Recovery and nonrecovery of freshwater food webs from the effects of acidification

Many previous attempts to understand how ecological networks respond to and recover from environmental stressors have been hindered by poorly resolved and unreplicated food web data. Few studies have assessed how the topological structure of large, replicated collections of food webs recovers from perturbations. We analysed food web data taken from 23 UK freshwaters, sampled repeatedly over 24 years, yielding a collection of 442 stream and lake food webs. Our main goal was to determine the effect of acidity on food web structure and to analyse the way food web structure recovered from the effects of acidity over time. Long-term monotonic reversals of acidification were evident at many of the sites, but the ecological responses were generally far less evident than chemical changes, or absent. Across the acidity gradient, food web linkage density and network efficiency declined with increasing acidity, while node redundancy (i.e. trophic similarity among species within a web) increased. Within individual sites, connectance, linkage density, trophic height, resource vulnerability and network efficiency tended to increase over time as sites recovered from acidification, while consumer generality and node redundancy tended to decrease. There was evidence for a lag in biological recovery, as those sites showing a recovery in both their biology and their chemistry were a nested subset of those which only showed a chemistry trend. These findings support the notion that food web structure is fundamentally altered by acidity, and that inertia within the food web may be hindering biological recovery. This suggestion of lagged recovery highlights the importance of long-term monitoring when assessing the impacts of anthropogenic stressors on the natural world. This temporal dimension, and recognition that species interactions can shape community dynamics, is missing from most national biomonitoring schemes, which often rely on space-for-time proxies

Modes, mechanisms and evidence of bet hedging in rotifer diapause traits

In this contribution, we review our knowledge on bet-hedging strategies associated with rotifer diapause. First, we describe the ecological scenario under which bet hedging is likely to have evolved in three diapause-related traits in monogonont rotifer populations: (1) the timing of sex (because diapausing eggs are produced via sexual reproduction), (2) the sexual reproduction ratio (i.e. the fraction of sexually reproducing females) and (3) the timing of diapausing egg hatching. Then, we describe how to discriminate among bet-hedging modes and discuss which modes and mechanisms better fit the variability observed in these traits in rotifers. Finally, we evaluate the strength of the empirical evidence for bet hedging in the scarce studies available, and we call for the need of research at different levels of biological complexity to fully understand bet hedging in rotifer diapause

The Role of Risk Aversion and Lay Risk in the Probabilistic Externality Assessment for Oil Tanker Routes to Europe

Oil spills are a major cause of environmental concern, in particular for Europe. However, the traditional approach to the evaluation of the expected external costs of these accidents fails to take into full account the implications of their probabilistic nature. By adapting a methodology originally developed for nuclear accidents to the case of oil spills, we extend the traditional approach to the assessment of the welfare losses borne by potentially affected individuals for being exposed to the risk of an oil spill. The proposed methodology differs from the traditional approach in three respects: it allows for risk aversion; it adopts an ex-ante rather than an ex-post perspective; it allows for subjective oil spill probabilities (held by the lay public) higher than those assessed by the experts in the field. In order to illustrate quantitatively this methodology, we apply it to the hypothetical (yet realistic) case of an oil spill in the Aegean Sea. We assess the risk premiums that potentially affected individuals would be willing to pay in order to avoid losses to economic activities such as tourism and fisheries, and non-use damages resulting from environmental impacts on the Aegean coasts. In the scenarios analysed, the risk premiums on expected losses for tourism and fisheries turn out to be substantial when measured as a percentage of expected losses; by contrast, they are quite small for the case of damages to the natural environment

Elevated temperatures drive the evolution of armour loss in the threespine stickleback Gasterosteus aculeatus

1. While there is evidence of genetic and phenotypic responses to climate change, few studies have demonstrated change in functional traits with a known genetic basis. 2. Here we present evidence for an evolutionary adaptive response to elevated temperatures in freshwater populations of the threespine stickleback Gasterosteus aculeatus. 3. Using a unique set of historical data and museum specimens, in combination with contemporary samples, we fitted a Bayesian spatial model to identify a population-level decline in the number of lateral bony plates, comprising anti-predator armour, in multiple populations of sticklebacks over the last 91 years in Poland. 4. Armor loss was predicted by elevated temperatures and is proposed to be a correlated response to selection for reduced body size. 5. This study demonstrates a change in a functional trait of known genetic basis in response to elevated temperature, and illustrates the utility of the threespine stickleback as a model for measuring the evolutionary and ecological impacts of environmental change across the northern hemisphere

Towards a simple global-standard bioassay for a key ecosystem process: organic-matter decomposition using cotton strips

Cotton-strip bioassays are increasingly used to assess ecosystem integrity because they provide a standardized measure of organic-matter decomposition – a fundamental ecosystem process. However, several different cotton- strip assays are routinely used, complicating the interpretation of results across studies, and hindering broader synthesis. Here, we compare the decay rates and assemblages of bacteria and fungi colonizing the three most commonly used cotton materials: Artist’s canvas, Calico cloth, and Empa fabric. Cotton strips from each material type were incubated in 10 streams that span a wide range of physicochemical properties across five ecoregions. Additionally, to evaluate responses to environmental stress without potentially confounding biogeographical effects, we deployed identical bioassays in five streams across an acidification gradient within a single ecoregion. Across all streams decomposition rates (as tensile strength loss [TSL]) differed among the three cotton ma- terials; Calico cloth decomposed fastest (time to 50% TSL [T50]=16.7d), followed by the Empa fabric (T50 = 18.3 d) and then Artist’s canvas (T50 = 21.4 d). Despite these differences, rates of TSL of the three cotton materials responded consistently to variation in environmental conditions; TSL of each fabric increased with stream temperature, dissolved-nutrient concentrations and acid-neutralizing capacity, although Artist’s canvas and Calico cloth were more sensitive than Empa fabric. Microbial communities were similar among the mate- rials, and values of community structure (e.g., phylotype richness and diversity) were comparable to those reported for decaying leaves in streams from the same region, the major natural basal carbon resource in forested-stream ecosystems. We present linear calibrations among pairs of assays so that past and future studies can be expressed in a “common currency” (e.g., Artist’s-fabric equivalents) ‘past and future studies’ repeated two times in the sentence. Lastly, given its relatively low within-site variability, and the large number of streams where it has been used (> 700 across the globe), we recommend Artist’s fabric for future work. These results show that cotton provides an effective and realistic standardized substrate for studying heterotrophic microbial assemblages, and acts as a reasonable proxy for more chemically complex forms of detritus. These findings add to growing evidence that cotton-strip bioassays are simple, effective and easily standardized indicators of het- erotrophic microbial activity and the ecosystem processes that result