Population biology of a rare hemiparasite, Aureolaria patula (Chapman) Pennell (Scrophulariaceae): demographic trends, host interactions, and reproductive biology

Author

Maureen Cunningham

Date of Award

5-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Mitch B. Cruzan, Thomas G. Hallam

Committee Members

Clifford Amundsen, Hazel Delcourt, Carolyn Hunsaker, Stephen Nodvin

Abstract

Aureolaria patula spreading felse-foxglove, is a rare herbaceous perennial restricted to calcareous slopes and bluffs along waterways in Alabama, Georgia, Kentucky, andTennessee,primarily along the Tennessee River and its tributaries. Aureolaria Patula isa root hemiparasite. It has green stems and leaves and functional chlorophyll, but it attaches via haustoria to the roots of host trees to access water and solutes in the vascular system of the host.I measured individual and population growth characteristics of four populations on public lands in east Tennessee and evaluated demographic structure and processes using a stage-based matrix projection model Plants were found to have the ability to be dormant for a growing season,then return the following year. Probability of dormancy and mortality decreased with increasing plant size. Reproductive effort increased with increasing plant size. Dormant stages were incorporated in the population model and were shown to be important influences on population growth rate (λ)at some sites.Population growth rates varied both spatially and temporally and ranged from 0.35 to 1.6. The relative importance of fecundity, growth,and survival in the dynamics of the populations varied by site and year. Survival of larger plants had the greatest influence on λ at undisturbed, level sites, while fecundity and growth of a mix of size classes are important at sites on moderate slopes(15-18%). Characterization of demographic monitoring sites revealed that Ostrya virginiana, Carpirms carolinana, and Quercusrubra dominated the canopy vegetation. All sites had moderate to high levels of phosphorus in the soil.Studies of plant growth in containers in a greenhouse showed host tree had a significant effect on shoot and root biomass of A.patula and A. virginica,a common relative. The Most beneficial hosts for A. patula were Carpinus caroliniana, Quercus rubra>/i>, andComus Florida. Hosts promoting the greatest growth of A. virginica were Carpinusmost beneficial hosts for A. patula were Carpinus caroliniana, Quercus rubra, andCornus Florida. Hosts promoting the greatest growth ofv A. virginica were Carpinus caroliniana, Cercis canadensis ,and Camus florida. Aureolaria patula grew larger than A. virginica on all hosts and grew as well as A. virginica without a host in nutrient-poor soil. Number of haustoria was positively correlated with shoot biomass of the hemiparasites. Although the two hemiparasites formed haustoria on most host treestested, some host species were clearly more beneficial than others to the hemiparasites.The attachment to a host, however, was not without risk. The results of two experiments indicate evidence of harm to the hemiparasite when growing with or attached to some hosts. Survival of hemiparasite seedlings was significantly affected by host species, and growth of shoots and roots of both hemiparasites was significantly suppressed by the presence of Cercis canadensis. Both hemiparasites grew larger andformed more haustoria on the host when fertilized.An Investigation of reproductive biology in a small population revealed that A.patula is self-incompatible. Seedlings from open-pollinated flowers on seven maternal plants grew significantly larger in a greenhouse than seedlings from flowers hand-outcrossed with plants 30-m distant. There was no evidence of inbreeding depression in seedling growth in the small population studied. Aureolaria patula can be viewed as having a more opportunistic life history strategy than A. virginica, which has the strategy of a generalist. The conditions under which A.patula thrives include plant communities with a high density of the most beneficial hosts, lack of herbaceous competitors that block light, proximity to a river or stream,and calcareous substrate. Environmental conditions 9,000 years before present may have favored the most beneficial hosts of A. patula in the region of its current distribution. Today A. patula remains geographically restricted because its favored habitat is patchy, and because self-incompatibility makes colonization of new sites by long distance seed dispersal less probable.