Archbold Biological Station
Biennial Report 1995-1996
P.O. Box 2057 Lake Placid, Florida 33862 USA
Phone: 863-465-2571 FAX: 863-699-1927
Published 9 papers in peer-reviewed journals such as Conservation Biology and American Journal of Botany, on subjects in plant demography, fire ecology, pollination biology, metapopulation dynamics, monitoring methods, and conservation. Submitted 9 additional manuscripts for publication in journals or books.
Presented over 12 talks at regional, national, and international scientific meetings.
Worked under 11 grants and fellowships from several agencies, studying basic and applied ecological questions in 8 species.
Served on graduate committees for 5 Master's and Ph.D. students at 4 universities.
Made 2 revisions to a computer model projecting stochastic population dynamics of stage-structured populations.
Created a database of the 1500 plant species represented in the Station's herbarium.
Participated in numerous meetings, workshops, field trips, hearings, and advisory groups on conservation and management of Florida scrub and Florida's native plant species
Plant Ecology Research
Project Director: Eric S. Menges
[Saving Florida ziziphus: recovery of a rare Lake Wales Ridge endemic]
One of the fascinations of Florida scrub is not knowing, when walking into an unfamiliar patch of vegetation, which plant species you will find. At both large and small scales, the distributions of scrub plants are notably patchy. The sporadic presence of certain species is particularly relevant to attempts at identifying scrub parcels for protection and for fire management. Our research over the past eight years has used long- and short-term data collection, field experiments, and population modeling to help us understand and predict the distribution and persistence of scrub plants.
Metapopulations in Florida Scrub Plants. Locally, Florida's rosemary scrub supports most of our endangered and threatened plant species, yet covers only 4% of Archbold Biological Station. In the late 1980's, Eric Menges collected data on the occurrence of all vascular plants and ground lichens in each of about 90 rosemary scrub patches on the Station. A recent article by Pedro Quintana-Ascencio and Menges in Conservation Biology analyzes these data and shows that about 2/3 of the species had distributions that were related to patch size, patch isolation, or fire history. Plants occurring mainly on larger, less-isolated patches tended to be herbaceous, rosemary-scrub specialists, and were inferred to have metapopulation dynamics. This predicts that some patches are suitable for certain species, but are not occupied merely because the plants have not arrived and colonized.
Experimental support for the metapopulation view comes from two studies. Pedro Quintana-Ascencio has shown that one species, Hypericum cumulicola, whose distribution is consistent with metapopulation dynamics, can grow, flower, fruit, disperse seed, and recruit a second generation of plants, when transplanted to non-occupied rosemary scrub patches. Similarly, Rebecca Yahr's transplant experiments using the endangered lichen Cladonia perforata show that growth rates do not differ between occupied and non-occupied sites. As a whole, the rosemary scrub system may be a constantly-shifting mosaic of patches with various species appearing and disappearing. Because both currently-occupied and non-occupied sites may be needed for a functional metapopulation structure, conservation efforts need to consider broad spatial and temporal scales. Habitat fragmentation could disrupt the continuity of dispersal among patches and threaten metapopulations of scrub plants.
Coping With Fire. Scrub plant distribution is also affected by fire. Analyses published by Menges and Nancy Kohfeldt in 1995 (Bull. Torrey Bot. Club) document a diversity of strategies of postfire recovery. Species recovering from fire via seedling recruitment are relatively successful in rosemary scrub, relative to oak-dominated scrub. Even these "seeders" have a diversity of patterns with respect to fire, microhabitat, and demography. Plants such as Polygonella basiramia, studied by Christine Hawkes, do not have a soil seed bank and disperse into burned areas from unburned patches. P. basiramia can persist in openings between fires. Also persisting in openings, but with reduced demographic performance with increased time-since-fire, is Hypericum cumulicola. Data collection and modeling by Quintana-Ascencio shows that variable fire return intervals promote its population persistence, and that the survival of seeds in the seed bank is critical to long-term persistence. A third species, Eryngium cuneifolium, is even more sensitive to fire suppression. We linked a short-term, intensive study on its microhabitats to an ongoing, long-term demographic study to characterize the specific microhabitat, openings without nearby Florida rosemary shrubs, that supports low mortality of Eryngium. We are beginning to model E. cuneifolium dynamics in relation to fire, based on nine years of demographic data from many rosemary scrub patches. Finally, transplants of the lichen Cladonia perforata grow poorly on recently burned substrates, perhaps in part explaining its slow recovery after fire.
Landscape-scale Genetic Patterns. Patchy spatial structuring of scrub plants has implications for the patterns of genetic structure across the landscape. We are examining range-wide patterns of isozyme variation in seven scrub species to test hypotheses that genetic variation is higher for larger, clumped populations in large contiguous habitat patches. Isozyme variation, quantified by Rebecca Dolan (Butler Univ.), is quite low, but typical for narrowly endemic plants. Differences among the species in the amount and distribution of genetic diversity may best be explained by their idiosyncratic responses to fire, their breeding systems, and pollinator movements. Experiments conducted by Margaret Evans have shown that five of seven species can set seeds after self-fertilization, a capability that allows inbreeding to occur and can shape genetic population structure. Geographic Information System databases on soils, habitat patches, and species' distributions were manipulated by Christina Casado to assess the relationships between geographic position and population genetic variation and differentiation.
The Importance of Long-term Data. We will be working to integrate shorter-term projects, such as our investigation of the genetics of seven scrub plants, with long-term data collection. How is demographic performance affected by the genetics of plant populations and how do demographic fluctuations affect the distribution and abundance of genetic variation? Long-term datasets are also necessary to evaluate the importance of rare events on population fluctuations and persistence. Biological stations such as Archbold are among the few institutions that support this effort, and we believe that many important ecological questions can only be answered using long-term data.
Lohrer, F.E . (Editor). 1998. Archbold Biological
Station, Biennial Report 1995-1996. Archbold Biological Station, Lake Placid. 62 pp.
© Archbold Biological Station, 1998, October, revised 2 November 1999.
Webmaster: Fred Lohrer.