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Université de Fribourg

The feasibility of equilibria in large ecosystems: A primary but neglected concept in the complexity-stability debate

Dougoud, Michaël ; Vinckenbosch, Laura ; Rohr, Rudolf P. ; Bersier, Louis-Félix ; Mazza, Christian

In: PLOS Computational Biology, 2018, vol. 14, no. 2, p. e1005988

The consensus that complexity begets stability in ecosystems was challenged in the seventies, a result recently extended to ecologically-inspired networks. The approaches assume the existence of a feasible equilibrium, i.e. with positive abundances. However, this key assumption has not been tested. We provide analytical results complemented by simulations which show that equilibrium...

Université de Fribourg

The perfect mixing paradox and the logistic equation: Verhulst vs. Lotka

Arditi, Roger ; Bersier, Louis-Félix ; Rohr, Rudolf P.

In: Ecosphere, 2016, vol. 7, no. 11, p. e01599

A theoretical analysis of density-dependent population dynamics in two patches sheds novel light on our understanding of basic ecological parameters. Firstly, as already highlighted in the literature, the use of the traditional r-K parameterization for the logistic equation (due to Lotka and Gause) can lead to paradoxical situations. We show that these problems do not exist with Verhulst's...

Université de Fribourg

The relative contributions of species richness and species composition to ecosystem functioning

Sandau, Nadine ; Fabian, Yvonne ; Bruggisser, Odile T. ; Rohr, Rudolf P. ; Naisbit, Russell E. ; Kehrli, Patrik ; Aebi, Alexandre ; Bersier, Louis-Félix

In: Oikos, 2017, vol. 126, no. 6, p. 782–791

How species diversity influences ecosystem functioning has been the subject of many experiments and remains a key question for ecology and conservation biology. However, the fact that diversity cannot be manipulated without affecting species composition makes this quest methodologically challenging. Here, we evaluate the relative importance of diversity and of composition on biomass...

Université de Fribourg

Do spiders respond to global change? A study on the phenology of ballooning spiders in Switzerland

Blandenier, Gilles ; Bruggisser, Odile T. ; Bersier, Louis-Félix

In: Écoscience, 2014, vol. 21, no. 1, p. 79–95

We studied ballooning spiders captured weekly over an 11-y period using a 12.2-m- high suction trap in an agricultural landscape of western Switzerland. We analyzed population trends, changes in phenology, and species composition. Yearly trends in population size of the most abundant species were studied with nonparametric correlations. We found that these trends were markedly different for...

Université de Fribourg

Effects of temperature variability on community structure in a natural microbial food web

Zander, Axel ; Bersier, Louis-Félix ; Gray, Sarah M.

In: Global Change Biology, 2017, vol. 23, no. 1, p. 56–67

Climate change research has demonstrated that changing temperatures will have an effect on community-level dynamics by altering species survival rates, shifting species distributions, and ultimately, creating mismatches in community interactions. However, most of this work has focused on increasing temperature, and still little is known about how the variation in temperature extremes will...

Université de Fribourg

Persist or produce: a community trade-off tuned by species evenness

Rohr, Rudolf P. ; Saavedra, Serguei ; Peralta, Guadalupe ; Frost, Carol M. ; Bersier, Louis-Félix ; Bascompte, Jordi ; Tylianakis, Jason M.

In: The American Naturalist, 2016, vol. 188, no. 4, p. 411–422

Understanding the effects of biodiversity on community persistence and productivity is key to managing both natural and production systems. Because rare species face greater danger of extinction, species evenness, a measure of how similar abundances are across species in a community, is seen as a key component of biodiversity. However, previous studies have failed to find a consistent...

Université de Fribourg

Mismatch in microbial food webs: predators but not prey perform better in their local biotic and abiotic conditions

Parain, Elodie C. ; Gravel, Dominique ; Rohr, Rudolf P. ; Bersier, Louis-Félix ; Gray, Sarah M.

In: Ecology and Evolution, 2016, vol. 6, no. 14, p. 4885–4897

Understanding how trophic levels respond to changes in abiotic and biotic conditions is key for predicting how food webs will react to environmental perturbations. Different trophic levels may respond disproportionately to change, with lower levels more likely to react faster, as they typically consist of smaller-bodied species with higher reproductive rates. This response could cause a...

Université de Fribourg

Top predators affect the composition of naive protist communities, but only in their early-successional stage

Zander, Axel ; Gravel, Dominique ; Bersier, Louis-Félix ; Gray, Sarah M.

In: Oecologia, 2016, vol. 180, no. 2, p. 519–528

Introduced top predators have the potential to disrupt community dynamics when prey species are naive to predation. The impact of introduced predators may also vary depending on the stage of community development. Early-succession communities are likely to have small-bodied and fast-growing species, but are not necessarily good at defending against predators. In contrast, late-succession...

Université de Fribourg

Matching–centrality decomposition and the forecasting of new links in networks

Rohr, Rudolf P. ; Naisbit, Russell E. ; Mazza, Christian ; Bersier, Louis-Félix

In: Proc. R. Soc. B, 2016, vol. 283, no. 1824, p. 20152702

Networks play a prominent role in the study of complex systems of interacting entities in biology, sociology, and economics. Despite this diversity, we demonstrate here that a statistical model decomposing networks into matching and centrality components provides a comprehensive and unifying quantification of their architecture. The matching term quantifies the assortative structure in which node...