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Sampling Effects (sampling + effects)
Selected AbstractsShould we use proportional sampling for species,area studies?JOURNAL OF BIOGEOGRAPHY, Issue 8 2004José H. Schoereder Abstract Aim, In this paper we aim to show that proportional sampling can detect species,area relationships (SARs) more effectively than uniform sampling. We tested the contribution of alpha and beta diversity in ant communities as explanations for the SAR. Location, Tropical forest remnants in Viçosa, Minas Gerais, Brazil (20 °45, S, 42 °50, W). Methods, We sampled 17 forest remnants with proportional sampling. To disentangle sampling effects from other mechanisms, species richness was fitted in a model with remnant size, number of samples (sampling effects) and an interaction term. Results, A SAR was observed independent of the number of samples, discarding sampling effects. Alpha diversity was not influenced by remnant size, and beta diversity increased with remnant size; evidence to the fact that habitat diversity within remnants could be the dominant cause of the SAR. Such a relationship between beta diversity and remnant area may have also arisen due to the combined effects of territoriality and aggregation of ant species. Main conclusions, The proposed model, together with proportional sampling, allowed the distinction between sampling effects and other mechanisms. [source] Effects of species diversity on the primary productivity of ecosystems: extending our spatial and temporal scales of inferenceOIKOS, Issue 3 2004Bradley J. Cardinale The number of studies examining how species diversity influences the productivity of ecosystems has increased dramatically in the past decade as concern about global loss of biodiversity has intensified. Research to date has greatly improved our understanding of how, when, and why species loss alters primary production in ecosystems. However, because experiments have been performed at rather small spatial and short temporal scales, it is unclear whether conclusions can be readily extrapolated to the broader scales at which natural communities are most likely to influence ecosystem functioning. Here we develop a simple patch-dynamics model to examine some of the scale-dependent and independent qualities of the diversity-productivity relationship. We first simulate a typical diversity-productivity experiment and show that the influence of species richness on productivity is temporally dynamic, growing stronger through successional time. This holds true irrespective of whether resource partitioning or a sampling effect is the underlying mechanism. We then increase the spatial scale of the simulation from individual patches to a region consisting of many patch types. Results suggest that the diversity-productivity relationship is not influenced by spatial scale per se, but that the mechanism producing the relationship can change from sampling effects within individual patches to resource partitioning across patch types composing the region. This change occurs even though model dynamics are the same at both scales, suggesting that sampling effects and resource partitioning can represent different descriptions of the same biological processes operating concurrently at differing scales of observation. Lastly, we incorporate regional processes of dispersal and disturbance into the model and show that these processes can amplify the effect of species richness on productivity, resulting in patterns not easily anticipated from experiments. We conclude that the relative control of community structure by local versus regional processes may be a primary determinant of the diversity-productivity relationship in natural ecosystems. Therefore, past experiments having focused only on local processes might not reflect patterns and processes underlying diversity-productivity relationships in communities where disturbance and dispersal regulate species biomasses. [source] Nutrient enrichment overwhelms diversity effects in leaf decomposition by stream fungiOIKOS, Issue 2 2003Felix Bärlocher Mass losses of oak leaves were studied in microcosms, where numbers of aquatic hyphomycete species (1,5) and nutrient concentrations (2 levels each of N, P, and Ca) were varied. Species numbers, species identities, N, P and N×P interactions all had significant effects on leaf mass loss, but the magnitude of the effect was greater for N and P than for species numbers. Mass loss in multicultures was greater than predicted from average contributions of the component species in single cultures. This may have been due to sampling effects or niche complementarity. [source] Gene flow and melanism in garter snakes revisited: a comparison of molecular markers and island vs. coalescent modelsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2003TONYA D. BITTNER Within populations, the stochastic effect of genetic drift and deterministic effect of natural selection are potentially weakened or altered by gene flow among populations. The influence of gene flow on Lake Erie populations of the common garter snake has been of particular interest because of a discontinuous colour pattern polymorphism (striped vs. melanistic) that is a target of natural selection. We reassessed the relative contributions of gene flow and genetic drift using genetic data and population size estimates. We compared all combinations of two marker systems and two analytical approaches to the estimation of gene flow rates: allozymes (data previously published), microsatellite DNA (new data), the island model (FST -based approach), and a coalescence-based approach. For the coalescence approach, mutation rates and sampling effects were also investigated. While the two markers produced similar results, gene flow based on FST was considerably higher (Nm > 4) than that from the coalescence-based method (Nm < 1). Estimates of gene flow are likely to be inflated by lack of migration-drift equilibrium and changing population size. Potentially low rates of gene flow (Nm < 1), small population size at some sites, and positive correlations of number of microsatellite DNA alleles and island size and between M, mean ratio of number of alleles to range in allele size, and island size suggest that in addition to selection, random genetic drift may influence colour pattern frequencies. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 389,399. [source] | ||||||||||