Correlates of female choice in resource-defending antelope

Summary Where males offer their mates assistance in rearing offspring as well as access to defended resources, female mate choice should be influenced by both male phenotype and resource quality. In contrast, where there is no paternal care the relative importance of choice for male and territory traits is less well understood. We looked at female distribution across male territories in order to assess mate choice criteria in puku Kobus vardoni, and topi Damaliscus lunatus, two antelope where males defend resources but are not involved in parental care. In both species female distribution was correlated with male phenotype as well as the quality of forage and risk of predation on different territories. Male and territory characteristics were intercorrelated, but statistical analysis revealed that male traits, forage quality and predation risk were all significant, independent predictors of female choice in both study species. This is the first demonstration that female choice in mammals might be simultaneously influenced by male phenotype as well as the quality of defended resources.Correspondence to: A. Balmford     

Occurrence and determination of organic oxidants in rivers and wastewaters

Two iodometric methods for the concentration and analysis of water samples containing organic oxidants were applied to rivers and wastewaters in Illinois, Delaware, and Pennsylvania. Oxidant concentrations detected were as high as 2.5 § 10⁻⁵ M; the methods were capable of detecting as little as 10⁻⁸ M. Compounds possibly responsible for the observed oxidizing activity include N-chloro compounds, organic peroxides, or quinones.     

Reconstruction of historical trends of PCDD/Fs and PCBs in the Venice Lagoon, Italy

Historical trends of PCDD/Fs and PCBs from the year 1900 have been reconstructed for the Venice Lagoon area by using a fugacity-based dynamic multimedia model. A novel approach to estimate the inputs to the system was applied. Emissions to the lagoon were estimated by studying dated sediment cores taken from salt marshes located in the lagoon area. These cores have recently proven to be a suitable tool to reconstruct the temporal trends of atmospheric deposition of POPs. According to the model, concentrations of PCBs and PCDD/Fs in air and water reflect the trends of their production and usage, peaking during the 1960s. The peaks in the sediment were delayed by 5-40 years depending on the congener. Predicted concentrations are in good agreement with experimental results. The most important input parameters, identified by a sensitivity analysis, are the degradation constants, K(ow), the Henry's law constant, vapour pressure, active sediment depth, sediment resuspension, and deposition rates, and water residence time in the lagoon.     

Identifying optimal agricultural countermeasure strategies for a hypothetical contamination scenario using the strategy model

A spatially implemented model designed to assist the identification of optimal countermeasure strategies for radioactively contaminated regions is described. Collective and individual ingestion doses for people within the affected area are estimated together with collective exported ingestion dose. A range of countermeasures are incorporated within the model, and environmental restrictions have been included as appropriate. The model evaluates the effectiveness of a given combination of countermeasures through a cost function which balances the benefit obtained through the reduction in dose with the cost of implementation. The optimal countermeasure strategy is the combination of individual countermeasures (and when and where they are implemented) which gives the lowest value of the cost function. The model outputs should not be considered as definitive solutions, rather as interactive inputs to the decision making process. As a demonstration the model has been applied to a hypothetical scenario in Cumbria (UK). This scenario considered a published nuclear power plant accident scenario with a total deposition of 1.7x10(14), 1.2x10(13), 2.8x10(10) and 5.3x10(9)Bq for Cs-137, Sr-90, Pu-239/240 and Am-241, respectively. The model predicts that if no remediation measures were implemented the resulting collective dose would be approximately 36 000 person-Sv (predominantly from 137Cs) over a 10-year period post-deposition. The optimal countermeasure strategy is predicted to avert approximately 33 000 person-Sv at a cost of approximately 160 million pounds. The optimal strategy comprises a mixture of ploughing, AFCF (ammonium-ferric hexacyano-ferrate) administration, potassium fertiliser application, clean feeding of livestock and food restrictions. The model recommends specific areas within the contaminated area and time periods where these measures should be implemented.     

The effects of UVB radiation on temperate southern hemisphere forests

The temperate forests of the southern hemisphere are the most likely forests to be affected by increased levels of ultraviolet-B (UVB) radiation resulting from reduced ozone. The review describes these forests and then discusses the morphological changes, physiological effects, and protection mechanisms, particularly UV absorbing compounds that result from present day and increasing UVB radiation. Possible avenues for future research are explored.     

Generalized site occupancy models allowing for false positive and false negative errors

Site occupancy models have been developed that allow for imperfect species detection or "false negative" observations. Such models have become widely adopted in surveys of many taxa. The most fundamental assumption underlying these models is that "false positive" errors are not possible. That is, one cannot detect a species where it does not occur. However, such errors are possible in many sampling situations for a number of reasons, and even low false positive error rates can induce extreme bias in estimates of site occupancy when they are not accounted for. In this paper, we develop a model for site occupancy that allows for both false negative and false positive error rates. This model can be represented as a two-component finite mixture model and can be easily fitted using freely available software. We provide an analysis of avian survey data using the proposed model and present results of a brief simulation study evaluating the performance of the maximum-likelihood estimator and the naive estimator in the presence of false positive errors.     

Estimating species richness and accumulation by modeling species occurrence and detectability

A statistical model is developed for estimating species richness and accumulation by formulating these community-level attributes as functions of model-based estimators of species occurrence while accounting for imperfect detection of individual species. The model requires a sampling protocol wherein repeated observations are made at a collection of sample locations selected to be representative of the community. This temporal replication provides the data needed to resolve the ambiguity between species absence and nondetection when species are unobserved at sample locations. Estimates of species richness and accumulation are computed for two communities, an avian community and a butterfly community. Our model-based estimates suggest that detection failures in many bird species were attributed to low rates of occurrence, as opposed to simply low rates of detection. We estimate that the avian community contains a substantial number of uncommon species and that species richness greatly exceeds the number of species actually observed in the sample. In fact, predictions of species accumulation suggest that even doubling the number of sample locations would not have revealed all of the species in the community. In contrast, our analysis of the butterfly community suggests that many species are relatively common and that the estimated richness of species in the community is nearly equal to the number of species actually detected in the sample. Our predictions of species accumulation suggest that the number of sample locations actually used in the butterfly survey could have been cut in half and the asymptotic richness of species still would have been attained. Our approach of developing occurrence-based summaries of communities while allowing for imperfect detection of species is broadly applicable and should prove useful in the design and analysis of surveys of biodiversity.     

Adding infection to injury: synergistic effects of predation and parasitism on amphibian malformations

We explored the importance of interactions between parasite infection and predation in driving an emerging phenomenon of conservation importance: amphibian limb malformations. We suggest that injury resulting from intraspecific predation in combination with trematode infection contributes to the frequency and severity of malformations in salamanders. By integrating field surveys and experiments, we evaluated the individual and combined effects of conspecific attack and parasite (Ribeiroia ondatrae) infection on limb development of long-toed salamanders (Ambystoma macrodactylum). In the absence of Ribeiroia, abnormalities involved missing digits, feet, or limbs and were similar to those produced by cannibalistic attack in experimental trials. At field sites that supported Ribeiroia, malformations were dominated by extra limbs and digits. Correspondingly, laboratory exposure of larval salamanders to Ribeiroia cercariae over a 30-day period induced high frequencies of malformations, including extra digits, extra limbs, cutaneous fusion, and micromelia. However, salamander limbs exposed to both injury and infection exhibited 3-5 times more abnormalities than those exposed to either factor alone. Infection also caused significant delays in limb regeneration and time-to-metamorphosis. Taken together, these results help to explain malformation patterns observed in natural salamander populations while emphasizing the importance of interactions between parasitism and predation in driving disease.