Ecological problem: Several factors act more at the same time than they combined

As an integral part of climate change, global warming is probably one of the
most well-known risks to ecosystem ecological balance and global biodiversity.
However, as the number and intensity of simultaneous factors increase, global ecosystems are also exposed to
many other human-induced global change factors (GCFs).
Examples include light pollution, where artificial light sources brighten the night sky, or the accumulation
of pesticides (such as fungicides) in the environment.
"We know very well how these factors alone affect parts of ecosystems, such as plant communities
.
In fact, their personal impact on the community can be very different, or even the opposite," explains Benedikt Speißer, first author of the recent study and a PhD student in the laboratory of Mark van Kleunen at the Department of Biology at the University of Constance
.

What happens when an ecosystem is exposed to several of these factors at the same time has not been well studied, although this may be the case for
most natural ecosystems.
To address this lack of knowledge, ecologists led by Mark van Kleunen investigated how simultaneous GCFs affect the composition and productivity of plant communities, and the role of numerous factors
.
To this end, they created small artificial ecological communities – often referred to as medium-sized ecosystems – consisting of nine different species of grasses and frogs native to Central Europe, and these selected species are widely distributed in Central Europe and often coexist
.
Under controlled conditions, the researchers then exposed these medium-sized ecosystems to varying amounts of GCFs (0, 1, 2, 4, or 6) for several weeks
.
Van Kleunen explains: "In our experiments, we selected GCFs
that do often act simultaneously on ecosystems, but differ greatly in their respective chemical and physical properties.
" In addition to the already mentioned GCFs (climate warming, light pollution and accumulation of fungicides), microplastic pollution, eutrophication (accumulation of nutrients in ecosystems) and soil salinization are other factors
studied.
The researchers found that as the number of simultaneous effects of GCFs increased, so did biomass production in plant communities
.

"The more GCFs, the more likely it is to contain high influencing factors such as eutrophication
.
In these cases, one can expect higher productivity due to the high availability of nutrients," explains
Speißer.
However, the researchers' analysis showed that interactions between other factors also contribute to this effect
.
In terms of plant community diversity, the researchers found that as the number of GCFs acting simultaneously on the community increased, species diversity in meso ecosystems declined – regardless of the quality of the factors involved
.
What's more, none of the GCFs studied had a negative impact
on diversity within the mesobiosphere when considered separately.
"This suggests that when multiple GCFs are working at the same time, new effects
may occur.
" van Kleunen concludes: "Given that the number and intensity of GCFs acting simultaneously are likely to increase in the future, it is important to
better study this 'multifactorial process' to avoid unpleasant surprises.
"