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Tolerant Species (tolerant + species)
Selected AbstractsConservation value of degraded habitats for forest birds in southern Peninsular MalaysiaDIVERSITY AND DISTRIBUTIONS, Issue 5 2006Kelvin S.-H. ABSTRACT Clearance of tropical forest for agricultural purposes is generally assumed to seriously threaten the survival of forest species. In this study, we quantified the conservation value, for forest bird species, of three degraded habitat types in Peninsular Malaysia, namely rubber tree plantations, oil palm plantations, and open areas. We surveyed these degraded habitats using point counts to estimate their forest bird species richness and abundance. We assessed whether richness, abundance, and activities of different avian dietary groups (i.e. insectivores and frugivores) varied among the habitats. We identified the critical habitat elements that accounted for the distribution of forest avifauna in these degraded habitats. Our results showed that these habitats harboured a moderate fraction of forest avifauna (approximately 46,76 species) and their functions were complementary (i.e. rubber tree plantations for moving; open habitats for perching; shrubs in oil palm plantations for foraging). In terms of species richness and abundance, rubber tree plantations were more important than oil palm plantations and open habitats. The relatively high species richness of this agricultural landscape was partly due to the contiguity of our study areas with extensive forest areas. Forecasts of forest-species presence under various canopy cover scenarios suggest that leaving isolated trees among non-arboreal crops could greatly attract relatively tolerant species that require tree canopy. The conservation value of degraded habitats in agricultural landscapes seems to depend on factors such as the type of crops planted and distance to primary forest remnants. [source] Tolerance of Antarctic cyanobacterial mats to enhanced UV radiationFEMS MICROBIOLOGY ECOLOGY, Issue 1 2001Alison L. George Abstract To assess the biological implications of ozone depletion over the Antarctic Peninsula, the ultraviolet (UV) regime of two Antarctic cyanobacterial communities (composed of Leptolyngbya sp. and Phormidium sp.) was manipulated using screens that cut out UV radiation and a lamp which enhanced the dose of UV-B radiation (280,315 nm). The biological response of the cyanobacterial mats was monitored by measurement of chlorophyll fluorescence and pigment concentrations. The Leptolyngbya mat showed significant photochemical inhibition due to increased UV-B relative to photosynthetically active radiation (400,700 nm). The effect of UV on the Phormidium mat was less pronounced and dependent on the method of analysis: significantly lower photochemical yields were observed in UV-enhanced Phormidium mats compared to UV-excluded treatment, but if the yield data relative to the time zero control were considered then no effect of UV enhancement was observed. The Phormidium mat contained over 25 times the absolute concentration of UV-protecting mycosporine-like amino acid (MAA) and double the concentration of carotenoids compared to the Leptolyngbya mat, but the latter contained a higher ratio of carotenoids+MAAs to chlorophyll. There were no significant treatment-related changes in the concentrations of MAA, carotenoids and chlorophyll a in the Phormidium mat. The Leptolyngbya mat showed significantly lower chlorophyll a concentrations under UV enhancement, which could account for the lower photochemical yield in this sample. Our results show that different cyanobacterial species have differing photochemical sensitivity to UV-B radiation, which may confer a subtle advantage to the UV-B tolerant species over the less tolerant type during a period of high UV-B irradiance. [source] Phytoplankton communities and antecedent conditions: high resolution sampling in Esthwaite WaterFRESHWATER BIOLOGY, Issue 10 2006G. MADGWICK Summary 1. The succession of a phytoplankton community was investigated through an intensive period of sampling and related to physical, chemical and biological conditions sampled at an equal, or higher, temporal resolution. 2. Phytoplankton samples were taken on a weekly basis from June to September 2004 and analysed for diversity, species composition, and contribution of different functional groups to total biomass. Physical and chemical data were collected on the sampling days, and physical environmental factors were also logged continuously throughout the period by automatic measuring stations. This continuous logging allowed community structure to be compared with physical data averaged over periods from a day to a week before each sampling date. 3. The Schmidt stability of the lake, a measure of the strength of stratification calculated from thermal data, showed a negative correlation with phytoplankton species diversity. This is consistent with the hypothesis that mixing was preventing exclusion by species that would otherwise dominate in stratified conditions. 4. At a functional level, stress tolerant (S-type) species dominated during the stratified summer conditions, with small, colonising species (C types) and ruderal, disturbance tolerant species (R types) contributing little to the overall biomass. Of the stress tolerant species, the faster growing (SC) phytoplankters were significantly favoured by more stable, stratified conditions and higher solar radiation. Increased abundance of this group resulted in decreased species diversity. Correlations were generally strongest when using the 6- to 7-day averaged physical data, stressing the importance of continuous measurements of these drivers in phytoplankton studies. [source] The use of periphytic diatoms as a means of assessing impacts of point source inorganic nutrient pollution in south-eastern AustraliaFRESHWATER BIOLOGY, Issue 5 2006JOCELYN DELA-CRUZ Summary 1. Periphytic diatoms are used as indicators of water quality because their ecological tolerances or preferences to environmental variables are thought to be predictable. However, much of the present autecological information for periphytic diatoms has been derived from studies conducted in the northern hemisphere. In this present study we used periphytic diatoms to determine the impacts of inorganic nutrient pollution in a tidal river system in the temperate latitudes of south-east Australia. In so doing, we assess the suitability of the use of the ,northern hemisphere' ecological tolerance/preference data for periphytic diatoms. 2. Artificial substrates were used to collect periphytic diatoms at 35 sites, which were positioned along the riverbanks and the middle of the river at various distances upstream and downstream of the sewage outfall. The sampling design took into account tidal excursions and the observed sewage plume dynamics. Periphytic diatoms were collected during the austral winter month of August and the austral spring months of September and October. We deployed the artificial substrates for 4 weeks to allow the periphytic diatoms to recruit and colonise, before identifying and enumerating the assemblages. 3. Data analysis included two approaches: multivariate visualisations of combinations of environmental and biological data to investigate shifts in species structure of the periphytic diatom assemblage and multimetric indices based on ecological tolerance/preference data. 4. We found that the spatial patterns inferred from multivariate and multimetric analyses were consistent. Temporal variation in the composition of the periphytic diatom assemblage was greater than the spatial variation along horizontal sections of the river (in any one deployment) due mainly to shifts between winter and spring species. 5. Outfall effects were most apparent in winter, possibly because subsequent deployments were swamped by growth of spring periphytic diatoms. The outfall effects included a shift towards pollutant tolerant species and a reduction in the variability of the periphytic diatom assemblage across the river. 6. We conclude that the use of periphytic diatoms and associated ecological tolerance/preference data as a means of assessing impacts of point source inorganic nutrient pollution is effective. An understanding of river and sewage flow patterns is essential to the design of appropriate monitoring programmes and to the interpretation of results, especially as periphytic diatoms are sensitive to many environmental variables. [source] Aquatic Coleoptera Distribution and Environmental Relationships in a Large Patagonian RiverINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5 2006María Laura Miserendino Abstract The benthic coleopteran assemblages of the Chubut River basin were studied in order to assess the main factors affecting species composition and distribution along the upper, middle and lower catchments. A total of 13 sampling sites were selected and sampled seasonally. Eight taxa and 1,601 individuals were collected during the study. Richness was higher in the main channel of Chubut River at the upper basin than at the middle basin. Beetles were completely absent at the lower basin. Mean monthly density per sites varied from 0 to 85 ind m,2. Stethelmis kaszabi had a more restricted distribution whereas Hemiosus dejeanii, Austrelmis sp. and Austrolimnius spp. were more frequent and abundant. Austrelmis sp. appears as the most tolerant species, especially to higher TSS, ammonia, and conductivity values. Luchoelmis cekalovici was absent in stations associated with urban areas. A Canonical Correspondence Analysis shows that conductivity, total suspended solids, wet width, water temperature and pH were the most important variables structuring beetle assemblages. Land use related variables such as NH4, TP, and NO3 were less important but still significant. An increase in TSS affected negatively the coleopteran community; this could be related to both hydrogeological characteristics and agricultural activities (including overgrazing). This is the first approach to the knowledge of the ecological range of distribution of the coleopteran species in Patagonian rivers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Submergence-induced leaf acclimation in terrestrial species varying in flooding toleranceNEW PHYTOLOGIST, Issue 2 2007Liesje Mommer Summary ,,Earlier work on the submergence-tolerant species Rumex palustris revealed that leaf anatomical and morphological changes induced by submergence enhance underwater gas exchange considerably. Here, the hypothesis is tested that these plastic responses are typical properties of submergence-tolerant species. ,,Submergence-induced plasticity in leaf mass area (LMA) and leaf, cell wall and cuticle thickness was investigated in nine plant species differing considerably in tolerance to complete submergence. The functionality of the responses for underwater gas exchange was evaluated by recording oxygen partial pressures inside the petioles when plants were submerged. ,,Acclimation to submergence resulted in a decrease in all leaf parameters, including cuticle thickness, in all species irrespective of flooding tolerance. Consequently, internal oxygen partial pressures (pO2) increased significantly in all species until values were close to air saturation. Only in nonacclimated leaves in darkness did intolerant species have a significantly lower pO2 than tolerant species. ,,These results suggest that submergence-induced leaf plasticity, albeit a prerequisite for underwater survival, does not discriminate tolerant from intolerant species. It is hypothesized that these plastic leaf responses may be induced in all species by several signals present during submergence; for example, low LMA may be a response to low photosynthate concentrations and a thin cuticle may be a response to high relative humidity. [source] Root traits associated with nutrient exploitation following defoliation in three coexisting perennial grasses in a semi-arid savannaOIKOS, Issue 2 2001C. A. Busso Experiments were conducted to evaluate root traits associated with nutrient exploitation following defoliation in three coexisting perennial grasses in a semi-arid savanna. Root length density was determined within soil cores directly beneath plants, nitrogen uptake was evaluated by excised-root assay with (15NH4)2SO4, and mycorrhizal root colonization was estimated by observation of root segments. Root length density was lowest for Bouteloua curtipendula, intermediate for Eriochloa sericea, and highest for Aristida purpurea indicating that root length density was a more important trait for the mid-seral than the late-seral species. Rates of 15N uptake were greatest in the least grazing tolerant late-seral species, E. sericea, intermediate in the mid-seral species, A. purpurea, and lowest in the most grazing tolerant late-seral species, B. curtipendula. Two successive defoliations reduced 15N uptake 60% in the late-seral species with the greatest uptake rate (E. sericea), but not in species with lowest uptake rates (B. curtipendula). Root length colonization was consistently high (33,61%) in all three species suggesting that these C4 perennial grasses may function as obligate mycotrophs. Contrasting responses among the two late-seral species indicate that the least grazing tolerant species, E. sericea, appears best adapted for nutrient exploitation while the most grazing tolerant species, B. curtipendula, appears best adapted for efficient nutrient retention. Contrasting responses of nitrogen uptake to short-term defoliation parallel the population responses of these two coexisting late-seral species to long-term herbivory. These data indicate that herbivory may shift interspecific competitive interactions by mediating nutrient exploitation and that a trade-off may exist between nutrient exploitation and herbivory tolerance in these species. [source] Flooding induced emissions of volatile signalling compounds in three tree species with differing waterlogging tolerancePLANT CELL & ENVIRONMENT, Issue 9 2010LUCIAN COPOLOVICI ABSTRACT To gain insight into variations in waterlogging responsiveness, net assimilation rate, stomatal conductance, emissions of isoprene and marker compounds of anoxic metabolism ethanol and acetaldehyde, and stress marker compounds nitric oxide (NO), volatile products of lipoxygenase (LOX) pathway and methanol were studied in seedlings of temperate deciduous tree species Alnus glutinosa, Populus tremula and Quercus rubra (from highest to lowest waterlogging tolerance) throughout sustained root zone waterlogging of up to three weeks. In all species, waterlogging initially resulted in reductions in net assimilation and stomatal conductance and enhanced emissions of ethanol, acetaldehyde, NO, LOX products and methanol, followed by full or partial recovery depending on process and species. Strong negative correlations between gs and internal NO concentration and NO flux, valid within and across species, were observed throughout the experiment. Isoprene emission capacity was not related to waterlogging tolerance. Less waterlogging tolerant species had greater reduction and smaller acclimation capacity in foliage physiological potentials, and larger emission bursts of volatile stress marker compounds. These data collectively provide encouraging evidence that emissions of volatile organics and NO can be used as quantitative measures of stress tolerance and acclimation kinetics in temperate trees. [source] Biodiversity of semi-arid Mediterranean grasslands: Impact of grazing and afforestationAPPLIED VEGETATION SCIENCE, Issue 2 2007M.A. Alrababah Zohary & Feinbrun (1966,1986) Abstract Question: What is the impact of grazing and/or afforestation on grassland diversity, species composition and cover parameters? Location: Semi-arid Mediterranean grasslands of Jordan. Methods: Vegetation, litter, bare soil and rock cover were compared among four management types , free grazing and protected from grazing with three levels of tree cover. Species composition, plant cover, species richness and evenness were used to evaluate differences in vegetation among management types. Species composition differences among management types were also investigated. Results: Semi-arid Mediterranean grasslands harbour appreciable levels of plant biodiversity. Grazing did not affect plant diversity, indicating the high resilience against and adaptation to grazing; however,grazing affected species composition and cover parameters. Afforestation seems to protect soil through higher litter cover but its impact on plant biodiversity was negative and markedly affected species composition. Conclusions: Neither protection from grazing or massive afforestation alone are sufficient for conserving biodiversity in this system. A management model is suggested where the landscape should be maintained as a mosaic of four management types: complete protection from grazing, grazing rotation, planting sparse trees in eroded areas and revegetating degraded areas using native, herbaceous and grazing tolerant species. [source] Effect of rearing density on the growth and welfare indices of juvenile spotted wolffish, Anarhichas minor (Olafsen)AQUACULTURE RESEARCH, Issue 8 2010Sarah Tremblay-Bourgeois Abstract The goal of this study was to determine the optimal stocking density for rearing juvenile spotted wolffish, Anarhichas minor (Olafsen), at two different sizes and assess the welfare status in relation to density. No major growth impairment was observed, although smaller fish (50,100 g) were significantly affected by density during the 120 days of the experiment, with final mean weights of 119.6 ± 11.6, 118.0 ± 5.8 and 88.7 ± 0.6 g for initial rearing densities of 10, 20 and 40 kg m,2 respectively. No effect of rearing density was seen for larger fish (100,160 g) during the 90 days of the experiment, with final mean weights of 160.2 ± 5.9, 159.7 ± 3.7 and 163.7 ± 11.5 g at fixed rearing densities of 20, 30 and 40 kg m,2 respectively. Our results suggest that the optimal rearing density of juvenile spotted wolffish is below 40 kg m,2 for smaller size fish (,50,100 g) and probably ,40 kg m,2 for the larger fish (100,160 g). Furthermore, it appears that the range of rearing density used did not have a significant effect on a selection of stress indicators (Na+ and K+ concentration, haematocrit, hepatosomatic index, total amount of plasma proteins and liver and muscle water content) and immunity response (plasma lysozyme activity) of juvenile spotted wolffish, making it a very tolerant species to crowding. [source] Variation in the impact of exotic grasses on native plant composition in relation to fire across an elevation gradient in HawaiiAUSTRAL ECOLOGY, Issue 5 2000Carla M. D'Antonio Abstract The impact that an exotic species can have on the composition of the community it enters is a function of its abundance, its particular species traits and characteristics of the recipient community. In this study we examined species composition in 14 sites burned in fires fuelled by non-indigenous C4 grasses in Hawaii Volcanoes National Park, Hawaii. We considered fire intensity, time since fire, climatic zone of site, unburned grass cover, unburned native cover and identity of the most abundant exotic grass in the adjacent unburned site as potential predictor variables of the impact of fire upon native species. We found that climatic zone was the single best variable for explaining variation in native cover among burned sites and between burned and unburned pairs. Fire in the eastern coastal lowlands had a very small effect on native plant cover and often stimulated native species regeneration, whereas fire in the seasonal submontane zone consistently caused a decline in native species cover and almost no species were fire tolerant. The dominant shrub, Styphelia tameiameia, in particular was fire intolerant. The number of years since fire, fire intensity and native cover in reference sites were not significantly correlated with native species cover in burned sites. The particular species of grass that carried the fire did however, have a significant effect on native species recovery. Where the African grass Melinis minutiflora was a dominant or codominant species, fire impacts were more severe than where it was absent regardless of climate zone. Overall, the impacts of exotic grass-fuelled fires on native species composition and cover in seasonally dry Hawaiian ecosystems was context specific. This specificity is best explained by differences between the climatic zones in which fire occurred. Elevation was the main physical variable that differed among the climatic zones and it alone could explain a large percentage of the variation in native cover among sites. Rainfall, by contrast, did not vary systematically with elevation. Elevation is associated with differences in composition of the native species assemblages. In the coastal lowlands, the native grass Heteropogon contortus, was largely responsible for positive changes in native cover after fire although other native species also increased. Like the exotic grasses, this species is a perennial C4 grass. It is lacking in the submontane zone and there are no comparable native species there and almost all native species in the submontane zone were reduced by fire. The lack of fire tolerant species in the submontane zone thus clearly contributes to the devastating impact of fire upon native cover there. [source] Root/Shoot Allocation and Root Architecture in Seedlings: Variation among Forest Sites, Microhabitats, and Ecological Groups1BIOTROPICA, Issue 3 2003Horacio Paz ABSTRACT I analyzed patterns of variation in root mass allocation and root morphology among seedlings of woody species in relation to environmental factors in four Neotropical forests. Among forests, I explored the response of root traits to sites varying in water or nutrient availability. Within each forest, I explored the plastic response of species to different microhabitats: gaps and understory. Additionally, I explored evidence for life history correlation of root and shoot traits by comparing species differing in their successional group (light-demanding [22 spp.] or shade tolerant [27 spp.]) and germination type (species with photosynthetic cotyledons or species with reserve cotyledons). At each forest site, young seedlings from 10 to 20 species were excavated. A total of 55 species was collected in understory conditions and 31 of them were also collected in gaps. From each seedling, six morphological ratios were determined. Allocation to roots was higher in forest sites with the lowest soil resources. Roots were finer and longer in the most infertile site, while roots were deeper in the site with the longest dry season. Seedling traits did not differ between germination types. Shade tolerant species allocated more to roots and developed thicker roots than light-demanding species. Light-demanding species showed stronger plastic responses to habitat than shade tolerant species, and species with photo-synthetic cotyledons showed lower plasticity than species with reserve cotyledons. Overall, these results suggest that among Neotropical species, root allocation and root morphology of seedlings reflect plant adjustments to water or nutrient availability at geographic and microhabitat scales. In addition, life history specialization to light environments is suggested by differences among groups of species in their allocation to roots and in their root morphology. RESUMEN Analicé los patrones de variación en la asignación de biomasa y en la morfología de raíces de plántulas de especies leñosas en relación a factores ambientales en cuatro bosques Neotropicales. Entre los bosques, exploré la respuesta promedia de características de las plántulas en sitios que varían en disponibilidad de agua o nutrientes en el suelo. Dentro de cada bosque, exploré la respuesta fenotípica de las especies entre claros y sotobosque. Además, explore correlaciones de la historia de vida de las especies con características de raíces y parte aérea, comparando especies con diferente hábito sucesional (demandante de luz [22 spp.] o tolerante a la sombra [27 spp.]) y tipo de germinación (especies con cotiledones fotosintéticos o cotiledones de reserva). En cada bosque, se excavaron plántulas de 10 a 20 especies manteniendo la integridad de sus raíces. Se colectaron 55 especies en el sotobosque y 31 de ellas fueron colectadas también en claros. De cada plántula obtuve seis parámetros morfológicos de raíces y parte aérea. La asignación de biomasa a raíces fue mayor en los bosques con menos recursos. Las plántulas desarrollaron raíces más finas, y con mayor longitud por unidad de superficie fotosintética, en el sitio menos fértil. En cambio, las raíces tendieron a ser más profundas en relación al área fotosintética en el sitio más estacional. Las especies tolerantes a la sombra asignaron más biomasa a raíces y desarrollaron raíces más gruesas que las especies demandantes de luz. Las características morfológicas de las plántulas no difirieron entre tipos de germinación. Las especies demandantes de luz mostraron mayor plasticidad al hábitat en la asignación de biomasa a raíces, que las especies tolerantes a la sombra. Las especies con cotiledones fotosintéticos mostraron menor plasticidad al hábitat en la asignación de biomasa a raíces que las especies con cotiledones de reserva. En conjunto, mis resultados sugieren que para especies Neotropicales la asignación de biomasa y la morfología de raíces en plántulas reflejan ajustes de las plantas a la disponibilidad de agua o nutrientes a escala geográfica y de micro-hábitat. Además, se sugiere que la asignación de biomasa y la morfología de raíces son componentes del síndrome de especialización a ambientes lumínicos en el bosque. [source] | |||||||||||||||||||||||||