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

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

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...

Université de Fribourg

Including community composition in biodiversity–productivity models

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

In: Methods in Ecology and Evolution, 2014, vol. 5, no. 8, p. 815–823

Studies on biodiversity and ecosystem functioning (BEF) have elicited debate over the interpretation of the positive relationship between species richness and plant productivity. Manipulating richness cannot be achieved without affecting composition; it is thus essential to consider the latter in statistical models.We firstly review existing approaches that use species richness as an explanatory...

Université de Fribourg

Structure comparison of binary and weighted niche-overlap graphs

Sokhn, Nayla ; Baltensperger, Richard ; Bersier, Louis-Félix ; Ultes-Nitsche, Ulrich ; Hennebert, Jean

In: Complex Networks, 2014, vol. 5, p. 119–127

In ecological networks, niche-overlap graphs are considered as complex systems. They represent the competition between two predators that share common resources. The purpose of this paper is to investigate the structural properties of these graphs considered as weighted networks and compare their measures with the ones calculated for the binary networks. To conduct this study, we select four...

Université de Fribourg

Plant diversity in a nutshell: testing for small-scale effects on trap nesting wild bees and wasps

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

In: Ecosphere, 2014, vol. 5, no. 2, p. art18

Declining plant species richness in agro-ecosystems and thus reduced habitat quality can have cascading effects on ecosystem functioning, leading to reduced pollination and biological control. Here we test if plant diversity can affect arthropod diversity and abundance on a very small scale, manipulating plant species richness (2, 6, 12 and 20 sown species) in small adjacent subplots (6 × 9 m)...

Université de Fribourg

Sown wildflower strips for insect conservation: a review

Haaland, Christine ; Naisbit, Russell E. ; Bersier, Louis-Félix

In: Insect Conservation and Diversity, 2011, vol. 4, no. 1, p. 60-80

1. Sown wildflower strips are increasingly being established in European countries within agri-environmental schemes to enhance biodiversity, especially in intensively used agricultural areas.2. The regulations vary between countries regarding the seed mixture, intensity of management and period of time over which subsidies are given. Insects in particular are intended to benefit from these...

Université de Fribourg

Phylogenetic signal in predator–prey body-size relationships

Naisbit, Russell E. ; Kehrli, Patrik ; Rohr, Rudolf Philippe ; Bersier, Louis-Félix

In: Ecology, 2011, vol. 92, no. 12, p. 2183–2189

Body mass is a fundamental characteristic that affects metabolism, life history, and population abundance and frequently sets bounds on who eats whom in food webs. Based on a collection of topological food webs, Ulrich Brose and colleagues presented a general relationship between the body mass of predators and their prey and analyzed how mean predator–prey body-mass ratios differed among...