Search results for "Annual plant"
showing 8 items of 8 documents
Seed Bank in Annuals: Competition Between Banker and Non-banker Morphs
2002
Seed bank is a plant life history strategy against the unpredictability of the biotic and the abiotic environment. We simulated competition between a seed banking and a non-banking morph of an annual plant. A constant fraction of the banker morph seeds was allocated to the seed bank, where they had a constant mortality and germination rate. All surviving seeds of the non-banker morph germinated in the next generation. The seedlings of both morphs experienced similar density-dependent mortality. Whether one of the morphs wins or the morphs coexist was evaluated from parameter space plots and statistically with logistic regression analysis. All parameters of the model had a significant, nonli…
Effect of vernalization on the development and growth of Alopecurus myosuroides
2002
Alopecurus myosuroides is an annual winter grass weed present in many winter and spring crops. The vernalization responses of three populations of A. myosuroides were assessed using natural exposure during winter in two field experiments and using cold exposure of imbibed seeds in a refrigerator in two greenhouse experiments. It was observed that a period of chilling during the pregermination phase had a marked effect on subsequent phenology. In the greenhouse, the major effect of vernalization was the reduction in the vegetative period because of an early reproductive induction of the apex. Plant morphology was affected by vernalization via a decrease in biomass resulting from a reduced ti…
Morphology, anatomy and germination response of heteromorphic achenes of Anthemis chrysantha J. Gay (Asteraceae), a critically endangered species
2011
[EN] This study demonstrates that Anthemis chrysantha, a 'Critically Endangered' annual plant, produces two morphs of achenes: white and dark achenes, which differ in size, mass, anatomy and germination behaviour. Fresh white achenes germinated at all temperatures assayed from 10 to 25 degrees C in both continuous darkness and 12-h photoperiod, ranging between 24% at 25 degrees C in darkness and 89% at 12/20 degrees C in light, whereas fresh dark achenes did not germinate under any temperature or light conditions. To identify differences in dormancy type between the two morphs, germination of dry-stored achenes, and achenes stratified at 5 or 25 degrees C for 2 months were tested in both da…
Contribution to the knowledge of the therophytic flora of Sardinia
2003
The abundance of therophytes, largely contributes to the naturalistic value of Sardinia. Moreover, most of the annual species belonging to the Sardinian flora have an historical and cultural value, as they followed the men in his migrations and still reflect the different ways of traditional land exploitation characterising the island. As a matter of fact, the development of human technology increased number and frequency of the annual plants of Sardinia. Nowadays, annuals occur in several habitats of the island, where they play a primary ecological role, both as biomass producers and protecting the soil from rill erosion during the rainy season, at least where the environmental factors do …
Floristic, phenological and chorological differences in the annual vegetation of Sardinia.
2007
The therophytic flora of Sardinia has been split into four main groups, basing on the ecologic requirements of species. The following groups have been recognized: flora of dry entisoils, flora of periodically swampy or submerged entisoils, flora of coastal sites, flora of fields, road edges and human settlements. Either, most frequent or exclusive species were ascribed to each group. A species was considered “exclusive” when its relative frequency outside a given group was estimated ≤10%. Differences have been highlighted within the groups, dealing with chorology, growth form, flowering time, colour of flowers, pollination and seed dispersal strategies.
Effects of temperatures on the spatial arrangement in Mediterranean annual dry grasslands
2009
Some preliminary results of diachronic researches on the spatial arrangement and species richness in Mediterranean annual dry grasslands belonging to the class Tuberarietea guttatae are presented. Our results are based on 12 permanent plots, set in three places at different heights in Southern and Central Sardinia. Sites were chosen to have annual species richness and plant density not significantly different. The relationship between patchiness and temporal stability was investigated at the scale of the square plots. We used the mean abundance divided by the SD in abundance (S = xm/r), as the measure of temporal stability of populations (Tilman 1999) and the Shannon-Wiener index to evaluat…
Using coupled hidden markov chains to estimate colonization and seed bank survival in a metapopulation of annual plants
2022
The study of ecological systems is often impeded by components that escape perfect observation, such as the trajectories of moving animals or the status of plant seed banks. These hidden components can be efficiently handled with statistical modeling by using hidden variables, which are often called latent variables.Notably, the hidden variables framework enables us to model an underlying interaction structure between variables (including random effects in regression models) and perform data clustering, which are useful tools in the analysis of ecological data.This book provides an introduction to hidden variables in ecology, through recent works on statistical modeling as well as on estima…
The vegetation of temporary ponds of Sardinia
2009
The Mediterranean temporary ponds are considered priority habitat in the Directive 92/43/EEC (habitat n. 3170*) and detailed information on their floristic composition and susceptibility to invasive species seems a central issue for their preservation, because the development and maintenance of seasonal vegetation is merely the resultant of the development and maintenance of its component individuals. Sardinia presents fairly large extensions of land where such habitats are still well represented, thought not investigated in depth. Basing on literature and unpublished data, a survey on the current phytosociological knowledge of the temporary ponds of Sardinia is presented. Our field studies…