The identification of beetle, and other invertebrate, biotopes based on the recording of species assemblages has become a
regular occurrence as a result of increased survey work, with the approach expanded into classifications of grid square pooled
species lists at the national scale. A reassessment of beetle biotopes and distribution has been attempted by interpreting
the classifications in terms of the major environmental factors of productivity and disturbance, identified as being important
drivers in work on habitat templates and strategic triangles. For grassland ground beetle biotopes, productivity was generally
related to soil quality whilst disturbance was associated with land management or cover. Productivity of exposed riverine
sediment ground beetle biotopes was dependent on deposited organic matter and disturbance on the effects of water flow on
site structure. With both ground beetle biotopes, the distribution of assemblages was also affected by substrate water, another
abiotic driver. Productivity in aquatic beetle biotopes was a function of base-status, generally reflected by pH, whilst disturbance
was mainly due to water flow and wave action. However, disturbance in ditches was also the result of site vegetation management
whilst another factor affecting assemblage distribution was water permanence, with temporary water having specific assemblages.
For large-scale British, grid-based, classifications productivity and disturbance were interpreted from satellite-derived
land cover data. At the national scale, the other important factor influencing distribution was temperature. There is a requirement
for better quantification of a number of the factors influencing biotope and assemblage definition. Species strategies employed
to cope with the various environmental variables were reflected in traits in such factors as morphology and life-cycles. The
effects of environmental perturbations including climate change, pollution and land use are discussed in relation to the environmental
variables and to the various species strategies. Biotope classifications, using standardised and reproducible survey methods,
allied to a better understanding of the underlying environmental pressures, could produce a unified approach for the conservation
of beetle and other invertebrate species. 相似文献
In landscapes subject to intensive agriculture, both soil fertility and vegetation disturbance are capable of impacting strongly, evenly and simultaneously on the herbaceous plant cover and each tends to impose uniformity on the traits of constituent species. In more natural and ancient grasslands greater spatial and temporal variation in both productivity and disturbance occurs and both factors have been implicated in the maintenance of species‐richness in herbaceous communities. However, empirical data suggest that disturbance is the more potent driver of trait differentiation and species co‐existence at a local scale. This may arise from the great diversity in opportunities for establishment, growth or reproduction that arise when the intensity of competition is reduced by damage to the vegetation. In contrast to the diversifying effects of local disturbances, productivity‐related plant traits (growth rate, leaf longevity, leaf chemistry, leaf toughness, decomposition rate) appear to be less variable on a local scale. This difference in the effects of the productivity and disturbance filters arises from the relative constancy of productivity within the community and the diversity in agency and in spatial and temporal scales exhibited by disturbance events. Also, evolutionary responses to disturbances involve minor adaptive shifts in phenological and regenerative traits and are more likely to occur as micro‐evolutionary steps than the shifts in linked traits in the core physiology associated with the capacity to exploit productive and unproductive habitats. During the assembly of a community and over its subsequent lifespan filters with diversifying and convergent effects may operate simultaneously on recruitment from the local species pool and impose contrasted effects on the similarity of the trait values exhibited by co‐existing species. Moreover, as a consequence of the frequent association of productivity with the convergence filter, an additional difference is predicted in terms of the effects of the two filters on ecosystem functioning. Convergence in traits selected by the productivity filter will exert effects on both the plant community and the ecosystem while divergent effects of the disturbance filter will be restricted to the plant community. 相似文献
Seagrass productivity, as leaf extension, was measured using the hole punch and needle punch techniques. These methods have been widely implemented to determine seagrass leaf extension rates, yet there is no evidence in the literature of a comparison between methods. The hole punch method involves removing part of the basal area of a seagrass leaf and it was proposed that this measurement technique may affect the leaf extension rates that are being measured. Leaf extension rates were measured in Posidonia sinuosa meadows off the coast of Perth, Western Australia. There were no significant differences in seagrass leaf extension between the two methods. The hole punch method is favoured, as measurement of incremental leaf growth is facilitated by the obvious hole left by the punch. The needle punch method leaves lesions on seagrass leaves that are easily confused with other lesions, possibly left by invertebrate grazers. These findings are likely to be applicable to other straplike seagrass species, though a similar comparison is recommended in the initial stages of a study. 相似文献
Understanding the factors that encourage or inhibit plant invasions is vital to focusing limited invasive control efforts within areas where they are most practical and cost-effective. To extend the range of contexts in which invasibility is studied and aid the development of practical strategies to limit damaging plant invasions, we set out to test the relative importance of native species richness, native seedling density, and invasive propagule pressure, on the invasibility of artificial assemblages of naturally occurring tropical woody seedling communities. Our greenhouse mesocosms included a species pool of twelve trees and woody shrubs native to South Florida's tropical hardwood hammocks, and an increasingly prevalent noxious woody invader of this system, Ardisia elliptica. We found that invader propagule pressure was the single most important factor determining community invasibility. We also revealed a positive relationship between invasibility and native species richness in our polyculture mesocosms. Because A. elliptica biomass production significantly differed among different native monocultures and was not related to overyielding in native polycultures, we suggest that the effect of species richness on invasibility in this experiment was the result of sampling effects rather than a true effect of diversity.Three broad findings hold potential for application in preventing and controlling plant invasions, especially in the seedling layers of tropical dry forests: (1) effective invasive control efforts will likely benefit from measures to minimize propagule pressure; (2) managers might do well to prioritize invasive monitoring and removal efforts on the most diverse habitats within a management region; and (3) while more data are necessary to further understand our finding of a lack of association between productivity and invasibility, management regimes aimed at maximizing primary productivity might not increase invasibility, and in fact, strategies for controlling invasive plants via the management of ecosystem productivity may be ineffective. 相似文献
The aim of this paper is to analyze the recruitment effects of susceptible and infected individuals in order to assess the productivity of an organizational labor force in the presence of HIV/AIDS with preventive and HAART treatment measures in enhancing the workforce output. We consider constant controls as well as time-dependent controls. In the constant control case, we calculate the basic reproduction number and investigate the existence and stability of equilibria. The model is found to exhibit backward and Hopf bifurcations, implying that for the disease to be eradicated, the basic reproductive number must be below a critical value of less than one. We also investigate, by calculating sensitivity indices, the sensitivity of the basic reproductive number to the model’s parameters. In the time-dependent control case, we use Pontryagin’s maximum principle to derive necessary conditions for the optimal control of the disease. Finally, numerical simulations are performed to illustrate the analytical results. The cost-effectiveness analysis results show that optimal efforts on recruitment (HIV screening of applicants, etc.) is not the most cost-effective strategy to enhance productivity in the organizational labor force. Hence, to enhance employees’ productivity, effective education programs and strict adherence to preventive measures should be promoted. 相似文献
Abstract Theoretical yields of poly- d (−)-3-hydroxybutyrate (PHB) from several carbon sources have been estimated from biochemical pathways leading to PHB. In estimating the yields, a special emphasis is made on recycling (or regeneration) of NADP+ which is the co-substrate of acetoacetyl-CoA reductase, one of three key enzymes involved in the biosynthesis of PHB. As a NADP+-regenerating enzyme, glucose-6-phosphate dehydrogenase or isocitrate dehydrogenase is conceived. Theoretical and observed yields have been compared when polyhydroxyalkanoates (PHA) were synthesized from methanol and from n -amyl alcohol by a methylotroph, Paracoccus denitrificans . An equation, which predicts the overall yield of PHB when allowance is made for non-PHB biomass formation in actual bacterial PHB production, has been derived as a function of both theoretical yields and PHB content of the total dry cell mass. The ratio of the overall (yield) to be theoretical yield is roughly proportional to the PHB content. A novel specific PHB formation rate on the basis of the residual biomass (total biomass-PHB contained) was proposed. The specific PHB formation rate decreased according to a mono-molecular decay model whose decay constant depended solely on the C/N ratio of the feed solution. From this model, an equation has been derived to calculate the volumetric productivity of PHB on the assumption that the total amount of the residual biomass is unchanged in the nitrogen-deficient PHB formation phase. Also, a graphical procedure has been shown to calculate the volumetric productivity of PHB. A comparison has been made between several data of PHB productivities that have been calculated from the literature. 相似文献
Two late Quaternary sediment cores from the northern Cape Basin in the eastern South Atlantic Ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition. The locations of the cores were selected such that both of them presently are bathed by North Atlantic Deep Water (NADW) and past changes in deep water circulation should be recorded simultaneously at both locations. However, the areas are different in terms of primary production. One core was recovered from the nutrient-depleted Walvis Ridge area, whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high. Recent data served as the basis for the interpretation of the late Quaternary faunal fluctuations and the paleoceanographic reconstruction.
During the last 450,000 years, NADW flux into the eastern South Atlantic Ocean has been restricted to interglacial periods, with the strongest dominance of a NADW-driven deep water circulation during interglacial stages 1, 9 and 11. At the continental margin, high productivity faunas and very low epibenthic δ13C values indicate enhanced fluxes of organic matter during glacial periods. This can be attributed to a glacial increase and lateral extension of coastal upwelling. The long term glacial-interglacial paleoproductivity cycles are superimposed by high-frequency variations with a period of about 23,000 yr. Enhanced productivity in surface waters above the Walvis Ridge, far from the coast, is indicated during glacial stages 8, 10 and 12. During these periods, cold, nutrient-rich filaments from the mixing area were probably driven as far as to the southeastern flank of the Walvis Ridge. 相似文献