Abiotic Parameters (abiotic + parameter)

Distribution by Scientific Domains
Life Sciences80%

Selected Abstracts

Latitudinal gradient of taxonomic richness: combined outcome of temperature and geographic mid-domains effects?

JOURNAL OF ZOOLOGICAL SYSTEMATICS AND EVOLUTIONARY RESEARCH, Issue 3 2005
A. Brayard
Abstract For several decades, the origin and ecological consequences of large-scale continental and marine Latitudinal Gradients of Taxonomic Richness (LGTR) have been intensively debated. Among the various hypotheses, it has been proposed that a LGTR is the by-product of a geographic mid-domain effect, i.e. the result of a random distribution of ranges of taxa between physical hard boundaries such as the continent/ocean interface. In order to more realistically evaluate the role of the mid-domain effect on the origin and evolution of the LGTR of marine planktonic organisms, we present a 2D model based on a cellular-automaton approach in which sea surface temperatures (SST) and currents are forced in the biogeographic dispersal of a randomly generated clade (a 2D ,geophyletic' model). Sensitivity experiments allow to evaluate the effects of currents, SST and the geographical origin of a clade on the formation and shape of a LGTR for planktonic organisms when coupled with a geographic mid-domain effect. Results are discussed in the light of the empirical LGTR of extant planktonic Foraminifera in the Atlantic Ocean. Independently of any other biotic or abiotic parameter, inclusive of the surface currents and origination/extinction absolute and relative rates, our simulations show that the coupling of the mid-domain effect with two critical parameters, namely the shape and intensity of the SST gradient and the geographic origin of a clade, produces realistic patterns of diversity when compared with the observed LGTR of extant atlantic planktonic foraminifera. The results illustrate a non-linear relation between a unimodal latitudinal SST gradient and a resulting bimodal LGTR characterized by a drop in species richness near the equator. This relation indicates that the SST gradient exerts a mid-domain effect on the LGTR. The latitudinal positions of the modal values of the LGTR are also found to be influenced by the geographic origin of the simulated clade. Résumé Depuis plusieurs décennies, l'origine et l'interprétation écologique des Gradients Latitudinaux de Richesse Taxonomique (LGTR) marins ou continentaux, ont été intensivement débattues. Parmi de nombreuses hypothèses, il a été proposé qu'un LGTR puisse être le sous-produit d'un effet de milieu de domaine géographique, i.e. le résultat d'une distribution aléatoire des répartitions des taxa entre deux limites physiques telles que l'interface continent/océan. Afin d'évaluer plus efficacement le rôle de cet effet sur l'origine et l'évolution des LGTR des organismes planctoniques marins, nous proposons un modèle 2D basé sur une approche de type automate cellulaire dans laquelle les températures des eaux de surface (SST) et les courants régulent la dispersion biogéographique d'une phylogénie générée aléatoirement (un modèle «géophylétique»). Ce modèle permet d'évaluer les effets des courants, des SST et de la dépendance thermique des espèces sur la mise en place et la forme d'un LGTR impliquant des organismes planctoniques. Il permet aussi de discuter des influences respectives de ces paramètres quand ils sont superposés à l'effet de milieu de domaine géographique. Les résultats sont discutés à partir du LGTR empirique des foraminifères planctoniques atlantiques actuels. Indépendamment de tout autre paramètre biotique ou abiotique, y compris les courants ainsi que les taux relatifs et absolus d'apparition et d'extinction, les simulations font apparaître que le couplage de l'effet de milieu de domaine à deux contraintes principales, la forme et l'intensité du gradient de SST ainsi que la localisation géographique de l'origine du clade, produit des représentations réalistes de la diversité comparées au LGTR observé pour les foraminifères planctoniques actuels de l'océan atlantique. Nos résultats indiquent une relation non-linéaire entre la structure globale d'un gradient unimodal de SST et le LGTR bimodal correspondant, montrant une baisse de richesse spécifique au niveau de l'équateur. Cette relation suggère que le gradient de SST exerce un effet de milieu de domaine thermique sur le LGTR. Les positions latitudinales des modes du LGTR sont aussi influencées par le lieu d'origine du clade simulé. [source]

Suitability of Molluscs as Bioindicators for Meadow- and Flood-Channels of the Elbe-Floodplains

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4 2006
Francis Foeckler
Abstract The goals of the subproject "molluscs" within the inter-disciplinary research project "Indicator systems for the characterisation and prediction of ecological changes in floodplain systems" were: , develop further existing mollusc-based indicator systems of site quality and to test their transferability, , characterise grassland sites within the recent floodplains of three study areas along the Elbe River, , analyse the relationships between indicator species-/groups and abiotic parameters, , compile and use selected species traits in the analytical process. The results clearly show several characteristic species groups related to the hydrology of the sites (i.e. inundation and desiccation regime) and on to the degree of agricultural use. These dependencies can be interpreted by the simultaneous analysis of the species traits. "Models" are proposed, that are applicable to nature protection measures at the landscape scale. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

An ecological study of the relationship between two living fossils in Malawi: the Mulanje Tiger Moth (Callioratis grandis) and the Mulanje Cycad (Encephalartos gratus)

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Julian Bayliss
Abstract The Mulanje tiger moth (Callioratis grandis) has recently been discovered feeding solely on the Mulanje Cycad, Encephalartos gratus. In its type locality Encephalartos gratus is severely threatened through habitat destruction and human population growth. As a result the first detailed demographic survey of Encephalartos gratus on Mount Mulanje was undertaken with particular emphasis on the relationship between E. gratus and Callioratis grandis. What is unusual about C. grandis is that the males exhibit lekking behaviour, for which aposematism may be a prerequisite. Cycads were surveyed in a systematic manner. Both the biotic and abiotic parameters were recorded from 532 wild Encephalartos gratus. Results showed the morphological range of measurements differed from that of previously published literature on this species. Results also showed that the incidence of Callioratis larval damage was related to the maturity of the wild cycads , moth damage was greater on more mature plants. Approximately 50% of surveyed cycads showed evidence of Callioratis moth damage, however, there was no apparent preference from the moth to select either male or female cycads as food plants for the larvae. In some cases there was severe damage to cycad fronds, but this did not seem to affect the production of reproductive cones or even the survival of individual cycads. Résumé On a découvert récemment que le papillon du Mulanje (Callioratis grandis) ne se nourrit que sur le cycadale Mulanje Encephalartos gratus. Dans son milieu type, Encephalartos gratus est gravement menacé dans la nature à cause de la destruction de l'habitat et de la croissance de la population humaine. Par conséquent, la première étude démographique détaillée d'Encephalartos gratus réalisée sur le mont Mulanje fut entreprise en insistant particulièrement sur la relation entre Encephalartos gratus et Callioratis grandis. Ce qui est inhabituel chez C. grandis, c'est que les mâles présentent un comportement territorial (lek). Les cycadales ont été systématiquement surveillées. On a enregistré les paramètres biotiques et abiotiques pour 532 Encephalartos gratus poussant dans la nature. Les résultats ont montré que l'amplitude des mesures morphologiques différait de ce que la littérature existante décrit sur cette espèce. Ils ont aussi montré que l'incidence des dommages causés par les larves de Callioratisétait liée à la maturité des cycadales sauvages , les dégâts causés par les papillons étaient plus graves sur les plants plus matures. Environ 50% des cycadales suivis montraient des traces de dommages causés par ce papillon, mais il n'y avait pas de preuve qui aurait pu montrer que le papillon sélectionnait des cycadales mâles ou femelles pour en nourrir ses larves. Dans certains cas, il y avait des dégâts sérieux dans les feuilles de cycadales; cependant, cela ne semblait pas affecter la production de cônes reproducteurs, pas plus que la survie des individus. [source]

Structure and distribution of the benthic macrofauna on a Northwest African sandy beach close to a freshwater river discharge

MARINE ECOLOGY, Issue 2008
Abdellatif Chaouti
Abstract The effects of the freshwater discharge of the Oued Sebou River on the macroinfauna, was studied on the sandy beach of Mehdia through the analysis of the abiotic parameters and of the macrozoobenthos. In autumn 2002 and spring 2003, three beach sites, each with two transects, localized at 50, 3500 and 5720 m from the river mouth respectively, were studied. Positive correlations were recorded for beach slope and pH whereas negative ones were obtained for organic matter content and salinity at increasing distances from the river mouth. Significant differences between beach sites and seasons occurred for median grain size, organic matter content and pH. For each beach site, mean macroinfauna abundance varied between 30 and 100 ind.·m,2 and in spring there was a significant correlation between this parameter and the increasing distance from the river mouth. No significant correlation was instead found between species richness and the increasing distance, although the farthest beach site from the mouth had the highest number of species during both seasons. The results indicated the importance of organic matter content and salinity for the macrofaunal abundance whereas the diversity indices were more affected by beach slope and grain size. The results showed that there was no clear spatial trend in compound indices of the macrofauna across the sampled sites and the influence of the river discharge of Sebou River did not seem to be significant and consistent on the macrobenthos of this mesotidal shore. Comparison with microtidal shores revealed the influence of the tidal excursion and swell characteristics on the response of the benthic structures of sandy beaches to discharges of freshwater. [source]

Oyster greening by outdoor mass culture of the diatom Haslea ostrearia Simonsen in enriched seawater

AQUACULTURE RESEARCH, Issue 10 2001
V Turpin
Abstract Oyster greening was first described in the seventeenth century as a natural phenomenon. However, it has recently been discovered that the diatom Haslea ostrearia Simonsen causes greening by synthesis of a blue pigment designated as ,marennine'. This phenomenon, which involves massive proliferation of H. ostrearia in oyster ponds, was not understood or controlled by oyster farmers in the Marennes-Oléron region (Atlantic coast of France). As greening oysters improved their market value, they tried to develop empirical methods to guarantee oyster fattening and improve profits. In this context, the present study investigated the feasibility of mass culture of diatoms outdoors in 10-m3 ponds, using enriched seawater. Different biotic and abiotic parameters were monitored daily to determine the influence of the day,night temperature range. After 8 days, H. ostrearia was the dominant diatom species (66%), reaching a mean cell concentration of 2 × 105 cell mL,1 and a marennine concentration of 3.4 mg L,1. Although intensive greening was obtained, further studies are required to optimize the production stages before this technology can be transferred to oyster farmers. [source]