Liatris Cylindracea Research Articles

Natural analogues of degraded ecosystems enhance conservation and reconstruction in extreme environments

Ecosystem rehabilitation strategies are grounded in the concept that coexisting species fit their environments as an outcome of natural selection operating over ecological and evolutionary timescales. From this perspective, re-creation of historical environmental filters on community assembly is a necessary first step to recovering biodiversity within degraded ecosystems; however, this approach is often not feasible in severely damaged environments where extensive physiochemical changes cannot be reversed. Under such circumstances management goals may shift from restoring historical conditions to reconstructing entirely new ecosystems or replicating natural ecosystems that may be locally novel but of regional conservation importance. This latter goal may be achieved by introducing to damaged sites species already adapted to filters maintaining the degraded state, through targeting assemblages from natural ecosystems biophysically analogous to the degraded state, here termed "degraded-state analogue" (DSA) ecosystems. This hypothesis predicts that, in high-stress sites where recruitment of previous inhabitants is strongly microsite-limited, DSA species will be primarily propagule-limited; furthermore, communities invaded by DSA species should shift in structure to reflect properties associated with high-value DSA target ecosystems. We tested these predictions by experimentally sowing long-abandoned limestone quarry floors with 18 perennial grass and forb species characteristic of rare natural limestone pavements called "alvars." Alvar species established successfully under a range of microsite conditions manipulated to alter suspected constraints on colonization, including nitrogen deficiency, excessive CaCO3, and competition with weeds. Alvar species performed equivalently to seeded weed species known to thrive on quarry floors. Resident communities doubled in species richness following alvar species addition, supporting 17-20 species/0.18 m2 (95% confidence interval) and providing refuge to regionally restricted or threatened species including Iris lacustris, Solidago ptarmicoides, and Liatris cylindracea. In contrast, maximum-diversity reference plots on a pristine alvar supported 20-23 species/0.18 m2. Strong propagule limitation but weak microsite constraints on quarry colonization by alvar species combined with establishment of species-rich communities comparable to natural alvar biodiversity hot spots confirms that targeting DSA assemblages in ecosystem reconstruction can promote both efficient site colonization and ex situ biodiversity conservation within difficult-to-restore anthropogenic wastelands.

The Extent and Floristic Composition of the Rice Lake Plains Based on Remnants

A study of the floristic composition and extent of the Rice Lake Plains in central southern Ontario was undertaken to provide a basis for protection and management and to contribute to a better understanding of pre-settlement vegetation. During field reconnaissance 42 remnant sites were discovered. Complete species lists were generated for 24 of these sites and a total of 260 native species was recorded of which 61 were present at more than half of the sites. Less than 10% of the native flora of dry, open ground is believed to be extirpated. The most frequent species and those dominating many of the remnants included Andropogon gerardii, Carex siccata, Ceanothus americanus, Pteridium aquilinum, Sorghastrum nutans, and Toxicodendron rydbergii, all of which are characteristic dominants of tallgrass prairie and related habitats in the midwest. It is believed that both composition and frequency are much the same, but not exactly the same, as existed in pre-settlement times. A principal coordinate analysis based on Jaccard’s coefficient derived from a matrix of presence/absence data for 84 regionally rare species in 24 sites revealed three major groupings: (1) open sand and characteristic sand barren flora, including Dichanthelium sabulorum, Carex merritt-fernaldii, Cyperus lupulinus, Polygonum douglasii, Selaginella rupestris, and Sporobolus cryptandrus; (2) prairie sites with Desmodium canadense, Monarda fistulosa, Penstemon hirsutus, Ranunculus rhomboideus, and Schizachyrium scoparium; (3) high-diversity sites with savannah vegetation, including species characteristic of both prairie and open woodland, including Asclepias exaltata, Desmodium glutinosum, Erigeron pulchellus, Solidago arguta, and Taenidia integerrima. Correspondance analysis suggested a succession from sand barren to woodland and ordered species along a successional axis. In addition to three major associations, there was some regional variation with closer sites sharing species such as Lupinus perennis, Liatris cylindracea and Dichanthelium oligosanthes. The probable extent of plains vegetation revealed by remnants was determined by overlaying remnant sites on the soil landscapes and soil types to determine the extent of the associated soil or landscape thus providing a clue to the extent of the plains vegetation. Results of both the soil landscape and soil data analyses were subjected to restrictions based on exposure, elevation and historical information so as to develop a concept of minimum area. The minimum area of plains vegetation including prairie, sand barren and savannah was estimated to be 263 km2 on the basis of distribution of appropriate soils and 590 km2 on the basis of soil landscapes. Thus the Rice Lake Plains included an area of prairie, savannah and sand barrens approximately 600 km2 in extent and extending as an essentially continuous band 123 km long and up to 25 km wide along the top and north slope of the Oak Ridges Moraine from the Ganaraska Highland west of Rice Lake eastward to the Murray Hills and the Trent River and was one of the largest areas of plains vegetation in the eastern Great Lakes region.

Demographic consequences of inflorescence-feeding insects for Liatris cylindracea, an iteroparous perennial.

While floral herbivores and predispersal seed predators often reduce plant reproductive output, their role in limiting plant fitness and population growth is less clear, especially for iteroparous perennial plant species. In this study we experimentally excluded floral herbivores and predispersal seed predators (insecticide spray versus water control) over a 2-year period to examine the effect of inflorescence-feeding insects on levels of seed production, seedling emergence, and juvenile establishment for Liatris cylindracea, an iteroparous perennial plant. In addition, we collected detailed demographic data on all life stage transitions for an additional set of individuals in the same population over 4years. We used the experimental and demographic data to construct stochastic individual-based simulations to evaluate the overall effect of inflorescence-feeding insects on adult recruitment per maternal plant (a fitness component) and population growth rate. The insect exclusion experiments showed that damage due to insects decreased seed production, seedling emergence, and juvenile establishment for both years' experiments. These results indicate that recruitment was seed-limited through juvenile establishment, and that inflorescence-feeding insects influenced the degree of seed limitation. Results of the individual-based simulation models, which included individual demographic and temporal stochasticity, showed that inflorescence-feeding insects negatively affected the number of adult offspring per maternal plant recruited into the population and population growth rate for both years' experiments. Taken together, the results of the experimental exclusions and the individual-based models indicate that inflorescence-feeding insects can influence population growth rate, and have the potential to act as a selective force for the evolution of traits in this plant species.

446 Long-term Evaluation of Susceptibility of Selected Prairie Species to the Root Lesion Nematode Pratylenchus penetrans

Because of the need to find plants that suppress root lesion nematodes for use in rotation or cover-crops, 16 native sand-prairie species were evaluated for host status for 6 years. Plants were grown on a Fox sand soil at a local prairie plant nursery. Soil cores were taken in the spring, summer, and fall and assayed for plant parasitic nematodes. Five species supported very low numbers (less than 100/kg soil) of root lesion nematodes. Brown-eyed Susan (Rudbeckia hirta) had no detectable nematodes for the duration. Switchgrass (Panicum virgatum L.) and Indiangrass (Sorghastrum nutans L., Nash) samples produced detectable nematodes on only two sampling dates over the 6 years and were statistically not different from brown-eyed Susan. Butterfly weed (Asclepias tuberosa L.) also had very low detectable nematodes as did sand dropseed [Sporobolus cryptandrus (Torr.) Gray.]. New Jersey tea (Ceanothus americanus L.), little bluestem [Schizachyrium scoparium (Michx.) Nash], and big bluestem (Andropogon gerardi Vitman) were poor hosts with <200 nematodes/kg soil. Mountain mint (Pycnanthemum virginianum L), wild bergamont (Monarda fistulosa L), horsemint (Monarda punctata L), and dwarf blazing star (Liatris cylindracea L) all had root lesion populations over 3000/kg soil. Horsemint and wild bergamont plants died out, possibly as a result of nematode infestation. Root lesion nematodes have an extremely wide host range in current agronomic and horticultural crops, and weeds and are difficult to manage using nonchemical means. Indiangrass, switchgrass, big bluestem, and little bluestem have all been used agriculturally for pastures and consequently have potential as beneficial long-term rotation crops for nematode management and soil building.

Native Sand-prairie Plants That are Poor Hosts for Pratylenchus penetrans

Root lesion nematodes (Pratylenchus penetrans Cobb) are well-adapted to sandy soils and have a host range including most agronomic, horticultural, and wild species grown in Ontario. As native climax sand-prairie species have coexisted with the nematode for millennia, resistance or tolerance may have developed. We have screened using the Baermann pan technique, soil samples taken from a private collection of sand-prairie species collected from local prairie remnants. Several species [Liatris cylindracea Michx., Monarda punctata L., Pycnanthemum virginianum L., Echinacea purpurea (L.) Moench] proved to be excellent hosts (>500/kg of soil) of root lesion nematode, confirming the presence of this nematode in the soil. Over two seasons, we determined that 10 plant species belonging to the families Asclepiadaceae, Compositae, Graminae, and Leguminosae to support very low numbers of P. penetrans. Brown-eyed susan (Rudbeckia hirta L.) had no root lesion nematodes throughout both seasons, Butterfly weed (Asclepias tuberosa L.) very low counts, while Switch grass (Panicum virgatum L.) and Indian grass [Sorghastrum nutans (L.) Nash] had detectable root lesion nematodes on only one sampling date each year. Big Bluestem (Andropogon gerardii Vitman), Little Bluestem [Schizachyrium scoparium (Michx) Nash], Sand Dropseed [Sporobolus cryptandrus (Torr.) Gray], Side-oats Grama [Bouteloua curtipendula (Michx.)) Torr], Broomsedge (Andropogon virginicus L.), Bush clover [Lespedeza capitata (Michx] also are poor hosts. These species have potential as cover or rotation crops useful for nematode management.

THE RELATION OF GROWTH TO HETEROZYGOSITY IN PITCH PINE.

The connection between fitness and heterozygosity has eluded geneticists for decades. The classic form of the Neo-Darwinian argument hypothesizes that heterozygosity confers genetic homeostasis (Lerner, 1954); i.e., multiple, molecular forms of the same enzyme endow the organism with a broader range of tolerance to environmental variation because different forms may differ in their optima for temperature, pH, and other factors (Johnson, 1976). In maize (Zea mays L.), inbred lines and their hybrids are similar in growth rate when raised under constant conditions at optimal temperatures, but hybrid superiority becomes progressively more obvious as conditions deviate from the optimum (McWilliam and Griffing, 1965). Apparently, homozygotes in maize can only deal successfully with a narrow range of conditions as compared to heterozygotes. In a variety of organisms, including butterflies, fish, and oysters, variance for morphological traits decreased with increasing heterozygosity at enzyme loci (Eanes, 1978; Mitton, 1978; Zouros et al., 1980), and bilateral symmetry, a measure of developmental homeostasis, increased with heterozygosity in lizards and bivalves (Soule, 1979; Kat, 1982). Growth rate increased with heterozygosity in oysters and salamanders (Singh and Zouros, 1978; Zouros et al., 1980; Pierce and Mitton, 1982). The perennial herb, cylindric blazing star (Liatris cylindracea Michx.), can be roughly aged by counting rings in the corm, the subterranean perennating organ. In natural populations, heterozygosity was higher among older than among younger individuals, suggesting poor survival for homozygotes (Schaal and Levin, 1976). Grown in a uniform environment, biomass production and reproductive potential of the herb were weakly, but positively, related to the level of enzyme heterozygosity. However, Mitton and colleagues (Mitton and Grant, 1980; Knowles and Grant, 1981; Mitton et al., 1981) noted conflicting results in forest trees, which are among the most polymorphic of organisms (Hamrick, 1979; Hamrick et al., 1979). In only one of three tree species was there a positive association between mean width of the annual ring, taken as a measure of growth and fitness, and heterozygosity. In two of the species, variance in ring width increased with increasing heterozygosity and in the third, it decreased. The relationship between growth and heterozygosity in trees is confusing, and more data are needed to draw firm conclusions. Our objective was to relate growth to heterozygosity in pitch pine (Pinus rigida Mill.), for which we had information on 21 enzyme loci in several populations. We were also interested in whether heterozygotes had greater longevity and whether annual growth was more or less well-buffered in heterozygotes than in homozygotes. A positive association be-

THE APPORTIONMENT OF GENETIC VARIATION WITHIN AND AMONG POPULATIONS OF DESMODIUM NUDIFLORUM.

A major aspect of the study of plant evolution has been the determination and comparison of the genetic structures of species. Features such as the levels of genetic variability, the factors which influence levels of variability, and the apportionment of genetic variability within and among populations all strongly affect the evolutionary potential of species. Measurements of differences in these characteristics have been used to assess the different evolutionary paths species have taken. From a number of studies of plant species there is evidence that levels of detectable variability vary widely from almost none in Typha (Masburn et al., 1978) to relatively high levels of variability in Stephanomera exigua ssp. carotifera (Gottlieb, 1975). The level of genetic variability is in some cases associated with variation in edaphic factors (Babbel and Selander, 1974), with karyotype (Levin, 1974), with geographical variation (Levin, 1977), or with population structure (Schwaegerle and Schaal, 1979). While many studies have examined genetic variability among populations of a species, less attention has been focused on the apportionment of genetic variability within individual populations. Genetic substructuring of plant populations may be a consequence of either local differentiation due to different selective values (Jain and Bradshaw, 1966), or gene flow restriction due to self-fertilization, nonrandom pollinator behavior or localized seed dispersal. Extensive work has shown that gene dispersal in many plant species is very restricted (see review by Levin and Kerster, 1974). Such limited gene flow in a single DoDulation may lead to genetic subdivision into subpopulations, each of which is characterized by different gene frequencies (Wright, 1943a). Studies of several plant species (e.g., Linanthus parryae, Wright, 1943b; Liatris cylindracea, Schaal, 1974) have indicated that populations of some plant species may be subdivided. The purpose of the current study is to determine the levels of genetic substructuring within populations of Desmodium nudiflorum (L) DC (Leguminosae) and to compare the apportionment of genetic variation within and among populations of the species. Desmodium nudifiorum is an herbaceous plant which occurs locally in black oak-white oak communities throughout the eastern deciduous forest. Extant populations of D. nudiflorum are restricted in much of the range to well established, secondary successional forests located in public and private nature preserves. Extant populations are geographically isolated, although the species was certainly more common before the clearing of the eastern forests. Populations of D. nudifiorum rarely exceed 200 individuals and the plant density rarely exceeds one or two plants per meter square. The species is perennial, reaching an estimated maximum age in excess of ten years. Adult plants of D. nudiflorum range in height from 14 to 29 cm and produce up to 109 flowers, with a mean of 50 flowers per plant (Smith, 1971). Twenty-two percent of the flowers produce fruit; each fruit contains an average of 2.8 seeds. Outcrossing is predominant in D. nudiforum with bumblebees as the major pollinators. Asexual reproduction does not occur. The seeds of D. nudiflorum are caDable of dis-

Morphological Differentiation and Neighborhood Size in Liatris cylindracea

Pollinator flight and seed dispersal distributions are leptokurtic in the perennial, prairie herb Liatris cylindracea Michx. (Compositae). From these dispersal data neighborhood size and area were determined to be 165 plants and 33 m2, respectively. An analysis of morphological variation along three transects of an edaphic gradient indicates that significant local differentiation for several characters occurs at the study site. The pattern of local differentiation is unrelated to edaphic factors.

MORPHOLOGICAL DIFFERENTIATION AND NEIGHBORHOOD SIZE IN LIATRIS CYLINDRACEA

Pollinator flight and seed dispersal distributions are leptokurtic in the perennial, prairie herb Liatris cylindracea Michx. (Compositae). From these dispersal data neighborhood size and area were determined to be 165 plants and 33 m2, respectively. An analysis of morphological variation along three transects of an edaphic gradient indicates that significant local differentiation for several characters occurs at the study site. The pattern of local differentiation is unrelated to edaphic factors.

Genetic Diversity in Liatris cylindracea

A genetically substructured population of the perennial, outbreeding herb, Liatris cylindracea was marked off into a grid with quadrat size that approximates the neighborhood size of Liatris. The plants were genotyped at 27 allozyme loci, 15 of which were polymorphic. The apportionment of genetic diversity within the population was determined by the Shannon information measure. Ninety-three percent of the total diversity is represented within each neighborhood. Five percent of the diversity is due to between neighborhoods, and about 2% is due to differences between sample rozs and columns. It is concluded that the subdivision of a population does not result in a loss of genetic diversity within neighborhoods. The properties of genetically subdivided populations have received considerable attention by theoreticians (e.g., Wright, 1943a; Kimura & Weiss, 1954; Maruyama, 1970). Because of the difficulty in the past of finding suitable single locus genetic markers, few experimental studies on genetic substructuring have been available. Now, with the advent of allozyme electrophoresis as a tool for the genetic analysis of natural populations, an increased number of studies on both animals (Selander 8c Yang, 1969; Workman gc Niswander, 1970; Neel gc Ward, 1972) and plants (Schaal, 1975) have indicated that populations of some organisms are genetically

Population Structure and Local Differentiation in Liatris cylindracea

An analysis of genetic population structure and local differentiation was conducted in the obligatory outbreeding prairie herb Liatris cylindracea. A single population located along an environmental gradient on a hillside in Zion, Lake County, Illinois, was divided into 60 3-m2 quadrats, the quadrat size approximating the neighborhood size of Liatris. Gene frequencies of 15 polymorphic and 12 monomorphic allozyme loci were determined on a per quadrat basis. The population exhibited marked local genetic differentiation; gene frequencies sometimes varied as much as 20% between adjacent quadrats. Correlation of gene frequency with edaphic factors at the site proved non-significant at 13 loci and negatively correlated at two loci, Est3 and Per-. Population structure was analyzed by both χ2 and F statistics. Both FIS, the within-subdivision deviation from Hardy-Weinberg equilibrium frequencies, and FST, the degree of population substructuring, are significant, with FIS values ranging from 0.1 to 0.506 and FST ranging from 0.009 to 0.224. The genetic substructuring of the L. cylindracea population is attributed to restricted gene flow, and the role of pollinator behavior and seed dispersal in population substructuring is discussed.

Isolation by distance in Liatris cylindracea.

SEVERAL factors may cause genetic correlation—that is a genetic relationship between individuals within a population—including small population size, self-fertilisation, positive assortative mating or isolation by distance. Isolation by distance occurs when gene dispersal is limited so that distant populations in a series or remote areas within a population become genetically differentiated. Under an isolation-by-distance model of genetic differentiation, spatial distance and genetic correlation between individuals or populations are expected to be negatively related, that is, the greater the distance the smaller the genetic correlation. I wish to present evidence for isolation by distance in the plant, Liatris cylindracea Michx. (Compositae), obtained by a genetic distance analysis of gene frequencies at 27 allozyme loci. This analysis revealed genetic differentiation across very small distances and demonstrated that a restriction of gene flow has a profound effect on the spatial distribution of alleles within a population.

BIOSYSTEMATIC STUDIES OF THREE SPECIES IN THE GENUS LIATRIS

An attempt has been made to clarify the genetic relationships of Liatris spicata, L. pycnostachya, and L. aspera, using hybridization experiments, transplant studies, and related biosystematic techniques. The species represent three different series within the genus, but are morphologically rather closely related, and are sympatric in at least five U. S. states of the Mississippi Valley. The species are homoploid, with n = 10. Two ecological races are recognized within each species, and a high degree of inter fertility exists between races and species, with the exception of ruderal races of L. pycnostachya and L. aspera. Further hybridization experiments involved the additional species punctata, cylindracea, and scariosa. The latter species shows a high degree of genetic isolation from the others. Liatris spicata, pycnostachya, aspera, punctata, and cylindracea should be termed ecotypes: they appear to be elements of a larger diploid complex (ecospecies) composed of at least these five taxonomic species.