Rachel J. Collins, Ph.D.

Forest Ecology, Community Ecology

Department of Biology
Frostburg State University
(301) 687-4170
rcollins2 at wisc.edu

Education
Research Interests
Current Research
Publications
Teaching
CV

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Education

Ph.D. Ecology and Evolution Program, Biology Department, University of Pittsburgh, Pittsburgh, PA
M.S. Zoology, Miami University, Oxford, OH
B.S. Wildlife and Fisheries Science, Zoology Department, North Carolina State University, Raleigh, NC

Research Interests

I use a theory driven approach to address applied questions in community ecology. My research program identifies the mechanisms controlling species composition and diversity using multi-factor, manipulative experiments. Forests are great model systems for tackling such issues because they are valuable to humans, are important components of global nutrient cycles, and house a great deal of diversity. Forest, however, are not always as they appear. Communities full of trees may seem healthy and sustaining when in fact they are losing natives, adding invasives, have altered ecosystem function, and are unable to regenerate following disturbance. Consequently, simply identify controlling mechanisms or ecological drivers regulating diversity and species composition may cause one to miss the forest for the trees. My research identifies the relative effects of drivers, characterizes the interactions among these drivers, and examines the dose effect of drivers. In other words, how the relative and interactive effects of ecological drivers change as the level of driver abundance or occurrence changes. My goal is to develop more accurate, conceptual models and effective management strategies for forest communities. Because my work empirically tests ecological theory, it can be used to develop more predictive computer models of forest dynamics.

Current Research

I. Roles of herbivory, invasive species, and climate change in driving changes in native plant communities: From patterns to mechanisms

Collaborators: Donald Waller, Sarah Wright

Check out this project’s webpage here.

Indian cucumber root (Medeola virginiana)

My particular interest in this work lies in the testing the relative and interactive effects of the ecological drivers (invasive plant species, dominant native plants, white-tailed deer, exotic earthworms) in upland forests across southern Wisconsin. This research offers an excellent opportunity test how competition from invasive plants or dominant native plants, top-down effects of herbivory, and distorted ecosystem function from exotic earthworms shape native plant communities.

Invasive species are a major cause of endangerment, worldwide. Yet in eastern and central forests, there is little evidence that plant invasions directly cause losses of native plant species. Our experiment is designed to tease apart whether invasives are a driver of ecological change or simply an effect of another driver. If the latter is true, then invasives may simply be more apt at resource uptake when there is a temporary influx of resources such as after a disturbance or due to eutrophication. Similarly, invasives could be taking advantage of newly freed resources when herbivores preferentially remove natives but avoid invasives due to greater toxicity (i.e., apparent competition and novel weapons). Alternatively, if invasives are a driver of native species loss through competition, we will further elucidate the nature of the interaction (e.g., superior resource uptake or retention, faster growth due to novel weapons or enemy release, pre-emptive resources uptake through differential phenology, differential resource allocation).

Recent work from our lab reveals that a few native species have become super-abundant in Wisconsin forest understories over the last 50 years. The rise of these dominant native species is associated with dramatic declines in diversity and tree regeneration here and elsewhere. Possible causes for the recent rise in these dominant natives include increases in white-tailed deer populations (which may promote apparent competition) and changes in disturbance regime (which may increase available resources). I am interested in whether dominant native species are out-competing rare natives or simply responding to another driver like herbivory. If the latter is true, our work will demonstrate whether dominant natives and invasives are responding to the same drivers of ecological change.

Although white-tailed deer have coevolved with native plants communities for millennia, overabundant deer populations represent novel conditions in forests. Deer, therefore, provide an opportunity to study the dose effect of a driver. I am particularly interested in how the dual roles of deer as herbivores and as seed dispersers change with changes in deer density. I hypothesize that deer disperse a greater proportion of native seeds at low deer densities, and deer disperse a greater proportion of invasive species at high deer densities. If deer do cause apparent competition between natives and invasives, then I hypothesize that there is a deer-density threshold below which, deer no longer drive the apparent competition between natives and invasives.

Earthworms, native to Europe and Asia (e.g., Lumbricus terrestris), are associated with distorted forest ecosystem function in midwestern forests (see Bohlen, P. et al. 2004. Ecosystems 7:13-27; Hale, C. et al. 2005. Ecological Applications 15: 848-860). These exotic earthworms arrived via soil relocation, horticultural activities, and the release of excess fishing bait. In unglaciated regions, exotic earthworms seem to out-compete and replace native species. In glaciated regions, where native earthworms are largely absent, exotic worms seem to have colonized more rapidly than natives earthworms have. In both areas, exotic earthworms change ecosystem function through altering detritus communities, increase rates of decomposition, alter C and P cycles, and reduce the litter layer. These changes are associated with declines in tree seedling and herb densities and a concomitant increase in invasive abundance. Researchers have struggled to identify just how invasive exotic worms affect plant communities, as it is hard to manipulate earthworm densities. I am interested in exploring (1) the patterns of native and exotic earthworm abundances S. Wisconsin, (2) whether patterns of earthworm abundance and species composition reflect observed patterns of ecological change, (3) the interactions of earthworms with other drivers of ecological change.

Northern red oak seedling (Quercus rubra)

The above summary of my interest in ecological drivers and their possible effects on forested communities in Wisconsin was only possible through illustrating some of the probable interactions among drivers (e.g., apparent competition). This highlights that conceptual models of forest dynamics must include multiple drivers simultaneously and allow for changes in driver interactions across changes in driver abundance or occurrence.

II. Effects of disturbance and herbivory: Tests of three forest dynamics models

Collaborators: Walter Carson, Mary Beth Adams, Henry Schumacher

My interests in this research center on evaluating current conceptual model of forest dynamics and building a conceptual model that accurately depicts shifts in species composition and successional trajectories after disturbance in eastern deciduous forests

Eastern deciduous forests have seen major shifts in tree species composition over the past 50 years. One of the most striking changes is the decline in oak species abundance and the concurrent increase in maple species abundance. These changes have impacted the timber industry because oaks have a higher economic value than maples. Research has failed to identify the causes of these changes likely because much of the work has either been observational or tested a single hypothesis at a time. I am testing three models proposed to explain forest dynamics (shade tolerance, initial floristics, and herbivory) by experimentally manipulating canopy gap formation, prescribed fire and the presence of white-tailed deer in two forest types in West Virginia. The experimental design is fully factorial with eight replicates in each forest type. I have data on nearly 50,000 permanently tagged individual seedling, sapling, and canopy trees of 26 species at two sites in West Virginia. The design allows me to examine both the relative and the interacting effects of three major forest processes (fire, canopy gaps, and deer herbivory) on species composition. This work goes beyond simply addressing the oak and maple issue to identify the processes that are controlling forest species diversity, composition, and successional trajectories.

In a nutshell, fires and gaps shifted species compositions towards pioneer species when deer were absent. This finding supports the long standing Shade Tolerance Model, which predicts as disturbance severity increases so does the proportion of fast growing pioneers. When deer were present, the species composition remained nearly unchanged (i.e., the conservation of species composition) because deer preferentially removed pioneer species that germinated following disturbance. Previously, the pattern of conservation of species composition following disturbance was attributed to the Initial Floristic Model, which predicts pre-established seedlings and saplings will out competes newly germinating pioneers. My work calls into question the widespread use of Initial Floristics Model to explain patterns of species composition and forest succession. The interaction between disturbance and overabundant deer suggests that current forest dynamics are driven more by top-down effects of herbivory than by preemptive competition from advanced regeneration. Management that includes reducing deer populations would likely be more effective than practices that solely rely on controlling competitors.

Two years after fire under a canopy gaps that are unfenced, woody vegetation is rare, ferns are abundant.

Prescribed fire

Two years after fire woody vegetation is 2 m tall under canopy gaps that are fenced.

Publications

Collins, Rachel J and Walter P. Carson. 2004. The effects of environment and life stage on Quercus abundance in the eastern deciduous forest, USA: Are sapling densities more responsive to environmental gradients? Forest Ecology and Management. 201: 241-258.

Collins, Rachel J. and Walter P. Carson. 2004. The fire and oak hypothesis: incorporating the effects of deer browsing and canopy gaps. Van Sambeek, J.W., J. O Dawson, F. Ponder, Jr., E. F. Loewenstein, J. S. Fralish, eds. Proceedings, 13th Central Hardwood Forest Conference; 2002 April 1-3; Urbana, IL. Gen. Tech. Rep. NC-234. St. Paul, MN: USDA, Forest Service, North Central Research Station. 565 p. Peer Reviewed.

McGill, David W., Rachel J. Collins, and Walter P. Carson. 2004. Response of pin cherry (Prunus pensylvanica L.f) to fire canopy disturbance, and deer herbivory on the Westvaco Wildlife and Ecosystem Research Forest. Van Sambeek, J.W., J. O Dawson, F. Ponder, Jr., E. F. Loewenstein, J. S. Fralish, eds. Proceedings, 13th Central Hardwood Forest Conference; 2002 April 1-3; Urbana, IL. Gen. Tech. Rep. NC-234. St. Paul, MN: USDA, Forest Service, North Central Research Station. 565 p. Peer Reviewed.

Schuler, Thomas, M, W. Mark Ford, and Rachel J. Collins. 2002. Successional dynamics and restoration implications of a montane coniferous forest in the central Appalachians. Natural Areas Journal. 22: 88-98.

McGill, David W., Vincent L. Ford, Rachel J. Collins, Walter P. Carson, W. Mark Ford. 2002 Controlling Pin Cherry (Prunus pensylvanica Lf.) in Central Appalachian Hardwood Stands. Popular summaries from the fourth International Conference of Forest Vegetation Management, Nancy, France, 17-21 June, 2002, INRA, p. 154-156.

Stevens, M.H.H., Raikow, D.F., Servedio, M.R., Collins, R.J., Schumann, T.L., Tipper, A.N., and W.P. Carson. 1996. Hutchinson's Chariot: A Review of Species Diversity in Space and Time. Bulletin of the Botanical Society of America 42:48-49.

Collins, Rachel J. and Gary W. Barrett. 1996. Effects of habitat fragmentation on meadow vole (Microtus pennsylvanicus) population dynamics in experimental landscapes. Landscape Ecology.12: 63-76.

Manuscripts in Prep.

Collins, Rachel J., Walter P. Carson, and Mary Beth Adams. Tests of three major conceptual models of forest dynamics: evaluating the influence of gaps, fire, and browsing. To be submitted to Ecological Monographs.

Collins, Rachel J., David Rogers, Thomas Rooney, and Donald Waller. 50-years of change in tree regeneration and forest cover in Wisconsin forests. To be submitted to Ecology.

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Teaching

Swarthmore students exploring the biodiversity at the Smoky Mountain National Park.

I have built solid teaching skills through two, one-year, sabbatical-replacement positions at Dickinson (2003-2004) and Swarthmore Colleges (2004-2005). I taught six courses in these two years; each course had lecture and laboratory components. At Dickinson, I taught Interactions Among Animals, Plants and Fungi, (an introductory biology course for majors and non majors), Plant Geography and Ecology, and Forest Biodiversity and Systematics. At Swarthmore, I taught Ecology, Biodiversity and Ecosystem Functioning, and Introduction to Organismal and Population Biology. The latter course was team-taught and I am a co-author on the laboratory manual.

I developed lab exercises that help students build skills in all areas of the scientific method from developing hypothesis and experimental design to analysis and synthesis. Many of the exercises are inspired from recently published research. In an experiment using prairie species grown in a greenhouse, students test current competition theory. In other experiments, students use protists to examined island biogeography theory and community assembly rules. I have developed a set of excel-based exercises that focuses student learning on statistical analyses and population modeling. Each lab exercise builds on the previous week’s activities. Thus, as students progress through the semester, their quantitative abilities and confidence strengthen.

Dickinson students standing in a pit left by a tree fall. Plant Ecology class trip to the Allegheny National Forest, September 2003

Diversity and ecosystem function in prairie plants. Competition experiment at the Swarthmore greenhouse, April 2005.