Office: 519 Hubbard Hall
|Education||Degree||Year||Field of Study|
|Michigan State University||PhD||2004||Plant Biology / EEBB|
|Illinois State University||MS||1988||Biology|
|AuSable Institute||1992||Naturalist Certificate|
2008-present. Assistant Professor, Wichita State University
2006-2008. Post-doctoral Fellow, University of Kansas
2004-2006. Research Associate, Kellogg Biological Station, Michigan State University
2006. Adjunct Professor, Kalamazoo College
I am broadly interested in the processes that control the development and maintenance of ecological communities, with emphasis on patterns of species diversity, invasion, and the ecosystem production. I approach these topics by testing ecological theory and look for new ideas that can be used to guide the management and restoration of ecosystems. Below are some specific examples my research:
Effects of Immigration Rates on Plant Diversity
It is now well-documented that species pools limit plant diversity in grasslands (see below). However, it remains unclear how variability in immigration rates affect the development of plant diversity on a site. Not only are immigration rates potentially important to explain extant patterns of diversity but are also critical to restoration projects attempting to restore a diverse ecosystem. For example in prairies, it is relatively easy to re-establish a small number of grass species but much harder to restore a species-rich grassland. Currently, I have an experiment testing how immigration rates enhance plant diversity in a species-poor, Kansas prairie.
Community Assembly and the Development of Diversity
While species pools and immigration are likely to influence diversity, it is unclear whether the results are sensitive to the sequence of colonization events (community assembly). If communities are structured by the interaction between species traits and environmental conditions, community assembly is predicted to be a deterministic process. However, neutral theory predicts that community assembly is a stochastic process driven by births, deaths, immigration and evolution. Currently, Bryan Foster and I are testing the relative importance of these neutral and niche based processes on community assembly in northeast Kansas. In this experiment, we are manipulating species diversity and composition of plant species. After removing extant species, we seeded 240 plots in various combinations of plant species diversity and species traits. We are monitoring changes in diversity through time as a function of initial species composition (note differences among plots marked by the white posts in the pictures below) In addition to providing a strong test of ecological theory, the results will quantify how initial diversity and species composition impact the development and maintenance of plant diversity in grassland restorations.
Invasive Species: searching for an Achilles’ heel
Although invasive species can have large negative effects on the structure and function of native ecosystems, they do provide an interesting opportunity to test underlying ecological principles while trying to find ways to minimize their effects. Currently, we are test how propagule pressure (immigration rate) influences the probability of invasion among systems that vary in soil fertility and disturbance regimes. We are also testing in the field and lab several potential competitive mechanisms by which Lespedeza cuneata (sericea) invades native grasslands in Kansas.
Community Responses to Perturbations
Because the outcome of species interactions is dependent on environmental conditions, climate change—including alteration of atmosphere deposition of N—may alter the structure of communities. One interesting way to test this for communities is to quantify the variability (dispersion) of communities in response to perturbations. For example, in a long-term nutrient addition experiment in low-productivity sand prairie, we found that increased fertility reduced diversity at small scales, but also led to greater variability in plant community composition than unfertilized plots. This increased variability following perturbation suggests that it may be difficult to predict the response of communities to human alteration of environmental conditions. Currently, we have an experiment underway to test how initial conditions may influence the community dispersion in grassland systems.
Houseman, G. R., G. G. Mittelbach, H. L. Reynolds, and K. L. Gross. 2008. Perturbations alter community convergence, divergence, and formation of
multiple community states. Ecology 89:2172-2180.
Influence of Species Pools on Plant Diversity
While much of ecology has focused on understanding the role that local mechanisms, such as competition, have on biodiversity, it is becoming clearer that ecological communities are part of larger landscapes where migration of individual among communities may alter the relative importance of species interactions within communities. In a four-year seed addition experiment, I was able to show that species pools enhance local diversity but that the relative importance varies with productivity. In this case, diversity was highest at intermediate productivity. Companion species removal experiments showed that—regardless of species pool size—diversity is reduced at low productivity because of abiotic conditions, while species interactions limit colonization at high productivity. The importance of seed addition in these experiments also suggests that augmenting seed inputs into isolated prairie communities can enhance plant diversity.
Houseman, G. R., G. G. Mittelbach, H. L. Reynolds, and K. L. Gross. 2008. Perturbations alter community convergence, divergence, and formation of multiple community states. Ecology 89:2172-2180.
Houseman, G. R. and R. C. Anderson. 2002. Effects of jack pine plantations on Kirtland’s warbler nest habitat and barrens flora. Restoration
Influence of species diversity on ecosystem production: Implications for Biofuel production?
One surprising result from my species pool manipulations is the extent to which the species pool can increase the productivity of a given habitat. These impacts on productivity can occur in addition to complementarity resource use—currently the most commonly discussed mechanism. While these ideas are important for ecological theory, they also have important consequences for the use of native grasslands for bioenergy production. While I do not support the use of high input/low diversity systems (e.g. corn, soybeans) for biofuels, high diversity/low input systems on marginal lands may have conservation value. For example, lands that are not suitable for row-crop agriculture could be restored and managed for plant diversity as well as biomass production. This approach could provide biofuel alternatives as well as enhance or maintain native plant diversity, particularly compared to alternative uses of such land, such as cool-season hay and pasture that require high inputs and have low diversity.
B. L. Foster, K. Kindscher, G. R. Houseman, C. A. Murphy. 2009. Effects of hay management and native species sowing on grassland community structure,
biomass, and restoration. Ecological Applications 19:1884-1896.
External Research Grants
NSF Kansas EPSCoR (2010) “Can spatial variability created by dispersal explain the accumulation of biodiversity” ($39,000)
USDA-NRI (2006) “Does propagule pressure change invasion risk under different agricultural management regimes” ($125,000)
NSF Doctoral Dissertation Improvement Grant 0308856 with Kay Gross (2003) “Species pools and plant traits as constraints on species diversity across productivity gradients”
Houseman, G. R. and K. L. Gross. 2011. Linking grassland plant diversity to species pools, sorting and plant traits. Journal of Ecology 99:464-472.
B. L. Foster, K. Kindscher, G. R. Houseman, C. A. Murphy. 2009. Effects of hay management and native species sowing on grassland community structure, biomass, and restoration. Ecological Applications 19:1884-1896.
Houseman, G. R., G. G. Mittelbach, H. L. Reynolds, and K. L. Gross. 2008. Perturbations alter community convergence, divergence, and formation of multiple community states Ecology 89:2172-2180.
Reynolds, H. L., G. G. Mittelbach, T. Darcy-Hall and G. R. Houseman, K. L. Gross. 2007. No effect of varying soil resource heterogeneity on plant species richness in a low fertility grassland. Journal of Ecology 95:723-733.
Houseman, G. R. and K. L. Gross. 2006. Does ecological filtering across a productivity gradient explain variation in species pool-richness relationships? Oikos 115:148-154.
Suding, K. N., K. L. Gross, and G. R. Houseman. 2004. Alternative states and positive feedbacks in restoration ecology. Trends in Ecology and Evolution 19:46-53.
Houseman, G. R. and R. C. Anderson. 2002. Effects of jack pine plantations on Kirtland’s warbler nest habitat and barrens flora. Restoration Ecology 10:27-36.
Anderson, R. C., R. M. Anderson and G. R. Houseman. 2002 American Ginseng. Native Plants Journal 3:93-97, 100-105.
Courses Taught at Wichita State University
BIOL211 General Biology II
BIOL503 Taxonomy and Geography of Flowering Plants
BIOL560-561 Plant Ecology
BIOL610 Ecosystem Management and Restoration
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