67 research outputs found
Pesticides: Can We Do Without Them?
These are the teaching notes for a case study in which students sift through and organize information on pesticide use presented to them from the perspective of different stakeholders. The case asks a fundamental question, "Can we do without pesticides?", and gives students an opportunity to explore the issues surrounding that question. Developed for an environmental issues course, the case would be appropriate for any introductory course that addresses human-environment interactions. As they pursue the case, students will be able to define the terms pest and pesticide and give specific examples; discuss benefits and harmful effects of pesticide use; discuss implications of banning pesticides; and articulate the ecological, ethical, economic, social, and political issues involved. Educational levels: High school, Undergraduate lower division
Projecting future expansion of invasive species: comparing and improving methodologies for species distribution modeling.
Modeling the distributions of species, especially of invasive species in non-native ranges, involves multiple challenges. Here, we developed some novel approaches to species distribution modeling aimed at reducing the influences of such challenges and improving the realism of projections. We estimated species-environment relationships for Parthenium hysterophorus L. (Asteraceae) with four modeling methods run with multiple scenarios of (i) sources of occurrences and geographically isolated background ranges for absences, (ii) approaches to drawing background (absence) points, and (iii) alternate sets of predictor variables. We further tested various quantitative metrics of model evaluation against biological insight. Model projections were very sensitive to the choice of training dataset. Model accuracy was much improved using a global dataset for model training, rather than restricting data input to the species' native range. AUC score was a poor metric for model evaluation and, if used alone, was not a useful criterion for assessing model performance. Projections away from the sampled space (i.e., into areas of potential future invasion) were very different depending on the modeling methods used, raising questions about the reliability of ensemble projections. Generalized linear models gave very unrealistic projections far away from the training region. Models that efficiently fit the dominant pattern, but exclude highly local patterns in the dataset and capture interactions as they appear in data (e.g., boosted regression trees), improved generalization of the models. Biological knowledge of the species and its distribution was important in refining choices about the best set of projections. A post hoc test conducted on a new Parthenium dataset from Nepal validated excellent predictive performance of our 'best' model. We showed that vast stretches of currently uninvaded geographic areas on multiple continents harbor highly suitable habitats for parthenium. However, discrepancies between model predictions and parthenium invasion in Australia indicate successful management for this globally significant weed
Modified Habitats Influence Kelp Epibiota via Direct and Indirect Effects
Addition of man-made structures alters abiotic and biotic characteristics of natural habitats, which can influence abundances of biota directly and/or indirectly, by altering the ecology of competitors or predators. Marine epibiota in modified habitats were used to test hypotheses to distinguish between direct and indirect processes. In Sydney Harbour, kelps on pier-pilings supported greater covers of bryozoans, particularly of the non-indigenous species Membranipora membranacea, than found on natural reefs. Pilings influenced these patterns and processes directly due to the provision of shade and indirectly by altering abundances of sea-urchins which, in turn, affected covers of bryozoans. Indirect effects were more important than direct effects. This indicates that artificial structures affect organisms living on secondary substrata in complex ways, altering the biodiversity and indirectly affecting abundances of epibiota. Understanding how these components of habitats affect ecological processes is necessary to allow sensible prediction of the effects of modifying habitats on the ecology of organisms
Pesticides: Can We Do Without Them?
These are the teaching notes for a case study in which students sift through and organize information on pesticide use presented to them from the perspective of different stakeholders. The case asks a fundamental question, "Can we do without pesticides?", and gives students an opportunity to explore the issues surrounding that question. Developed for an environmental issues course, the case would be appropriate for any introductory course that addresses human-environment interactions. As they pursue the case, students will be able to define the terms pest and pesticide and give specific examples; discuss benefits and harmful effects of pesticide use; discuss implications of banning pesticides; and articulate the ecological, ethical, economic, social, and political issues involved
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Usefulness of Annual Growth Rings of Cypress Trees (Taxodium Distichum) for Impact Analysis
Because of the propensity of cypress trees (Taxodium distichum) to form false or incomplete annual rings, the use of their growth rings for impact analysis is limited. However, the error associated with reading growth rings can be estimated by comparing two cores from the same tree, and the error inherent in a single core can be reduced by averaging the growth estimate over 6-10 years.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. It was digitized from a physical copy provided by the Laboratory of Tree-Ring research at The University of Arizona. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]
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