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Loehle C.,National Council for Air and Stream Improvement Inc.
Diversity and Distributions | Year: 2012

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation. © 2011 Blackwell Publishing Ltd. Source

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecography | Year: 2012

A new approach to habitat distribution modeling is presented and tested with data on North American plants. The relative frequency function (RFF) algorithm compares the relative frequencies of a species' sample points to that of random points or absence points on the landscape to compute a frequency ratio. The relative frequency ratio r is smoothed across the range of values using moving, overlapping windows. The ratio of frequencies at a sample point for each variable is used to compute the geometric mean score for all data with non-missing values. Variables are added using a forward stepwise method. Confidence intervals are computed with bootstrap resampling. The method was tested with artificial and species habitat and geographic range data. The RFF method in all cases gave results comparable to other methods tested. For the species with good geographic range maps, the results were consistent with known biogeography. The RFF method is particularly well-suited to irregularly shaped distributions and can classify sample points even when the data contain missing values. The method is extremely simple to use and comes with a free software tool, does not require a large sample size, does not require absence data, and is more interpretable and portable than certain other methods. © 2012 The Authors. Ecography © 2012 Nordic Society Oikos. Source

Loehle C.,National Council for Air and Stream Improvement Inc. | Irwin L.,PO Box 68
Forest Ecology and Management | Year: 2015

Bell et al. (2015) and Dunk et al. (2015) comment on our appraisal (Loehle et al., 2015) of biological insights from the US Fish and Wildlife Service models for northern spotted owl critical habitat. We here respond to those comments. We argue that while the low predictability of vegetation plot data by the gradient nearest neighbor (GNN) models may average out at very large scales and thus be useful in that context, errors at the site-specific scale may confound the modeling used to develop critical habitat designations. We further found that GNN errors violate statistical assumptions and are not propagated through the modeling exercise. We found multiple lines of evidence for habitat model instability, which may result from GNN uncertainty. We believe our evidence for lack of demographic predictability from the MaxEnt RHS values remains relevant to judicious use of these models for conservation. We similarly respond to other particular concerns with our analysis and conclude with suggestions. © 2015 Elsevier B.V.. Source

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecological Modelling | Year: 2012

The ideal free distribution posits that at equilibrium habitats of all degrees of quality should have similar population growth rate (λ) values (≈1), but in fact sink habitats are often observed with λ< 1 when source habitats have λ> 1. This is the source-sink paradox. Animals appear to be choosing habitat that will lower their fitness. It is argued that the paradox can be resolved by considering individual decisions in a conditional choice model with non-identical individuals that differ in competitive ability and current expected reproductive output. Individuals that are more mature, healthier, and/or arrive earlier to the source will acquire territory at lower cost and will defend it more vigorously and effectively. For other individuals, costs (including running out of time for breeding) of acquiring territory in the source become so high that moving to the sink increases their fitness. The model is implemented in an individual-based modeling framework. The cost-benefit decision model unites previously disparate topics into a single framework, including protandry, territoriality, philopatry, and juvenile dispersal. Simulation results and a literature survey support predictions. Results indicate that individuals with lower competitive ability (e.g., juveniles) obtain a fitness advantage from moving to a sink. Random sorting of individuals (simple pre-emption) results in lower population λ than competitive sorting. The effective population λ in the source is increased and in the sink is decreased by competitive sorting such that individual and population λ are not simple functions of habitat quality. The theory and models developed link individual behaviours to population processes and resolve the source-sink paradox. It is suggested that metapopulation modeling theory needs to be revisited based on the results presented. © 2012 Elsevier B.V. Source

Loehle C.,National Council for Air and Stream Improvement Inc.
Ecological Modelling | Year: 2014

Climate sensitivity summarizes the net effect of a change in forcing on Earth's surface temperature. Estimates based on energy balance calculations give generally lower values for sensitivity (<2°C per doubling of forcing) than those based on general circulation models, but utilize uncertain historical data and make various assumptions about forcings. A minimal model was used that has the fewest possible assumptions and the least data uncertainty. Using only the historical surface temperature record, the periodic temperature oscillations often associated with the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation were estimated and subtracted from the surface temperature data, leaving a linear warming trend identified as an anthropogenic signal. This estimated rate of warming was related to the fraction of a log CO2 doubling from 1959 to 2013 to give an estimated transient sensitivity of 1.093°C (0.96-1.23°C 95% confidence limits) and equilibrium climate sensitivity of 1.99°C (1.75-2.23°C). It is argued that higher estimates derived from climate models are incorrect because they disagree with empirical estimates. © 2014 Elsevier B.V. Source

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