Open Access. Powered by Scholars. Published by Universities.®

Life Sciences Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 28 of 28

Full-Text Articles in Life Sciences

Variation In The Local Population Dynamics Of The Short-Lived Opuntia Macrorhiza (Cactaceae), Chirakkal V. Haridas, Kathleen Keeler, Brigitte Tenhumberg Jan 2014

Variation In The Local Population Dynamics Of The Short-Lived Opuntia Macrorhiza (Cactaceae), Chirakkal V. Haridas, Kathleen Keeler, Brigitte Tenhumberg

Faculty Publications in the Biological Sciences

Spatio-temporal variation in demographic rates can have profound effects for population persistence, especially for dispersal-limited species living in fragmented landscapes. Long-term studies of plants in such habitats help with understanding the impacts of fragmentation on population persistence but such studies are rare. In this work we reanalyzed demographic data from seven years of the short-lived cactus Opuntia macrorhiza var. macrorhiza at five plots in Boulder, Colorado. Previous work combining data from all years and all plots predicted a stable population (deterministic log λ ≈ 0). This approach assumed that all five plots were part of a single population. Since the plots ...


Template-Based Structure Prediction And Classification Of Transcription Factors In Arabidopsis Thaliana, Tao Lu, Yuedong Yang, Bo Yao, Song Liu, Yaoqi Zhou, Chi Zhang Jan 2012

Template-Based Structure Prediction And Classification Of Transcription Factors In Arabidopsis Thaliana, Tao Lu, Yuedong Yang, Bo Yao, Song Liu, Yaoqi Zhou, Chi Zhang

Faculty Publications in the Biological Sciences

Transcription factors (TFs) play important roles in plants. However, there is no systematic study of their structures and functions of most TFs in plants. Here, we performed template-based structure prediction for all TFs in Arabidopsis thaliana, with their full-length sequences as well as C-terminal and N-terminal regions. A total of 2,918 model structures were obtained with a high confidence score. We find that TF families employ only a smaller number of templates for DNA-binding domains (DBD) but a diverse number of templates for transcription regulatory domains (TRD). Although TF families are classified according to DBD, their sizes have a ...


Clone Size Of Andropogon Gerardii Vitman (Big Bluestem) At Konza Prairie, Kansas, Kathleen H. Keeler, Charles F. Williams, Linda S. Vescio Jan 2002

Clone Size Of Andropogon Gerardii Vitman (Big Bluestem) At Konza Prairie, Kansas, Kathleen H. Keeler, Charles F. Williams, Linda S. Vescio

Faculty Publications in the Biological Sciences

Clone size of plants of Andropogon gerardii from Konza Prairie Biological Station, Manhattan, Kansas was estimated from spatial patterns of genetic variation, using proteins detected by starch gel electrophoresis and DNA content (ploidy) measured by flow cytometry. Unique multi-locus protein banding patterns and differences in ploidy were used to exclude plants as members of the same clone. Individual clones averaged about 2 m in diameter and areas of prairie of 100 m2 were calculated to contain an average of 31.8 genetic individuals.


Clonal Growth Of Lithospermum Caroliniense (Boraginaceae) In Contrasting Sand Dune Habitats, Stephen G. Weller, Kathleen H. Keeler, Barbara A. Thomson Jan 2000

Clonal Growth Of Lithospermum Caroliniense (Boraginaceae) In Contrasting Sand Dune Habitats, Stephen G. Weller, Kathleen H. Keeler, Barbara A. Thomson

Faculty Publications in the Biological Sciences

The occurrence of clonal growth of distylous Lithospermum caroliniense was investigated in a population in the Nebraska Sandhills, an area where sand dunes have been relatively stable for at least 1,500–3,000 yr, and compared to a population occurring at the Indiana Dunes, an area of active sand dune formation. Spatial autocorrelation analysis indicated the occurrence of significant clonal propagation of genetically based floral morphs at Arapaho Prairie, but not for the Indiana Dunes. Apparent clonal growth in the Sandhills population had no overall negative effect on pollen deposition or fecundity relative to the Indiana population, although in ...


Comparison Of Common Cytotypes Of Andropogon Gerardii (Andropogoneae, Poaceae), Kathleen H. Keeler, Geoffrey A. Davis Jan 1999

Comparison Of Common Cytotypes Of Andropogon Gerardii (Andropogoneae, Poaceae), Kathleen H. Keeler, Geoffrey A. Davis

Faculty Publications in the Biological Sciences

Many plant species contain populations with more than one polyploid cytotype, but little is known of the mechanisms maintaining several cytotypes in a population. Andropogon gerardii cytotypes were compared to evaluate different models of autopolyploid cytotype coexistence. The enneaploid (90 chromosome, 9x) cytotype was found to be larger and taller than the hexaploid (60 chromosome, 6x) cytotype. Seed production is significantly more efficient in hexaploids, but seed production per area was not significantly different. The two cytotypes are not exomorphologically separable in the field because of great plasticity in response to environmental variation and wide variation within each ...


Population Biology Of Intraspecific Polyploidy In Grasses, Kathleen H. Keeler Jan 1998

Population Biology Of Intraspecific Polyploidy In Grasses, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Polyploidy is the duplication of an entire nuclear genome, whether diploid or higher level (Stebbins, 1971; Thompson & Lumaret, 1992) and a frequent occurrence in plants. Stebbins (1971) estimated that 30-35% of flowering plant species are polyploid, and that many more had a polyploid event in their evolutionary history, including all members of such important families as the Magnoliaceae, Salicaceae, and Ericaceae. Goldblatt (1980) estimated 55%, but probably up to 75%, of monocotyledons had at least one polyploid event in their history, using the criterion that if the species has a base number higher than n=13 it is derived from a polyploid. Using the same criterion, Grant (1981) estimated that 52% of angiosperms, 49% of dicotyledon species and 60% of monocotyledons are polyploid. Masterson (1994) supports high frequencies of ancestral polyploidy using fossil evidence. Clearly, polyploids have been fixed in many lineages.

Within many genera of higher plants, individual species often have different, but uniform, ploidy levels (e.g. Draba, Brassicaceae, Brockman & Elven, 1992), the grasses being no exception, e.g. Bromus, Elymus (Seberg & von Bothmer, 1991; Ainouche, Misset & Huon, 1995). Intrageneric polyploid series provide another indicator of frequent polyploid events. For example, of a miscellaneous collection of 87 grass genera for which I had chromosome numbers for two or more species, 65 (75%) formed a polyploid series in relation to other members of the genus (Table 7.1).


Evolutionary Implications Of Meiotic Chromosome Behavior, Reproductive Biology, And Hybridization In 6x And 9x Cytotypes Of Andropogon Gerardii (Poaceae), Guillermo A. Norrmann, Camilo L. Quarín, Kathleen H. Keeler Jan 1997

Evolutionary Implications Of Meiotic Chromosome Behavior, Reproductive Biology, And Hybridization In 6x And 9x Cytotypes Of Andropogon Gerardii (Poaceae), Guillermo A. Norrmann, Camilo L. Quarín, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Andropogon gerardii, big bluestem, has 60 and 90 chromosome cytotypes. Meiosis in the hexaploid was shown to be regular, although some secondary associations of bivalents form. Meiosis in the enneaploid (2n = 9x = 90) is irregular, leading to most gametes having unbalanced chromosome complements. Both cytotypes show considerable self-incompatibility. Cytotypes crossed freely, forming a variety of fertile euploids and aneuploids. Indistinguishable exomorphology, intermixing in natural populations, and compatibility suggest that A. gerardii is best understood as a cytotypically complex single species.


Movement Of Crop Transgenes Into Wild Plants, Kathleen H. Keeler, Charles E. Turner, Margaret R. Bolick Jan 1996

Movement Of Crop Transgenes Into Wild Plants, Kathleen H. Keeler, Charles E. Turner, Margaret R. Bolick

Faculty Publications in the Biological Sciences

Despite the great potential and increasing importance of other weed control options (Turner et al. 1992) and unwanted environmental side effects of some herbicides, herbicides constitute a very important means of weed control. The escape of herbicide resistance genes to wild, weedy plants could cause more severe weed problems, and presents a very real threat to the efficacy of herbicides as a weed control option. Therefore, management strategies that prevent, or reduce the likelihood and frequency of HRG escape through containment methods are advisable, as are mitigation plans in the event of HRG escape to wild plants.


Getting The Lay Of The Land: Introducing North American Native Grasslands, Anthony Joern, Kathleen H. Keeler Jan 1995

Getting The Lay Of The Land: Introducing North American Native Grasslands, Anthony Joern, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

The expected catastrophic extinction of species (already under way in many places) will alter the planet’s biological diversity so profoundly that, at the known rate of extinction, it will take millions of years to recover. Yet few ecologists study extinction. Indeed, very little ecology deals with any processes that last more than a few years, involve more than a handful of species, and cover an area of more than a few hectares. The temporal, spatial and organizational scales of most ecological studies are such that one can read entire issues of major journals and see no hint of impending ...


Introduction From The Changing Prairie: North American Grasslands, Anthony Joern, Kathleen H. Keeler Jan 1995

Introduction From The Changing Prairie: North American Grasslands, Anthony Joern, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Preserving remaining North American grasslands requires a multiability approach. In this book, we investigate three aspects of an admittedly larger problem: (1) how we as humans perceive grasslands; (2) the ecology of grasslands, in order to define the framework within which conservation and preservation efforts must operate; and (3) conservation issues. Additional sociological, economic, philosophical, and cultural considerations will provide important additional insights to preserving and managing grasslands, but are not included here. By restricting our focus to only three issues, we feel that we can provide a basic, but appropriate, understanding of grassland ecosystems for the prairie enthusiast. This ...


Population Processes, Kathleen H. Keeler, Anthony Joern Jan 1995

Population Processes, Kathleen H. Keeler, Anthony Joern

Faculty Publications in the Biological Sciences

Within the prairies, myriad populations of plants, insects, small mammals, and other organisms form distinct levels of organization. The physical forces of weather and fire and the complex networks of species interactions control each species’s structure and dynamics and determine its abundance or rarity. Variation in population dynamics and interactions over time and space determine the distribution and abundance of species, and ultimately the composition and dynamics of entire prairie communities.

To the casual observer, plant populations on prairies may seem quite static, like museums containing a diverse collection of specimens that can be seen again and again on ...


Preface From The Changing Prairie: North American Grasslands, Kathleen H. Keeler, Anthony Joern Jan 1995

Preface From The Changing Prairie: North American Grasslands, Kathleen H. Keeler, Anthony Joern

Faculty Publications in the Biological Sciences

North American grasslands have figured prominently in our North American heritage. Prairies first provided significant barriers to westward expansion, and then offered both economic and sociological opportunity, as well as heartache, for settlers. Many artists have gained significant inspiration from the beauty as well as the harshness of this region and its biota. And because of ideal climate and soil conditions, these grasslands have provided the agricultural foundation of which much of the economic growth and stability of the United States has historically depended.

Yet many see North American prairies as beautiful only when manipulated or exploited: Green croplands or ...


Molecular Approaches For Control Of Tomato Bushy Stunt Virus, H. B. Scholthof, M. Borja, Thomas Jack Morris, A. O. Jackson Jan 1993

Molecular Approaches For Control Of Tomato Bushy Stunt Virus, H. B. Scholthof, M. Borja, Thomas Jack Morris, A. O. Jackson

Faculty Publications in the Biological Sciences

I N this overview strategies are discussed that are currently being tested in our laboratory in an effort to engineer resistance against tomato bushy stunt virus (TBSV) in plants. TBSV is chosen as a model-system since this is an economically important RNA virus that is well characterized at the molecular level and the virus has some interesting and potentially useful features that can be exploited to produce resistant plants. Moreover, we anticipate that the information derived from our studies with TBSV will be applicable in developing resistance to other plant viruses. Some approaches that we are attempting to apply to ...


Local Polyploid Variation In The Native Prairie Grass Andropogon Gerardii, Kathleen H. Keeler Jan 1992

Local Polyploid Variation In The Native Prairie Grass Andropogon Gerardii, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

The microscale distribution of polyploid variants of the dominant grass big bluestem (Andropogon gerardii) in virgin tallgrass prairie was mapped using flow cytometry. The correlation between DNA content and polyploidy allows the use of flow cytometry for nondestructive determination of polyploidy in intact plants. At Konza Prairie, local plots contained from 0 to 100% hexaploid cytotypes but most showed fine-scale mixing of the polyploid variants. The relationship of cytotype frequency to moisture availability or burning history was nonsignificant


Origin And Evolution Of Defective Interfering Rnas Of Tomato Bushy Stunt Virus, David A. Knorr, Thomas Jack Morris Jan 1991

Origin And Evolution Of Defective Interfering Rnas Of Tomato Bushy Stunt Virus, David A. Knorr, Thomas Jack Morris

Faculty Publications in the Biological Sciences

Viruses with defective genomes have been identified in association with virtually every major family of viruses and have been widely utilized as tools for investigating virus functions in animal cell culture systems (Perrault, 1981). It is generally thought that defective interfering viruses (DIs) arise through deletion, rearrangement, or recombination of a competent viral genome. DIs tack the ability for independent existence relying on their parental helper viruses to supply factors required for replication, maturation, and/or encapsidation (Huang and Baltimore, 1977). The interference attributed to DIs is thought to result from competition with the helper virus for factors required in ...


Extrafloral Nectaries On Plants In Communities Without Ants: Hawaii, Kathleen H. Keeler Jan 1985

Extrafloral Nectaries On Plants In Communities Without Ants: Hawaii, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Since the Hawaiian Islands lack native ants, it was hypothesized that extrafloral nectaries, an ant-related mutualistic trait, should be lacking on native species. Presence of extrafloral nectaries (EFNs) on plants was determined by direct observation and related to vegetation structure and floral composition. Frequency of plants with EFNs was low by all possible comparisons. However, several endemic species had functional EFNs. The hypotheses to explain these anomalies are (1) phylogenetic inertia or (2) mutualism with some other organism than ants.


Comparison Of Old Field Succession On A Tallgrass Prairie And A Nebraska Sandhills Prairie, Mary Bomberger Brown, Shelly L. Shields, A. Tyrone Harrsion, Kathleen H. Keeler Mar 1983

Comparison Of Old Field Succession On A Tallgrass Prairie And A Nebraska Sandhills Prairie, Mary Bomberger Brown, Shelly L. Shields, A. Tyrone Harrsion, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Long held to be reasonably well understood, the process of ecological succession has recently come under attack. The predictability of successional changes has been doubted (Walker 1970), the mechanism of species replacement has been questioned (Connell and Slatyer 1977), and the reality of steady-state (climax) challenged (Botkin and Sobel 1975, Connell and Slatyer 1977, Connell 1978). In particular, several communities are presently recognized as having "cyclic succession" (Ricklefs 1973), in which the process is continually repeating. Such communities include heaths (Watt 1947), prairie pot-hole marshes (Vander Valk and Davis 1978), spruce-fir forests (Sprugel 1976, Sprugel and Bormann 1981), and intertidal ...


Function Of Mentzelia Nuda (Loasaceae) Postfloral Nectaries In Seed Defense, Kathleen H. Keeler Feb 1981

Function Of Mentzelia Nuda (Loasaceae) Postfloral Nectaries In Seed Defense, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Mentzelia nuda is a coarse, short-lived perennial of the High Plains of North America. The flowers secrete nectar which serves as an attractant for pollinating bees. Postfloral nectar secretion attracts ants whose presence significantly enhances seed set. This is the first demonstration of advantage to postflowering activity of a floral nectary.


Cover Of Plants With Extrafloral Nectaries At Four Northern California Sites, Kathleen H. Keeler Jan 1981

Cover Of Plants With Extrafloral Nectaries At Four Northern California Sites, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Percent cover of plants with extrafloral nectaries was investigated in three California habitats with the same physiognomy as habitats previously studied in Nebraska (perennial native grassland, riparian forest, deciduous forest). In contrast to Nebraska where cover of plants with extrafloral nectaries reached 14 percent, no plants with extrafloral nectaries were found in any California transect. Chaparral was also studied; no plants with extrafloral nectaries were found.


The Flora And Sandhills Prairie Communities Of Arapaho Prairie, Arthur County, Nebraska, Kathleen H. Keeler, A. T. Harrison, L.S. Vescio Sep 1980

The Flora And Sandhills Prairie Communities Of Arapaho Prairie, Arthur County, Nebraska, Kathleen H. Keeler, A. T. Harrison, L.S. Vescio

Faculty Publications in the Biological Sciences

The Arapaho Prairie is a 526-hectare (two-section) tract of upland Sandhills prairie located approximately nine miles southwest of the town of Arthur in Arthur Co., Nebraska (Sec. 31, 32 T18N R39W). The Prairie is at the extreme southwest edge of the 52,000-km2 Nebraska Sandhills (see Kaul 1975) and is floristically and ecologically typical of the slightly drier, western part of this vegetation type. Sandhills prairie which stretches across much of north central Nebraska is a unique type of "mixed" grassland (Pool 1914, Rydberg 1931, Tolstead 1942, Weaver 1965) created by impact of the dry, continental climate on the ...


Morphology And Distribution Of Petiolar Nectaries In Ipomoea (Convolvulaceae), Kathleen H. Keeler, Robert B. Kaul Sep 1979

Morphology And Distribution Of Petiolar Nectaries In Ipomoea (Convolvulaceae), Kathleen H. Keeler, Robert B. Kaul

Faculty Publications in the Biological Sciences

The distribution of petiolar nectaries in 24 species of Ipomoea was investigated. Petiolar nectaries were found on 12 species (8 new reports, 4 confirmations of previous reports) and quoted from the literature as being found on 3 other species; they were absent from 9 species investigated. The structure of petiolar nectaries in the genus ranges from simple beds of superficial nectar-secreting trichomes (1 species), to slightly recessed "basin nectaries" (8 species), to "crypt nectaries," which are structurally the most complex extrafloral nectaries known (3 species). (Structures were not determined for 3 species.) Petiolar nectaries are present in all subgenera, but ...


Distribution Of Plants With Extrafloral Nectaries And Ants At Two Elevations In Jamaica, Kathleen H. Keeler Jun 1979

Distribution Of Plants With Extrafloral Nectaries And Ants At Two Elevations In Jamaica, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Frequencies of plants with extrafloral nectaries were determined for two elevations in Jamaica. Extrafloral nectaries were found on 0.28 of the plants at sea level (Happy Grove, Portland) and 0.00 of the plants at 1310 m (Whitfield Hall, St. Thomas). Ant abundance, as indicated by discovery of and recruitment to baits, was greater at the lower elevation site. However, despite the apparent absence of plants with extrafloral nectaries, there were abundant ants at 1310 m.


Species With Extrafloral Nectaries In A Temperate Flora (Nebraska), Kathleen H. Keeler Mar 1979

Species With Extrafloral Nectaries In A Temperate Flora (Nebraska), Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Extrafloral nectaries (EFNs) are glands on a plant, not involved in pollination, that produce solutions containing sugars (and other compounds). Long noted by morphologists, EFNs have recently been observed to be part of ant-plant mutualisms. The function of EFNs appears to be to attract aggressive insects, especially ants, which by disturbing or preying upon herbivores, reduce damage to the plant (Janzen, 1966a,b; Elias and Gelband, 1975; Keeler, 1975, 1977; Bentley, 1976, 1977a,b; Schemske, 1978; Tilman, 1978; Inouye and Taylor, 1979; Pickett ad Clark, 1979). Furthermore, they constitute an unusual plant defense against herbivores: at EFNs plants employ ants ...


Nocturnal Pollination Of Abronia Fragrans (Nyctaginaceae), Kathleen H. Keeler Jan 1979

Nocturnal Pollination Of Abronia Fragrans (Nyctaginaceae), Kathleen H. Keeler

Faculty Publications in the Biological Sciences

Abronia fragrans Nutt. (Nyctaginaceae) is a white-flowered herb of dry sandy soils from Idaho and South Dakota to Arizona and Texas. It can be readily observed to fit a night-blooming, moth-pollinated syndrome (Faegri and van der Pijl, The principle of pollination ecology, 1971). This does not seem to have been noted: in all references to A. fragrans we could find, the only indication of nocturnal anthesis was the comment of Nelson (Handbook of Rocky Mountain plants, 1969), who observed that the fragrance was more noticeable at night. Tillett (Brittonia 19:299-327, 1967), working on Pacific species, suggested that the pink ...


Anatomical Observations On Floating Leaves, Robert B. Kaul Jan 1976

Anatomical Observations On Floating Leaves, Robert B. Kaul

Faculty Publications in the Biological Sciences

An examination of 24 genera of aquatic plants having floating leaves and leaf-like thalli has been made. Functional stomata occur on the adaxial sides of floating leaves of angiosperms and some ferns, and in some floating leaves there are stomata on the abaxial surface as well. Most floating leaves have prominently chambered mesophyll, and in some instances the chambers are locally enlarged and form buoys.


Ipomoea Carnea Jacq. (Convolvulaceae) In Costa Rica, Kathleen H. Keeler Jan 1975

Ipomoea Carnea Jacq. (Convolvulaceae) In Costa Rica, Kathleen H. Keeler

Faculty Publications in the Biological Sciences

This is the first report of Ipomoea carnea (Convolvulaceae) from lowland Costa Rica. These populations are unusual for the species in flower color, flowering season and pollinator. Other aspects of the biology of the species in Guanacaste, especially pollination, flower robbing and extrafloral nectary visitors, are discussed.


Floral Morphology And Phylogeny In The Hydrocharitaceae, Robert B. Kaul Mar 1968

Floral Morphology And Phylogeny In The Hydrocharitaceae, Robert B. Kaul

Faculty Publications in the Biological Sciences

The vascular anatomy of 13 of the 15 genera of the Hydrocharitaceae has been studied, and certain aspects of floral morphology are considered. The flowers of the family show a broad range of specialized structures combined with primitive characteristics. The origin of paired and single stamens is interpreted as probable modifications of fascicled stamens. Extreme reduction in the androecium is shown for several genera. Tendencies toward reduction and fusion within the gynoecium are pronounced. Most genera are at least slightly syncarpous, but a few are apocarpous. The inferior ovary is appendicular in nature, with some genera exhibiting more complete fusion ...


The Relation Of Leaf Structure To Physical Factors, Edith Schwartz Clements Jan 1905

The Relation Of Leaf Structure To Physical Factors, Edith Schwartz Clements

Faculty Publications in the Biological Sciences

The leaf, as the seat of important physiological functions of the plant, and because of its modification by external factors, has long been a fruitful subject for investigation. As a rule, however, investigators have confined themselves solely to the histology and morphology of the leaf, independent of its relations to physical factors. Where the latter have been considered at all, it has been in a more or less general way, or undue importance has been assigned to one or another of the physical factors, and others have been ignored entirely. In no case have they been carefully measured. The aim ...