Department Chair

I. Martha Skerrett, Chair and Associate Professor of Biology

Date of Award


Access Control

Open Access

Degree Name

Biology, M.A.


Biology Department


Robert J. Warren II, Ph.D., Assistant Professor of Biology

Department Home page

First Reader

Robert J. Warren II, Ph.D., Assistant Professor of Biology

Second Reader

Daniel Potts, Ph.D., Associate Professor of Biology

Third Reader

Amy McMillan, Ph.D., Associate Professor of Biology


Ecological communities always contain a few common species and an abundance of rare species. Mechanisms determining commonness and rarity require experimental investigation. Given that most plant mortality occurs in seeds and seedlings, recruitment best predicts plant community assemblage and distributions. In northeastern North America, grassland plant species constitute a sizable portion of the native flora. Approximately 30% of western New York’s threatened and endangered flora are associated with grasslands, apparent leftovers from a post-glacial landscape. I investigated the mechanisms behind grassland species commonness and rarity by examining how habitat type, disturbance and biotic interactions limit seed recruitment for three rare grassland species and their common congeners. If grassland species rarity is determined by habitat suitability, then the rare grassland species will be more responsive to habitat heterogeneity and manipulation than are the common species. Rare species successfully recruited where burning reduced initial competitor density, but otherwise appeared severely limited by interspecific competition. Because both the rare and common plant species survived equally well in the forest and edge habitats, but only common plant species did much better in the meadows, the competition for space may be the limiting factor for rare grassland plants. Pollinator limitation may explain grassland plant rarity, which suggests that small populations may be limited by a lack of pollinator visits. Commoness and rarity are temporal designations that can change as disturbance alters the landscape. The results of this experiment suggest that for rare grassland plants, widespread burning and planting appears to be required, both to create suitable habitat and encourage positive biotic interactions.