Robert J. Warren II
Postdoctoral associate
Department of
Biolocal Sciences
Wright State
University
Diggs Laboratory 248
3640 Colonel Glenn Highway
Dayton, OH 45435, USA
t: (937) 775-4152
f: (937) 775-3320
robert 'dot' warren 'at' wright 'dot' edu
Map
Education
Ph.D. Ecology, University of Georgia, 2007
M.S. Biology, Western Carolina University, 2002
B.A. Journalism, Indiana University, 1991
Publications
Warren, R.J. (in press). “An experimental test of well-described vegetation patterns across slope aspects using woodland herb transplants and manipulated abiotic drivers.” New Phytologist.
Warren, R.J. and E. Mordecai (in press). “Soil moisture mediated interaction between Polygonatum biflorum and leaf spot disease.” Plant Ecology.
Warren, R.J. (in press). “A field test of theoretical incident radiation estimations and a simple method for integrating altitude into temperature prediction models.” Castanea.
Rossell, I.M., K.K. Moorhead and R.J. Warren. 2009. “Succession of a southern Appalachian mountain wetland six years following hydrologic and microtopographic restoration.” Restoration Ecology 17: 205-214.
Warren, R.J. 2008. “Mechanisms driving understory evergreen herb distributions across slope aspects – as derived from topographic position.” Plant Ecology 198: 297-308.
Warren, R.J., I.M. Rossell and K.K. Moorhead. 2007. “Impact of woody vegetation succession upon ground-layer communities in a southern Appalachian wetland.” American Midland Naturalist 157: 39-51.
Warren, R.J., I.M. Rossell and K.K. Moorhead. 2004. “Colonization and establishment of red maple (Acer rubrum) in a southern Appalachian wetland.” Wetlands 24: 364-374.
Warren, R.J., J.D. Pittillo and I.M. Rossell. 2004. “Vascular flora of a southern Appalachian wetland complex.” Castanea 69: 116-124.
Research interests
Species distributions as a function of current and future climate
A venerable goal in ecology continues to be the mapping of species distributions and deriving the habitat parameters that explain those distributions; the impending impacts of global climate change and a potential re-alignment of suitable habitat makes this all the more crucial. Yet, an accurate assessment of suitable habitat continues to be hampered by a tacit assumption: species presence equals suitable habitat; species absence equals unsuitable habitat. That is, a 1:1 correspondence exists between species distribution and suitable habitat. However, established ecology theory – such as source/sink, remnant , meta- and dispersal-limited population – demonstrates that the mere presence or absence of an organism does not provide sufficient evidence of habitat suitability.
My research interest centers upon the response of organisms to
current and predicted climates within the context of niche theory and
without the assumption that current distributions and suitable habitat
are in equilibrium. This requires collecting habitat-specific abiotic
data at the same scale as biotic data so that biological mechanisms
(beyond mere presence and absence) can be paired with environmental
drivers making the results predictive in novel environments. For example,
the analysis of both distribution and demographic data for three
understory evergreen plants (Hexastylis arifolia, Hepatica nobilis and Goodyera pubescens), followed by
experimental field manipulation of environmental variables, indicated
that these three species often exist outside their ecological niche –
that is, within environmental conditions that do not promote a positive
per capita growth rate. These data are important in constructing
predictive models based on the environmental response of the organism
rather than its current presence or abundance, which may reflect
biological or environmental interactions that no longer exist. By using
demographic models coupled with associated predictor variables, such as
soil moisture and light, these data delineate actual ecological niches
and, even more importantly, parameterize predictive models with
ecologically sound error distributions.
My current research augments habitat-specific demography by considering
multi-trophic interactions as additional dimensions within Hutchinson’s
n-dimensional hypervolume rather
than as constrictions (historically competition) of niche space. I ask
whether suitable habitat is determined by the combination of abiotic and
biotic tolerances rather than single resource optima and pairwise
interactions. That is, if biotic interactions change as a function of
abiotic gradients the traditional realized and fundamental niche
dichotomy breaks down. For example, the distribution of two ant-dispersed
herbs, H. arifolia and
H. nobilis, in Eastern
deciduous forests exhibits a unimodal (hump-shaped) response to soil
moisture. This unimodal response typically is interpreted as an optimal
resource response. However, the performance of experimental transplants
does not saturate, even in response to augmented soil moisture. I am
currently working on projects that show it the response of soil fungi and
ant dispersers to soil moisture – not the physiological limits of the
plants – that explain their “optimal” response to soil moisture. This
expands consideration of the niche to include habitat-dependent
interactions such as that between myrmecochores and ants; orchids and
mycorrhizal fungi; and summergreens and pathogenic fungus. This current
research seeks to decouple biological (ant seed dispersal) versus
environmental (light, soil moisture) drivers of variation in herbaceous
plant (H. arifolia and
H. nobilis) distributions via
environmental monitoring and seed depot experiments.