Trophic plasticity of omnivorous fishes in natural and human‐dominated landscapes

The persistence of diverse communities and functioning ecosystems under increasing anthropogenic pressure relies on food web rewiring and the ability of animals to expand or change their diet in disturbed ecosystems. We combined a suite of diet tracing techniques to study trophic plasticity in omnivorous fishes, ecomorphologically similar species with high competition potential, across different human land uses in subtropical streams. We found that the proportion of native forest cover, associated with intensive land use, altered the isotopic composition of fishes, which were more enriched in 13C, without affecting the carbon isotope ratios of their prey and basal resources. There was also evidence for a nonlinear effect of native forest cover on the δ15N values of basal resources, macroinvertebrates, and omnivorous fishes, indicating that nutrient pollution from agriculture propagated through stream food webs. The most widely distributed fish species shifted their diet from autochthonous resources to terrestrial invertebrates and sedimentary organic matter in disturbed streams. Moreover, the isotopic niche of this fish species was broader in streams with higher fish species richness, indicating the combined impacts of environmental change and competition on species coexistence. Therefore, our findings showed that the dominance and trophic niche breadth of dominant omnivores depend not only on the availability of resources but also on the interactions with their putative competitors

Higher biodiversity is required to sustain multiple ecosystem processes across temperature regimes

Natural Environment Research Council. Grant Number: NE/D013305/

Emergence of heat extremes attributable to anthropogenic influences

Climate scientists have demonstrated that a substantial fraction of the probability of numerous recent extreme events may be attributed to human-induced climate change. However, it is likely that for temperature extremes occurring over previous decades a fraction of their probability was attributable to anthropogenic influences. We identify the first record-breaking warm summers and years for which a discernible contribution can be attributed to human influence. We find a significant human contribution to the probability of record-breaking global temperature events as early as the 1930s. Since then, all the last 16 record-breaking hot years globally had an anthropogenic contribution to their probability of occurrence. Aerosol-induced cooling delays the timing of a significant human contribution to record-breaking events in some regions. Without human-induced climate change recent hot summers and years would be very unlikely to have occurred.111411Ysciescopu

Systematic variation in food web body-size structure linked to external subsidies.

The relationship between body mass (M) and size class abundance (N) depicts patterns of community structure and energy flow through food webs. While the general assumption is that M and N scale linearly (on log-log axes), nonlinearity is regularly observed in natural systems, and is theorized to be driven by nonlinear scaling of trophic level (TL) with M resulting in the rapid transfer of energy to consumers in certain size classes. We tested this hypothesis with data from 31 stream food webs. We predicted that allochthonous subsidies higher in the web results in nonlinear M-TL relationships and systematic abundance peaks in macroinvertebrate and fish size classes (latter containing salmonids), that exploit terrestrial plant material and terrestrial invertebrates, respectively. Indeed, both M-N and M-TL significantly deviated from linear relationships and the observed curvature in M-TL scaling was inversely related to that observed in M-N relationships. Systemic peaks in M-N, and troughs in M-TL occurred in size classes dominated by generalist invertebrates, and brown trout. Our study reveals how allochthonous resources entering high in the web systematically shape community size structure and demonstrates the relevance of a generalized metabolic scaling model for understanding patterns of energy transfer in energetically 'open' food webs

Populations of high-value predators reflect the traits of their prey

The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass-effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait-based approaches in predator–prey research

Large woody debris "rewilding" rapidly restores biodiversity in riverine food webs

Extensive habitat destruction and pollution have caused dramatic declines in aquatic biodiversity at local to global scales. In rivers, the reintroduction of large woody debris is a common method aimed at restoring degraded ecosystems through "rewilding." However, causal evidence for its effectiveness is lacking due to a dearth of replicated before-after control-impact field experiments. We conducted the first replicated experiment of large woody debris rewilding across multiple rivers and organisational levels, from individual target species populations to entire food webs. For the first time, we demonstrate causal links between habitat restoration, biodiversity restoration and food web responses. Populations of invertebrates and an apex predator, brown trout (Salmo trutta), increased, and food web analysis suggested increased biomass flux from basal resources to invertebrates and subsequently fishes within restored reaches. Synthesis and applications. This study contributes significant new evidence demonstrating that large woody debris rewilding can help to restore human-impacted river ecosystems, primarily through altering the abundance and biomass of consumers and resources in the food web. We also outline a means to gauge the magnitude of ecological responses to restoration, relative to environmental stressors, which could help to prioritise the most effective conservation efforts

Is There a Role for Adversariality in Teaching Critical Thinking?

Although there has been considerable recent debate on the topic of adversariality in argumentation, this debate has rarely found its way into work on critical thinking theory and instruction. This paper focuses on the implications of the adversariality debate for teaching critical thinking. Is there a role for adversarial argumentation in critical thinking instruction? Is there a way to incorporate the benefits of adversarial argumentation while mitigating the problems

The antisaccade task as an index of sustained goal activation in working memory: modulation by nicotine

The antisaccade task provides a laboratory analogue of situations in which execution of the correct behavioural response requires the suppression of a more prepotent or habitual response. Errors (failures to inhibit a reflexive prosaccade towards a sudden onset target) are significantly increased in patients with damage to the dorsolateral prefrontal cortex and patients with schizophrenia. Recent models of antisaccade performance suggest that errors are more likely to occur when the intention to initiate an antisaccade is insufficiently activated within working memory. Nicotine has been shown to enhance specific working memory processes in healthy adults. MATERIALS AND METHODS: We explored the effect of nicotine on antisaccade performance in a large sample (N = 44) of young adult smokers. Minimally abstinent participants attended two test sessions and were asked to smoke one of their own cigarettes between baseline and retest during one session only. RESULTS AND CONCLUSION: Nicotine reduced antisaccade errors and correct antisaccade latencies if delivered before optimum performance levels are achieved, suggesting that nicotine supports the activation of intentions in working memory during task performance. The implications of this research for current theoretical accounts of antisaccade performance, and for interpreting the increased rate of antisaccade errors found in some psychiatric patient groups are discussed

Purification and functional characterisation of rhiminopeptidase A, a novel aminopeptidase from the venom of Bitis gabonica rhinoceros

This study describes the discovery and characterisation of a novel aminopeptidase A from the venom of B. g. rhinoceros and highlights its potential biological importance. Similar to mammalian aminopeptidases, rhiminopeptidase A might be capable of playing roles in altering the blood pressure and brain function of victims. Furthermore, it could have additional effects on the biological functions of other host proteins by cleaving their N-terminal amino acids. This study points towards the importance of complete analysis of individual components of snake venom in order to develop effective therapies for snake bites

Application of Nitrogen and Carbon Stable Isotopes (δ15Ν and δ13C) to Quantify Food Chain Length and Trophic Structure

Increasingly, stable isotope ratios of nitrogen (delta N-15) and carbon (delta C-13) are used to quantify trophic structure, though relatively few studies have tested accuracy of isotopic structural measures. For laboratory-raised and wild-collected plant-invertebrate food chains spanning four trophic levels we estimated nitrogen range (NR) using delta N-15, and carbon range (CR) using delta C-13, which are used to quantify food chain length and breadth of trophic resources respectively. Across a range of known food chain lengths we examined how NR and CR changed within and between food chains. Our isotopic estimates of structure are robust because they were calculated using resampling procedures that propagate variance in sample means through to quantified uncertainty in final estimates. To identify origins of uncertainty in estimates of NR and CR, we additionally examined variation in discrimination (which is change in delta N-15 ordelta C-13 from source to consumer) between trophic levels and among food chains. delta N-15 discrimination showed significant enrichment, while variation in enrichment was species and system specific, ranged broadly (1.4‰ to 3.3‰), and importantly, propagated variation to subsequent estimates of NR. However, NR proved robust to such variation and distinguished food chain length well, though some overlap between longer food chains infers a need for awareness of such limitations. delta C-13 discrimination was inconsistent; generally no change or small significant enrichment was observed. Consequently, estimates of CR changed little with increasing food chain length, showing the potential utility of delta C-13 as a tracer of energy pathways. This study serves as a robust test of isotopic quantification of food chain structure, and given global estimates of aquatic food chains approximate four trophic levels while many food chains include invertebrates, our use of four trophic level plant-invertebrate food chains makes our findings relevant for a majority of ecological systems