MegaBiCycle - Megafauna and Biogeochemical Cycles
Up until 12,000 years ago, the megafauna (large terrestrial mammals with body mass > 100 kg), occupied every continent and sported high biodiversity. After that time, most of these giants quickly became extinct, and now the remnants of those communities can be observed only in the African savanna. The causes of this extinction (AKA late Quaternary megafauna exctinction) have been debated for over four centuries, and still remain unclear (SPOILER: humans likely played a key role). The ecological consequences of this extinction have been studied only recently, but evidence shows that the disappearance of large animals had significant effects on ecosystems with indirect effects on climate.
During the MegaBiCycle project I will investigate the causes and consequences of the extinction of large herbivores to understand the ecological role of megafauna at the global scale. I will cover distinct historical periods: from the past (120,000 years ago), when megafauna were globally widespread, through the Last Glacial Maximum (26,000 year ago), and on to the present when megafauna persists in a few places and have been introduced in others. This project aims at evaluating the importance of megafauna for ecosystem services and the implications for their present and future conservation.
I will use a dynamic global vegetation model (ORCHIDEE) to test hypothesis on the effect of past and present changes in megafauna populations on a) plant primary productivity and carbon cycling, b) greenhouse gases fluxes (methane and nitrous oxide), and c) any possible consequences on climate. The goal of MegaBiCycle is to advance our understanding of the connection between climate, biosphere, and megafauna and provide new insights into the role of megafauna in past, present, and near future global changes.
Plant trait variability
Plants constantly adapt to environmental changes through plastic responses. These adaptions to changes in climate, weather, and competition, can happen on short, weekly/monthly, and long time-scales, years/generations. This variability in plant traits is a fundamental mechanism driving eco-evolutionary processes and is key to understanding how plants respond and evolve to environmental changes. Through a collaboration with other researchers from Europe and Ian Wright from Macquarie University, we are developing new approaches to better integrate plant trait variability in dynamic vegetation models. The goal is not only to use these improved models to better understand plant ecology, but also to evaluate how plants will respond to ongoing climatic changes. To do so we are considering concepts from eco-evolutionary and quantitative genetics studies. Another goal of this project is to make better use of the trait data available in databases such as TRY, which have not been fully exploited in vegetation modelling.
Animals in vegetation models
Vegetation models are an important tool that I use to study the role of animals in ecosystems. However, vegetation models have been developed to study vegetation dynamics and plant ecology, and animals are not usually included in these models because a) the complexity of describing animal behavior and b) the effect of animals was deemed negligible. More and more research is showing that animals play an important role in the functioning of ecosystems, and that by simulating "empty" forests or grasslands, we are missing some key processes performed by animals. During my PhD, by combining knowledge from zoology and plant-animal interactions, I described methodological approaches to incorporate animals in vegetation models. Now I am continuing this project by developing a global classification of mammalian herbivores, which will allow to pair herbivore types with the corresponding plant type. This classification will allow me to study biome-specific herbivore-plant interactions at the global scale using a global vegetation model.
Seed masting is the synchronous and periodic production of large amount of seeds in some plant species. Masting has important implications not only for plants but also for animals, yet we have limited knowledge on the mechanisms controlling masting and its functions in the ecosystem. I joined an international group of researchers to work on this topic, part of the EU PROFOUND COST Action, a large collaborative research network. This collaboration resulted in a publication, and we are now building a large masting dataset to study the effects of masting on forests across space and time.
Previous research projects
Large mammal populations are rapidly declining in tropical regions. Animals such as elephants, primates, and ungulates are illegally and unsustainably hunted for meat and ivory. These animals provide several ecosystem services to tropical forests such as seed dispersal and nutrient cycling, which benefit the forests and other animals. What are the consequences of their decline? During my PhD I studied the role that large mammals play in the dynamics of tropical forests, particularly in regards to seed dispersal and disturbance.
Disturbance by large animals: Elephants are the largest terrestrial animal and have the potential to shape ecosystems in various ways. However, little is known on their ecosystem engineer effect in the tropical forests of the Congo Basin, the second largest rainforest in the world. My goal was to determine the effect of elephant disturbance in the Congo Basin, and its consequences for above-ground biomass and forest composition. I used a dynamic vegetation models called Ecosystem Demography to study how elephants, by trampling and killing small trees, change forest succession and tree species composition.
Seed dispersal: The seeds of most tropical forest trees are dispersed by animals such as birds and mammals, whose populations are declining in the tropics. Field studies have shown that the loss of these seed disperers can significantly affect the recruitment of new trees with changes in tree species composition, tree biodiversity, and carbon stocks. So far, we mostly know about the short-term effects of defaunation, but much less is known about the long-term consequences. In this project I explored how the loss of tropical mammals, including seed dispersers and predators, will affect forest structure and species composition over long time scales (> 50 years). To do this I am using a forest model called TROLL, developed by Isabelle Maréchaux and Jerome Chave, and collaborating with Pierre-Michel Forget who has been working on seed ecology for many years.
In 2010, a group of ornithologists from the Field Museum of Natural History in Chicago, described a new species of bush-strike, Willard's Sooty Boubou (Laniarius willardi), found only in the Albertine Rift in East Africa. John Bates, the bird curator at the Field, asked me if I could help them understand where in the Albertine Rift this new species might be more likely to occur, compared to its sister species Mountain Sooty Boubou (Lanarius poensis). We were wondering how much habitat was left for this newly described species, which lives in mid-elevation forests, and what would be the implication for its conservation status. We published a paper and a blog post about this project.
At Aarhus University I worked on a project to assess the impact of human activities on fish, sea birds, and marine mammals in the Arctic Ocean on the west coast of Greenland. We combined data from many different sources, from ship GPS tracks, fish surveys, climate data, and more. We created maps for each animal species to assess which are at higher risk and determined the human activities underlying this risk. We published a peer-reviewed article and a scientific report for the Nordic Council of Ministers.
"You are what you eat". The diversity and abundance of microflora in mammals' guts are highly correlated with their physical and mental state. This has been shown in humans but less in animals. I ran a short pilot project aimed at testing the correlation between dietary stress in caribou and the abundance of gut microflora. Dietary stress was assessed from glucocorticoid hormones levels in caribou feces, which were also used to extract DNA of two species of common gut bacteria. The results showed that individuals with lower dietary stress had slightly higher relative abundance of bacteria. Promising results that require more analysis.
The history and management of the Yellowstone Bison population is a complex socio-ecological issue involving many stakeholders. One of the key management issues is that in the winter, bison try to migrate outside the Yellowstone National Park boundaries and into private/grazing lands. I developed a small project using GIS and remote sensing data trying to find alternative winter migration routes that could lead to public land to avoid conflicts with private land owners. I presented the preliminary results of this project at the American Geographers conference in 2012.