BELL1, TIMOTHY J.*, MARLIN BOWLES2, JENNY MCBRIDE2, AND KAYRI HAVENS3. 1Department of Biological Sciences, Chicago State University, Chicago, IL, 60628; 2Morton Arboretum, Lisle, IL, 60532; and 3Chicago Botanic Garden, Glencoe, IL, 60022. - Viability analysis of a restored population of the federal threatened Pitcher's Thistle (Cirsium pitcheri) in Illinois.
Pitcher's thistle (Cirsium pitcheri) is a federal threatened
monocarpic herbaceous perennial of the western Great Lakes shoreline
dune habitats. The plant is self-compatible, with little allozyme
variation across its range. Population maintenance of this species
depends on cohort replacement and recolonization of successional
habitat maintained by shoreline processes. Succession also eliminates
populations, while disturbances can either eliminate or create new
habitat for populations. These dynamics require metapopulation
persistence, in which local populations avoid simultaneous extinction
by reacting independently to landscape-scale disturbances and
colonizing newly formed habitats. Our population restoration in former
Illinois habitat along Lake Michigan comprises Wisconsin, Indiana and
Michigan seed sources. Because this species is monocarpic, annual
translocation of greenhouse propagated plants was used to build up
large cohort numbers. Spontaneous seedlings from flowering plants are
now replacing these artificial cohorts, and the first flowering of
these plants occurred in 1998. Morphological, demographic, and genetic
(as shown by RAPDs) differences occur between geographically different
seed sources, with Indiana plants having larger cotyledons and greater
growth, survivorship and reproduction in the restoration. The restored
Illinois population is now in its seventh year with nearly 150 plants,
but population growth rate (lambda) is less than 1. Stage structured
demographic analysis projects cohort sizes, number of spontaneous
seedlings and, or, translocations, and amount of flowering needed to
sustain population viability. For example, the minimum number of
translocated seedlings needed to achieve a positive growth rate is
twice the number of currently observed spontaneous seedlings.
Key words: Cirsium pitcheri, demography, dune habitat, population viability analysis, restoration, threatened