UMR 5175 CEFE - Centre d'Ecologie Fonctionnelle et Evolutive (CNRS), 1919 Route de Mende, F-34293 Montpellier Cedex 05, France.
Ann Bot. 2012 Nov;110(6):1245-51. doi: 10.1093/aob/mcs203. Epub 2012 Sep 28.
The competition-colonization trade-off theory postulates that the competitive and colonizing abilities of organisms are negatively related; this trade-off has been proposed as a major force in the maintenance of diversity. In plants, the competition-colonization trade-off is often considered to result from variation in resource partitioning, thus generating heavy competitive (non-dispersing) seeds and light (dispersing) non-competitive seeds. Here, the possibility is explored that early germination provides a competitive advantage, thus mediating competitive interactions.
Using eight populations of the heterocarpic species Crepis sancta (Asteraceae), the possibility was tested that dispersing and non-dispersing achenes differ in germination timing, and the impact of early germination on individual fitness components was analysed in the context of intraspecific competition. To evaluate whether seed reserve varies among achene types, endosperm size was also measured by analysing photographs of cross-sections taken under a binocular microscope.
The results show that non-dispersing achenes germinated 4 d earlier (on average) than dispersing achenes. It is also shown that early germination provides a positive advantage for the survival and final biomass of individuals, a pattern that was consistent over the eight populations and independent of achene type. Dispersing and non-dispersing achenes did not differ in terms of seed reserve (endosperm size). It is proposed that germination phenology may mediate the competition-colonization trade-off in Crepis sancta and the evolutionary significance of this phenomenon is discussed.
竞争-扩散权衡理论假定生物的竞争和扩散能力呈负相关；这种权衡被认为是维持多样性的主要力量。在植物中，竞争-扩散权衡通常被认为是由于资源分配的变化而产生的，从而产生了竞争激烈（不扩散）的种子和轻（扩散）的非竞争种子。在这里，我们探讨了早期萌发提供竞争优势从而调节竞争相互作用的可能性。
使用 8 个异花受精物种 Crepis sancta（菊科）的种群，检验了分散和非分散瘦果在萌发时间上是否存在差异，并在种内竞争的背景下分析了早期萌发对个体适应度成分的影响。为了评估种子储备是否在瘦果类型之间存在差异，还通过分析双筒显微镜下拍摄的横切面照片来测量胚乳的大小。
结果表明，非分散瘦果的萌发时间比分散瘦果早 4 天（平均）。此外，还表明早期萌发为个体的生存和最终生物量提供了积极的优势，这种模式在 8 个种群中是一致的，并且与瘦果类型无关。分散和非分散瘦果在种子储备（胚乳大小）方面没有差异。我们提出，萌发物候可能在 Crepis sancta 中调节竞争-扩散权衡，并且讨论了这种现象的进化意义。
