The BIOMAN project looked at how biodiversity in shallow lakes, a habitat threatened throughout Europe, is affected by environmental conditions and human impacts. We wanted to develop an index that could track how biodiversity and nature value of shallow lakes respond to management.
Our work, on a sample of 98 shallow lakes, resulted in a huge database that we exploited to reveal many interesting relationships between species, diversity patterns, lake characteristics and environmental conditions. Our work quickly revealed that ecosystem diversity is far from simple. Several taxonomic groups, such as cladocerans and ciliates, show a higher diversity in clear-water than in turbid lakes, the pattern that is expected from literature. Others, however, show a different and sometimes unexpected pattern For example, phytoplankton in the water column are more diverse in turbid than in clear-water systems. Our work showed beyond any doubt that biodiversity in these ecosystems is complex and multidimensional.
We discovered that the diversity of trophic groups depends on the characteristics and environmental conditions of the lake - just as we had expected. But when we started to analyse the diversity patterns across trophic levels and taxonomic groups (including bacterioplankton, protozoans, phytoplankton, zooplankton, fish, macro-invertebrates and macrophytes), we had a surprise. The relationship between the diversity of trophic groups and the environmental conditions in the lake varies greatly from one trophic group to the next. Indeed, a relationship that governs one group may be exactly the opposite of the one governing the diversity of another group. Different organisms respond quite differently to environmental changes, and as a result the responses of the various trophic groups are not coordinated with one another. If some external effect drives changes in the diversity of some organisms in some particular direction, we cannot necessarily predict its impact on the diversity of other organisms.
Does this mean that all our work went for nothing? Of course not. Everyone probably has an instinctive feeling that part of the fascination and beauty of life on our planet is its complexity and unpredictability. We have been able to show scientifically that biodiversity of this ecosystem is intrinsically multi-dimensional. As a result, changes in the communities in these lakes cannot be grasped by a simple, general index. The implication of this discovery is that one can not construct a straightforward indicator of the biodiversity of shallow lakes. One has to design multiple indexes, that each grasp a different aspect of the complex whole. Our observation has also important consequences for the management of these systems with the aim of conserving biodiversity. First, the multidimensionality of biodiversity implies that one has to make choices: restoration or conservation measures that are good for one group of organisms may be harmful to another group. One overall recommendation that we can make from our observatios is that it is very important to maintain a diversity of ecosystems at a regional scale. Different ecosystem types and states are important for the maintenance of diversity at different taxonomic groups and trophic levels, and their combined presence is a guarantee for high regional diversity.
If we are to stop the loss of biodiversity by 2010, the target set by the Goteborg Council, we must have a cost-effective means of measuring biodiversity. Unfortunately our results suggest that if we want to track biodiversity changes in this one ecosystem - shallow lakes - it will cost much more, and require much more work and many more human resources, than we thought at first.