PARENT SESSION
Poster Session 19: Biodiversity
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

The effects of initial plant composition on patterns of community assembly.

Meredith, Rebecca^*,1, Hooper, David¹, Dukes, Jeffrey², ¹ Western Washington University, Bellingham, WA² University of Massachusetts - Boston, Boston, MA

ABSTRACT- Understanding how plant diversity affects ecosystem properties requires understanding how plant functional traits related to resource use and partitioning influence patterns of community assembly. To address this question, we used experimental communities established in 1992 in a California serpentine grassland. Ten experimental treatments included 1-, 2-, 3-, and 4-way mixtures of four plant functional groups: early season annuals (E), late season annuals (L), perennial bunchgrasses (P), and nitrogen-fixers (N). In 2002, weeding to maintain species composition was halted and we examined how the communities changed over the following 3 years. Here we focus on the following questions: 1) Did initial community composition influence final levels of species diversity? 2) Did initial community composition determine which species ultimately become dominant? And, 3) did communities that started with similar initial compositions remain similar or diverge in terms of both species and functional group composition? Despite strong differences in initial composition and diversity, by 2004 species richness was similar among all treatments. Evenness, however, was still significantly affected by initial composition – higher with E's, lower with P's. Three main trends were evident for species dominance: 1) Calcadenia multiglandulosa (L) was commonly dominant in B, N and P treatments in 2002, but was much reduced by 2004; 2) Bromus madritensis (E) was present in mostly low quantities in 2002, but by 2004 had become one of the top three species in over half the plots, particularly those initially dominated by L's; and 3) Plantago erecta (E) and Lessingia micradenia (L) remained relatively abundant and dominant in the majority of plots throughout the three years. Replicates of most treatments diverged in terms of species composition, probably from stochastic factors (e.g., proximity of seed sources). On the other hand, replicates of only three treatments diverged in terms of functional group composition, and functional group composition became more similar over time across all treatments. Thus, despite some historical effects on evenness and individual species' success, convergence of functional structure may indicate the importance of resource partitioning in these communities.

Key words: biodiversity, functional groups, species richness, community composition