Brian J. Wilsey

Brian J. Wilsey

B.S. 1986 Henderson State University
M.S. 1988 Louisiana State University
Ph.D. 1995 Syracuse University

Title and Mailing Address:
Professor, Department of Ecology, Evolution, and Organismal Biology,
253 Bessey Hall,
Iowa State University, Ames, IA 50011-1020
Office: 131 Bessey Hall
Lab: 40 Bessey Hall
Phone: (515)294-0232
Fax: (515)294-1337


In the Wilsey lab, we are interested in the ecology of grasslands. Tallgrass prairies are among the most species-diverse ecosystems. We commonly count 20-30 plant species in Iowa within small quadrats (0.4 m2), and most small prairies (< 10 ha) support more than one hundred species ( Martin et al. 2005, Wilsey et al. 2005a). It is still largely unknown how this very high species diversity develops and is maintained over time. Developing a better understanding of mechanisms behind diversity maintenance is a central focus of work in the lab (e.g. Wilsey et al. 2005, Polley et al. 2005, Martin and Wilsey 2006, Isbell et al. 2009, Wilsey et al. 2009). Furthermore, we are studying how changes in species diversity influence community stability and ecosystem process rates (i.e. ecosystem services). Information from our studies will be useful in the management and restoration of grassland ecosystems.

    Loess Hills Loess Hills, Iowa (Sylvan Runkel Preserve)

Biodiversity and ecosystem process rates in native and exotic communities (MEND - Maintenance of Exotic vs. Native Diversity). Funded by the U.S. Department of Agriculture NIFA Carbon Cycling Science Program

The homogenization of the earth's biota is affecting nearly every region of the earth, and is expected to increase due to increased movement of people and goods between regions. Grasslands, which cover roughly 25% of the planet, contain perhaps the most homogenized communities. Many exotic (i.e. non-native or "invasive") species have been introduced or have escaped into grasslands where they form 'novel ecosystems' (Hobbs et al. 2006) of species with a very recent history of interacting with each other. This has led to a patchwork of exotic- and native-dominated fields on modern landscapes. Species interactions, biodiversity, niche overlap, and ecosystem functioning could all differ between these novel ecosystems and the native systems that they replaced. We are testing whether there are fundamental differences in biodiversity maintenance mechanisms and ecosystem functioning between exotic- and native-dominated grasslands with large numbers species (e.g. 40 native and exotic species in Wilsey et al . 2009). Hypotheses are being tested by comparing paired exotic and native species in planted mixtures and monocultures in common garden experiments and with observational studies of intact grasslands. Treatments also include altered rainfall (Wilsey et al. 2011) or cattle grazing (Isbell and Wilsey 2011). Summer precipition treatments are either no precipitation or 128 mm added from July 15-August 15 (or 15% increase in annual precipitation) during the driest part of the year. The most important findings so far are: 1) species diversity and richness was consistently much lower in exotic communities than in native communities, even when communities were compared in a common environment, 2) species interactions were fundamentally different, with complementary resource use occurring in native but not exotic communities, 3) niche overlap was much higher in exotic than in native communities, and this was related to temporal (Wilsey et al. in press) or canopy overlap (Isbell and Wilsey 2011), 4) spring green-up was consistently about four weeks earlier in exotic communities and three and a half weeks earlier in exotic monocultures than natives, and 5) intercorrelations among phenology measures (green-up, flowering date, senescence date) were highly altered in exotic communities, and 6) all these effects were similar between irrigation treatments. The earlier green-up by exotic species suggests that some of the earlier green-up attributed to climate change may be a result of an increase in abundance of exotics, and this deserves further study. Thus, our our results suggest that there are key differences between novel ecosystems and the native ones that they replaced.

Is plant diversity an important predictor of ecosystem process rates?

Biodiversity is declining worldwide from human activities. In recent years, we have focused on how diversity can impact community and ecosystem processes. Species diversity may influence processes independently of, or interactively with, the abiotic components of the environment. Species diversity has two components, 1) richness, or the number of species in a given area, and 2) evenness, or how evenly distributed biomass or abundance is among species. Several high profile studies in the 1990's found that net primary productivity and resistance to invasions declined as species richness was reduced in experimental plots (Naeem et al. 1994, Tilman et al. 1997, Hector et al. 1999). We have been experimentally varying the other component of diversity, evenness, in experimental grassland plots. By varying evenness instead of (and in addition to) richness, plots with different levels of diversity are created, but without the variability caused by different species compositions. In the first experiment, which was done in an old field in 1997, we found that total primary productivity decreased linearly as community diversity (evenness) was reduced, and that it was largely invariant to changes in species composition. (Wilsey and Potvin 2000). A second experiment found that communities with lowered evenness were less resistant to invasion by plants and spittle bugs (Wilsey and Polley 2002). Others found that species richness-productivity relationship were similar between communities planted with equal relative abundances and communities with realistically unequal abundances across species (Wilsey and Polley 2004, Isbell et al. 2009a,b), and that invasion resistance and NPP can vary between extinction scenarios in prairie communities (Losure et al. 2007, Isbell et al. 2008). Species that green-up early in the growing season were especially important in preventing invasion because their growth period matched the period of maximum invasion pressure (Losure et al. 2007). Studies with litter decomposition found that higher evenness, but not richness, resulted in higher decomposition rates, and that diversity effects were smaller than microtopographic effects (Dickson and Wilsey 2009).

Species diversity partioning

What should we be measuring in biodiversity studies? Are species relative abundances related to local extinction risk? Do changes in rarity (quantified with evenness measures) occur before local extinctions (quantified with richness) or is rarity unrelated to extinction risk? Under what conditions is seed limitation important and how do they alter these biodiversity components? Species diversity has multiple components, and we are attempting to develop a better understanding of how components are related and whether they respond similarly to ecological processes. We have found that a diversity partitioning approach provides us with a more complete understanding of diversity compared to using single measures alone (Stirling and Wilsey 2001, Wilsey et al. 2005b, Martin et al. 2005, Wilsey 2010). Evidence from plant communities suggested that evenness and richness are acting as diversity components (Stirling and Wilsey 2001) each responding in their own way to changes in the environment, with richness responding more to migration during seed dispersal events and evenness responding more to competition intensity and ungulate grazing (Martin and Wilsey 2006, Wilsey and Stirling 2007). Changes in evenness often precede (and predict) changes in richness (Wilsey and Polley 2004, Wilsey and Stirling 2007, Wilsey et al. 2009). Thus, studies of both dimensions of diversity (evenness and richness) can be more informative than studies with richness alone.

Recent Exciting Results

  • There are two ways to maintain stable biomass production in ecosystems
  • Exotic grassland species have stronger priority effects than native species

    Past Interests:

    We have studied how native ungulates (bison and a few elk) affect tallgrass prairie restoration success at Neal Smith National Wildlife Refuge. Exlosures were erected and maintained for five years to study how grazing has altered tallgrass prairies community development (Martin et al. 2005, Martin and Wilsey 2006). The recruitment of rare prairie species into grass-dominated stands was higher with grazing than without grazing, but an important finding was that rare species were not recruited without seed additions. bison

    Selected Current and Past Projects

    1. MEND: Maintenance of Exotic vs. Native Diversity
    2. Effects of Dominant Species on Loess Hill Prairie Restorations
    3. Grazing Effects on Plant and Ecosystem Processes
    4. Quantifying Prairie Restoration Success


  • Kaitlin Barber, Ph.D. student
  • Andrew Kaul, Ph.D. student
  • Leanne Martin, Ph.D. 2013, M.S., May 2005, now Univ. Kansas
  • Yue Huang, Visiting student from Northeast Normal University, Changchun, China
  • Xiaofei Li, Visiting student from Northeast Normal University, Changchun, China
  • Forest Isbell, Ph.D., May 2010, now at Univ. Georgia
  • Kathryn Yurkonis, Ph.D., Jan. 2010, now Univ. North Dakota
  • Andrea Blong, M.S., May 2007
  • David Losure, M.S., May 2006
  • Xia Xu, Postdoc
  • Tim Dickson, Postdoc, now at Univ. Nebraska - Omaha
  • Pedram Daneshgar, Postdoc, now at Monmouth University, N.J.


    Date Last Modified: April 28, 2015
    Copyright 2000 Brian J Wilsey