Sex ratio, sexual dimorphism and mating structure in bethylid wasps

Sexual dimorphism has been linked to parasitoid mating structure by several authors. In turn mating structure has an important influence on predicted sex ratio optima. Here we test the relationship between sexual dimorphism and sex ratio using data from 19 species of bethylid wasps. Using phylogenetically based comparative methods we confirm the findings of a previous cross-species analysis that sex ratio (proportion of males) is strongly and negatively correlated with clutch size. Using cross-species comparisons we show an additional positive correlation of sex ratio and relative male size, as predicted. The relationship however is not significant when using phylogenetically based methods. The cross-species result is largely due to differences between two bethylid sub-families: the Epyrinae have relatively large males and relatively high sex ratios, whereas the Bethylinae have relatively small males and lower sex ratios. Our study illustrates the benefits and drawbacks of using cross-species versus phylogenetically based comparisons. Received: 13 May 1997 / Accepted after revision: 12 January 1998     

Understanding and predicting ecological dynamics: are major surprises inevitable?

Ecological surprises, substantial and unanticipated changes in the abundance of one or more species that result from previously unsuspected processes, are a common outcome of both experiments and observations in community and population ecology. Here, we give examples of such surprises along with the results of a survey of well-established field ecologists, most of whom have encountered one or more surprises over the course of their careers. Truly surprising results are common enough to require their consideration in any reasonable effort to characterize nature and manage natural resources. We classify surprises as dynamic-, pattern-, or intervention-based, and we speculate on the common processes that cause ecological systems to so often surprise us. A long-standing and still growing concern in the ecological literature is how best to make predictions of future population and community dynamics. Although most work on this subject involves statistical aspects of data analysis and modeling, the frequency and nature of ecological surprises imply that uncertainty cannot be easily tamed through improved analytical procedures, and that prudent management of both exploited and conserved communities will require precautionary and adaptive management approaches.     

Neglected biological patterns in the residuals

One of the fundamental assumptions underlying linear regression models is that the errors have a constant variance (i.e., homoscedastic). When this assumption is violated, standard errors from a regression can be biased and inconsistent, meaning that the associated p values and 95% confidence intervals cannot be trusted. The assumption of homoscedasticity is made for statistical reasons rather than biological reasons; in most real datasets, some form of heteroscedasticity is likely to exist. However, a survey of the behavioural ecology literature showed that only about 5% of articles explicitly mentioned heteroscedasticity, leaving 95% of articles in which heteroscedasticity was apparently absent. These results strongly indicate that the prevalence of heteroscedasticity is widely under-reported within behavioural ecology. The aim of this article is to raise awareness of heteroscedasticity amongst behavioural ecologists. Using topical examples from fields in behavioural ecology such as sexual dimorphism and animal personality, we highlight the biological importance of considering heteroscedasticity. We also emphasize that researchers should pay closer attention to the variance in their data and consider what factors could cause heteroscedasticity. In addition, we introduce some simple methods of dealing with heteroscedasticity. The two methods we focus on are: (1) incorporating variance functions within a generalised least squares (GLS) framework to model the functional form of heteroscedasticity and; (2) heteroscedasticity-consistent standard error (HCSE) estimators, which can be used when the functional form of heteroscedasticity is unknown. Using case studies, we show how both methods can influence the output from linear regression models. Finally, we hope that more researchers will consider heteroscedasticity as an important source of additional information about the particular biological process being studied, rather than an impediment to statistical analysis.     

Palatability mapping: a koala's eye view of spatial variation in habitat quality

Ecologists trying to understand the value of habitat to animals must first describe the value of resources contained in the habitat to animals and, second, they must describe spatial variation in resource quality at a resolution relevant to individual animal foraging. We addressed these issues in a study of koalas (Phascolarctos cinereus) in a Eucalyptus woodland. We measured beneficial and deterrent chemical characteristics as well as the palatability of trees using a near-infrared spectroscopic model based on direct feeding experiments. Tree use by koalas was influenced by tree size and foliar quality but was also context-dependent: trees were more likely to be visited if they were surrounded by small, unpalatable trees or by large, palatable trees. Spatial autocorrelation analysis and several mapping approaches demonstrated that foliar quality is spatially structured in the woodland at a scale relevant to foraging decisions by koalas and that the spatial structure is an important component of habitat quality.     

Farmer knowledge and a priori risk analysis: pre-release evaluation of genetically modified Roundup Ready wheat across the Canadian prairies

Background, aim, and scope  

The controversy over the world’s first genetically modified (GM) wheat, Roundup Ready wheat (RRW), challenged the efficacy of ‘science-based’ risk assessment, largely because it excluded the public, particularly farmers, from meaningful input. Risk analysis, in contrast, is broader in orientation as it incorporates scientific data as well as socioeconomic, ethical, and legal concerns, and considers expert and lay input in decision-making. Local knowledge (LK) of farmers is experience-based and represents a rich and reliable source of information regarding the impacts associated with agricultural technology, thereby complementing the scientific data normally used in risk assessment. The overall goal of this study was to explore the role of farmer LK in the a priori risk analysis of RRW.     

Mercury in the Mediterranean. Part 2: processes and mass balance

Mass balance of contaminants can provide useful information on the processes that influence their concentrations in various environmental compartments. The most important sources, sinks and the equilibrium or non-equilibrium state of the contaminant in individual environmental compartments can also be identified. Using the latest mercury speciation data, the results of numerical models and the results of recent studies on mercury transport and transformation processes in the marine environment, we have re-evaluated the total mercury (HgT) mass balance in the Mediterranean Sea. New calculations have been performed employing three distinct marine layers: the surface layer, the thermocline and the deep sea. New transport mechanisms, deep water formation and density-driven sinking and upwelling, were included in the mass balance calculations. The most recent data have even enabled the calculation of an approximate methylmercury (MeHg) mass balance. HgT is well balanced in the entire Mediterranean, and the discrepancies between inputs and outputs in individual layers do not exceed 20 %. The MeHg balance shows larger discrepancies between gains and losses due to measurement uncertainties and gaps in our knowledge of Hg species transformation processes. Nonetheless, the main sources and sinks of HgT (deposition and evasion) and MeHg (fluxes from sediment, outflow through the Gibraltar Strait) are in accordance with previous studies on mercury in the Mediterranean Basin. Mercury in the Mediterranean fish harvest is the second largest MeHg sink; about 300 kg of this toxic substance is consumed annually with sea food.     

Wasser: Flüssiges Gold der Alpen

Ohne Zusammenfassung