PARENT SESSION
Contributed Oral Session 15: Populations and Genetics: Succession; Reproduction
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal
Effects of intraspecific competition on size variation among genetically related and non-related individuals.
Monzeglio, Ursula*,1, Stoll, Peter1, 1 University of Basel, Basel, Switzerland
ABSTRACT- The members of natural populations often differ in size and relatedness to each other, which may affect the division of limited resources and have consequences on reproductive success and population dynamics. Using genetically related and non-related individuals, we tested the hypothesis that competition among related individuals is more symmetric than among non-related individuals. If this were true, we expected a smaller coefficient of variation (CV) among individuals competing with related compared to individuals competing with non-related individuals. Using six maternal seed families of Helianthus annuus (sunflower), we set up a field experiment including two blocks each containing three main plots corresponding to three sequential, destructive harvests. Each main plot was further subdivided into six subplots sown either as a monoculture (i.e. individuals from the same mother plant) or as mixture (i.e. 5 seeds of each of the six mother plants). We found significant interactions among treatments and harvests for CVs of length and biomass (i.e. total, vegetative and reproductive). After 25 days from sowing we found higher CVs of vegetative biomass among individuals competing with non-related individuals, while after 84 days the CVs were higher among individuals competing with related individuals. The CV of reproductive biomass was significantly higher among individuals competing with related compared to individuals competing with non-related individuals after 84 days from sowing. At the end of the experiment (after 112 days) all CVs were similar. The CV for vegetative biomass showed significant harvest-family interactions, i.e. size variation and the hierarchies of the seed families changed during stand development. Our hypothesis that competition among related individuals is more symmetric than among non-related individuals was only supported early in stand development. Later in time, competition became more size-asymmetric among related compared to non-related individuals. At the final harvest, no differences could be detected.
Key words: sibling competition, asymmetric competition, size variation, Helianthus annuus