Research in the Miller Lab

My research interests are in community ecology and in looking at the factors that determine species success and diversity. Most of my work has been in two very different systems: the invertebrate communities found in the water-filled leaves of pitcher plants and the ever changing mosaic of vegetation found on St. George Island, a typical microtidal barrier island. Most recently, we have also been establishing additional long-term vegetation plots on six more barrier islands around the Northern Gulf of Mexico, both to better understand the ecology and to monitor for the possible chronic effects of oil from the Deepwater Horizon oilspill.

Metacommunities in the pitcher plant, Sarracenia purpurea

In the last 15 years, ecologists have recognized that population and community patterns are determined by both local species interactions, as well as larger patterns of migration and extinction occuring across larger heterogeneous regions. This work was built on earlier ideas about patch dynamics and migration, and has recently led to newer theory and experiments brought together under a loose theory of "metacommunities."

We have been testing a number of recent theories about community patterns across metacommunities, as well as developing some theory of our own. This work has taken advantage of the unique natural microcosms found in the water-filled leaves of the purple pitcher plant, Sarracenia purpurea (see Miller and Kneitel 2005 for a review). The leaves of this carnivorous plant attract insects that drown in the contained water, ultimately providing nutrients for the plant. However, these prey insects also serve as the basis for an aquatic community that lives in the leaves. Bacteria break down the insects, while serving as a resource for protozoa, rotifers, and mites. These bacteriovores are in turn consumed by the larvae of a specialist mosquito, Wyeomyia smithii. A variety of other specialist species also depend on Sarracenia purpurea, including two other dipterans (Metriocnemus knabi and Fletcherimyia fletcheri and a specialist moth herbivore, Exyra fax.

Our current work in this system has been in two areas, both supported through grants from the National Science Foundation. First, we have teseted theory on how the effects of migration in metacommunities depends on the heterogeneity among local communities with a large region. We completed a series of experiments in which we manipulated both the migration rates and the among-leaf heterogeneity. In general, we found that migration rate does increase diversity, confirming earlier theory and experiments. However, metacommunity heterogeneity had no effect on diversity, contrary to a theory we earlier proposed. We are looking further at the individual species patterns to see if we can explain the mechanisms behind these results.

Second, we are very interested in the evolutionary processes that occur with this community, especially as they relate to species diversity. These communities provide a natural system in which to follow the evolution of competing species. The evolution of competitors has been of long-standing interest in ecology and evolutionary biology; this interest has again come to the forefront due to questions about evolution of niche-partitioning vs. equivalence and nuetral theory. We followed the evolution of competitive ability and predator tolerance among a suite of protozoa during 17 weeks of succession in naturally occuring communities found in pitcher plant leaves. Niche theory would predict that each species should evolve to utliize some unique suite of resources, thereby reducing its interactions with competitors. A neutral theory view would predict that at least some species might evolve to have increased effects on one another as they converge on the same niche. Our preliminary results confirm neither of theise predictions. Instead, some sort of frequency dependent selection seems to occur in which poor competitors evolve to become better competitors, while better competitors evolve to have reduced competitive effects on other species. This "Robin Hood" effect of the rich getting poorer and the poor getting richer has not previously been described and may require a new look at current theory.

Long-term Vegetation Dynamics on Barrier Islands in the Gulf of Mexico

Barrier island provide very harsh environments for plants, as they are highly disturbed with soils that are often saline, nutrient poor, and subject to extremes in water availability. Such islands occur along over 70% of the northern Gulf of Mexico, as well as along most of the eastern US coast and are important for ecological and economic reasons. They support a number of unique plant species, while serving as breeding areas for a number of birds and marine organisms. Barrier islands also serve as important buffers that protect more inland areas from both normal wave-action and storms. Finally, they are also serve as a coastal "canary in the mine" for observing and understanding the effects of global climate change related to storms and sea-level rise.

We are involved in two projects on St. George Island, appoximately 60 miles SW of Tallahassee. First, we initiated a long-term study of the vegetation dynamics on the island in 1998. An annual census is conducted each fall, along with other studies to periodically monitor dune dynamics and characteristics. This long-term study suggests that dune vegetation is strongly affected by two very different types of climatic events: spring droughts and early fall tidal surge associated with major storms (Miller, Gornish, and Buckley 2010). Second, we used this long-term database to quantify how different species are likely to respond following storms, with the goal of identifying the best species to use for coastal restoration following storms. With funding from the U.S. Fish and Wildlife service and the Apalachicola National Estuarine Research Reserve, we have completed a small restoration project on St. George to test the efficacy of different species for restoration and conservation.

Everything changed in 2010. The Deepwater Horizon oil spill resulted in oil residue occurring over a significant portion of the Northern Gulf of Mexico. While some of this oil was in the form of surface slicks or tar balls that were observed on vegetation and beaches, much is thought to be in much lower concentrations that may persist for years. Little is known about the effects of such long-term exposure on natural ecosystems.

Our work on St. George Island provided us with the experience and background data to conduct the long-term censuses necessary to determine if such effects do or do not occur. With funds from NSF and the Northern Gulf Institute, we have now initiated six additional long-term study on barrier islands spread across the northern Gulf of Mexico. These sites are approximately 160 km apart along a gradient of oil exposure and include Trinity Island (LA), Horn Island (MS), Santa Rosa Island (FL), East Crooked Island (FL), Anclote Key (FL),and Cayo Costa (FL), all censused using the methods developed for the on-going census on St. George Island, FL.

Our plan is to continue to monitor these seven barrier island sites for the next 5 years, with the dual goals of quantifying possible effects of the Deepwater Horizon oil spill and learning more about the basic natural history of these important coastal habitats. More information about these sites can be found on the barrier islands research webpages, which are constantly under construction. All of the data are also available through these pages or by contacting us directly.

Many thanks to our hardworking crews, including Elise Gornish, Loury Migliorelli, John Mola, Jackie Monge, John Owenby, Abigail Pastore, Chelse Prather, and Alice Winn. For further information about any of these topics, please contact T. Miller.


Revised March 14 2012