Biological invasions and eutrophication reshape the spatial patterns of stream fish size spectra in France

Aim

The global patterns of body size distributions are affected by global environmental changes (GEC), but our knowledge of the interaction effects between GEC and natural drivers is still limited. In this study, we aimed to test the effects of these interactions on fish community size spectra, that is, the variation in a community property across the body size range of individuals in the community.

Location

One thousand and ninety-five stream locations across France between 2015 and 2018.

Methods

We fitted size spectrum slopes for each fish community based on individual biomass size and using binning and maximum-likelihood methods through regression models across size classes and negative log-likelihood functions, respectively. Interactions between natural drivers and GEC were tested using model-averaging and the best models were selected with information criterion.

Results

Our results demonstrated that size spectra were steeper (i.e. higher proportion of small-bodied individuals) in warmer than colder locations, as expected by temperature-size rules. However, eutrophication (total phosphorus concentration) and biological invasions (percentage of non-native individuals) modulated the effect of temperature, with flatter size spectrum slopes in streams with more nutrients and higher proportion of non-native individuals. In addition, fish size spectrum slopes were generally steeper in upstream than in downstream locations, and this effect was more pronounced in stream locations with more nutrients. Finally, size spectrum slopes were flatter in species-rich communities when nutrient concentration was high.

Main Conclusions

Our study highlights that accounting for GEC, such as eutrophication and biological invasions, can help understanding the complex patterns of fish body size distributions in ecological communities.     

Links between estuarine condition and spatial distributions of marine invaders

Aim Non‐indigenous species pose a significant threat to the environment and to global economies. Predictive and preventative measures are widely considered more effective in curtailing invasions than are eradication or control measures. Of key importance in the prediction of regional invasion risk are the environmental conditions that enable successful establishment. Location We surveyed native and non‐indigenous sessile invertebrate diversity in each of two commercial (600–1500 vessels per year) and two recreational estuaries (seven to nine marinas) in New South Wales, Australia. Methods A nested hierarchical design was employed to investigate variation in sessile invertebrate diversity at the scales of site (1–3 km apart) and estuary (40–180 km apart). Settlement plates (15 × 15 cm) were used to sample invertebrates and background heavy metal loads were assessed using bioaccumulation in experimentally deployed oysters. Other physico‐chemical variables were monitored monthly. Manipulative experiments were used to test the direct effects of exposure to copper and tributyltin (TBT) antifouling paints on sessile invertebrates. Results Native and non‐indigenous species richness differed at various spatial scales, but showed no consistent difference between commercial and recreational estuaries. Instead, individual species distributions were strongly related to metal contamination, temperature, turbidity and pH. In experimental studies, several species (mostly invaders) were more abundant on plates exposed to copper and/or TBT antifouling paints. We found higher levels of copper (and in some instances TBT) in recreational marinas than in commercial harbours. Main conclusions Our results demonstrate the importance of metal pollution and physico‐chemical variables in the establishment of invaders in new regions. We have identified several native Australian species that have been exported overseas and suggested mechanisms contributing to their transport and establishment. Combining physico‐chemical information about donor and recipient regions with species tolerances could go some way to predicting where future invasions may occur.     

A metabolic signature predicts biological age in mice

Our understanding of the mechanisms by which aging is produced is still very limited. Here, we have determined the sera metabolite profile of 117 wild‐type mice of different genetic backgrounds ranging from 8 to 129 weeks of age. This has allowed us to define a robust metabolomic signature and a derived metabolomic score that reliably/accurately predicts the age of wild‐type mice. In the case of telomerase‐deficient mice, which have a shortened lifespan, their metabolomic score predicts older ages than expected. Conversely, in the case of mice that overexpress telomerase, their metabolic score corresponded to younger ages than expected. Importantly, telomerase reactivation late in life by using a TERT‐based gene therapy recently described by us significantly reverted the metabolic profile of old mice to that of younger mice, further confirming an anti‐aging role for telomerase. Thus, the metabolomic signature associated with natural mouse aging accurately predicts aging produced by telomere shortening, suggesting that natural mouse aging is in part produced by presence of short telomeres. These results indicate that the metabolomic signature is associated with the biological age rather than with the chronological age. This constitutes one of the first aging‐associated metabolomic signatures in a mammalian organism.     

Elevational gradients in species abundance,assemblage structure and energy use of rainforest birds in the Australian Wet Tropics bioregion

Elevational patterns of species richness, local abundance and assemblage structure of rainforest birds of north‐eastern Australia were explored using data from extensive standardized surveys throughout the region. Eighty‐two species of birds were recorded with strong turnover in assemblage structure across the elevational gradient and high levels of regional endemism in the uplands. Both species richness and bird abundance exhibited a humped‐shaped pattern with elevation with the highest values being between 600 and 800 m elevation. While much of the variability in species richness could be explained by the species–area relationship, analyses of net primary productivity (NPP) and total daily energy consumption of the bird community (energy use) suggest that ecosystem energy flow or constraints may be a significant determinant of species richness. Species richness is positively correlated with local bird abundance which itself is closely related to total energy use of the bird community. We suggest the hypothesis that lower NPP limits bird abundance and energy use in the uplands (>500 m) and that low bird energy use and species richness in the lowlands is limited by a seasonal bottleneck in available primary productivity and/or a species pool previously truncated by an extinction filter imposed by the almost complete disappearance of rainforest in the lowlands during the glacial maxima. We suggest that some of the previously predicted impacts of global warming on biodiversity in the uplands may be partially ameliorated by increases in NPP because of increasing temperatures. However, these relationships are complex and require further data specifically in regard to direct estimates of primary productivity and detailed estimates of energy flow within the assemblage.     

Temporal variation in foraging group structure of a size-structured stream fish community

Temporal variation in foraging group structure of a fish assemblage was examined in a flood-prone stream in southern Hokkaido, Japan. Foraging behaviour was observed underwater for four species which inhabit the water column: ayu, Plecoglossus altivelis, white-spotted charr, Salvelinus leucomaenis, masu salmon, Oncorhynchus masou, and Japanese dace, Tribolodon hakonensis, with each species being categorized into five size classes (species-size group; SSG). Based on foraging behaviour, each SSG of the fish assemblage was classified into one of four foraging groups: algae grazers, drift foragers, benthos-drift foragers, and omnivores, defined as SSG exhibiting similar foraging behaviour. All size classes of ayu, and of charr and salmon were categorized as algae grazers and drift foragers, respectively, throughout the study period. In contrast, size classes of dace were categorized as drift foragers, benthos-drift foragers, or omnivores with the same size classes often assigned to different foraging groups from month to month. Digestive tract contents of the fishes in the four foraging groups reflected their observed foraging behaviour, and foraging groups were therefore regarded as representing trophic groups. Abundance and membership of each foraging group varied in accordance with changes in abundance of SSG due to their growth, immigration, emigration, and/or mortality. Moreover, due to numerical dominance within the assemblage, plasticity in foraging behaviour of small- and medium-sized dace also played a key role in determining variability in the foraging group structure. Relative frequencies of two types of foraging behaviour, algae nipping and benthos foraging, of the small-sized dace were significantly correlated with the level of each resource, whereas no significant relationship was detected between foraging frequencies of the medium-sized dace and either resource. Fluctuations in foraging group structure within this assemblage occurred through niche shifts of some component members and by changes in SSG composition.     

Structure of two macrolepidopteran assemblages on Salix nigra (Marsh) and Acer negundo L.: abundance,diversity, richness,and persistence of scarce species

1. Most insect species occur at low abundance but a greater research effort has been devoted to so‐called outbreak species and little research is available on scarce (low abundance) species that are typical of most insect species. 2. Larval free‐feeding macrolepidoptera of two riparian trees Salix nigra (Marsh) (black willow) and Acer negundo L. (box elder) were sampled and sorted by species and abundance. 3. Data collected established that the majority of species in the assemblages in each tree species occurred at low abundance in each of the 5 years when larvae were sampled. 4. Species in the Noctuidae and Geometridae dominated both assemblages. 5. On both trees, assemblages were dominated numerically by relatively few species, a pattern that has been observed for insect assemblages on plants in managed and unmanaged habitats.