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Community Properties (community + property)
Selected AbstractsEffects of Acer platanoides invasion on understory plant communities and tree regeneration in the northern Rocky MountainsECOGRAPHY, Issue 5 2005Kurt O. Reinhart Quantitative studies are necessary to determine whether invasive plant species displace natives and reduce local biodiversity, or if they increase local biodiversity. Here we describe the effects of invasion by Norway maple Acer platanoides on riparian plant communities and tree regeneration at two different scales (individual tree vs stand scales) in western Montana, USA, using both descriptive and experimental approaches. The three stands differed in community composition with the stand most dominated by A. platanoides invasion being more compositionally homogenous, and less species rich (,67%), species even (,40%), and diverse (,75%) than the two other stands. This sharp decrease in community richness and diversity of the highly invaded stand, relative to the other stands, corresponded with a 28-fold increase in A. platanoides seedlings and saplings. The dramatic difference between stand 1 vs 2 and 3 suggests that A. platanoides invasion is associated with a dramatic change in community composition and local loss of species diversity; however, other unaccounted for differences between stands may be the cause. These whole-stand correlations were corroborated by community patterns under individual A. platanoides trees in a stand with intermediate levels of patchy invasion. At the scale of individual A. platanoides canopies within a matrix of native trees, diversity and richness of species beneath solitary A. platanoides trees declined as the size of the trees increased. These decreases in native community properties corresponded with an increase in the density of A. platanoides seedlings. The effect of A. platanoides at the stand scale was more dramatic than at the individual canopy scale; however, at this smaller scale we only collected data from the stand with intermediate levels of invasion and not from the stand with high levels of invasion. Transplant experiments with tree seedlings demonstrated that A. platanoides seedlings performed better when grown beneath conspecific canopies than under natives, but Populus and Pinus seedlings performed better when grown beneath Populus canopies, the dominant native. Our results indicate that A. platanoides trees suppress most native species, including the regeneration of the natural canopy dominants, but facilitate conspecifics in their understories. [source] Biodiversity and resource use of larval chironomids in relation to environmental factors in a large riverFRESHWATER BIOLOGY, Issue 6 2002CHRISTIAN FESL 1.,Larval chironomids were examined at four sites on a cross-section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability. 2.,Species,accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area. 3.,Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32,91), H, diversity (1.5,2.3), evenness (0.23,0.28), spatial resource width (0.01,0.06), spatial resource overlap (0.13,0.20), spatial species aggregation (0.60,0.77), temporal community persistence (Kendal's correlation coefficient: 0.47,0.60) and beta-diversity (6.2,9.7). 4.,Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness. 5.,Species-abundance patterns agreed well with the log-normal model. Moderate community persistence and stability of the streambed sediments suggest that the log-normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats. [source] Biotic homogenization: a new research agenda for conservation biogeographyJOURNAL OF BIOGEOGRAPHY, Issue 12 2006Julian D. Olden Abstract Aim, Biotic homogenization describes the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more biotas over a specified time interval. The study of biotic homogenization is a young and rapidly emerging research area in the budding field of conservation biogeography, and this paper aims to synthesize our current knowledge of this process and advocate a more systematic approach to its investigation. Methods, Based on a comprehensive examination of the primary literature this paper reviews the process of biotic homogenization, including its definition, quantification, underlying ecological mechanisms, environmental drivers, the empirical evidence for different taxonomic groups, and the potential ecological and evolutionary implications. Important gaps in our knowledge are then identified, and areas of new research that show the greatest promise for advancing our current thinking on biotic homogenization are highlighted. Results, Current knowledge of the patterns, mechanisms and implications of biotic homogenization is highly variable across taxonomic groups, but in general is incomplete. Quantitative estimates are almost exclusively limited to freshwater fishes and plants in the United States, and the principal mechanisms and drivers of homogenization remain elusive. To date research has focused on taxonomic homogenization, and genetic and functional homogenization has received inadequate attention. Trends over the past decade, however, suggest that biotic homogenization is emerging as a topic of greater research interest. Main conclusions, My investigation revealed a number of important knowledge gaps and priority research needs in the science of biotic homogenization. Future studies should examine the homogenization process for different community properties (species occurrence and abundance) at multiple spatial and temporal scales, with careful attention paid to the various biological mechanisms (invasions vs. extinctions) and environmental drivers (environmental alteration vs. biotic interactions) involved. Perhaps most importantly, this research should recognize that there are multiple possible outcomes resulting from the accumulation of species invasions and extinctions, including biotic differentiation whereby genetic, taxonomic or functional similarity of biotas decreases over time. [source] Plant community properties predict vegetation resilience to herbivore disturbance in the ArcticJOURNAL OF ECOLOGY, Issue 5 2010James D. M. Speed Summary 1.,Understanding the impact of disturbance on vegetation and the resilience of plant communities to disturbance is imperative to ecological theory and environmental management. In this study predictors of community resilience to a simulated natural disturbance are investigated. Responses to disturbance are examined at the community, plant functional type and species level. 2.,Field experiments were set up in seven tundra plant communities, simulating disturbance based on the impact of grubbing by an increasing herbivore population of pink-footed geese (Anser brachyrhynchus). The short-term resilience of communities was assessed by comparing community dissimilarity between control plots and plots subject to three disturbance intensities based on the foraging impact of these geese. Potential for long-term recovery was evaluated across different disturbance patch sizes. 3.,Resilience to disturbance varied between communities; those with higher moss cover and higher soil moisture, such as wetlands and mires, were most resilient to disturbance. 4.,The wetter communities demonstrated greater long-term recovery potential following disturbance. In wetland communities, vegetative recovery of vascular plants and moss was greater in smaller disturbed patches and at the edges of patches. 5.,The response of vegetation to disturbance varied with intensity of disturbance, plant community and plant species. The use of functional type classifications only partially explained the variation in species responses to disturbance across communities, thus their use in predicting community changes was limited. 6.,Synthesis. The impact of disturbance is shown to be plant-community specific and related to the initial abiotic and biotic properties of the community. By showing that resilience is partly predictable, the identification of disturbance-susceptible communities is possible, which is of relevance for ecosystem management. [source] | ||||||||||