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Abstract
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.
Highlights
In ecology, the competition – colonization trade-off is postulated to be a major factor shaping life-history traits and contributing to the maintenance of interspecific diversity in communities at the regional scale (Tilman, 1994; Kneitel and Chase, 2004)
The results show that early germination provides a strong competitive advantage and we discuss the potential for the joint evolution of germination phenology and dispersal ability under natural selection
The way in which evolutionary processes shape the joint evolution of dispersal and germination phenology within a season has rarely been considered
Summary
The competition – colonization trade-off is postulated to be a major factor shaping life-history traits and contributing to the maintenance of interspecific diversity in communities at the regional scale (Tilman, 1994; Kneitel and Chase, 2004). According to this trade-off, good competitors exhibiting low colonizing ability are favoured locally while good colonizers exhibiting poor competitive ability are favoured by recurrent colonization, overall favouring the maintenance of both types in the landscape. The Smith and Fretwell (1974) model provides mechanistic support for competition – colonization trade-offs While such theoretical models are appealing, empirical studies analysing such trade-offs in plants have reached conflicting conclusions (Jakobsson and Eriksson, 2003). 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
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