Upland vernal pool, Bald Eagle State Forest, PA
Current Research Projects
Fine-scale Habitat Structure and Plant Species Diversity
This work builds on the competitive uncoupling hypothesis I developed in my doctoral dissertation at the University of Wisconsin-Madison. The basic idea is that negative intraspecific interactions at the scale of individuals reduce species richness in plant communities, strong patterns of fine-scale microhabitat structure can decouple these interactions and, thus, species richness should be positively correlated with measures of fine-scale habitat structure. Field studies on the Carrizozo Lava Flow in southern New Mexico support this proposal.
One implication of this mechanism is that habitats with the type of fine-scale spatial structure that enhances diversity are essentially habitats that are forgiving of oddballs (poorly competitive species that are excluded elsewhere), which include rare native species and newly arrived exotic ones. Such habitats may, therefore, simultaneously harbor endangered species and function as "waystations" where exotic species that otherwise might be competitively excluded from a new region are able to maintain marginal populations. Competitive hierarchies shift with fluctuations in environmental conditions, and marginal immigrants may be able to maintain viable populations in such settings long enogh for conditions to change in their favor or for natural selection to produce adaptations to their new environments and thus colonize beyond the waystation habitat. If so, the uncoupling mechanism has interesting implications for biogeography (e.g. colonization and subsequent adaptive radiation on volcanic islands, such as Hawaii) and conservation in a changing worl.
A few years ago, I began working with Phil Marquis ('07) to investigate these ideas using simulation models. We developed an individual-based simulation program based on the mathematical models I'd developed in my dissertation. I presented the first set of experimental results from the model at the 2007 AAG conference in San Francisco and am currently running more experiments and working on a manuscript.
|Three-species simulation in progress in a highly fragmented landscape (blue = non-habitat barrier). The competitively dominant species (orange) occupies most of the cells, while the two competitively inferior (green) species are persist in the most isolated fragments.|
We developed two versions of the program, one for research (no graphics) and one for teaching. Click here for more info and downloadable files.
Upland Vernal Pools of the Ridge and Valley Province
Vernal pools are small, isolated, ephemeral wetlands that occur throughout the high elevations of the Ridge and Valley Province. They function as critical breeding habitat for many amphibian species and also harbor Scirpus ancistrochaetus, a federally listed endangered plant species. I've been mapping pools using air- and field-based surveys and from aerial photographs since 2001, and have located over 300 pools. Cheryl Cottine ('04) and Trevor Gibson ('03) have helped with fieldwork, as have my kids, Bic and Deanne. Lance Lippencott pilots the Cessna 172 that saved countless hours of walking and biking. Dave Penick has also served as pilot and fearless ground crew member, and bear consultant. My dog, Jasper (RIP), provided good conversation and companionship in the field and, being exactly 1 meter long, scale in many photographs. During the 2008 growing season, I plan to begin a floristic inventory of vascular plants that make the pools their home.
Landscape Spatial Structure and Amphibian Genetics and Development
Collaboration with Dr.s Don Dearborn and Tristan Stayton (Bucknell Univ. Biology Dept.). Vernal pools in the Ridge-and-Valley region generally occur in clusters of a few to twenty or more pools and are critical breeding habitat for a number of amphibian and invertebrate species. As habitats, there are two critical scales at which landscape spatial structure affects biological processes: 1) most pools are <1,000 m2 and are separated from others within the same cluster by distances of tens of meters, while 2) the clusters themselves are isolated at the scale of kilometers.
These isolation patterns affect different types of organisms in different ways. Mole salamanders (Ambystoma spp) and some frog species depend on vernal pools for breeding. Past research has found low vagility and high natal pool loyalty in mole salamanders, while frogs are both more mobile and less loyal. Both types of organisms can readily move between pools within clusters, but the distance between clusters should inhibit dispersal between them. Thus, we hypothesize, the genetic population structure of each species should reflect the landscape and habitat spatial structure to greater or lesser degree, depending on their vagility and natal pool loyalty. We're testing the hypothesis using DNA microsatellite analysis from tissue samples collected in the spring 2007 breeding season. A second component of the research, led by Tristan, investigates fluctuating asymmetry (FA) and addresses the question of whether there are patterns of FA that correlate with habitat spatial, genetic, or environmental characteristics. A third ongoing vernal pool research project is Tracey Crumb's master's thesis research. Tracey is investigating relationships between environmental characteristics and species diversity for vertebrates and invertebrates at sites on Jacks Mountain.
Hana Nower and Tom Sherman were tireless field workers and did the preliminary lab work. We also had field assistance from Mark Spiro, Steve Jordan, Maggie Haines, Leo Zacks, Mark and Lynn Berg, Geoff Goodenow, and Kathy Rowe.
Eventually I'll get some photos from these projects uploaded.
Oh Captain, My Captain: Lance Lippencott, flying high and in control.
Cheryl Cottine and Jasper.
Me, stuck on a log.
Some side projects and old, abandoned ones.
The Hollow Earth
This is an oddball back-burner project that I haven't been able to resist. It's been highlighted in David Standish's (2006) book Hollow Earth: The Long and Curious History of Imagining Strange Lands, Fantastical Creatures, Advanced Civilizations, and Marvelous Machines Below the Earth's Surface (Cambridge, MA: Da Capo Press), and "What Curiosity..." has been translated into Portuguese and published online here (among some very good company, I have to say).
The idea that Earth is hollow has a surprising long and not entirely loopy pedigree. Edmund Halley's hollow Earth was the first hypothesis deduced from Newton's Principia, and John Cleves Symmes's theory (far less reasonable than Halley's) was instrumental in the development of 19th century American science and exploration. The web has given it new life and wings. It's a useful teaching case for several reasons. First, it's weird enough to grab students' attention. Second, tracing the history of the idea provides opportunities to trace the history of science more generally, explain inductive and deductive reasoning, talk about critical thinking and the role of skepticism in science, and a host of other "meta-" things. And third, explaining how we know Earth isn't hollow covers a lot of basic geophysics, geology, and geography. There are fascinating parallels in the strategies hollow-Earthers use to bolster their conceptions and those used by creationists and global warming skeptics, but hollow Earth theory avoids the political overtones, undertones, and general messiness involved with those topics and thus provides a neutral venue for students to build an understanding of how science works and doesn't work.
Hollow and Habitable Within:
Symmes's Theory of Earth's Internal Structure and Polar Geography
Physical Geography 25: 382-397
What Curiosity in the Structure:
The Hollow Earth in Science
In Mercator Projection to Freudian Fantasm:
The Hollow Earth in Literature, Science, and Art,
Hanjo Berressem and Uwe Schwagmeier, eds.
Amsterdam/New York: Rodopi (This one has been "in press" forever.)
Global Wildlands Project
This was a GIS project that uses the LandScan ambient population database and USGS land use and land cover data to assess the degree of human impact on Earth's ecosystems at the global scale. I published the results of an analysis of North America in the Proceedings of the Applied Geography Conference (2002) and presented the results for both North and South America at the 2003 Association of American Geographers conference in New Orleans. As it turned out, various NGOs had been working on similar, but more elaborate projects, and began releasing similar results around the same time. That being the case, I've stopped working on this project. See the Wildlife Conservation Society and Center for International Earth Science Information Network's Last of the Wild (recently featured in a National Geographic map) and UNEP's GLOBIO projects.
Much of North America is Still Wild?
2002 Applied Geography Conference