PARENT SESSION
Wednesday, August 9, 1:30-5:00 pm
OOS 9 - Niche verses neutral: a look at an iconic idea in community ecology, its challenger, and the middle ground, Part II
Ballroom C, Ballroom Level, Cook Convention Center
Organized by: A Ostling (nsanders@utk.edu), NJ Sanders, and J Lake

In this organized oral session we will explore the latest advances in our understanding of how communities assemble, focusing on the ongoing debate over niches versus neutrality and keeping an eye towards finding the middle ground.

Neutral niche specialists drive historically contingent evolutionary assembly.

Fukami, Tadashi^*,1, ¹ University of Hawaii at Manoa, Honolulu, HI

ABSTRACT- Diversity in ecological communities can be influenced by assembly history, or the order and timing in which different species arrive. Although such historical contingencies have been studied at ecological time scales, effects of assembly history over evolutionary time scales remain unclear. Adaptive radiation, a key evolutionary process that has generated much of biodiversity, is normally assumed to have occurred with a single ancestral species colonizing open habitats. However, it is likely that other species also arrived from outside the habitats during the course of adaptive radiation, and that the order and timing of their arrivals varied among communities. Using a microbial microcosm, I show experimentally that the history of arrivals can greatly affect the extent of diversification during adaptive radiation. When an ancestral bacterial type was introduced by itself into a spatially structured habitat, it rapidly diversified, giving rise to multiple specialist types coexisting within the same niche. This diversification was suppressed when a niche-specialist bacterial type was also introduced before other niche-specialist types evolved from the ancestral type. However, no effect was apparent when the specialist type was introduced after other specialist types evolved from the ancestral type. Further experiments indicated that the specialist types were competitively neutral to one another and that this neutrality made diversification sensitive to assembly history. These results suggest that assembly history can determine not only the role of immigration (the ecological source of diversity) but also that of diversification (the evolutionary source of diversity) in community structuring.

Key words: Assembly rules, Neutral theory, Priority effects