Multigenerational analysis of spatial structure in the terrestrial, food‐deceptive orchid Orchis mascula

Abstract

Summary In long‐lived, terrestrial orchids, strong aggregation of adults and recruits within populations and pronounced spatial association between recruits and adults can be expected when seed dispersal is limited, probabilities of seed germination decrease with increasing distance from mother plants and/or not all mother plants contribute to future generations. When individuals are distributed evenly across life‐history stages, these processes can also be expected to result in a significant fine‐scale spatial genetic structure in recruits that will persist into the adult‐stage class. We combined detailed spatial genetic and point pattern analyses across different generations with parentage analyses to elucidate the role of the diverse processes that might determine spatial structure in Orchis mascula. Analyses of spatial point patterns showed a significant association between adults and recruits and similar clustering patterns for both. Weak, but highly significant spatial genetic structure was observed in adults and recruits, but no significant differences were observed across life stages, indicating that the spatial genetic structure present in recruits persists into the adult stage. Parentage analyses highlighted relatively short seed dispersal distances (median offspring‐recruitment distance: 1.55 and 1.70 m) and differential contribution of mother plants to future generations. Persistence of fine‐scale spatial genetic structure from seedlings into the adult stage class is consistent with the life history of O. mascula, whereas relatively large dispersal distances of both pollen and seeds compared to the fine‐scale clustering of adults and seedlings suggest overlapping seed shadows and mixing of genotypes within populations as the major factors explaining the observed weak spatial genetic structure. Nonetheless, comparison of the spatial association between recruits and adults with the genetic analysis of offspring‐parent distances suggests that the tight clustering of recruits around adults was probably caused by decreasing probabilities of seed germination with increasing distance from mother plants. Synthesis. This study shows that the approach presented here, which combines spatial genetic and spatial pattern analyses with parentage analyses, may be broadly applied to other plant species to elucidate the processes that determine spatial structure within their populations.