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Species Replacement (species + replacement)
Selected AbstractsDiscontinuity 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] Temperature-dependent changes in the soil bacterial community in limed and unlimed soilFEMS MICROBIOLOGY ECOLOGY, Issue 1 2003Marie Pettersson Abstract A humus soil with a pH(H2O) of 4.9 was limed to a pH of 7.5 and was incubated together with samples from unlimed and field limed (pH 6.1) soils at 5, 20 and 30°C for up to 80 days. The changes in the phospholipid fatty acid (PLFA) pattern were most rapid for the bacterial community of the soil incubated at 30°C, while no changes were found in the soil incubated at 5°C. The response of the community activity to temperature was measured using the thymidine incorporation method on bacteria extracted from the soil. The bacterial community in soil incubated at 30°C became more adapted to high temperature than that in soil samples incubated at 5°C. When soil samples incubated at 30°C and 20°C were returned to 5°C for 35 days, only small changes in the PLFA pattern were found. No significant shift in community temperature adaptation was found. Thus, higher temperatures (with higher turnover) led to higher rates of change in both the PLFA pattern and the activity response to temperature, compared with lower temperatures. No effect of liming as a way of increasing substrate availability and turnover on the rate of change was observed. Changes in the PLFA pattern appeared sooner than changes in the activity response to temperature, indicating that changes in the PLFA pattern were mainly due to phenotypic acclimation and not to species replacement. [source] The relationships between local and regional species richness and spatial turnoverGLOBAL ECOLOGY, Issue 5 2002Patricia Koleff Abstract Aim To determine the empirical relationships between species richness and spatial turnover in species composition across spatial scales. These have remained little explored despite the fact that such relationships are fundamental to understanding spatial diversity patterns. Location South-east Scotland. Methods Defining local species richness simply as the total number of species at a finer resolution than regional species richness and spatial turnover as turnover in species identity between any two or more areas, we determined the empirical relationships between all three, and the influence of spatial scale upon them, using data on breeding bird distributions. We estimated spatial turnover using a measure independent of species richness gradients, a fundamental feature which has been neglected in theoretical studies. Results Local species richness and spatial turnover exhibited a negative relationship, which became stronger as larger neighbourhood sizes were considered in estimating the latter. Spatial turnover and regional species richness did not show any significant relationship, suggesting that spatial species replacement occurs independently of the size of the regional species pool. Local and regional species richness only showed the expected positive relationship when the size of the local scale was relatively large in relation to the regional scale. Conclusions Explanations for the relationships between spatial turnover and local and regional species richness can be found in the spatial patterns of species commonality, gain and loss between areas. [source] Community development along a proglacial chronosequence: are above-ground and below-ground community structure controlled more by biotic than abiotic factors?JOURNAL OF ECOLOGY, Issue 5 2010Matthew L. Carlson Summary 1.,We studied vascular plant and soil-dwelling testate amoeba communities in deglaciated sites across a range of substrate ages in Kenai Fjords, Alaska, USA to test four hypotheses. (i) Patterns of community assembly are similar for vascular plants and testate amoebae. (ii) Vascular plant and testate amoeba communities are more strongly correlated to abiotic variables than to each other, since these communities are not directly linked trophically. (iii) Plant community structure becomes less associated with abiotic condition in succession relative to testate amoebae, as species replacement is believed to be more common for plants than testate amoebae. (iv) Above- and below-ground communities become more strongly linked over the succession, due a shift from predominantly allogenic to autogenic forces. 2.,We assessed relationships among biotic communities and abiotic site variables across the chronosequence using multiple factor analysis, redundancy analysis (RDA) and a moving-window analysis. 3.,The diversity patterns and the communities' response to site and soil variables differed between groups. The composition of both communities was significantly explained by bedrock type and moisture regime. The vascular plant community, however, was more influenced by distance from the glacier. 4.,Testate amoeba and vascular plant community patterns were significantly linked to each other and to location and physical conditions. The moving-window RDA indicates the variation explained by the physical and chemical environment tended to slightly decrease through the chronosequence for testate amoebae, while a bell-shape response was evidenced for vascular plants. The variation of the microbial community explained by the plant community was very low in the early stages of the succession and became higher than the variation explained by the environmental variables later in the chronosequence. 5.,Synthesis. These results suggest that vascular plants and testate amoebae are as linked or more in ecosystem development than either community is to changes in site condition. Furthermore, the strength of interactions varies along the succession. Thus, ecological links may be more important than macro-scale abiotic site condition is to community development, even between communities without direct trophic interactions. [source] Quantifying patterns and controls of mire vegetation succession in a southern boreal bog in Finland using partial ordinationsJOURNAL OF VEGETATION SCIENCE, Issue 6 2007E.-S. Tuittila Abstract Question: How do we distinguish between concurrent allogenic and autogenic forcings behind changing patterns in plant community structures during mire development? Location: Lakkasuo raised bog, southern Finland. Methods: Two radiometrically dated peat profiles were studied using high resolution plant macrofossil analysis. A combination of partial direct and indirect gradient analyses (CCA and DCA) was applied to quantify the role of different drivers of vegetation changes. Results: Autogenic hydroseral succession explained 16% of the compositional variation in the vegetation. Disturbance successions initiated by fire explained 15% of the variation in the hummock, but only 9% in the wetter lawn. The early post-disturbance successional stages were characterized by Eriophorum vaginatum. After partialling out the effects of peat depth and time since fire, a moisture gradient explained 29% of variation in the hummock core and 26% in the lawn. The analyses also indicated alternation between species with a similar niche. This interaction gradient explained 26% and 31% of the compositional variation in the hummock and lawn, respectively. The similar order of species replacement from both cores supported the existence of general directional succession in mire vegetation, both during the mire development and after fire events. The autogenic succession was slow and gradual while the disturbance successions were episodic and fast. Conclusion: Our results support the paradigm of the complex nature of mire vegetation dynamics where several interlinked agents have simultaneous effects. The approach of combining partial ordinations developed here appeared to be a useful tool to assess the role of different environmental factors in controlling the vegetation succession. [source] Light partitioning among species and species replacement in early successional grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 5 2002Marinus J.A. Werger Makino (1962); Ohwi (1965) Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ,later successional' species had higher light harvesting efficiencies for the same plant height than ,early successional' species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series. [source] The predatory impact of the freshwater invader Dikerogammarus villosus on native Gammarus pulex (Crustacea: Amphipoda); influences of differential microdistribution and food resourcesJOURNAL OF ZOOLOGY, Issue 1 2005Calum MacNeil Abstract Predation between invading and native species can produce patterns of exclusion and coexistence. Dikerogammarus villosus, a Ponto-Caspian amphipod species, has invaded many central European freshwaters in the past decade, replacing native Gammarus amphipod species. For instance, the arrival of D. villosus in Holland has been accompanied by the decline of Gammarus duebeni and G. tigrinus populations within invaded systems. This study examined what may happen when D. villosus eventually encounters native Dutch populations of Gammarus pulex, and how factors such as microhabitat and food resource availability could contribute to a future species replacement or coexistence. A laboratory simulation of a lake/pooled area of river indicated that G. pulex and D. villosus differed in distribution within the same habitat, and showed that although the distribution of the native differed in the presence of the invader, the presence of the native had no effect on the distribution of the invader. Gammarus pulex suffered severe intraguild predation (IGP) from D. villosus in mixed species treatments with no reciprocal predation of D. villosus by G. pulex. This IGP occurred regardless of whether no alternative food resource was available (91% of the G. pulex population eliminated after 7 days), or alternative foods/prey were available to excess, such as leaf material (85%), chironomids (77%) or fish food flakes (74%). We conclude that although differential microdistribution of the two species could promote coexistence, the presence of alternative foods/prey resources, merely slow the rate of IGP and replacement of the native by the invader. Our study joins one of an increasing number emphasizing the potential damaging impacts of D. villosus on native communities. [source] Defoliation and site differences influence vegetative spread in grasslandNEW PHYTOLOGIST, Issue 2 2002G. T. Barthram Summary ,,Plants spread vegetatively at rates that depend on both their own and their neighbours' traits. We tested hypotheses that such rates also interact with defoliation intensity and differ between sites. ,,Well-established monoculture patches (20 × 20 cm) of five grass species were arranged in plots so that every species patch had all the remaining species as neighbours. Sites were in central Scotland, UK, and at a drier location in eastern Scotland. Plots were cut at 3 cm (,short') or 6 cm (,tall'), either uniformly or in a chessboard pattern. ,,Invasiveness and resistance to invasion followed the transitive hierarchy, Agrostis capillaris > Festuca rubra > Lolium perenne = Holcus lanatus > Poa trivialis , except that P. trivialis strongly invaded H. lanatus at the damper, more fertile site. ,Tall' patches spread and intermixed most, independent of species. The effects of cutting neighbouring patches depended on both invading and invaded species' traits. ,,Thus, defoliation altered the relationships between species, as did differences between sites, influencing both the speed and direction of species replacement. [source] When does ecosystem engineering cause invasion and species replacement?OIKOS, Issue 8 2008Andrew Gonzalez Introduced exotic species can dominate communities and replace native species that should be better adapted to their local environment, a paradox that is usually explained by the absence of natural enemies and by habitat alteration resulting from anthropogenic disturbance. Additionally, introduced species can enhance their invasion success and impact on native species by modifying selection pressures in their new environment through ecosystem engineering. We analyse a simple dynamic model of indirect competition for habitat between a non-engineering resident species and an engineering exotic species. The conditions for invasion and competitive exclusion of the resident by the exotic species and the range of dynamic outcomes suggested by the model are determined by the form of density dependence. We give simple criteria for the success of the invading species on dimensionless quantities involving rates of ecosystem engineering and of habitat degradation. The model's predictions offer an additional explanation for a range of invasion dynamics reported in the literature, including lag times between introduction and establishment. One intriguing result is that a series of failed invasions may successively reduce environmental resistance to subsequent invasion, through a cumulative effect of habitat transformation. More work is needed to determine the frequency and conditions in which engineering is required for successful establishment, and whether highly-successful (or high-impact) invaders are more likely to possess ecosystem engineering traits. [source] Inter-annual variability in amphibian assemblages: implications for diversity assessment and conservationAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2010Carola Gómez-Rodríguez Abstract 1.Diversity assessments and conservation management should take into account the dynamic nature of populations and communities, particularly when they are subject to highly variable and unpredictable environmental conditions. 2.This study evaluates the inter-annual variability in the assemblage composition (temporal turnover) of an amphibian community breeding in a highly dynamic habitat, a Mediterranean temporary pond system, during a 4-year period. 3.A comprehensive framework is provided to evaluate temporal turnover from data of a differing nature (species richness, presence/absence and relative abundance) and, especially, to discern variation in richness (species loss) from changes in the identity or abundance of species (species replacement). 4.Results show that the pond amphibian assemblages in Doñana National Park exhibited high inter-annual variability during the study period, both in the number of species, species identity and their relative abundance. This result provides evidence for the inadequacy of surveys conducted only in one breeding season to characterize the species assemblage associated with a given pond. Besides, it suggests that a given pond offers different breeding opportunities over time, being suitable for different species depending on the year. This alternation will contribute to the medium-term preservation of all species in the assemblage. 5.It is highly relevant to preserve the natural dynamism and spatial variability of temporary pond systems, which will favour the conservation of populations through their intrinsic variability. Copyright © 2010 John Wiley & Sons, Ltd. [source] Relative impacts of native and non-native crayfish on shelter use by an indigenous benthic fishAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 4 2009Damian H. Bubb Abstract 1.The North American signal crayfish Pacifastacus leniusculus has been widely introduced throughout Europe where it is expanding its range and in many areas replacing the native white-clawed crayfish Austropotamobius pallipes. There is concern with regards to the impact of this species replacement on benthic fish. Interspecific behavioural interactions and competition for shelter between the benthic fish, bullhead Cottus gobio and A. pallipes and P. leniusculus were measured to assess the comparative impact of native and non-native crayfish. 2.Both white-clawed crayfish and signal crayfish were dominant over bullhead. Bullheads moved away from approaches of crayfish, left shelters on entry of crayfish and rarely entered an occupied shelter. Signal crayfish made significantly more aggressive approaches towards bullheads than white-clawed crayfish. 3.Alone, bullheads spent most of their time by day under shelter (median 96%), reflecting a highly entrained behavioural response, which was relaxed by night (median 60%). Both crayfish species reduced shelter use by bullheads although the extent of shelter sharing by bullheads was higher in trials with white-clawed crayfish than with signal crayfish. 4.Sampling in the River Wharfe, northern England, where signal and white-clawed crayfish and bullhead currently exist, demonstrated a negative relationship between the densities of signal crayfish and bullhead, with high bullhead abundance where crayfish were absent or where white-clawed crayfish were present at low density. 5.Assuming that shelter is sometimes limited under natural conditions, crayfish are likely to displace bullheads from shelters, which may increase predation risk for bullheads. Although the effects of signal crayfish on bullhead shelter use were more intense, the pattern was highly evident for the native white-clawed crayfish. The higher fecundity and densities attained by signal crayfish may be more significant than differences in the behaviour of the two crayfish species in determining the impact of crayfish on bullheads. Copyright © 2008 John Wiley & Sons, Ltd. [source] Forest Succession in Tropical Hardwood Hammocks of the Florida Keys: Effects of Direct Mortality from Hurricane Andrew,BIOTROPICA, Issue 1 2001Michael S. Ross ABSTRACT A tree species replacement sequence for dry broadleaved forests (tropical hardwood hammocks) in the upper Florida Keys was inferred from species abundances in stands abandoned from agriculture or other anthropogenic acitivities at different times in the past. Stands were sampled soon after Hurricane Andrew, with live and hurricane-killed trees recorded separately; thus it was also possible to assess the immediate effect of Hurricane Andrew on stand successional status. We used weighted averaging regression to calculate successional age optima and tolerances for all species, based on the species composition of the pre-hurricane stands. Then we used weighted averaging calibration to calculate and compare inferred successional ages for stands based on (1) the species composition of the pre-hurricane stands and (2) the hurricane-killed species assemblages. Species characteristic of the earliest stages of post-agricultural stand development remains a significant component of the forest for many years, but are gradually replaced by taxa not present, even as seedlings, during the first few decades. This compositional sequence of a century or more is characterized by the replacement of deciduous by evergreen species, which is hypothesized to be driven by increasing moisture storage capacity in the young organic soils. Mortality from Hurricane Andrew was concentrated among early-successional species, thus tending to amplify the long-term trend in species composition. [source] Plant invaders and their novel natural enemies: who is naïve?ECOLOGY LETTERS, Issue 2 2009Koen J. F. Verhoeven Abstract Introduced exotic species encounter a wide range of non-coevolved enemies and competitors in their new range. Evolutionary novelty is a key aspect of these interactions, but who benefits from novelty: the exotic species or their new antagonists? Paradoxically, the novelty argument has been used to explain both the release from and the suppression by natural enemies. We argue that this paradox can be solved by considering underlying interaction mechanisms. Using plant defenses as a model, we argue that mismatches between plant and enemy interaction traits can enhance plant invasiveness in the case of toxin-based defenses, whereas invasiveness is counteracted by mismatches in recognition-based defenses and selective foraging of generalist herbivores on plants with rare toxins. We propose that a mechanistic understanding of ecological mismatches can help to explain and predict when evolutionary novelty will enhance or suppress exotic plant invasiveness. This knowledge may also enhance our understanding of plant abundance following range expansion, or during species replacements along successional stages. [source] Centrifugal speciation and centres of originJOURNAL OF BIOGEOGRAPHY, Issue 5 2000John C. Briggs Abstract Aim To discuss the development and usefulness of the theory of centrifugal speciation and its practical application to the centre of origin hypothesis. Location The Indo-West Pacific Ocean. Methods Utilization of patterns demonstrating species diversity, generic age, dispersal tracks, phylogenetics, extinction and genetic diversity. Results The centrifugal speciation hypothesis appears to provide a suitable explanation for the way in which centres of origin theoretically operate. Recent information about the centre of origin in the marine East Indies suggests that it is the source of evolutionary radiation for the Indo-West Pacific. Its mechanism appears to conform to the centrifugal prediction. Main conclusions The East Indies Triangle is the origin of a series of dynamic systems that extend across the entire Indo-West Pacific. These systems are apparently maintained by a continuous outflow from the centre of origin. A series of species replacements from the East Indies over the past 10 million years would create and perpetuate the systems that have been identified. [source] | ||||||||||