Donald M. Waller
Chair of Botany, Professor of Botany and Environmental Studies
232 Birge Hall
Ph.D. (1978) Princeton University
Plant ecology /evolution; tracking long-term ecological change; effects of deer, nitrogen deposition, habitat fragmentation, and climate change; conservation biology and genetics; metapopulation / metacommunity dynamics
Conservation biologists seek to discover mechanisms that threaten the persistence of native species and communities, and to use this knowledge to implement effective conservation strategies. We use the tools of plant demography, community ecology, and population genetics to investigate plant population and community dynamics.
On a coarse scale, we are interested in tracking how forest herb communities are changing over time and space. Using a unique historical data set collected by John Curtis and colleagues, we are tracking 50 year shifts in plant community composition, structure, and diversity. We are particularly interested in patterns of community impoverishment and homogenization, and how the invasion of the region by exotic species is affecting native plant diversity and abundance.
On a fine scale, we study how demography and genetics influence the dynamics and persistence of rare species like Pedicularis furbishiae, Aconitum novaboracense, Cirsium pitcherii, and Polygonella basiramea. We are interested in how reproductive characters influence the abilities of rare plants to persist via repeated recolonization (metapopulation dynamics). We also use isozyme and DNA markers to assess population genetic structure in relation to population size and environmental conditions. Such information leads, in turn, to a better understanding of how the size and arrangement of habitat patches and patterns of disturbance affect long-term persistence.
Small and inbred populations face multiple hazards including the accumulation of deleterious mutations (increasing the genetic load) and the increased expression of these mutations upon inbreeding (inbreeding depression). While inbred populations may eliminate some of their load via selection against deleterious recessive alleles, such purging may be inefficient in small populations with a history of inbreeding. In lab experiments with the fast-cycling annual Brassica rapa, we are attempting to track how the genetic load shifts in response to population size and levels of inbreeding. Evaluating how much purging occurs in small inbred populations compliments existing theory and enhances our understanding of the short-term dynamics of mating system evolution and the genetic hazards faced by small populations.
We also study how high densities of white-tailed deer are affecting populations of sensitive herbaceous and woody species. Much of this work centers on Tsuga canadensis (an old-growth dominant in the region), Thuja occidentalis (an important community type), and Trillium grandiflorum (a charismatic woodland wildflower). We use the tools of demography and experimental exclosures to assess how seedling recruitment relates to local site conditions and deer densities. Such data are vital for making ecologically informed deer management decisions.