plants: relationships between seed shadows, germination requirements, and forest dynamic processes

Abstract

This study compares the reproductive consequences of different seed dispersal patterns to gap-dependent plants having different germination requirements and seed dormancy capabilities. Using data on the frequency and size distribution of treefall gaps in cloud forest at Monteverde, Costa Rica, a computer simulation model of reproductive success revealed that: 1) Spatial and temporal availability of potential colonization sites differs among plant species whose germination success varies with gap size and gap age. For species that require large, young gaps (e.g., pioneer trees), suitable habitat patches may be as much as 15 times less common than for species capable of establishment in smaller or older gaps. 2) Because germination success is a continuous function of both gap size and gap age, the landscape does not consist of a mosaic of discrete ‘safe sites’ surrounded by unsuitable habitat. Instead, each patch has an associated probability of germination for each plant species. 3) While plant reproductive success is enhanced by dispersal, immediate reproductive success remains low for individuals with all but the most extensive seed shadows, especially for species that require large, young gaps. 4) When reproduction from dormant seeds is also considered, however, reproductive success is greatly increased. For plants whose seeds can remain dormant for just two years, reproductive success may be increased as much as 2000%. Furtnermore, seed dormancy magnifies the differences in reproductive success resulting from different seed shadows. Even animals that produce quite similar seed shadows may ultimately provide substantially different dispersal quality to plants that have the capacity for long seed dormancy.Key words‘colonization hypothesis’Costa Ricadispersal qualitygermination requirementsreproductive successseed dormancyseed shadowtreefall gap