To address objectives 1 and 2, two Work Packages used an experimental approach to analyse behavioural and trophic variation in round goby populations within Danish waters along their invasion front. For the first Work Package, proof-of-concept pilot experiments were conducted in 2020, to test behavioural assays for analysing round goby traits in a well-established invasive population from Guldborgsund strait in Southern Denmark (54.69645N 11.84067E). These 2020 experiments showed that it is viable to analyse behavioural traits in wild fish alongside non-lethal methods to measure their food-web position (i.e. fin clips for stable isotope analysis). One publication from this package describing the behavioural experiments and their novel methodology is currently in preparation.
The second Work Package expanded on 2020’s experiments, by using the same experimental approach at four sites along 100 km of the round goby’s invasion front, from Dragør near the invasion front (55.58034N 12.65598E) to Grønsund a well-established population in southern Denmark (54.90371N 12.10367E). This work successfully sampled four round goby populations in May 2021, so that their behavioural traits, physiological variation and food web position could be analysed. Final data analysis on this major experimental program is still underway, with preliminary results suggesting that there significant within-species variation in behavioural traits and food-web position across their invasion front. The major publication from this work is currently in preparation, and a second publication analysing the impacts of round goby feeding on benthic fauna in Guldborgsund has been published (van Deurs, Moran et al. 2021, NeoBiota doi:10.3897/neobiota.68.67340). A Master’s student project was also conducted as part of this work package (Thesis “The effects of behavioural and physiological variation on the spread of a marine invasive fish / the round goby”, Andrea Galli, to be submitted Feb 2022), and a third manuscript is also expected to be produced based on this Master's project.
To address objective 3, the third Work Package in this project used systematic review and meta-analysis methods to review existing literature and analyse how individual trait variation can alter the outcome of ecological interactions. Given the major interruptions to experimental work in this project due to COVID, more focus was placed on this theoretical work than initially expected, and multiple publications have resulted from this Work Package. The main study was a systematic synthesis review, focusing on how individual trait variation can influence the outcome of ecological interactions. This collected information from 96 studies showing qualitative shifts in ecological interactions driven by individual variation, and described a new framework for understanding how these processes occur. This was recently published, and selected as a ‘Editor’s Choice’ paper in the journal Oikos (Moran et al. 2021, Oikos doi:10.1111/oik.08201). Additional systematic review studies that have been published under the Work Package are: a large meta-analysis focusing on the effects of diet on risk-taking behavioural traits in animals (Moran et al. 2020, Biol Revs, doi:10.1111/brv.12655); a methodological paper focusing on the use of statistical approaches to analyse effects on trait variance in meta-analyses (Sánchez‐Tójar, Moran et al. 2020, J Evol Biol, doi:10.1111/jeb.13661); and a meta-analysis on body size trait variation of male-female interactions in the invasive mosquitofish (Kim, Moran et al. 2021, J Anim Ecol doi:10.1111/1365-2656.13554; led by Master’s student Bora Kim, Bielefeld University).
