Date of Award

June 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Mark E. Ritchie

Second Advisor

Jason D. Fridley


community ecology, intraspecific variation, old field, plant traits

Subject Categories

Life Sciences


Trait-based approaches are increasingly used in plant community ecology, but previous research has largely ignored functional trait variation within species. Here I investigated the role of intraspecific trait variation in community assembly and responses to spatial and temporal environmental variation in old-field plant communities in the eastern United States. In the first study I analyzed spatial patterns of functional divergence in old fields in central New York on spatial scales from 1-1500 m. Results showed that spatial divergence in functional traits at the community and intraspecific levels corresponded with spatial heterogeneity in edaphic variables, consistent with predicted patterns resulting from trait-based environmental filtering. In the second study I tested for evidence of environmental filtering and niche differentiation based on trait dispersion patterns, with or without accounting for intraspecific trait variation. The tests provided evidence of strong trait-based environmental filtering and weak niche differentiation, and these patterns were strengthened by the inclusion of intraspecific trait variation, demonstrating its importance for community assembly. In the third study I examined the contributions of intraspecific variation and species turnover to community trait responses to environmental gradients across a 1200-km latitudinal extent in the eastern United States. Community trait shifts in response to broad-scale climatic variation were driven primarily by species turnover, but intraspecific variation contributed strongly to trait shifts along edaphic gradients and at fine spatial scales. Finally I investigated the role of intraspecific variation in community trait responses to experimental nutrient enrichment in old-field communities and the influence of community functional diversity and dispersal in mediating these responses. After three years, community functional responses were driven almost entirely by intraspecific trait shifts, which were strongest in communities with high initial intraspecific variation for some traits. Taken together, my results suggest that intraspecific trait variation plays a strong role in the assembly of old-field plant communities and shed light on the circumstances in which intraspecific variation is likely to be important for plant community ecology in general.


Open Access

Included in

Life Sciences Commons