Ecological interaction networks for action

• INT70 • Meta-food web theory informs landscape planning. > U. Ulrich BROSE
Content : BROSE, Ulrich, iDiv, Friedrich-Schiller University Jena, ulrich.brose@idiv.de

Classic meta-community and landscape ecology addressed how habitat fragmentation and reduction in landscape connectivity may cause biodiversity loss in fragmented landscapes. Landscape planning can establish dispersal corridors in fragmented landscapes to facilitate rescue effects. However, this concept ignores effects of local species interactions. Recently, meta-food web theory has demonstrated important interactions between species dispersal, local interactions and multi-trophic community assembly in driving biodiversity patterns. This revealed that landscape heterogeneity can buffer against increasing nutrient eutrophication on local habitat patches. An interaction between eutrophication and landscape homogenization precipitates the decline of biodiversity. In addition to the “rescue effect” that maintains local biodiversity by rapid recolonization after a local crash in population densities, these studies unraveled a “drainage effect” that allows a more uniform spreading of biomass across the landscape, reducing overall interaction strengths and therefore stabilizing dynamics. In complex food webs on large spatial networks of habitat patches, these effects yield systematically higher biodiversity in heterogeneous than in homogeneous landscapes. This meta-food web approach provides a mechanistic explanation of how landscape heterogeneity promotes biodiversity and fosters novel ways of landscape planning. • INT71 • The simplification of ecological communities: effects of habitat loss on network structure > N. Nuria GALIANA IBANEZ
Content : GALIANA, Nuria, Museo Nacional de Ciencias Naturales (CSIC), Madrid, galiana.nuria@gmail.com

Larger geographical areas contain more species—an observation raised to a law in ecology. Less explored is whether biodiversity changes are accompanied by a modification of interaction networks. We use data from 32 spatial interaction networks from different ecosystems to analyse how network structure changes with area. We find that basic community structure descriptors (number of species, links and links per species) increase with area following a power law. Yet, the distribution of links per species varies little with area, indicating that the fundamental organization of interactions within networks is conserved. Our null model analyses suggest that the spatial scaling of network structure is determined by factors beyond species richness and the number of links. We demonstrate that biodiversity–area relationships can be extended from species counts to higher levels of network complexity. We then discuss how the consequences of anthropogenic habitat destruction may extend from species loss to wider simplification of natural communities. • INT72 • Indirect effects in plant-pollinator networks: consequences for agricultural systems? > E. Elisa THÉBAULT
Content : THEBAULT, Elisa, iEES Paris, CNRS, Sorbonne Université, elisa.thebault@upmc.fr

Indirect effects among species are known to play a fundamental ecological and evolutionary role in species interaction networks. In mutualistic networks such as plant-pollinator networks, species coexistence is expected to strongly depend on the relative importance of indirect competition and indirect facilitation within guilds, either plant or pollinator. A recent theoretical analysis shows that networks structured by phenology favour facilitation over competition within guilds of pollinators and plants, thereby increasing network persistence. We discuss the consequences of these findings for indirect effects between natural vegetation and crops, and among crops in the context of agricultural systems. • INT73 • The complex response of plankton food webs to shifts in seasonal forcing. > S. Sabine WOLLRAB
Content : WOLLRAB, Sabine, IGB Berlin, Sabine.Wollrab@igb-berlin.de

Predictions on food web responses to global warming are difficult because of the complex interplay between abiotic forcing and biotic interactions. Mechanistic models of species interaction networks in seasonal environments can help understand the effects of global change in different ecosystems. In aquatic systems plankton dynamics are closely correlated to seasonal changes in the physical environment. For deep lakes of temperate regions phytoplankton bloom formation typically starts with the onset of the summer stratification in spring. Lakes that experience pronounced periods of ice-coverage, like in boreal regions, phytoplankton bloom formation can also happen under the ice, especially if not covered by snow and is often formed by winter specialists. Global warming leads to large changes in the stratification regime of lakes, extending the period of summer stratification and decreasing the length of the ice-covered season for boreal, increasing the frequency of ice-free winters of temperate lakes, respectively. Using idealized phytoplankton-zooplankton food webs, I theoretically investigated how changes in the length of winter versus summer periods affect plankton dynamics and community composition for boreal and temperate lakes. Using a dynamic model approach the results reveal a complex interplay of predator-prey dynamics which can cause multi-annual cycle dynamics. Furthermore the results show that even gradual environmental change, such as declining ice cover duration, may cause discontinuous or abrupt transitions between dynamic regimes in food webs. • INT74 • Fishing reference points assessed by a marine individual-based food web model. > M. Morgane TRAVERS-TROLET
Content : TRAVERS-TROLET, Morgane, IFREMER Nantes, morgane.travers@ifremer.fr

In marine ecosystems, predation is highly opportunistic and food web structure emerges from local interactions between predators and prey. This feature allows marine food webs to be flexible to pressures. Using the multi-species individual-based model OSMOSE assuming size-based opportunistic predation, we explore how fishing reference points evolve under different climate conditions for the Eastern English Channel. The modelled food web structure changes under two contrasted climate change scenarios, which leads to changes in reference points such as Maximum Sustainable Yield (MSY). Evolution of MSYs with climate change is compared across species having different trophic levels, temperature affinities and fishing pressure. Results show that overexploited cold-water species are likely to have a declining MSY with climate warming, but with no clear link with their trophic position. This result constitutes a risk for fisheries management, and anticipation of climate change impacts on fish community would require targeting a smaller fishing effort than the one derived from the current MSY to ensure sustainable exploitation of marine stocks. • INT75 • Assessing trophic multifunctionality of food webs using energy flux approach > A. Anton POTAPOV
Content : POTAPOV, Anton, University of Göttingen, anton.potapov@biologie.uni-goettingen.de

Soil food webs regulate functioning, ensure stability and support biodiversity both below and above ground. Strengths of the feeding interactions between consumers and their resources in soil depend primarily on the metabolic demands of consumers and can be quantitatively expressed in ‘energy fluxes’. Energy fluxes reflect processes of carbon and nutrients transformation, thus being directly (herbivory, microbivory, predation, C and N mineralisation) and indirectly (translocation and transformation of organic matter, changing microbial community composition) linked to soil processes and related ecosystem functions and services. Multiple energy fluxes support multiple trophic-related functions and thus support multiple functions at the ecosystem level. By quantifying energy fluxes along resource, size, and spatial dimensions of soil food webs, I assess “trophic multifunctionality” i.e. simultaneous support of multiple trophic functions by the food web (analogous to ecosystem multifunctionality). This approach can be used to calculate a number of quantitative food-web indicators and compare them across ecosystems spanning beyond the soil. With further validation, energy flux approaches would allow to embrace functioning of soil communities from microorganisms to large animals and in perspective include them as active agents in biogeochemical models, not only locally but also on regional and global scales. • INT76 • A general ecosystem model to predict soil functioning > P. Pierre QUÉVREUX
Content : QUÉVREUX, Pierre, INRAE Clermont-Ferrand, pierre.quevreux@inrae.fr

A number of emergent features of detritic food webs have been empirically studied, including litter decomposition and the effect of fertilization on soil invertebrates. We however lack a general predictive framework that builds upon such empirical knowledge and would enable to guide agro-ecological actions. To this end, we developed a general soil ecosystem model that brings together recent advances on the general organization and dynamics of soil food webs and of organic matter pools, taking into account stoichiometric constraints. We assess whether this model succeeds in predicting various empirical features of soil functioning.