It depends on the position of the species in the food web. If the species occurs in high abundance, and especially if it is the dominant or the only species using a certain resource in a habitat, its decline can become apparent very quickly. If, on the other hand, several species use the same resource, the decline of one species may be compensated for by the increase of another species. The presupposes that the other species does not also suffer from the changing factors. This is called the portfolio effect, which is derived from economics. If investments are spread more widely, then the collapse of a sub-market will not immediately have such a negative impact on the overall value of the investments. But as more species disappear, the resilience of a system decreases. And when too many species have disappeared, sudden changes occur that can affect the entire ecosystem.
In recent years, your team has revised the taxonomy of whitefish in Swiss lakes. Whitefish are now included in a separate appendix at species level and no longer only at genus level. What does this change about the overall picture of the Red List?
We are now talking about a total of 100 species (instead of 71) that are considered native. An endangerment status could be determined for 81 (instead of 66). Unfortunately, we then arrive at 18 species already extinct in Switzerland: nine whitefish species listed for the first time and nine of the fish and cyclostomes classified in 2007. Even worse: Because the whitefish species are endemic, i.e. only occur in one or a few neighbouring lakes, these nine extinct species have been lost globally and not just in Switzerland. This also applies to one of the other extinct species – the Jaunet (Salvelinus neocomensis), which was found exclusively in Lake Neuchâtel. With whitefish, we also arrive at a total of 40 endangered and 12 potentially endangered species, as well as 19 with insufficient data. Switzerland has one of the highest extinction rates of freshwater fish in the world.
Whitefish shoal in the Eawag aquarium
A third of the whitefish species (genus Coregonus) documented in 1950 are already extinct. The whitefish was classified at species level for the first time according to the guidelines of the International Union for Conservation of Nature (IUCN). Video: Eawag)