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Loss of biodiversity: climate change is secondary
Rivers and streams are in constant motion, from their source to their mouth, and are some of the most dynamic habitats on Earth. Although they cover only a few per cent of the land surface, in near-natural state these ecosystems are home to a great diversity of creatures – insects, fish, algae, shellfish and water fleas are just a few of the inhabitants of lotic water. “But flowing waters are also the most endangered ecosystems worldwide, and respond particularly sensitively to environmental changes,” warns Dr Mathias Kuemmerlen from the Department of River Ecology and Conservation at the Senckenberg Research Institute, Frankfurt/Main.
Together with Chinese and German colleagues, the biologist studied a tract covering over 1,700 square kilometres in the catchment area of the Yangtze River. “For the first time we developed a model of biodiversity in flowing waters and future changes in land use,” explains Dr Sonja Jähnig, a researcher at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin who initiated the study, adding, “Loss of biodiversity is very often studied in connection with global climate change, Other important anthropogenic influences on the environment – like the change in land use – are often neglected in the process.”
The team of scientists with Kuemmerlen developed three scenarios for the development of macroinvertebrates living in flowing waters – animals without a spine which can be seen with the naked eye – for the period 2021-2050, with one scenario for climate change, one for land use change, and a combined climate and land use change scenario.
The 72 organisms living in flowing water behaved in very different ways in the models. For example, the stonefly Togoperla sp., which lives in water, loses 85 per cent of its habitat in the course of the change in land use in the catchment area studied, so that it is threatened with extinction locally. By contrast, the damselfly Protoneuridae sp. gains 9 per cent of potential habitat. “In all our models, there are ‘losers’ and ‘winners’ in both land use and climate change. However, taking all the species into consideration, we can say that the change in land use has the strongest negative effect on biodiversity in flowing waters – in this model, local biodiversity fell by 20 per cent,” Kuemmerlen explains.
In the scientists’ models, climate change is relatively secondary in its impact on biodiversity in flowing waters. Kuemmerlen also explains that there is a very close relationship between flowing waters and the landscape in the catchment area. This is why biodiversity is affected very strongly by land use. The results of the modelling also show that land use and climate change together could cause a general decrease in local biodiversity. Shifts can also be expected in habitats of many aquatic macroinvertebrates.
Although the change in land use – for example, clearing forests for agricultural use – is the most obvious change in an ecosystem, Kuemmerlen feels too little consideration is given to this factor in developing concepts for conservation. “To preserve biodiversity, we need to take into account both global climate changes and changes in land use,” Kuemmerlen stresses.
Kuemmerlen, M., Schmalz, B., Cai, Q., Haase, P., Fohrer, N. and Jähnig, S. C. (2015), An attack on two fronts: predicting how changes in land use and climate affect the distribution of stream macroinvertebrates. Freshwater Biology. doi: 10.1111/fwb.12580