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We developed a mean field, metapopulation model to study the consequences of habitat destruction on a predator-prey interaction. The model complements and extends earlier work published by Bascompte and Solé (1998, J. theor. Biol.195, 383-393) in that it also permits use of alternative prey (i.e., resource supplementation) by predators. The current model is stable whenever coexistence occurs, whereas the earlier model is not stable over the entire domain of coexistence. More importantly, the current model permits an assessment of the effect of a generalist predator on the trophic interaction. Habitat destruction negatively affects the equilibrium fraction of patches occupied by predators, but the effect is most pronounced for specialists. The effect of habitat destruction on prey coexisting with predators is dependent on the ratio of extinction risk due to predation and prey colonization rate. When this ratio is less than unity, equilibrial prey occupancy of patches declines as habitat destruction increases. When the ratio exceeds one, equilibrial prey occupancy increases even as habitat destruction increases; i.e., prey "escape" from predation is facilitated by habitat loss. Resource supplementation reduces the threshold colonization rate of predators necessary for their regional persistence, and the benefit derived from resource supplementation increases in a nonlinear fashion as habitat destruction increases. We also compared the analytical results to those from a stochastic, spatially explicit simulation model. The simulation model was a discrete time analog of our analytical model, with one exception. Colonization was restricted locally in the simulation, whereas colonization was a global process in the analytical model. After correcting for differences between nominal and effective colonization rates, most of the main conclusions of the two types of models were similar. Some important differences did emerge, however, and we discuss these in relation to the need to develop fully spatially explicit analytical models. Finally, we comment on the implications of our results for community structure and for the conservation of prey species interacting with generalist predators.

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Most human biologists are aware of controversies regarding the use of DNA profiles in the courtroom. Much attention has been given to estimating the probability of obtaining matches between DNA samples from an innocent suspect and those from a crime scene, but considerably less attention has been given to the critical issue of determining the probability of guilt given a match. Using Bayes' rule and simple algebra, we develop a measure of the strength of DNA evidence that indicates the amount of incriminating evidence needed in combination with DNA match evidence to meet a given conviction standard. Based on current standards and practices, we use this measure to demonstrate that (1) the amount of non-DNA evidence needed to convict, given a DNA match, generally is quite small, even if errors can occur in the processing of DNA evidence; (2) DNA match evidence alone is insufficient to convict, even for the lowest recognized conviction standards; (3) failure to match DNA evidence samples should be exculpatory unless laboratory proficiency is poor; and (4) if errors in handling evidentiary samples occur (even rarely) that tend to produce a false DNA match, then the legal significance of DNA evidence is remarkably insensitive to estimates of chance match probability.

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Morris and Spieth (1978) described a method of calculating unbiased estimates of diploid genotype frequencies given information on the genotypes of haploid cells derived from diploid individuals. They concluded that three haploids per diploid would minimize sampling variance of genotype frequencies, given a fixed total number of haploids examined. If the identity of individual diploid genotypes is needed, Morris and Spieth (1978) stated that more haploids should be collected per diploid. We extend this work by showing from a Bayesian perspective that the probability of misclassification of individuals depends not only on the number of haploids sampled, but also on the genetic structure of the population since misclassification error will increase as the frequency of heterozygotes increases. Since information on the genetic structure (allele frequencies, inbreeding coefficient) of a population is rarely known prior to the initiation of an empirical study, the usefulness of our Bayesian approach is in experimental design, by revealing the magnitude of possible misclassification errors given a particular choice of number of haploids.

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The use of stable carbon isotopes as a means of studying energy flow is increasing in ecology and paleoecology. However, secondary fractionation and turnover of stable isotopes in animals are poorly understood processes. This study shows that tissues of the gerbil (Meriones unguienlatus) have different δ13C values when equilibrated on corn (C4) or wheat (C3) diets with constant 13C/12C contents. Lipids were depleted 3.0‰ and hair was enriched 1.0‰ relative to the C4 diet. Tissue δ13C values were ranked hair>brain>muscle>liver>fat. After changing the gerbils to a wheat (C3) diet, isotope ratios of the tissues shifted in the direction of the δ13C value of the new diet. The rate at which carbon derived from the corn diet was replaced by carbon derived from the wheat diet was adequately described by a negative exponential decay model for all tissues examined. More metabolically active tissues such as liver and fat had more rapid turnover rates than less metabolically active tissues such as hair. The half-life for carbon ranged from 6.4 days in liver to 47.5 days in hair.The results of this study have important implications for the use of δ13C values as indicators of animal diet. Both fractionation and turnover of stable carbon isotopes in animal tissues may obscure the relative contributions of isotopically distinct dietary components (such as C3 vs. C4, or marine vs. terrestrial) if an animal's diet varies through time. These complications deserve attention in any study using stable isotope ratios of animal tissue as dietary indicators and might be minimized by analysis of several tissues or products covering a range of turnover times.

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