Sujet: Status and trends

Setting appropriate conservation strategies is a challenging goal, especially because of the complexity of threats and responses from species, and budget limitations. To overcome this challenge, the team of scientists, including researchers from CNRS, IFREMER, IRD and international organizations, has simulated the response of species communities to a wide range of disturbances, providing a robust estimation of their vulnerability, in a world where future threats are diverse and difficult to predict.

Quantifying the vulnerability of biodiversity is crucial to safeguard the most threatened ecosystems. Published in Nature Communications on the 1^st of September 2022, this new tool stands out from previous work as it estimates the degree to which functional diversity, that is biodiversity and associated ecosystem functions, is likely to change when exposed to multiple pressures. It was developed as part of two projects funded by the French Foundation for Research on Biodiversity (FRB) within its Centre for Biodiversity Synthesis and Analysis (CESAB) and with the support of Electricité de France (EDF) and France Filière Pêche (FFP).

The team of 20 scientists used repeated computer simulations of disturbances on species communities to calculate the ecosystem’s vulnerability. From climate change and land use changes to pollution or resource overexploitation, these disturbances simulate the impacts of a large range of potential threats on species communities. “By simulating all possible scenarios, even the worst ones, explains Arnaud Auber, researcher at IFREMER and first author of the publication, we are able to identify the most vulnerable ecosystems from a functional view-point. Moreover, we can now estimate their vulnerability by taking into account unknown, unpredictable or poorly documented pressures, which is a major advance over previous work.” This safer approach offers decision-makers the possibility to classify various sites according to their associated functional vulnerability, which is now urgently needed to move forward adaptive management of biodiversity.

In this study, the functional diversity of communities was made central to the calculation of vulnerability. Overall, biodiversity conservation has mainly focused on taxonomic diversity (e.g., the number of species in an ecosystem). However, recent studies including work from the FREE project, have shown that examining functional diversity can provide a more precise assessment of whether or not an ecosystem is functioning properly. Indeed, a species may have the same function as another (e.g. the same preys or reproductive cycle) and so if one species disappears, another may still fulfil its role in the ecosystem. But if all species sharing the same essential function disappear, the ecosystem will become less functionally diverse, less resilient to threats and thus more vulnerable. In other words, taxonomic diversity in an ecosystem is important but not sufficient to properly assess ecosystem vulnerability. Parrotfishes for example, are one of the only fish species that can directly feed on corals. If they disappear, an essential component of the carbon cycle in coral reefs will be lost. Functional and taxonomic diversity are therefore complementary and should be used together to better guide decision-makers in identifying priority areas for biodiversity protection.

This new approach can be applied to all ecosystems, whether marine, terrestrial or freshwater. “As an example, explains Arnaud Auber, we applied our functional vulnerability framework to the past temporal dynamics of the North Sea fish community. Using fish abundance data and species traits linked to ecosystem functioning such as fecundity, offspring size and feeding mode, our tool revealed a high functional vulnerability of fish communities in the North Sea. However, we found a significant decrease in functional vulnerability throughout the last four decades, dropping from 92 to 86%. During the same period, the North Sea fishing pressure had decreased, following the Common Fisheries Policy, with a progressive decrease in catch quotas and improvement in gears’ selectivity.”

Finally, this tool is open access and can be used to predict ecosystem vulnerability using for example future climate change scenarios or to compare different ecosystems. This highlights the need for synthesis as we continue to improve our understanding of the complexity of nature. Only when put together will data and knowledge help quantify the impact of multiple threats on the world’s ecosystems and assist decision-makers in rationalizing ecosystem management and conservation actions in an uncertain future.

Reference

Arnaud Auber¹, Conor Waldock^2,3, Anthony Maire⁴, Eric Goberville⁵, Camille Albouy^6,7, Adam C. Algar⁸, Matthew McLean⁹, Anik Brind’Amour¹⁰, Alison L. Green¹¹, Mark Tupper^12,13, Laurent Vigliola¹⁴, Kristin Kaschner¹⁵, Kathleen Kesner-Reyes¹⁶, Maria Beger^17,18, Jerry Tjiputra¹⁹, Aurèle Toussaint²⁰, Cyrille Violle²¹, Nicolas Mouquet^22,23, Wilfried Thuiller24, David Mouillot^23,25. “A functional vulnerability framework for biodiversity conservation”. 2022. Nature Communications. doi: https://doi.org/10.1038/s41467-022-32331-y/

People depend on lakes for many ecosystem services such as water, food, transportation, and recreation, but these services are at an unknown level of risk because we do not understand how lakes are affected by climate change. A network of 39 scientists from 20 countries on five continents are collaborating to put long-term and high-frequency data to work to understand, predict, and communicate the role and response of lakes in our changing global environment. This work was partly funded by the John Wesley Powell from U.S. Geological Survey and the Foundation for Research on Biodiversity (FRB), through the research projects GEISHA of the FRB’s Center for Biodiversity Synthesis and Analysis (CESAB).

Many of the scientists hypothesized that storms would have strong impacts on water temperature and water column mixing, based on a prior synthesis study. However, the team’s most recent study found that wind- and rainstorms do not cause major temperature changes in lakes.

They examined how wind- and rainstorms affected lake temperature across 18 lakes and 11 countries using meteorological and water column temperature data and found minimal changes to lake temperature from storms. In fact, they found that day-to-day changes in lake temperature during non-storm periods were often more extreme than storm-induced temperature changes. As expected, storms impacted the temperature of deep lakes less than shallow lakes because more energy is needed to mix layers of water with different temperatures in deep lakes than in shallow lakes. For example, storm-induced temperature changes in Lake Superior (average depth almost 500 feet) will be smaller than in Lake Okeechobee (average depth about 10 feet).

A storm rolls over Lake Superior. Photo credit: Jessica Wesolek, Lake Superior State University’s Center for Freshwater Research and Education

“Because storm-induced changes to lake temperature were minimal overall, storm-induced changes in other environmental conditions such as nutrient concentrations or light may have larger impacts on lake animals and plants,” said Jonathan Doubek, Assistant Professor at Lake Superior State University in the School of Natural Resources & Environment and the Center for Freshwater Research and Education, who joined the network while at the University of Vermont. These findings represent concrete progress in understanding how lakes are weathering storms.

“Professor Doubek’s study highlights the usefulness of high-frequency data: we were able to discover that the effect of storms on lake temperatures may not be as strong as we previously believed,” said Dr. Jason Stockwell, Professor and Director of the Rubenstein Ecosystem Science Laboratory at the University of Vermont.

The team of scientists has begun analyzing the impact of storm-related changes in nutrient concentrations and light availability on organisms using the same global dataset and has recently had a proposal funded to help continue this work into the future. “The power of global collaborative teamwork to pool data and ideas is improving our understanding about how our planet functions and may function in the future,” Stockwell said. “We need this information to protect ecosystem and human health.”

It has long been thought that rare species contribute little to the functioning of ecosystems. Yet recent studies have discredited that idea: rarity is a matter not only of the abundance or geographical range of a species, but also of the distinctiveness of its ecological functions. Because these functionally distinct species are irreplaceable, it is essential we understand their ecological characteristics, map their  distributions, and evaluate how vulnerable they are to current and future threats.

Using two databases that collect information on the world’s terrestrial mammals (4,654 species) and birds (9,287 species), scientists from the FRB’s Centre de Synthèse et d’Analyse de la Biodiversité (CESAB), CNRS research laboratories, Université Grenoble Alpes, the University of Montpellier, and partner institutes divided the earth’s surface into 50 × 50 km squares and determined the number of ecologically rare species within each. They showed that ecological rarity among mammals is concentrated in the tropics and the southern hemisphere, with peaks on Indonesian islands, in Madagascar, and in Costa Rica. Species concerned are mostly nocturnal frugivores, like bats and lemurs, and insectivores, such as small rodents. Ecologically rare bird species are mainly found in tropical and subtropical mountainous regions, especially in New Guinea, Indonesia, the Andes, and Central America. The birds in question are essentially frugivorous or nectarivorous, hummingbirds being an example. For birds and terrestrial mammals alike, islands are hotspots of ecological rarity.

The researchers also ranked these species according to their IUCN Red List status¹ and found they made up the bulk of the threatened species categories. That is, ecologically rare mammals account for 71% of Red List threatened species (versus 2% for ecologically common mammals); and ecologically rare birds, 44.2% (versus 0.5% for ecologically common birds). For each species, they determined (i) anthropogenic pressure exerted; (ii) human development indexes (HDIs) of host countries; and (iii) exposure to armed conflicts. The last two of these elements shape conservation policies. The scientists observed that  human activity had a greater impact on ecologically rare mammals and birds than on more common species, and that these rare species were found in countries of every kind of profile, irrespective of HDI or the prevalence of warfare² They used models to demonstrate that ecologically rare species will be the greatest victims of climate change, many of them facing extinction within 40 years.

This profiling of ecologically rare species makes it clear that current conservation efforts, even in zones already protected, are insufficient. Conservation strategies still too often ignore functional distinctiveness and focus instead on population sizes. But it is essential to take this distinctiveness into account, letting this knowledge guide steps taken to protect these rare species. As they are necessary for healthy ecosystems, a true paradigm shift in conservation policy is needed to ensure their survival.

For more information... some examples of ecologically rare species

[1] The International Union for Conservation of Nature (IUCN) is a leading international NGO focused on nature conservation. It evaluates the risk of extinction faced by different species, assigning each to a particular category (e.g., ‘Least Concern’, ‘Near Threatened’, ‘Vulnerable’, ‘Endangered’, or ‘Extinct’).

[2] For example, the Philippines, where HDI is low and armed conflicts prevalent, are a hive for ecologically rare species (19 terrestrial mammals and 15 birds). Yet Australia, where HDI is high and armed conflict rare, is also home to many ecologically rare species (10 terrestrial mammals and 10 birds).