PARENT SESSION
Oral Session 4: Biodiversity I: Communities and Function.
Presiding: C Holzapfel and D Ellsworth
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room B 110.

Genotypic diversity in plant populations shapes arthropod community composition.

Johnson, Marc^*,,

ABSTRACT- Genetic variation in plant traits can affect the abundance and distribution of arthropod populations. Research on the community genetics of plant-arthropod interactions has led to the hypothesis that genetic variation in plant resistance traits is an important determinant of arthropod community composition. I tested this hypothesis by asking whether arthropod diversity and abundance are affected by: 1) genotypic differences between individual plants, and 2) the number of plant genotypes (genotypic diversity) within plant populations. In 2003, I simulated small Oenothera biennis (Evening Primrose) populations in the field by planting patches of eight plants while manipulating patches to contain one, four, or eight plant genotypes. Genetic differences between individual plants had strong affects on arthropod species richness, total arthropod abundance, Simpsons diversity index of arthropods, and Simpsons evenness index. Increased genotypic diversity in plant patches led to a 18% increase in arthropod richness from monocultures to patches with eight plant genotypes. The effect of plant genotypic diversity on arthropod richness became most prominent once plants began to flower. Genotypic diversity also affected arthropod abundance, Simpsons diversity index of arthropods and arthropod species evenness, but these affects depended on sampling date. The variance in community variables between plant patches frequently decreased with increasing genotypic diversity. These changes in arthropod community composition were accompanied by a 29% increase in plant patch fitness from patch monocultures to patch mixtures. This is the first report that intraspecific genetic diversity in a natural system affects the diversity of arthropods and variability in abundance of insect herbivores. These results have implications for the diversity-stability concept by demonstrating that the preservation of genetic diversity in plant populations can affect the conservation of communities.

Key words: biodiversity, genetic variation, community genetics, plant-insect