Résumé
Responses of ecosystems to modifications of their environmental conditions are usually considered in terms of biodiversity or function. Maybe because they represent a hidden part of ecosystems, responses of ecological interactions are rarely studied. A more comprehensive view of the processes underlying the restructuring of food webs under environmental gradients appears crucial to understand how ecosystems functionalities are altered. We address this general issue in an experiment where trophic interactions are reorganized under a gradient of top–down effects (predation pressure) and bottom–up effects (nutrient availability). Unimodal relationships of species diversity are pervasive in ecology; we extend this principle to food-web topology: in our study, most topological descriptor values peak at intermediate predation intensity. The same unimodal pattern holds for network complexity, measured by entropy and scaled entropy (a measure independent of species diversity). Moreover, food web complexity is maximized at higher fish abundance when nutrient availability is increased. We infer that whereas in absence of top predators, a mechanism of competitive exclusion takes place, and indirect facilitation process underlies systems with a moderate predation pressure. These results highlight the importance of the dynamic reorganization of trophic links in response to bottom–up and top–down effects. Interaction between bottom–up and top–down forces argue for multifactorial studies of ecological effects.
Auteurs, date et publication :
Auteurs Benoit Gauzens , Stéphane Legendre , Xavier Lazzaro , Gérard Lacroix
Publication : Oikos
Date : 2016
Volume : 125
Issue : 4
Pages : 595-603
Catégorie(s)
#CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs Kejun Zou , Elisa Thébault , Gérard Lacroix , Sébastien Barot , Shawn Leroux
Publication : Functional Ecology
Date : 2025
Volume : 30
Issue : 8
Pages : 1454-1465
Catégorie(s)
#CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs LoïC Harrault , Beatrice Allard , Michael Danger , Florence Maunoury-Danger , Alexis Guilpart , Gerard Lacroix
Publication : Freshwater Biology
Date : 2025
Volume : 57
Issue : 11
Pages : 2390-2400
Catégorie(s)
#CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs Loïc Harrault , Béatrice Allard , Jacques Mériguet , David Carmignac , Samuel Perret , Sylvain Huon , Eric Edeline , Gérard Lacroix
Date : 2025
Volume : 15
Catégorie(s)
#⛔ No DOI found #CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs Béatrice Allard , Michaël Danger , Loïc Ten-Hage , Gérard Lacroix
Publication : Aquatic Sciences
Date : 2025
Volume : 73
Issue : 1
Pages : 113-126
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Eutrophication and climate change have increased the frequency of hypoxic conditions in the
hypolimnia of lakes and reservoirs worldwide. Hypoxia can alter zooplankton migration from
vertical to horizontal because zooplankton require oxygen for respiration, and thus may be forced
to littoral refuge during the day. Fish communities can also affect zooplankton migration as well
as zooplankton community composition and size structure. However, the interaction of fish
communities and hypoxia on zooplankton migration has not been studied. We tested the
hypothesis that zooplankton exhibit more extensive (greater magnitude) vertical and horizontal
migration when piscivores are rare than when they are abundant, and also under hypoxic vs. oxic
hypolimnetic conditions. We sampled zooplankton and other environmental variables across six
consecutive days and nights during summer 2019 in a 16-lake experimental system, as part of
AQUACOSM. Half of the artificial lakes received a fertilization treatment with N and P
(eutrophic lakes with hypolimnetic hypoxia), and lakes were manipulated in order to enrich half
of them with European Perch (potentially piscivorous), and to reduce perch individuals in the
other lakes (all lakes had planktivorous Roach). Zooplankton were sampled in the epilimnion and
hypolimnion of the open water habitat and just outside and inside of the vegetated littoral zone.
We will report on the effects of fish communities and dissolved oxygen conditions on
zooplankton density and biomass in littoral vs. pelagic zones, and their diel vertical and
horizontal movements.
Auteurs, date et publication :
Auteurs J. P. Doubek , R. J. Chapina , S. Fiorini , S. K. Goldfarb , G. Lacroix , H. L. Wander , J. D. Stockwell
Date : 2025
Catégorie(s)
#⛔ No DOI found #CNRS #ENS #PLANAQUARésumé
Zooplankton perform daily migrations between pelagic surface waters, where they feed at night, and either deeper waters (diel vertical migration, DVM) or littoral areas (diel horizontal migration, DHM), where they avoid visual predators or damaging ultraviolet radiation during the day. Diel migration patterns can change based on environmental stressors and food web perturbations, and these behavioral changes have implications for ecological processes in lakes. We hypothesized that crustacean DVM decreases and DHM increases in ponds with hypoxic bottom waters and that DVM and DHM are more extensive with higher planktivory by fish. To address our hypotheses, we assessed crustacean and rotifer community composition and daily migration behavior across pelagic and littoral zones of 16 shallow experimental ponds with differing dissolved oxygen concentrations and planktivorous fish densities in August 2019. Community metrics were driven by habitat, with littoral samples containing a higher taxa richness and diversity of crustaceans and rotifers compared to pelagic samples. DVM and DHM behaviors varied widely based on taxonomic groups. Hypoxia and planktivory had minor effects on zooplankton community metrics and migration behaviors. Our findings contribute to the body of knowledge regarding interactive impacts of hypoxia and planktivory on zooplankton communities and behavioral dynamics in shallow ponds.
Auteurs, date et publication :
Auteurs Anna G. Schmidt , Isabel M. Anderson , Rosalie Bruel , Rosaura J. Chapina , Jonathan P. Doubek , Sarah Fiorini , Sadye K. Goldfarb , Gérard Lacroix , Heather L. Wander , Savannah Zigic , Jason D. Stockwell
Publication : Hydrobiologia
Date : 2024
Catégorie(s)
#CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs Benoît Sotton , Alain Paris , Séverine Le Manach , Alain Blond , Gérard Lacroix , Alexis Millot , Charlotte Duval , Qin Qiao , Arnaud Catherine , Benjamin Marie
Publication : Science of The Total Environment
Date : 2025
Volume : 590-591
Pages : 333-342
Catégorie(s)
#ANR-Citation #CNRS #ENS #PLANAQUAAuteurs, date et publication :
Auteurs Vincent Médoc , Hélène Albert , Thierry Spataro
Publication : Biological Invasions
Date : 2025
Volume : 17
Issue : 12
Pages : 3625-3637
Catégorie(s)
#CNRS #ENS #PLANAQUARésumé
Sound emissions from human activities represent a pervasive environmental stressor. Individual responses in terms of behaviour, physiology or anatomy are well documented but whether they propagate through nested ecological interactions to alter complex communities needs to be better understood. This is even more relevant for freshwater ecosystems that harbour a disproportionate fraction of biodiversity but receive less attention than marine and terrestrial systems. We conducted a mesocosm investigation to study the effect of chronic exposure to motorboat noise on the dynamics of a freshwater community including phytoplankton, zooplankton, and roach as a planktivorous fish. As expected under the trophic cascade hypothesis, roach predation induced structural changes in the planktonic communities. Surprisingly, although roach changed their feeding behaviour in response to noise, the dynamics of the roach-dominated planktonic communities did not differ between noisy and noiseless mesocosms. This suggests that the top-down structuring influence of roach on planktonic communities might be resilient to noise and reveals the difficulties on extrapolating impacts form individual responses to complex communities.
Auteurs, date et publication :
Auteurs Emilie Rojas , Mélanie Gouret , Simon Agostini , Sarah Fiorini , Paulo Fonseca , Gérard Lacroix , Vincent Médoc
Date : 2022