Nav: Home

Biodiversity hypothesis called into question

September 21, 2020

Biologists have long considered the origins and continued coexistence of the immense diversity of species found in our environment. How can we explain the fact that no single species predominates? A generally accepted hypothesis is that there are trade-offs, which means that no organism can do best in all conditions. One trade-off that is commonly assumed is that between gleaner organisms --which are able to acquire and consume more food than other species when resources are scarce-- and exploiters, which rapidly consume large quantities of the same resources when they are in abundance. However, when scientists from the University of Geneva (UNIGE) and the Technical University of Denmark (DTU) analysed the consumption of food resources of over 500 terrestrial and aquatic species, they showed that organisms that are efficient when there are low quantities of food, are also best when food resources are abundant. Consequently, biodiversity cannot be explained as a trade-off between gleaners and exploiters. Instead, the idea of risk taking to obtain food needs to be considered, as explained in this PNAS publication.

Dealing with trade-offs is one of the challenges organisms faces when they have to gain the energy needed to grow, defend themselves and reproduce. "If there were no trade-offs, the species that is the most effective in all conditions would come out on top," begins Mridul Thomas, senior research and teaching assistant in the Department F.-A. Forel for Environmental and Aquatic Sciences in UNIGE's Faculty of Sciences and the study's second author. "These trade-offs--and variations in environmental conditions--help explain why species are different and why we have diversity. No species can be best in all conditions."

Indeed, there is wide agreement in the scientific community that biodiversity can be explained partly through the gleaner-exploiter trade-off, which arises from the need to invest in both acquiring food and in quickly extracting energy and nutrients from it. Scientists expect organisms living in low-food environments to be gleaners that can quickly search for resources over large areas. Conversely, organisms living in food-rich environments are exploiters that consume resources in abundance and at great speed. Both these strategies can result in success depending on the environmental conditions encountered. And if the food availability changes through time or across space, it can allow competing gleaners and exploiters to co-exist, leading to diversity.

No gleaner-exploiter trade-off in nature

"Although it's taught commonly and is found in text books, there's little experimental evidence for the gleaner-exploiter trade-off," says Mridul. This is exactly the subject that Thomas Kiørboe, professor at the National Institute of Aquatic Resources at DTU--and first author of the study--decided to investigate. In an attempt to provide an answer, Professor Kiørboe has been collecting data found in the scientific literature on the food consumption of hundreds of species, derived from estimates from organisms ranging from single cells to large mammals living both in terrestrial and aquatic environments.

This immense collection of data has made it possible to analyse the speed at which over 500 species acquire and consume food. "For each species, such as a spider, scientists measured how fast it was able to capture and eat food, and they did this when food was abundant and when it was rare. Thanks to this valuable work by many scientists for hundreds of species, we were able to compare this across many organisms," continues Mridul. Curves of the speed of consumption as a function of the abundance of food are derived from this data, making it possible to describe the performance of the organisms in both low and high food conditions. "A negative correlation is expected from the gleaner-exploiter trade-off, but our results show a positive relationship", a clear indication, according to the biologist, that the gleaner-exploiter trade-off does not exist. Kiørboe and Mridul have demonstrated that species that perform well in an environment where energy resources are scarce are also the best in a rich environment.

Unexplained biodiversity

However, the researchers' interpretation does not call the concept of trade-offs into question. "Without trade-offs, it is very hard to maintain diversity. Our research does not explain biodiversity, but it does overturn an existing theory about precisely why we have biodiversity," says Mridul. Accordingly, there should be another trade-off: "A trade-off about risk-taking to access food is more likely, and would be consistent with our results. For instance, an organism may be better at getting food whether food is scarce or abundant because it takes more risks. Getting more food is generally good because it helps organisms grow and reproduce. But if in searching for food the organism gets eaten itself, it cannot reproduce. So it can sometimes be good to avoid taking these risks even if it means getting less food --which would explain why we see in our study that some species seem very good at getting food and some very bad at it." Whatever this other trade-off is, the Danish-Swiss study fundamentally changes an important idea about why we have biodiversity that is still being taught and has been taken for granted. It follows that our understanding of ecosystems must be revisited, since this knowledge is essential in the face of the environmental upheavals we are witnessing today.

Université de Genève

Related Biodiversity Articles:

Biodiversity hypothesis called into question
How can we explain the fact that no single species predominates?
Using the past to maintain future biodiversity
New research shows that safeguarding species and ecosystems and the benefits they provide for society against future climatic change requires effective solutions which can only be formulated from reliable forecasts.
Changes in farming urgent to rescue biodiversity
Humans depend on farming for their survival but this activity takes up more than one-third of the world's landmass and endangers 62% of all threatened species.
Predicting the biodiversity of rivers
Biodiversity and thus the state of river ecosystems can now be predicted by combining environmental DNA with hydrological methods, researchers from the University of Zurich and Eawag have found.
About the distribution of biodiversity on our planet
Large open-water fish predators such as tunas or sharks hunt for prey more intensively in the temperate zone than near the equator.
Bargain-hunting for biodiversity
The best bargains for conserving some of the world's most vulnerable salamanders and other vertebrate species can be found in Central Texas and the Appalachians, according to new conservation tools developed at the National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee, Knoxville.
Researchers solve old biodiversity mystery
The underlying cause for why some regions are home to an extremely large number of animal species may be found in the evolutionary adaptations of species, and how they limit their dispersion to specific natural habitats.
Biodiversity offsetting is contentious -- here's an alternative
A new approach to compensate for the impact of development may be an effective alternative to biodiversity offsetting -- and help nations achieve international biodiversity targets.
Biodiversity yields financial returns
Farmers could increase their revenues by increasing biodiversity on their land.
Biodiversity and wind energy
The location and operation of wind energy plants are often in direct conflict with the legal protection of endangered species.
More Biodiversity News and Biodiversity Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Sound And Silence
Sound surrounds us, from cacophony even to silence. But depending on how we hear, the world can be a different auditory experience for each of us. This hour, TED speakers explore the science of sound. Guests on the show include NPR All Things Considered host Mary Louise Kelly, neuroscientist Jim Hudspeth, writer Rebecca Knill, and sound designer Dallas Taylor.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

Kittens Kick The Giggly Blue Robot All Summer
With the recent passing of Ruth Bader Ginsburg, there's been a lot of debate about how much power the Supreme Court should really have. We think of the Supreme Court justices as all-powerful beings, issuing momentous rulings from on high. But they haven't always been so, you know, supreme. On this episode, we go all the way back to the case that, in a lot of ways, started it all.  Support Radiolab by becoming a member today at