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Climate change induced changes in fish populations due to differences in species composition among nested assemblages: new Biofresh study

June 21, 2012

Since the early 1990s scientists have been working to enhance the impact and efficiency of site-based conservation approaches. The field of systematic conservation Planning (1) is guided by the so-called ‘representation principle’, an influential policy goal formulated by IUCN ecologist Raymond Dasman in 1972 (2) and simply stated as “The creation of world-wide network of natural reserves that encompass within their boundaries the variety of species and habitats found on earth”. Initially the scientific focus was on developing principles and tools to optimize reserve network design assuming a largely static biota (e.g. the MARXAN conservation planning software). The new scientific frontier in conservation planning is about taking into account the changes in species distribution and occurrence in response to climate and other environmental change. This is so that ‘long-term persistence’ can be incorporated into reserve system design. Needless to say conservation planning for freshwater biodiversity under changing environmental conditions is particularly challenging given the fluid and dynamic nature of freshwater systems!

Writing in the May issue of Global Ecology and Biogeography, BioFresh team member Clément Tisseuil and colleagues add a significant new dimension to our ability to predict how assemblies of fish species (termed beta diversity) will change in time and space in response to climate change. They applied two concepts in biogeography to explore and project the future distributions of 18 fish species for the 2010-2100 period based on data from 50 sites in the Adour-Garone River Basin in France.

The Tarn River France by By Thomas Rosenau [CC-BY-SA-2.5 (

The first concept of species turn-over seeks to understand how some species may be replaced by others under different scenarios. The second, and slightly more difficult concept of nestedness, refers to how an ecological system is organized. So for instance, we might prioritize a site for conservation based on the richness of the species assembly (Alpha diversity), however it is vital to know the extent to which other less species rich sites contain sub-sets of the species of the rich sites (degree of nestedness). The concept of nestedness thus enables scientists to identify the processes that lead to species loss or gain in sites .

The significance of this new study is that it is the first to take nestedness fully into account when projecting changes (differences) in fish assemblages at different places and at different times along a river gradient .

Commenting on the significance of the research Clement Tisseuil notes “We showed that the composition of local fish assemblages will greatly change over the 21st century, but this is consistent with previous studies of fish faunas. Our contribution is to distinguish between the turnover and nested components of fish diversity and how these shape the processes that lead to changes in fish species assemblies over time and space. Our key finding was that changes in species composition projected in upstream and downstream sites were mainly caused by differences in species richness among nested fish assemblages, whereas those projected in midstream sites were almost entirely caused by a process of species turnover ”

Tisseuil1, C., Leprieur, F., Grenouillet, G., Vrac, M & S. Lek (2012) Projected impacts of climate change on spatio-temporal patterns of freshwater fish beta diversity: a deconstructing
approach Global Biogeography and Ecology: 773

(1) Margules, C.R.& R. L. Pressey (2000) Systematic Conservation Planning. Nature, 405, 243-253.

(2) Dasmann, R.F. (1972) Towards a system for classifying natural regions of the world and their representation by national parks and reserves. Biological Conservation, 4, 247-255.

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