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30 août 2017

Ecosystem functioning is enveloped by hydrometeorological variability [Nature Ecology & Evolution]

Keywords : carbon cycle, climate-change ecology, ecological modelling, hydrology

Terrestrial ecosystem processes, and the associated vegetation carbon dynamics, respond differently to hydrometeorological variability across timescales, and so does our scientific understanding of the underlying mechanisms. Long-term variability of the terrestrial carbon cycle is not yet well constrained and the resulting climate–biosphere feedbacks are highly uncertain. Here we present a comprehensive overview of hydrometeorological and ecosystem variability from hourly to decadal timescales integrating multiple in situ and remote-sensing datasets characterizing extra-tropical forest sites. We find that ecosystem variability at all sites is confined within a hydrometeorological envelope across sites and timescales. Furthermore, ecosystem variability demonstrates long-term persistence, highlighting ecological memory and slow ecosystem recovery rates after disturbances. However, simulation results with state-of-the-art process-based models do not reflect this long-term persistent behaviour in ecosystem functioning. Accordingly, we develop a cross-time-scale stochastic framework that captures hydrometeorological and ecosystem variability. Our analysis offers a perspective for terrestrial ecosystem modelling and paves the way for new model–data integration opportunities in Earth system sciences.

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30 août 2017

Trophic consequences of introduced species : comparative impacts of increased inter-specific versus intra-specific competitive interactions [Functional Ecology]

Keywords : biological invasions, global change, isotopic niche, niche divergence

1.Invasive species can cause substantial ecological impacts on native biodiversity. Whilst ecological theory attempts to explain the processes involved in the trophic integration of invaders into native food webs and their competitive impacts on resident species, results are equivocal. In addition, quantifying the relative strength of impacts from non-native species (inter-specific competition) versus the release of native conspecifics (intra-specific competition) is important but rarely completed.
2.Two model non-native fishes, the globally invasive Cyprinus carpio and Carassius auratus, and the model native fish Tinca tinca, were used in a pond experiment to test how increased intra- and inter-specific competition influenced trophic niches and somatic growth rates. This was complemented by samples collected from three natural fish communities where the model fishes were present. The isotopic niche, calculated using stable isotope data, represented the trophic niche.(...)

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30 août 2017

Scrutinizing key steps for reliable metabarcoding of environmental samples [Methods in Ecology and Evolution]

Keywords : biodiversity assessment, environmental DNA, faecal samples, high throughput sequencing, metabarcoding primers, molecular diet analyses, operational taxonomic unit, PCR replicates, primer bias, taxonomic assignment

1. Metabarcoding of environmental samples has many challenges and limitations that require carefully considered laboratory and analysis workflows to ensure reliable results. We explore how decisions regarding study design, laboratory set-up, and bioinformatic processing affect the final results, and provide guidelines for reliable study of environmental samples.
2. We evaluate the performance of four primer sets targeting COI and 16S regions characterizing arthropod diversity in bat faecal samples, and investigate how metabarcoding results are affected by parameters including : (1) number of PCR replicates per sample, (2) sequencing depth, (3) PCR replicate processing strategy (i.e. either additively, by combining the sequences obtained from the PCR replicates, or restrictively, by only retaining sequences that occur in multiple PCR replicates for each sample), (4) minimum copy number for sequences to be retained, (5) chimera removal, and (6) similarity thresholds for Operational Taxonomic Unit (OTU) clustering. Lastly, we measure within- and between-taxa dissimilarities when using sequences from public databases to determine the most appropriate thresholds for OTU clustering and taxonomy assignment.(...)

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11 juillet 2017

Human disturbance and upward expansion of plants in a warming climate [Nature Climate Change]

Subject terms : climate-change ecology, invasive species

Climate change is expected to trigger an upward expansion of plants in mountain regions and, although there is strong evidence that many native species have already shifted their distributions to higher elevations, little is known regarding how fast non-native species might respond to climate change. By analysing 131,394 occurrence records of 1,334 plant species collected over 20 years in the European Alps, we found that non-natives are spreading upwards approximately twice as fast as natives.(...)

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11 juillet 2017

Induced defences in plants reduce herbivory by increasing cannibalism [Nature Ecology & Evolution]

Keywords : ecology, plant ecology

Plants are attacked by myriad herbivores, and many plants exhibit anti-herbivore defences. We tested the hypothesis that induced defences benefit tomato plants by encouraging insects to eat other members of their species. We found that defences that promote cannibalism benefit tomatoes in two ways : cannibalism directly reduces herbivore abundance, and cannibals eat significantly less plant material. This previously unknown means of defence may alter plant–herbivore dynamics, plant evolution and pathogen transmission.

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