Dispersion is an essential biological process for the survival of individuals and species. A UCLouvain research team led by Nicolas Schtickzelle, professor of ecology and biodiversity at the Earth and Life Institute, recently published the results of two concomitant studies on dispersion in the prestigious journals PNAS and Nature Ecology and Evolution.
Go elsewhere, settle, reproduce. Originally, several reasons spurred this need for movement: a lack of food, needing a place to make a home, finding a partner, seeking better temperatures, etc. ‘It’s local conditions that first and foremost influence dispersal’, explains Prof. Schtickzelle. ‘Everything the organism needs to complete its life cycle but cannot find in its place of origin—this can motivate an individual to leave in the hope of finding it elsewhere. Things he wants to avoid, such as inbreeding, can also push an individual to move. In fact, the individual evaluates the chances of reproducing here rather than elsewhere, the risks associated with moving (loss of time, risk of getting lost or meeting a predator, etc.), weighs the pros and cons, then decides whether to see if the grass is greener elsewhere.’
Dispersal is therefore an essential biological process for the survival of species, especially in today's landscapes that are increasingly fragmented by human activity. The movement of individuals far from their place of origin makes it possible to occupy new habitats created, for example, by fire, logging, abandoned fields, etc.
Studying dispersal to predict the consequences of climate change
The UCLouvain team led by Prof. Schtickzelle focused on the study of unicellular microorganisms called ciliates, in microcosm under controlled laboratory conditions. ‘Using their tiny cilia, these cells can move, and disperse, under their own power and be easily observed’, the professor explains. ‘Studying them in the laboratory allows for experiments that are impossible in natural conditions’. Now their work has been recognised by two publications.
In an article in the prestigious journal PNAS, written in collaboration with researchers from the CNRS Station for Theoretical and Experimental Ecology in Moulis (France), Prof. Schtikzelle’s team reveals the fruit of several years’ work led by Dr Staffan Jacob. ‘What interested us was to understand the impact of temperature variations on the dispersion of these living organisms, because an adequate temperature is one of the indispensable resources for the healthy development of living organisms. It therefore impacts the dispersal of individuals, as we had shown in a previous study. Temperature has become a key parameter for species in the context of climate change.’ Prof. Schtikzelle says.
Ciliates include ‘generalists’, which tolerate a greater range of temperature, and ‘specialists’, which seek a temperature perfectly ideal for their development. ‘Faced with a choice between two temperatures, the specialists choose, as expected, a habitat whose temperature is optimal for them’, the researcher observes. ‘But generalists tend to choose the habitat whose temperature is sub-optimal for them’.
Among Tetrahymena thermophila ciliates, the most specialised individuals prefer the optimal temperature (which maximises their performance), whereas generalists prefer sub-optimal temperatures (photo: Alex Stemm-Wolf).
The reason behind this amazing observation? Generalists opt for a less favourable temperature in order to avoid specialists. Computer simulations have shown it to be the best choice, because at their optimal temperature the generalists would suffer too much from competition with the specialists who are also present.
‘The dispersion of species in natural landscapes is therefore much less random than had long been thought: individuals do not move at random’, Prof. Schtickzelle says.
Repartition of the European bee-eater spreads more and more North.
Temperature as a driver of dispersion
More and more species are now dispersing to the North. In Great Britain, studies compare insect dispersal maps of insects such as dragonflies and locusts: in 20 years, many species have extended their range to the north. ‘In Belgium, too, we see species arriving from the south’, Prof. Schtickzelle notes. ‘The magnificent European bee-eater and the scarlet dragonfly are two examples. Although other factors, such as landscape changes, influence the distribution of species, global warming is a very strong candidate for explaining these species movements. And it’s dispersion that allows individuals to perform these movements.’
While there is no direct prediction of how climate change will affect the dispersal of all species, these results are a further contribution to formulating one. They show that temperature can ‘guide’ dispersion; if ciliates do it, it’s reasonable to imagine that many species can do it too. Synthesising the cumulating laboratory studies on clearly defined species will make prediction possible, which is crucial to anticipating climate change challenges for biodiversity.
Trying out this study model on the ground ‘is the next ideal step,’ Prof. Schtickzelle concludes, ‘but it’s complex to implement. This can only be possible if we manage more effectively the multiple environmental factors in the field. Which is far from easy.’
|Predators and food, choice criteria
Published in Nature Ecology and Evolution, a second study is the result of a collaboration between several European laboratories, in which Prof. Schtickzelle's team participated. ‘This broad coordinated experiment made it possible to generalise studies, such as those we conducted at our Belgian scale, with others’, he explains. ‘The same experimental design was implemented for 21 species. Some laboratories worked on butterflies, others on lizards, we worked on ciliates...Using a simple scheme common to everyone, we were able to achieve more generalisable results on the dispersion of species. In habitats, this dispersal is governed by the presence of predators and food. A new community conception of ecological research is emerging. This type of study published "back-to-back" is the perfect illustration.’(M.D)
A glance at Nicolas Schtickzelle's bio
In 1997, Prof. Nicolas Schtickzelle finished biology studies at UCLouvain and started a PhD in Biology. In 2003, he became a postdoctoral researchers in different labs before obtaining a permanent research position as “Chercheur Qualifié FNRS” in 2007. At that time he took the lead of the UCLouvain Quantitative Conservation Biology research group. Since 2008, he has been a member of the Alumni College of the Royal Academy of Belgium. From 2010 to 2016, he was president of the UCLouvain Biodiversity Research Centre. His research is funded mainly by the FNRS and UCLouvain.
A glance at Staffan Jacob's bio
After a master’s degree and PhD in biodiversity, ecology and evolution at Université Paul Sabatier in Toulouse, France, Dr Staffan Jacob completed a postdoctorate at the CNRS Station for Theoretical and Experimental Ecology in Moulis (France). He completed another postdoctorate in 2016 at UCLouvain's Earth and Life Institute, joining Prof. Nicolas Schtickzelle's team via a ‘Move-In Louvain’ grant. Since 2018, he has been a postdoctoral researcher at the CNRS Station for Theoretical and Experimental Ecology in Moulis. Dr Jacob's research was funded mainly by the FNRS, UCLouvain, and the CNRS.