focus
Nadja Neumann

Is biodiversity being viewed in the right light?

Anyone who discusses the importance of biodiversity quickly ends up in a debate about values shaped by ethics and economics. Seven IGB scientists draw attention to aspects that are still often overlooked. They research genetic diversity, interactions between different species and across ecosystems, biological invasions and the smallest and most diverse organisms that colonise freshwaters.

Erdkrötenkaulquappen im Stechlinsee. I Foto: Solvin Zankl

Mr De Meester, to put it bluntly, is biodiversity valued in the "right" way and are the international goals for its protection - such as in the UN Convention on Biological Diversity (CBD)also adequate?

The bar should be higher. It is also an exceedingly difficult exercise, as one needs to have criteria that can be evaluated and checked – and this is indeed very important in the context of international conventions. Yet the problem is that numbers alone do not capture well what is at stake. To be on the safe side one should probably protect a substantial portion of land, freshwaters and marine areas of different types globally – likely in the order of 30 to 50%. But that is a huge challenge. Let’s hope that we move closer and closer to this bold ambition, for now using more detailed criteria that are suitable for reporting, but might miss part of the essence, as is evident from the data showing a continued decline in biodiversity. Let us not forget what is at stake: biodiversity is crucial, also in the context of providing resilience in the fact of global change. There will be a major transition necessary to change the trajectory of loss. A biodiversity check of all policies, similar to a climate check, would be a major step forward. The challenges to biodiversity and natural ecosystems are indeed daunting and multifaceted, linking to agricultural practices, urbanization, pollution, atmospheric deposition, warming, overharvesting, … Many of the killers are hidden, and may link to, for instance, a cocktail of substances that in isolation all meet the criteria set by authorities. It will need a fresh look at our priorities to get this solved.  

Ms Jähnig, species diversity is part of biodiversity, i.e. biological diversity. When it comes to the inherent value of biodiversity, larger animals are often considered worthy of special protection. Your field of research is the megafauna in aquatic ecosystems in other words, the large and usually charismatic animals. What is your opinion on this approach?

Well, it is quite human to perceive animals differently. Most people probably feel more empathy for a panda than for a mosquito. So, in order to draw attention to biodiversity, it is quite an established way to select so-called flagship species to convey certain aspects – like the biodiversity crisis. For freshwaters, however, there are so far only a few comparably prominent species like the panda - perhaps at the regional level the sturgeon or the river dolphin.

From a scientific point of view, there is also a case for protecting the large species. Large animals often have a complex life cycle and a lower reproduction rate than smaller creatures. This makes them particularly vulnerable to environmental changes. So, if the conditions and goals are targeted towards protecting the sensitive "big ones" as umbrella species, very often the smaller, inconspicuous species will also benefit.  However, this approach also has its limits – for example, in very local or small ecosystems such as ponds or springs where no large fish occur. Accordingly, small or inconspicuous species can also qualify as umbrella and flagship species. And there is one more aspect I would like to mention: Which species have large "flagship potential" and also to what extent the aforementioned umbrella effect works is especially in freshwater still largely unclear.

An inherent aspect of biodiversity is genetic diversity. Mr Stöck, your research includes how genetic diversity changes through interactions between species and populations. In your opinion, what shows particularly well the importance of high genetic diversity for evolution?

The destruction of the biosphere by our species – also called "the sixth mass extinction"  – obviously leads to a loss of species. What is less obvious is that there is also a loss of genetic diversity within species, resulting in less and less genetic variation in populations and subpopulations. This generally reduces the evolvability of species – their ability to adapt genetically to environmental changes. This threatens the "buffering capacity" of living organisms and ecosystems against biotic and abiotic changes. While the loss of species makes ecosystems more vulnerable, depauperating genetic diversity will most likely decrease the adaptive capacity of species – and make both even less resilient to anthropogenic change. Therefore, conservation of genetic diversity safes evolvability and strongly contributes to ecosystems resilience. 

Ms Govaert, you investigate how ecological and evolutionary processes influence species communities and their response to environmental change. Does biodiversity make the world more resilient to future changes?

When the environment changes, species have three response options: die, move or adapt. For those that survive, depending on the speed of environmental change, we find a combination of species expanding their native range and showing an adaptive response. Research into these ecological and evolutionary responses of species to environmental change is currently shifting from a population- to a community-level focus, taking species diversity and species interactions into account. Little is yet known about how species respond within a biodiverse community consisting of many other species, all responding simultaneously to a changing environment. Theoretical studies have shown that the presence of other species can both accelerate and inhibit the evolutionary response to environmental change. Empirical work also demonstrates that interactions between species can indeed alter evolutionary responses to environmental change. Moreover, evidence suggests that there is a link between the ability of species to adapt to environmental change and ecosystem resilience. For example, the adaptive evolution of macrophytes in a shallow lake can increase ecosystem resilience by delaying the transition from clear water to turbid water. However, such evolution also leads to a slower recovery of the system after the turbid state has occurred.

Mr Jeschke, one of your research areas is invasive species, i.e. species that open up new areas and come into contact with native species there. Dealing with these species is controversial, and their damage is often quantified in monetary terms. But asked quite banally: don't they increase biodiversity, and is there perhaps a double standard?

My simple answer is no, but this is a complex issue, also because there are different meanings of key terms in this context. These can lead to misunderstandings and sometimes very heated discussions. Therefore, it is helpful to agree on a terminology, or at least understand each other's terminology, especially in multi-stakeholder discussions. For example, "alien species" can be defined as species that have been intentionally or unintentionally introduced by human action into areas beyond their native range. "Invasive species" can be understood as a subset of alien species: While many alien species do not have negative impacts in their new environment, some do – these species are invasive. While they are also living organisms, they pose a serious threat to biodiversity. This particular situation sometimes leads to a dilemma when dealing with invasive species: to protect biodiversity, one may have to act against living organisms. In such a situation, it is not easy to decide whether and which management measures to take. Therefore, management decisions should be made for each individual case and after careful consideration of the relevant aspects and perspectives.

A hot topic in ecology is the connection between biological diversity and the functioning of ecosystems. Some examples show that various aspects of biodiversity promote the maintenance of important ecosystem processes, above all the production of plant biomass. Mr. Gessner, you recently co-authored a paper which makes the point that effects of biodiversity of one ecosystem can influence such processes also in other ecosystems. Does this recognition provide a new impetus to the debate on values?

The relationship between biodiversity and ecosystem functioning has now been analyzed and increasingly established for more than a quarter century. Our paper offers a new view on the topic by proposing to look at biodiversity effects not only within well-defined ecosystems, but also across ecosystem boundaries, for instance between streams and forests or between forests and agricultural fields. This extension also broadens the perspective of the debate on the value of biodiversity. The reason is that the multitude of services that ecosystems provide to humans are often closely tied to ecosystem processes. In other words, the recognition that the rapid loss of biodiversity we currently face entails changes in ecosystem functioning and services adds a strong utilitarian reason to the ethical argument about the intrinsic value of biodiversity. So, yes, if such cross-ecosystem biodiversity effects on ecosystem processes turn out indeed to be important, then the case for preserving and restoring biodiversity is further strengthened.

Mr Grossart, you study microbes in the water that play an important role in matter cycling. And you are also dedicated to aquatic fungi, which hardly anyone outside of science knows about. Why are these small organisms so fascinating and important? And does diversity also play a role with them?

The smallest organisms are often hard to see by naked eye, and even under the microscope they usually all look the same. Bacteria and fungi, however, make up the largest part of biological diversity in all ecosystems; with millions of species still waiting to be described. More importantly, microorganisms are at the base of each food web and contribute to an essential ecosystem function by remineralising organic matter, keeping nutrients and other compounds in the production loop. In addition, as parasites they can influence both phytoplankton and zooplankton and other organismic secondary producers – and thus the flow of organic matter and energy in the food web. In microorganisms, phylogenetic biodiversity is particularly linked to functional diversity. This can be illustrated with the following example: Humans have about 15,000 functional genes, while the bacteria associated with humans on our skin or in our bodies contain a total of up to 1.5 million functional genes. This shows the enormous range of functions driven and maintained by microbes. Although microbes are so critical to ecosystem functioning and our health, little is known about whether we will lose key species as a result of global change and how this might affect the functioning and therefore the health of our natural environment. At least for fungi, there is evidence that current environmental changes are leading to the loss of key species and thus ecosystem functions. So, we urgently need a Red List for microorganisms to ensure further environmental and hence human health.

Selected publications
Contact person

Sonja Jähnig

Head of Department
Research group
Aquatic Ecogeography

Matthias Stöck

Research Group Leader
Research group
Evolutionary Biology and Ecotoxicology of Amphibians and Fish

Lynn Govaert

Research Group Leader
Research group
Eco-Evolutionary Dynamics

Mark Gessner

Head of Department
Research group
Ecosystem Processes

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