Adrian C. Newton

Bio: Adrian C. Newton is an academic researcher from James Hutton Institute. The author has contributed to research in topics: Hordeum vulgare & Biodiversity. The author has an hindex of 74, co-authored 453 publications receiving 21814 citations. Previous affiliations of Adrian C. Newton include Seattle Children's Research Institute & University of Peradeniya.

Spatial Patchiness of Litter, Nutrients and Macroinvertebrates during Secondary Succession in a Tropical Montane Cloud Forest in Mexico

Abstract: We test the hypothesis that secondary succession in Tropical Montane Cloud Forest (TMCF) in Mexico is accompanied by an increase in the spatial structuring of litter resources, soil nutrient concentrations and the soil macroinvertebrate community at a within-plot scale (5–25 m). This increased spatial structuring is expected because secondary succession in these forests is associated with an increase in the diversity of trees that dominate the canopy. If each tree species generates a particular soil environment under its canopy, then under a diverse tree community, soil properties will be spatially very heterogeneous. Tree censuses and grid sampling were performed in four successional stages of a secondary chronosequence of TMCF. Variography was used to analyse spatial patterns in continuous variables such as nutrient concentrations, while Spatial Analysis by Distance Indices (SADIE) was applied to determine patchiness in the distribution of soil macroinvertebrate taxa. Secondary succession was found to be accompanied by the predicted increase in the spatial structuring of litter resources and the macroinvertebrate community at the within-plot scale. Spatial patterns in the macroinvertebrate community only became evident for all taxa in the oldest forest (100 years old). Patches with low Ca and Mg concentrations in early successional soils were associated with patches where pine litter was most abundant while those with low P concentrations in late successional stages were associated with patches where oak litter was most abundant. Results suggest that anthropogenic disturbance aboveground promotes a more homogeneous resource environment in the surface soil, which compared to older forests, sustains a less diverse and less spatially structured macroinvertebrate community.

Effects of Climate Change on the Potential Species Richness of Mesoamerican Forests

Abstract: The realized species richness of tropical forests cannot yet be reliably mapped at a regional scale due to lack of systematically collected data. An estimate of the potential species richness (PSR), however, can be produced through the use of species distribution modelling. PSR is interpretable as a climatically determined upper limit to observed species richness. We mapped current PSR and future PSR under climate change scenarios for Mesoamerica by combining the spatial distributions of 2000 tree species as predicted by generalized additive models built from herbaria records and climate layers. An explanatory regression tree was used to extract conditional rules describing the relationship between PSR and climate. The results were summarized by country, ecoregion and protected area status in order to investigate current and possible future variability in PSR in the context of regional biodiversity conservation. Length of the dry season was found to be the key determinant of PSR. Protected areas were found to have higher median PSR values than unprotected areas in most of the countries within the study area. Areas with exceptionally high PSR, however, remain unprotected throughout the region. Neither changes in realized species richness nor extinctions will necessarily follow changes in modelled PSR under climate change. However model output suggests that an increase in temperature of around 3°C, combined with a 20 percent decrease in rainfall could lead to a widespread reduction of around 15 percent of current PSR, with values of up to 40 percent in some moist lower montane tropical forests. The modelled PSR of dry forest ecoregions was found to be relatively stable. Some cooler upper montane forests in northern Mesoamerica, where few species of tropical origin are currently found, may gain PSR if species are free to migrate.

Pseudo-absences, pseudo-models and pseudo-niches: pitfalls of model selection based on the area under the curve

Abstract: The area under the curve AUC of the receiver operator characteristic ROC graph is regarded as an objective measure of the discrimination accuracy of predictive models. AUC scores calculated from background values, or pseudo-absences, have been proposed as a method of model selection for species distribution models SDMs fitted to presence-only data. However, the utility of AUC as a measure of model performance when data on confirmed absence are unavailable has not been fully investigated. We fitted SDMs using informative climatic variables for 2000 species of Mesoamerican trees. As a reference, we also built ‘pseudo-models’ using Gaussian random fields with no biological meaning. AUC correctly selected SDMs fitted to single environmental variables over ‘pseudo-models’ fitted to single random fields in almost all cases. However, when all seven variables were included in the models, AUC erroneously selected complex pseudo-models over complex climate models in 17% of the cases. The spatial distribution patterns predicted by the pseudo-models differed from the results derived from climate-based models, even when overall AUC scores were similar. Both model and pseudo-model AUC values increased when presence points were few and spatially aggregated. The results show that AUC calculated from presence-only data can be an unreliable guide for model selection. Pseudo-absences have ill-defined properties that challenge the interpretation of AUC values. Inference on multidimensional niche spaces should not be supported by AUC values calculated using pseudo-absences.

The effects of propagation environment and foliar area on the rooting physiology of Cordia alliodora (Ruiz & Pavon) Oken cuttings

Abstract: The effects of propagation microclimate and foliar area on the rooting of Cordiaalliodora (Ruiz & Pavon) Oken cuttings were investigated using non-mist propagators with and without shade. Photosynthetic rates (Pn), stomatal conductance (gs) and chlorophyll fluorescence ratio (Fv/Fm) of the cuttings were assessed during propagation. Pronounced differences in microclimate were recorded between treatments, with lower temperatures and vapour pressure deficit (VPD) under shade. During the first 8 days after insertion, Pn varied between 2.21 and 4.96 and 0.47 – 2.54 μmol CO2 m – 2s – 1 in the shaded and unshaded propagators, respectively. In the unshaded propagator, Fv/Fm decreased to a minimum of 0.72 2 days after insertion, recovering thereafter. In two separate rooting experiments, rooting percentage was reduced by high irradiance in the 20 and 30 cm2 leaf area treatments, but not in the 10 cm2 treatment. Pn decreased with an increase in leaf area in both shaded and unshaded propagators. Fv/Fm also declined with increasing leaf area in the high irradiance treatment. PAR and Pn were positively correlated under shade (r2 = 0.51) but negatively correlated in the unshaded treatment (r2 = 0.49); maximum Pn values were recorded at a PAR of 400 μmol m – 2 s – 1. No significant differences in gs were found between treatments, values ranging between 130 and 194 mmol H2O m – 2 s – 1. Positive correlations were found between rooting percentage and mean Fv/Fm. These results indicate that rooting of C. alliodora cuttings is related to photosynthetic activity during propagation, which is itself influenced both by propagator microclimate and cutting leaf area.

The Theory of Island Biogeography

Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

Ecosystems and human well-being: a framework for assessment

Abstract: This first report of the Millennium Ecosystem Assessment describes the conceptual framework that is being used in the MA. It is not a formal assessment of the literature, but rather a scientifically informed presentation of the choices made by the assessment team in structuring the analysis and framing the issues. The conceptual framework elaborated in this report describes the approach and assumptions that will underlie the analysis conducted in the Millennium Ecosystem Assessment. The framework was developed through interactions among the experts involved in the MA as well as stakeholders who will use its findings. It represents one means of examining the linkages between ecosystems and human well-being that is both scientifically credible and relevant to decision-makers. This framework for analysis and decision-making should be of use to a wide array of individuals and institutions in government, the private sector, and civil society that seek to incorporate considerations of ecosystem services in their assessments, plans, and actions.