Home About us Contact
|
Home About us Contact | ||
|
|
||
Many Rare (many + rare)
Selected AbstractsConifers as invasive aliens: a global survey and predictive frameworkDIVERSITY AND DISTRIBUTIONS, Issue 5-6 2004David M. Richardson ABSTRACT We summarize information on naturalized and invasive conifers (class Pinopsida) worldwide (data from 40 countries, some with remote states/territories), and contrast these findings with patterns for other gymnosperms (classes Cycadopsida, Gnetopsida and Ginkgoopsida) and for woody angiosperms. Eighty conifer taxa (79 species and one hybrid; 13% of species) are known to be naturalized, and 36 species (6%) are ,invasive'. This categorization is based on objective and conservative criteria relating to consistency of reproduction, distance of spread from founders, and degree of reliance on propagules from the founder population for persistence in areas well outside the natural range of species. Twenty-eight of the known invasive conifers belong to one family (Pinaceae) and 21 of these are in one genus (Pinus). The Cupressaceae (including Taxodiaceae) has six known invasive species (4%) in four genera, but the other four conifer families have none. There are also no known invasive species in classes Cycadopsida, Gnetopsida or Ginkgoopsida. No angiosperm family comprising predominantly trees and shrubs has proportionally as many invasive species as the Pinaceae. Besides the marked taxonomic bias in favour of Pinaceae, and Pinus in particular, invasiveness in conifers is associated with a syndrome of life-history traits: small seed mass (< 50 mg), short juvenile period (< 10 year), and short intervals between large seed crops. Cryptomeria japonica, Larix decidua, Picea sitchensis, Pinus contorta, Pinus strobus, and Pseudotsuga menziesii exemplify this syndrome. Many rare and endangered conifer species exhibit opposite characters. These results are consistent with earlier predictions made using a discriminant function derived from attributes of invasive and noninvasive Pinus species. Informative exceptions are species with small seeds (< 4 mg, e.g. Chamaecyparis spp., Pinus banksiana, Tsuga spp. , mostly limited to wet/mineral substrates) or otherwise ,non-invasive' characters (e.g. large seeds, fleshy fruits, e.g. Araucaria araucana, Pinus pinea, Taxus baccata that are dependent on vertebrates for seed dispersal). Most conifers do not require coevolved mutualists for pollination and seed dispersal. Also, many species can persist in small populations but have the genetic and reproductive capacity to colonize and increase population size rapidly. The underlying mechanisms mediating conifer invasions are thus easier to discern than is the case for most angiosperms. Further information is needed to determine the extent to which propagule pressure (widespread dissemination, abundant plantings, long history of cultivation) can compensate for low ,inherent invasiveness'. [source] Discontinuity in fish assemblages across an elevation gradient in a southern Appalachian watershed, USAECOLOGY OF FRESHWATER FISH, Issue 1 2005J. L. Robinson This region is noted for extreme topographical relief, high cumulative annual rainfall and many rare and endemic plants and animals. The study area encompasses a portion of the Blue Ridge Escarpment and the associated Brevard Fault Zone. We hypothesise that major waterfalls and cascade complexes have acted to limit invasion and colonisation by fishes from downstream. This hypothesis is supported by longitudinal fish assemblage patterns in our study streams. Fish species richness in Toxaway River increased from 4 to 23 between Lake Toxaway and Lake Jocassee, a distance of 10 river km. We found similar discontinuities in neighbouring Horsepasture River and Bearwallow Creek. We found no instances of species replacement along this elevation gradient, and the trend in increased diversity downstream showed discontinuities coincident with sharp elevation breaks. With regard to theories posited to explain community formation in headwater stream fish communities (especially in those characterised by high topographical relief), we suggest coloniser ,access' may be more important than other factors including competitive interactions. Resumen 1. En este estudio examinamos patrones en los ensamblajes de peces de los ríos Toxaway y Horsepasture, dos ríos de elevada altitud de Carolina del Norte (USA). Esta región se caracteriza por rupturas topografías extremas, gran cantidad de lluvia anual y numerosos endemismos animales y vegetales. El estudio incluye una porción de la región del Blue Ridge Escarpment y la zona asociada de Brevard Fault. 2. Nuestra hipótesis es que los complejos sistemas de cataratas han limitado la invasión y la colonización de los peces desde las localidades aguas abajo. Los patrones longitudinales de los ensamblajes de peces fueron consistentes con esta hipótesis. La riqueza de las especies de peces en el río Toxaway incrementó desde 4 a 23 especies en una distancia de 10 Km de río, entre los lagos Taxoway y Jocasee. Encontramos discontinuidades similares en los vecinos ríos Horsepasture y Bearwallow. No encontramos ningún caso de re-emplazamiento de especies a lo largo del gradiente de altitud y la tendencia a incrementar la diversidad aguas abajo mostró discontinuidades que coincidieron con rupturas de altitudes. 3. Al considerar teorías que explican la formación de comunidades en zonas altas de ríos (especialmente en regiones caracterizadas por rupturas topografías), sugerimos que el acceso para los colonizadores puede ser más importante que otros factores incluyendo interacciones competitivas. [source] Temporal dynamics of genotypic diversity reveal strong clonal selection in the aphid Myzus persicaeJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2006C. VORBURGER Abstract Parthenogenetic organisms often harbour substantial genotypic diversity. This diversity may be the result of recurrent formations of new clones, or it may be maintained by environmental heterogeneity acting on ecological differences among clones. In aphids, both processes may be important because obligate and cyclical parthenogens can form mixed populations. Using microsatellites, I analysed the temporal dynamics of clonal diversity in such a population of the aphid Myzus persicae over a 1-year period. The frequency distribution of clonal genotypes was very skewed, with many rare and few common clones. The relative frequencies of common clones underwent strong and rapid changes indicative of intense clonal selection. Differences in their host associations suggest that these shifts may partly be caused by changes in the abundance of annual host plants. Other selective factors of potential importance are also discussed. New, sexually produced genotypes made a minor contribution to clonal diversity, consistent with the observed heterozygote excess characteristic of predominantly asexual populations in M. persicae. [source] Management actions are required to improve the viability of the rare grassland herb Carlina biebersteiniiNORDIC JOURNAL OF BOTANY, Issue 1-2 2008Satu Ramula Small population size of many rare or endangered plant species makes a quantitative assessment of population status challenging because of the lack of detailed demographic data on different life-history stages. However, an urgent assessment is often required to start possible management actions. We performed a count-based population viability analysis (PVA) using discontinuous time series to quantitatively assess the viability of a rare, monocarpic, grassland herb Carlina biebersteinii Bernh. ex Hornem. (synonyms: C. vulgaris L. ssp. longifolia, C. vulgaris L. ssp. stricta) and examined demographic and environmental factors contributing to its viability. Based on 12 abundance counts of eight C. biebersteinii populations in Finland, we found that seven out of the eight population sizes declined during the observation period, and that annual population growth rates were slightly synchronised among the populations. Synchrony in annual population growth rates declined with increasing geographic distances among the populations, while fluctuations in the number of flowering plants were unrelated to geographic distances among the populations. According to stochastic simulations, the risk of losing all flowering individuals during the next 20,years will be high for unmanaged populations. To prevent the populations from gradually declining, our results suggest that summer grazing or removal of woody vegetation is required to increase habitat openness and consequently, to improve fecundity and seedling recruitment. [source] | ||||||||||