Crepis tectorum

About: Crepis tectorum is a research topic. Over the lifetime, 50 publications have been published within this topic receiving 585 citations.

Phenotypic plasticity in Crepis tectorum (Asteraceae): genetic correlations across light regimens

Abstract: Phenotypic plasticity in Crepis tectorum (Asteraceae): genetic correlations across light regimens

Paternal effects on seed size in a population of Crepis tectorum (Asteraceae)

Abstract: Two crossing experiments were designed to examine if there was a paternal (genetic) effect on three seed size parameters (length, width and weight), in a population of the annual Crepis tectorum. An ANOVA on paternal half-sib groups revealed a significant effect of pollen donor identity on seed width and seed weight. Some of the paternal effect reflected differences among pollen donors in the ability to initiate seed development on the recipient heads (% seed set), which was negatively correlated with seed size. This effect was greatest for seed width reflecting strong lateral compression of the seeds in heads with a high seed set. Increasing the number of pollen donors from one to five had no positive effect on seed size variability within flowering heads, suggesting that the expression of genetic variation is weaker at this level. An additional experiment showed that germinability increased with seed size, while only seed width affected seedling growth. These observations are used to discuss the potential for parent-offspring conflict and selective seed provisioning based on embryo size, in this population.

Seed size as a determinant of germination rate in Crepis tectorum (Asteraceae): evidence from a seed burial experiment

Abstract: The present study of the winter annual Crepis tectorum examines the relationship between seed (achene) size and the extent to which seeds resist germination during the year of their production. I carried out two seed burial experiments, one at an outcrop site occupied by a small-seeded population, and another in an experimental garden with soil from the same field site, with seeds representing the local population and a segregating generation of a cross between two other populations. Using logistic regression with data corrected for seed viability, I found an association between small seed size and failure to germinate in the first autumn. The small seed size characterizing many outcrop populations may have evolved as a response to selection for delaying germination in a habitat subject to unpredictable droughts during the growth season.

Phenotypic plasticity in Crepis tectorum (Asteraceae).

Abstract: Two experiments were carried out using two different approaches to compare populations ofCrepis tectorum (Asteraceae). One was based on a comparison of means of various vegetative and reproductive characters and another was based on a comparison of response patterns of the same characters in a series of environments. Population divergence within two earlier recognized form series, one from weed habitats and one from alvar habitats on Baltic islands, resulted in a partially overlapping pattern in cluster analyses based on character means. However, the pattern revealed by a comparison of the direction and amount of plastic response suggested that populations within the two form series had more similar response patterns than other combinations of populations. It was concluded that patterns of plasticity may provide useful additional information on the overall similarity among taxa. An hypothesis that plants in weed populations should exhibit a greater phenotypic response to the environments than plants in alvar populations was rejected.

Exotic plant species in the southern boreal forest of Saskatchewan

Abstract: Exotic species possess abilities to harm the ecosystems they invade. This study assesses the density, frequency and cover of exotic plants in roadside right-of-ways, logged areas and wildfire sites within mixedwood sections of the southern boreal forest of Saskatchewan. A total of 23 exotic species were observed including nine species of Gramineae, seven species of Leguminosae and five species of Compositae. Average density of exotic species in areas recently disturbed by timber harvesting or wildfire was 0.2 stems m −2 with a frequency of 72%. Exotic species adapted for wind dispersal were best represented including common dandelion ( Taraxacum officinale ), perennial sow thistle ( Sonchus arvensis ) and annual hawksbeard ( Crepis tectorum ). Only two exotic species, T. officinale and Canada bluegrass ( Poa compressa ), were observed in mature forest; both occurred with a frequency of 13% and an average density of 0.002 stems m −2 . A total of 22 exotic species was found in the right-of-ways quadrats with an average density of 117 stems m −2 and a frequency of 94%. The most frequently observed exotic species in the roadside right-of-way areas were T. officinale , alsike clover ( Trifolium hybridum ), S. arvensis , creeping red fescue ( Festuca rubra ) and smooth brome grass ( Bromus inermis ). These species are either common agricultural weeds or were part of the original seed mixture used to establish a plant cover in the roadside right-of-ways. Each of the exotic species observed was ranked to determine its current and potential threat to ecosystem attributes. The majority were considered a lesser threat and easy to control, with eight species ranked as a lesser threat and hard to control, and one species, B. inermis , ranked as a serious threat and hard to control. The distribution of exotic species was closely related to the management of roadside right-of-ways, wildfire events and timber harvesting. An increased distribution of exotic species was observed within roadside right-of-ways areas which had been subjected to more intensive management. Although the exotic species observed in this study are maintained and dispersed by management activities, the majority of exotic species are not a threat to this forest ecosystem in the southern boreal forest of Saskatchewan.