SIBLING COMPETITION IN PLANTS

1. Sibling competition can de defined as operating when there is a density-dependent reduction in growth, survival or reproduction in closely interacting siblings utilizing the same space and resources relative to the growth, survival or reproduction that occurs when siblings are not interacting. This definition should be distinguished from hypotheses that make predictions about the intensity of inter-actions between siblings relative to those between non-siblings at the same density. 2. Two general classes of theoretical model incorporate sibling competition: one concerns the evolution of sex, the other seed germination-dormancy patterns. Unfortunately, the lack of documentation of sibling competition as a significant selection pressure in nature limits the utility of models that attempt to explain the evolution of specific life-history features in response to sibling competition. At present there is little support for the notion that interactions between siblings are more severe than between genetically unrelated non-siblings. 3. Life-history factors likely to promote sibling competition include fruit, seed and dispersal dimorphisms, synaptospermy, amphicarpy, cleistogamy, barochory, the phalanx growth pattern, and low growth habit. 4. Future research should focus on determining: (i) how widespread sibling competition is in plant populations, including an assessment of its relative importance as a selection pressure; (ii) the relation of sibling competition to plant breeding and dispersal systems; (iii) the importance and relevance of sibling competition to models that attempt to explain the evolution of sex or seed-dormancy patterns; (iv) the influence of sibling competition on population genetic structure; (v) the possibility that some plants may benefit from sibling interactions (kin selection).