Spatial genetic structure in an understorey dioecious fig species: the roles of seed rain, seed and pollen‐mediated gene flow, and local selection

Abstract

Summary 1. The spatial genetic structure (SGS) of a plant population is mainly determined by gene flow via seed and pollen, various natural selection pressures and spatial patterns of existing plants. However, the role of those factors in shaping SGS requires further investigation. 2. We studied the relative importance of those factors in shaping the SGS of an understorey dioecious fig species (Ficus cyrtophylla). Spatial patterns of existing individuals and microhabitat were surveyed, patterns of seed rain were investigated, seed dispersers were observed in the field, and the gene flow and SGS of a focal population were determined. 3. Three mid‐sized bulbul (Pycnonotus spp.) species were the primary dispersers of Ficus cyrtophylla fruits. All the age cohorts exhibited clumped patterns with a decreasing trend from seeds to seedlings, saplings and adults. Seed rain occurred in a non‐random pattern with high clumping in moderately lit microhabitats. The observed pattern suggests disperser preferences for those microhabitats resulting in higher seed deposition. 4. Seeds and pollen of F. cyrtophylla were widely dispersed (ranging from 9 m to 2.75 km and 10 m to 3 km, respectively). About two‐thirds of seeds and half of the pollen grains were locally dispersed (≤ 250 m) within the focal population. 5. Significant positive autocorrelations occurred at a local scale (≤10 m) in seeds and seedlings but not in saplings and adults. The SGS pattern disappeared when we reduced the sample size of seedlings to that for the saplings, which suggests that demographic thinning effects (e.g. density‐dependent predation and competition) on spatial distribution may lead to the loss of SGS through transitions from seedlings to saplings and adults. 6. Synthesis. Although F. cyrtophylla seeds and pollen were widely dispersed, the significant SGS present in seedlings probably resulted from clumped seed dispersal due to dispersers’ behaviour and high seedfall beneath parent trees. The loss of SGS in sapling and adult life stages is probably caused by demographic selection effects during recruitment. Our study emphasizes the different roles of dispersal and local selection in shaping SGS of plant populations.