Habitat restoration and native grass conservation: a case study of switchgrass (Panicum virgatum)

Switchgrass (Panicum virgatum) has been planted extensively for habitat restoration across the United States, such as with the Conservation Reserve Program (CRP). However, genetic profiles of these populations have never been studied nor compared with those of remnant prairies or cultivars. In this study, we sampled 16 CRP and 17 prairie populations across eastern Kansas. We assessed ploidy levels of all populations and compared genetic diversity and structure of 10 prairies, 10 CRP areas, and 5 standard cultivars, using nine simple sequence repeat (SSR) DNA markers. All CRP and prairie populations were octaploid (8x), except two prairies with both hexaploid (6x) and octaploid (8x) individuals. Based on the results of SSR analyses, there were no significant differences between CRP and prairie populations in genetic diversity, and 94% of total variation was partitioned within populations. Similarities among prairie and CRP populations were also observed in Bayesian clustering algorithms and principal coordinate analysis, suggesting that they had similar genetic compositions. In addition, positive spatial autocorrelations were detected up to 42 and 46 km among prairie and among CRP populations, respectively. To conclude, the CRP and prairie populations shared similar genetic profiles. However, remnant prairies still harbored unique genotypes and a high level of genetic diversity, highlighting the importance of seed sources for restoration efforts, that is using local wild seeds or cultivars from the same geographical region. A popular tetraploid (4x) cultivar known as “Kanlow” was genetically distinct from the prairie populations and therefore is not recommended for habitat restoration in this region.     

Competitive effects of cultivar and wild switchgrass on other native grasses

There is mounting concern that selection and breeding of native grasses for greater biomass production could promote weediness. Yet little is known about the invasion potential or ecological impacts of such selectively bred native grasses. Here we focus on cultivars of native switchgrass (Panicum virgatum L.) that have undergone selection, breeding, and intraspecific hybridization to improve agronomic traits for biomass production. We evaluated the competitive effects of switchgrass cultivars (EG-2101 and ‘Trailblazer’) and wild switchgrass populations on two native prairie grasses [sideoats grama, Bouteloua curtipendula (Michx.) Torr., and Canada wild rye, Elymus canadensis L.] across a gradient of switchgrass density in a greenhouse. Cultivars produced 48–128% more biomass and reduced sideoats grama biomass by 25–59% more than wild switchgrass. Effects of switchgrass cultivars on Canada wild rye were minimal compared to sideoats grama. Later flowering and larger seed size of cultivars may be contributing to their greater biomass and competitive effects on sideoats grama. These data suggest that breeding switchgrass for enhanced biomass yield may increase competitive effects on some native grasses. Further studies are merited to test the potential for switchgrass biomass cultivars to spread and impact species diversity of restored and remnant native plant communities.     

Root Dynamics of Cultivar and Non‐Cultivar Population Sources of Two Dominant Grasses during Initial Establishment of Tallgrass Prairie

Dominance of warm‐season grasses modulates tallgrass prairie ecosystem structure and function. Reintroduction of these grasses is a widespread practice to conserve soil and restore prairie ecosystems degraded from human land use changes. Seed sources for reintroduction of dominant prairie grass species include local (non‐cultivar) and selected (cultivar) populations. The primary objective of this study was to quantify whether intraspecific variation in developing root systems exists between population sources (non‐cultivar and cultivar) of two dominant grasses (Sorghastrum nutans and Schizachyrium scoparium) widely used in restoration. Non‐cultivar and cultivar grass seedlings of both species were isolated in an experimental prairie restoration at the Konza Prairie Biological Station. We measured above‐ and belowground net primary production (ANPP and BNPP, respectively), root architecture, and root tissue quality, as well as soil moisture and plant available inorganic nitrogen (N) in soil associated with each species and source at the end of the first growing season. Cultivars had greater root length, surface area, and volume than non‐cultivars. Available inorganic N and soil moisture were present in lower amounts in soil proximal to roots of cultivars than non‐cultivars. Additionally, soil NO₃–N was negatively correlated with root volume in S. nutans cultivars. While cultivars had greater BNPP than non‐cultivars, this was not reflected aboveground root structure, as ANPP was similar between cultivars and non‐cultivars. Intraspecific variation in belowground root structure and function exists between cultivar and non‐cultivar sources of the dominant prairie grasses during initial reestablishment of tallgrass prairie. Population source selection should be considered in setting restoration goals and objectives.     

Intraspecific Chromosome Number Variation and Prairie Restoration—A Case Study in Northeast Iowa,U.S.A

Genome duplication has played an important role in plant evolution. Variation in genome size within species is common, particularly in grasses, but rarely considered when planning restorations. We surveyed ploidy variation within one habitat (tall grass prairie) in one region (northeast Iowa, U.S.A.) to assess the risk of ploidy mismatch in restoration plantings. Genome sizes were estimated using flow cytometry for samples from 19 remnant prairies, 5 restoration plantings, and 2 seed sources. Intraspecific ploidy variation in remnant prairie populations was found for two species of grasses, Andropogon gerardii (big bluestem) and Panicum virgatum (switchgrass). Restoration seeds differed from remnants in ploidy for three species of grass, P. virgatum, Sorghastrum nutans (Indian grass), and Spartina pectinata (prairie cordgrass), and for one species of forb, Amorpha canescens (lead plant). In the case of S. pectinata, local ecotype seeds were found to consist of two different ploidy levels. Restorations in grasslands in the United States and elsewhere are likely to create mixed ploidy populations, probably resulting in lower reproductive success for the remnant population. Prevention of mixed ploidy populations will require the screening of restoration seed sources and regional surveys for ploidy variation.     

Sourcing native plants to support ecosystem function in different planting contexts

Current guidance on sourcing native plants to support ecosystem function focuses on the high risk of failure when unsuitable material is used in ecological restoration. However, there is growing recognition that risks may be lower and rewards higher at highly disturbed sites isolated from remnant populations, especially when considering support for pollinators, wildlife, and other ecosystem functions. We developed the first decision support tool using expert opinion to assess suitability of different native plant sources, including horticultural cultivars, in two different planting contexts. We assessed the suitability of 761 sources for 72 commonly sold native species in two different planting contexts (small, isolated, highly disturbed sites vs. large, undisturbed sites near remnant populations). Information on genetic and adaptive backgrounds of sources was strikingly lacking, forcing us to exclude one‐third of sources from our assessment. While only 3% of cultivars received high suitability scores for use in large, undisturbed sites near remnant populations, 52% received high suitability scores in small, isolated, highly disturbed sites. However, nearly 25% of cultivars had floral or leaf traits that differed from wild plants in ways that may compromise their ability to support pollinators and other wildlife. Forbs and cultivars lacking genetic diversity and source information were most likely to have altered traits. We recommend that native plant breeders and sellers work together to ensure ecosystem function, adaptation, and diversity information is available to consumers, that consumers request this information to drive demand, and that researchers further investigate how context influences risks and benefits of different sources.     

Standing variation boosted by multiple sources of introduction contributes to the success of the introduced species, Lotus corniculatus

Although ecological differences between native and introduced ranges have been considered to drive rapid expansion of invasive species, recent studies suggest that rapid evolutionary responses of invasive species to local environments may also be common. Such expansion across heterogeneous environments by adaptation to local habitats requires genetic variation. In this study, we investigated the source and role of standing variation in successful invasion of heterogeneous abiotic environments in a self-incompatible species, Lotus corniculatus. We compared phenotypic and genetic variation among cultivars, natives, and introduced genotypes, and found substantial genetic variation within both native and introduced populations. Introduced populations possessed genotypes derived from both cultivars and native populations, and had lower population differentiation, indicating multiple sources of introduction and population admixture among the sources in the introduced range. Both cultivars and introduced populations had similarly outperforming phenotypes on average, with increased biomass and earlier flowering compared with native populations, but those phenotypes were within the range of the variation in phenotypes of the native populations. In addition, clinal variation within introduced populations was detected along a climatic gradient. Multiple introductions from different sources, including cultivars, may have contributed to pre-adaptive standing variation in the current introduced populations. We conclude that both introduction of cultivar genotypes and natural selection in local environments contributed to current patterns of genetic and phenotypic variation observed in the introduced populations.     

Genetic differentiation and gene flow between wild and cultivated Prunus avium: An analysis of molecular genetic evidence at a regional scale

The presence of conspecific wild-type and cultivar populations has been a common landscape feature for centuries. As orchards generally continue to expand towards the natural forest, two important issues are raised: the potential reduction of cultivar genetic diversity compared to wild populations and the extent of gene flow between the two population types. These questions were addressed in a study of Prunus avium in northern Greece using nine simple sequence repeat loci to analyse genetic variation in 93 wild-type individuals and 21 cultivars representing the local cultivated germplasm. Results showed a significant reduction of genetic diversity parameters in the cultivated germplasm compared to natural populations. Bayesian, frequency-based and Markov chain – Monte Carlo analyses have revealed that the wild and cultivar groups are genetically divergent and that realized between-group gene flow is almost completely absent. This result was further verified by a principal component analysis showing a clear separation of the two groups in low multivariate space after a principal coordinate analysis. The significant disjunction in flowering time and a considerable geographic distance between the two groups could primarily account for the absence of substantial gene flow. These findings indicate that local wild cherry can provide a source of genetic variation for future breeding in the genetically restricted cultivar group.     

Effects of competition with Bromus tectorum on early establishment of Poa secunda accessions: can seed source impact restoration success?

When landscapes are heavily impacted by biological invasion, local populations of native plant species may no longer be adapted to altered environmental conditions. In these cases, it is useful to investigate alternative sources of germplasm, such as cultivated varieties, for planting at restoration sites. This study compared cultivated and wild (local) varieties of the native perennial bunchgrass, Poa secunda J. Presl, grown with and without the exotic, invasive Bromus tectorum L. in a greenhouse setting. While P. secunda cultivars emerged and grew more rapidly than wild seed sources, this advantage declined in the presence of B. tectorum and cultivated germplasm did not outperform wild accessions in the presence of an invasive species. Given the novel genetic background of cultivars and their potential to alter patterns of dominance in native plant communities, we recommend the use of local or regional wild seed sources when possible to conserve regional patterns of genetic diversity and adaptation. Use of multiple seed sources may increase the potential for capturing vigorous genotypes in the restoration seed mix. In cases where sites are heavily impacted by exotic, invasive species, other control measures will be necessary to improve establishment of native species in grassland restoration programs.     

Population source affects competitive response and effect in a C4 grass (Panicum virgatum)

Grassland restoration success depends on the development of plant communities that accord with restoration goals. Intraspecific variation in competitiveness may affect community development. For some grassland species, germplasm can be obtained from sources ranging from wild collections to selectively bred cultivars. The extent to which population source affects competitive outcomes in restoration projects is unclear. We addressed this knowledge gap in a glasshouse experiment comparing competitive response and effect among three sources of switchgrass (Panicum virgatum) that are available for restoration: selectively bred cultivars, commercial ecotypes (commercially produced but not deliberately selected), and wild collections. Two strains per source type were grown with four associates chosen to encompass varied functional groups: conspecifics, Bromus inermis, Cirsium arvense, and Solanum ptycanthum. Switchgrass competitive response was evaluated for survival, height, biomass, and shoot:root biomass ratio; competitive effect was assessed as associate survival, height, biomass, and shoot:root ratio. Competitive responses of cultivars and commercial ecotypes were broadly similar, although cultivar biomass exceeded both that of ecotypes and wild collections, and ecotypes had the highest shoot:root ratio. Wild collections were most negatively affected by competition. The shoot:root ratios of all sources were highest when grown with S. ptycanthum, indicating that competitive responses were plastic; plasticity in fitness‐related traits can contribute to persistence in variable environments. Cultivars exerted negative effects on B. inermis. Secondary analyses indicated that all switchgrass sources were most inhibited by the annual S. ptycanthum. To summarize, population source affected multiple aspects of switchgrass competitive ability, when grown against functionally varied associates.     

Genetic diversity and relationships of wild and cultivated olives in Turkey

In the present study, we proposed to determine the genetic diversity and relationships between local cultivars and wild olive trees from three important olive-growing regions, i.e., Marmara, Aegean, and Mediterranean, of Turkey. This is the first known large-scale molecular study to investigate the relationships between local cultivars and wild olives from the eastern Mediterranean basin. Two hundred and four oleaster trees and 27 cultivars were sampled to represent molecular diversity. We used 11 simple sequence repeat and 13 sequence-related amplified polymorphism markers to assess genetic variations and inter-relationships among the samples. The results of the analysis showed differences in the levels of allelic composition and heterozygosity between cultivated and wild olive trees. The observation of a high proportion of a certain wild-type genetic background in the cultivars may indicate the former use of local wild trees in olive domestication in Turkey, a possible autochthonal origin of cultivars. “Gemlik” was found to be the most common olive cultivar in the Marmara region and most of the wild olive samples from this region may be feral forms derived from cultivar seed spreading. The information obtained from this study can help to assist the management of an olive collection and sheds some light on the origin of Turkish olive cultivars.     

Genetic Diversity of Twelve Switchgrass Populations Using Molecular and Morphological Markers

Switchgrass (Panicum virgatum L.) is a warm season, C₄ perennial grass native to most of North America with numerous applications, including use as a bioenergy feedstock species. To date, no studies on genetic diversity in switchgrass have been conducted that use both molecular and morphological markers. The objectives of this study were to assess genetic diversity and determine differences among and between 12 switchgrass populations grown in New Jersey by examining both morphological and molecular characteristics, and to determine whether morphological, molecular, and/or combined data sets can detect ecotype and/or geographical differences at the population level. Twelve plants from each population were characterized with 16 switchgrass expressed sequence tag-simple sequence repeat markers (EST-SSRs) and seven morphological characters. Data was analyzed using GenAlEx and Unweighted Pair-Group Method of Averages (UPGMA) cluster analysis. Most (64%) of the molecular variation in switchgrass populations exists among individuals within populations, with lesser amounts between populations (36%). Upland and lowland populations were distinguished in all three data sets. Some eastern US and midwestern US populations were distinct in all three data sets. Similarities were observed between all three data sets indicating molecular markers may be useful for identifying morphological differences or other adaptive traits. The combined data set was the most useful in differentiating populations based on geography and found separation between midwestern and eastern upland populations. The results indicate that the combination of morphological and molecular markers may be useful in future applications such as genetic diversity studies, plant variety protection, cultivar identification, and/or identifying geographic origin.     

Switchgrass (Panicum virgatum L.) Genotypes Differ between Coastal Sites and Inland Road Corridors in the Northeastern US

Switchgrass (Panicum virgatum L.) is a North American grass that exhibits vast genetic diversity across its geographic range. In the Northeastern US, local switchgrass populations were restricted to a narrow coastal zone before European settlement, but current populations inhabit inland road verges raising questions about their origin and genetics. These questions are important because switchgrass lines with novel traits are being cultivated as a biofuel feedstock, and gene flow could impact the genetic integrity and distribution of local populations. This study was designed to determine if: 1) switchgrass plants collected in the Long Island Sound Coastal Lowland coastal Level IV ecoregion represented local populations, and 2) switchgrass plants collected from road verges in the adjacent inland regions were most closely related to local coastal populations or switchgrass from other geographic regions. The study used 18 microsatellite markers to infer the genetic relationships between 122 collected switchgrass plants and a reference dataset consisting of 28 cultivars representing ecotypes, ploidy levels, and lineages from North America. Results showed that 84% of 88 plants collected in the coastal plants were most closely aligned with the Lowland tetraploid genetic pool. Among this group, 61 coastal plants were similar to, but distinct from, all Lowland tetraploid cultivars in the reference dataset leading to the designation of a genetic sub-population called the Southern New England Lowland Tetraploids. In contrast, 67% of 34 plants collected in road verges in the inland ecoregions were most similar to two Upland octoploid cultivars; only 24% of roadside plants were Lowland tetraploid. These results suggest that cryptic, non-local genotypes exist in road verges and that gene flow from biofuels plantations could contribute to further changes in switchgrass population genetics in the Northeast.     

Genotypic diversity effects on biomass production in native perennial bioenergy cropping systems

The perennial grass species that are being developed as biomass feedstock crops harbor extensive genotypic diversity, but the effects of this diversity on biomass production are not well understood. We investigated the effects of genotypic diversity in switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) on perennial biomass cropping systems in two experiments conducted over 2008–2014 at a 5.4‐ha fertile field site in northeastern Illinois, USA. We varied levels of switchgrass and big bluestem genotypic diversity using various local and nonlocal cultivars – under low or high species diversity, with or without nitrogen inputs – and quantified establishment, biomass yield, and biomass composition. In one experiment (‘agronomic trial’), we compared three switchgrass cultivars in monoculture to a switchgrass cultivar mixture and three different species mixtures, with or without N fertilization. In another experiment (‘diversity gradient’), we varied diversity levels in switchgrass and big bluestem (1, 2, 4, or 6 cultivars per plot), with one or two species per plot. In both experiments, cultivar mixtures produced yields equivalent to or greater than the best cultivars. In the agronomic trial, the three switchgrass mixture showed the highest production overall, though not significantly different than best cultivar monoculture. In the diversity gradient, genotypic mixtures had one‐third higher biomass production than the average monoculture, and none of the monocultures were significantly higher yielding than the average mixture. Year‐to‐year variation in yields was lowest in the three‐cultivar switchgrass mixtures and Cave‐In‐Rock (the southern Illinois cultivar) and also reduced in the mixture of switchgrass and big bluestem relative to the species monocultures. The effects of genotypic diversity on biomass composition were modest relative to the differences among species and genotypes. Our findings suggest that local genotypes can be included in biomass cropping systems without compromising yields and that genotypic mixtures could help provide high, stable yields of high‐quality biomass feedstocks.     

SRAP analysis of genetic diversity of nine native populations of wild sugarcane, Saccharum spontaneum, from Sichuan, China

Saccharum spontaneum is a wild sugarcane species that is native to and widely distributed in China. It has been extensively used in sugarcane breeding programs, and is being tested for the development of bioenergy cultivars. In order to provide basic information for the exploitation of this species, we analyzed genetic variation among and within native S. spontaneum populations collected from Sichuan, China. Eighty plants from nine native populations were sampled. Twenty-one sequence-related amplified polymorphism primer pairs generated 235 clearly scorable bands, of which 185 were polymorphic (78.7%). Nei's genetic diversity was 0.2801 and Shannon's information index was 0.4155 across the populations. Genetic diversity parameters, G(ST) value (0.2088) and N(m) value (1.8944), showed that the genetic variation within populations was greater than that among populations. In the cluster analysis, one major grouping was formed by populations from Ya'an and another one by populations from Sichuan basin; a population from Baoxing formed a single cluster. In order to fully comprehend the genetic diversity of cold-tolerant local germplasm in this species, germplasm should be collected from the heterogeneous environments along the northern regions of this species' distribution. The germplasm that we collected should be a valuable resource for Saccharum breeding.     

Restoration of species‐rich grasslands by transfer of local plant material and its impact on species diversity and genetic variation—Findings of a practical restoration project in southeastern Germany

Restoration of species‐rich grasslands is a key issue of conservation. The transfer of seed‐containing local plant material is a proven technique to restore species‐rich grassland, since it potentially allows to establish genetically variable and locally adapted populations. In our study, we tested how the transfer of local plant material affected the species diversity and composition of restored grasslands and the genetic variation of the typical grassland plant species Knautia arvensis and Plantago lanceolata.For our study, we selected fifteen study sites in southeastern Germany. We analyzed species diversity and composition and used molecular markers to investigate genetic variation within and among populations of the study species from grasslands that served as source sites for restoration and grasslands, which were restored by transfer of green hay and threshed local plant material.The results revealed no significant differences in species diversity and composition between grasslands at source and restoration sites. Levels of genetic variation within populations of the study species Knautia arvensis and Plantago lanceolata were comparable at source and restoration sites and genetic variation among populations at source and their corresponding restoration sites were only marginal different.Our study suggests that the transfer of local plant material is a restoration approach highly suited to preserve the composition of species‐rich grasslands and the natural genetic pattern of typical grassland plant species.     

Flowering Phenology and Genetic Similarity among Local and Recently Introduced Populations of Andropogon gerardii in Ohio

In Ohio and elsewhere, recent grassland plantings in the federal Conservation Reserve Program (CRP) have become much more extensive than native prairie remnants. The seed source for CRP grasslands in Ohio often comes from as far away as Missouri or Texas, which may be undesirable from the standpoint of conservation genetics. The goal of this study was to examine the potential for gene flow from large, recently introduced populations of Big bluestem (Andropogon gerardii, Poaceae) to small local populations of this outcrossing perennial species. We examined the potential for cross‐pollination between three local populations and three introduced CRP populations by comparing flowering phenologies. Flowering times overlapped extensively, indicating that cross‐pollination is possible where local and introduced genotypes co‐occur. To compare genetic variation in local and CRP populations, we analyzed variation at 68 RAPD loci in six populations of each type. Somewhat surprisingly, we found no significant differences in the genetic diversity or composition between the two groups (local vs. CRP). In summary, we found that local and introduced populations of Big bluestem have the potential to interbreed, based on their flowering periods, but further research is needed to determine whether local genotypes harbor unique genetic variation that could be jeopardized by hybridization with introduced genotypes.     

Genetic variation among wild and cultivated populations of the Chinese medicinal plant Coptis chinensis (Ranunculaceae)

To examine if the cultivation process has reduced the genetic variation of modern cultivars of the traditional Chinese medicinal plant, Coptis chinensis, the levels and distribution of genetic variation was investigated using ISSR markers. A total of 214 C. chinensis individuals from seven wild and three cultivated populations were included in the study. Seven ISSR primers were used and a total of 91 DNA fragments were scored. The levels of genetic diversity in cultivated populations were similar as those in wild populations (mean PPL = 65.2% versus PPL = 52.4%, mean H = 0.159 versus H = 0.153 and mean I = 0.255 versus I = 0.237), suggesting that cultivation did not seriously influence genetic variation of present-day cultivated populations. Neighbour-joining cluster analysis showed that wild populations and cultivated populations were not separated into two groups. The coefficient of genetic differentiation between a cultivar and its wild progenitor was 0.066 (G(st)), which was in good accordance with the result by amova analysis (10.9% of total genetic variation resided on the two groups), indicating that cultivated populations were not genetically differentiated from wild progenitors. For the seven wild populations, a significant genetic differentiation among populations was found using amova analysis (45.9% of total genetic variation resided among populations). A number of causes, including genetic drift and inbreeding in the small and isolated wild populations, the relative limited gene flow between wild populations (N(m) = 0.590), and high gene flow between cultivars and their wild progenitors (N(m) = 7.116), might have led to the observed genetic profiles of C. chinensis.     

Hierarchical classification of switchgrass genotypes using SSR and chloroplast sequences: ecotypes,ploidies, gene pools,and cultivars

Switchgrass (Panicum virgatum L.) is an important crop for bioenergy feedstock development. Switchgrass has two main ecotypes: the lowland ecotype being exclusively tetraploid (2n = 4x = 36) and the upland ecotype being mainly tetraploid and octaploid (2n = 8x = 72). Because there is a significant difference in ploidy, morphology, growth pattern, and zone of adaptation between and within the upland and lowland ecotypes, it is important to discriminate switchgrass plants belonging to different genetic pools. We used 55 simple sequence repeats (SSR) loci and six chloroplast sequences to identify patterns of variation between and within 18 switchgrass cultivars representing seven lowland and 11 upland cultivars from different geographic regions and of varying ploidy levels. We report consistent discrimination of switchgrass cultivars into ecotype membership and demonstrate unambiguous molecular differentiation among switchgrass ploidy levels using genetic markers. Also, SSR and chloroplast markers identified genetic pools related to the geographic origin of the 18 cultivars with respect to ecotype, ploidy, and geographical, and cultivar sources. SSR loci were highly informative for cultivar fingerprinting and to classify plants of unknown origin. This classification system is the first step toward developing switchgrass complementary gene pools that can be expected to provide a significant heterotic increase in biomass yield.     

Diversity and Distribution of Floral Resources Influence the Restoration of Plant–Pollinator Networks on a Reclaimed Strip Mine

Plant–pollinator mutualisms are one of the several functional relationships that must be reinstated to ensure the long‐term success of habitat restoration projects. These mutualisms are unlikely to reinstate themselves until all of the resource requirements of pollinators have been met. By meeting these requirements, projects can improve their long‐term success. We hypothesized that pollinator assemblage and structure and stability of plant–pollinator networks depend both on aspects of the surrounding landscape and of the restoration effort itself. We predicted that pollinator species diversity and network stability would be negatively associated with distance from remnant habitat, but that local floral diversity might rescue pollinator diversity and network stability in locations distant from the remnant. We created plots of native prairie on a reclaimed strip mine in central Ohio, U.S.A. that ranged in floral diversity and isolation from the remnant habitat. We found that the pollinator diversity declined with distance from the remnant habitat. Furthermore, reduced pollinator diversity in low floral diversity plots far from the remnant habitat was associated with loss of network stability. High floral diversity, however, compensated for losses in pollinator diversity in plots far from the remnant habitat through the attraction of generalist pollinators. Generalist pollinators increased network connectance and plant‐niche overlap. As a result, network robustness of high floral diversity plots was independent of isolation. We conclude that the aspects of the restoration effort itself, such as floral community composition, can be successfully tailored to incorporate the restoration of pollinators and improve success given a particular landscape context.     

RAPD variation within and among natural populations of outcrossing buffalograss [Buchloë dactyloides (Nutt.) Engelm.]

RAPD markers provide a powerful tool for the investigation of genetic variation in natural and domesticated populations. Recent studies of strain/cultivar identification have shown extensive RAPD divergence among, but little variation within, inbred species or cultivars. In contrast, little is known about the pattern and extent of RAPD variation in heterogeneous, outcrossing species. We describe the population genetic variation of RAPD markers in natural, diploid sources of dioecious buffalograss [Buchloë dactyloides (Nutt.) Engelm.]. Buffalograss is native to the semi-arid regions of the Great Plains of North America, where it is important for rangeland forage, soil conservation, and as turfgrass. Most sources of buffalograss germplasm are polyploid; diploid populations are previously known only from semi-arid Central Mexico. This is the first report of diploids from humid Gulf Coastal Texas. These two diploid sources represent divergent adaptive ecotypes. Seven 10-mer primers produced 98 polymorphic banding sites. Based on the presence/ absence of bands, a genetic distance matrix was calculated. The new Analysis of Molecular Variance (AMOVA) technique was used to apportion the variation among individuals within populations, among populations within adaptive regions, and among regions. There was considerable variation within each of the four populations, and every individual was genetically distinct. Even so, genetic divergence was found among local populations. Within-population variation was larger and among-population variation smaller in Mexico than in Texas. The largest observed genetic differences were those between the two regional ecotypes. These patterns of genetic variation were very different from those reported for inbred species and provide important baseline data for cultivar identification and continuing studies of the evolution of polyploid races in this species.