A new mechanistic approach for the further development of a population with established size bimodality

Abstract

Usually, the origin of a within-cohort bimodal size distribution is assumed to be caused by initial size differences or by one discrete period of accelerated growth for one part of the population. The aim of this study was to determine if more continuous pathways exist allowing shifts from the small to the large fraction within a bimodal age-cohort. Therefore, a Eurasian perch population, which had already developed a bimodal size-distribution and had differential resource use of the two size-cohorts, was examined. Results revealed that formation of a bimodal size-distribution can be a continuous process. Perch from the small size-cohort were able to grow into the large size-cohort by feeding on macroinvertebrates not used by their conspecifics. The diet shifts were accompanied by morphological shape changes. Intra-specific competition seemed to trigger the development towards an increasing number of large individuals. A stage-structured matrix model confirmed these assumptions. The fact that bimodality can be a continuous process is important to consider for the understanding of ecological processes and links within ecosystems.

Does behaviour contribute to the previously documented invasive success of topmouth gudgeon?

“…At the same time the density of P. fluviatilis (CPUE as proxy) decreased. This indicates a bottleneck caused by depleted food resources, leading to an initial steep decline in P. fluviatilis density which corresponds to other studies in experimental ponds (Heermann et al, 2017). However, it cannot be excluded that an introduction of Sphaerothecum destruens by P. parva may have caused the decline in P. fluviatilis .…”

Growth portfolios buffer climate‐linked environmental change in marine systems

“…Conversely, compensatory growth leading to size convergence has previously been noted in amphibians (Asquith & Vonesh, 2012) and in fish aggregations where there has been a competitive release following a reduction in population density (Ali et al, 2003). However, population‐level synchronized growth responses like those documented here would appear to require either reduced intra‐specific competition (Huss et al, 2008) or be the product of a narrowing initial size distribution caused by a reduced temporal width of hatching or recruitment windows (Heermann et al, 2017). Neither of these processes seem likely to simultaneously operate at the multi‐population scale observed here, given the differences in relative abundance among the populations.…”