Bottom-up effects of plant genotype on aphids, ants, and predators.
Theory predicts that bottom-up ecological forces can affect community dynamics, but whether this extends to the effects of heritable plant variation on tritrophic communities is poorly understood. In a field experiment, I contrasted the effects of plant genotype (28 genotypes; 1064 plants), aphid density, and the presence/absence of mutualistic ants in affecting the per capita population growth of a specialist aphid herbivore, as well as the effects of plant genotype on the third trophic level. Plant genotype strongly affected aphid population growth rate, explaining 29% of the total variation in growth rate, whereas aphid density and ant-aphid interactions explained substantially less variation (< 2%) in aphid population growth rate. Plant genotype also had direct and indirect effects on the third trophic level, affecting the abundance of aphid-tending ants and the richness of predators. Multiple regression identified several heritable plant traits that explained 49% of the variation in aphid growth rate and 30% of the variation in ant abundance among plant genotypes. These bottom-up effects of plant genotype on tritrophic interactions were independent of the effects of either initial aphid density or the presence/absence of mutualistic ants. This study shows that plant genotype can be one of the most important ecological factors shaping tritrophic communities.
Johnson
Marc T J
MT
Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario M5S 3B2, Canada. mtj5@duke.edu
D000818:Animals; D001000:Ants / Q000254:growth & development* / Q000502:physiology; D001042:Aphids / Q000254:growth & development* / Q000502:physiology; D044822:Biodiversity; D017753:Ecosystem; D005838:Genotype; D010944:Plants / Q000235:genetics* / Q000469:parasitology*; D011157:Population Dynamics; D011158:Population Growth; D011235:Predatory Behavior / Q000502:physiology*; D013045:Species Specificity; D013559:Symbiosis