Synthesis of spatial and trophic networks and their response to global change

Increasing human demands for production and goods continuously leads to the loss and fragmentation of habitat and eutrophication and threatens biodiversity. Organisms that comprise biodiversity interact with each other and depend on each other and thus, biodiversity is organised in complex interaction network. On the one hand, food-web research has addressed how trophic interactions shape local communities and how global change drivers such as eutrophication affects them. On the other hand, metacommunity research has been focused on spatial distributions and geographic drivers of local and regional biodiversity and how global change drivers such as habitat fragmentation species communities. These two realms have, however, mostly been separate. In this thesis, I present a meta-food-web model that synthesizes local trophic interactions and interpatch dispersal. This model employs species body masses as an interlinking trait that creates food webs and trophic dynamics through predator-prey body mass ratios and spatial networks through species dispersal capacities. With the meta-food-web model, I uncover mechanisms shaping biodiversity that only arise as a consequence of the synthesis of spatial and trophic interactions. The perspective from meta-food-webs reveals that the effect of global change drivers such as eutrophication and habitat fragmentation are highly context dependent and their effect depends on food-web and landscape structures. Furthermore, I show that interacting global change drivers can create non-linearities in biodiversity responses. Thus, this thesis provides a tool and theory derived hypotheses to shed light on consequences of global change and on what may be important to conserve biodiversity

Predator traits determine food-web architecture across ecosystems

Predator–prey interactions in natural ecosystems generate complex food webs that have a simple universal body-size architecture where predators are systematically larger than their prey. Food-web theory shows that the highest predator–prey body-mass ratios found in natural food webs may be especially important because they create weak interactions with slow dynamics that stabilize communities against perturbations and maintain ecosystem functioning. Identifying these vital interactions in real communities typically requires arduous identification of interactions in complex food webs. Here, we overcome this obstacle by developing predator-trait models to predict average body-mass ratios based on a database comprising 290 food webs from freshwater, marine and terrestrial ecosystems across all continents. We analysed how species traits constrain body-size architecture by changing the slope of the predator–prey body-mass scaling. Across ecosystems, we found high body-mass ratios for predator groups with specific trait combinations including (1) small vertebrates and (2) large swimming or flying predators. Including the metabolic and movement types of predators increased the accuracy of predicting which species are engaged in high body-mass ratio interactions. We demonstrate that species traits explain striking patterns in the body-size architecture of natural food webs that underpin the stability and functioning of ecosystems, paving the way for community-level management of the most complex natural ecosystems

Invasive spread in meta-food-webs depends on landscape structure, fertilization and species characteristics

Land use change and biological invasions collectively threaten biodiversity. Yet, few studies have addressed how altering the landscape structure and nutrient supply can promote biological invasions and particularly invasive spread (the spread of an invader from the place of introduction), or asked whether and how these factors interact with biotic interactions and invader properties. We here bridge this knowledge gap by providing a holistic network-based approach. Our approach combines a trophic network model with a spatial network model allowing us to test which combinations of abiotic and biotic factors can facilitate invasions and in particular invasive spread in food webs. We numerically simulated 6300 single-species invasions in clustered and random landscapes at different levels of nutrient supply. In total, our simulation experiment yielded 69% successful invasions - 71% in clustered landscapes and 66% in random landscapes, with the proportion of successful invasions increasing with nutrient supply. However, invasive spread was generally higher in random than in clustered landscapes. The latter can facilitate invasive spread within a habitat cluster, but prevent invasive spread between clusters. Low nutrient levels generally prevented the establishment of invasive species and their subsequent spread. However, successful invaders could have more severe impacts as they contribute more to total biomass density and species richness under such conditions. Good dispersal abilities drive the broad-scale spread of invasive species in fragmented landscapes. Our approach makes an important contribution towards a better understanding of what combination of landscape and invader properties can facilitate or prevent invasive spread in natural ecosystems. This should allow ecologists to more effectively predict and manage biological invasions.Funding Agencies|German Research Foundation (DFG)German Research Foundation (DFG) [FOR 1748, RA 2339/2-2, BR 2315/16-2, FOR 2716, BR 2315/21-1]; iDiv - German Research Foundation [DFG-FZT 118, 202548816]</p

Animal and plant space‐use drive plant diversity–productivity relationships

International audienceAbstract Plant community productivity generally increases with biodiversity, but the strength of this relationship exhibits strong empirical variation. In meta‐food‐web simulations, we addressed if the spatial overlap in plants' resource access and animal space‐use can explain such variability. We found that spatial overlap of plant resource access is a prerequisite for positive diversity–productivity relationships, but causes exploitative competition that can lead to competitive exclusion. Space‐use of herbivores causes apparent competition among plants, resulting in negative relationships. However, space‐use of larger top predators integrates sub‐food webs composed of smaller species, offsetting the negative effects of exploitative and apparent competition and leading to strongly positive diversity–productivity relationships. Overall, our results show that spatial overlap of plants' resource access and animal space‐use can greatly alter the strength and sign of such relationships. In particular, the scaling of animal space‐use effects opens new perspectives for linking landscape processes without effects on biodiversity to productivity patterns

Ryser et al 2019

This data package includes the files needed to reproduce the data and analyses of the following paper: The biggest losers: habitat isolation deconstructs complex food webs from top to bottom, Ryser, Remo, Häussler, Johanna, Stark, Markus, Brose, Ulrich, Rall, Björn C., Guill, Christia

Rush hours in flower visitors over a day–night cycle

Most research on pollination has focussed on a subset of insect taxa within a narrow time window during daylight hours. As a consequence, we have a limited understanding of the diversity and activity of flower visitors during the night or belonging to taxa other than bees or syrphid flies. Here, we quantified the abundance and species richness of flower visitors in ruderal meadows over repeated 24-h cycles (i.e. day and night), and identified abiotic factors influencing these patterns. From the plant perspective, we investigated the likelihood of being visited by an insect across a 24-h cycle. Activity of flower-visiting insects never dropped to zero over 24-h. During the day, non-syrphid Diptera and Hymenoptera were the most abundant, and species-rich groups of flower visitors, Lepidoptera and Coleoptera during night. While two of the seven most frequently visited plant species were most likely to be visited during the day, five also had a high likelihood to be visited during the night. The abundance and species richness of flower visitors was positively related to temperature during both the day and the night, whereas there was only a positive relationship with brightness during the day. We conclude that non-syrphid Diptera and nocturnal flower visitors are currently underappreciated. As the latter seem to respond differently to abiotic factors compared to diurnal species, they may potentially increase response diversity and resilience of plant-pollinator communities. There is an urgent need to improve our understanding of their ecological role and potential decline due to global change

Description of the theoretical food web model from How artificial light at night may rewire ecological networks: concepts and models

Artificial light at night (ALAN) is eroding natural light cycles thereby changing species distributions and activity patterns. Yet, little is known about how ecological interaction networks respond to this global change driver. Here, we assess the scientific basis of the current understanding of community-wide ALAN impacts. Based on current knowledge, we conceptualize and review four major pathways by which ALAN may affect ecological interaction networks by (i) impacting primary production, (ii) acting as an environmental filter affecting species survival, (iii) driving the movement and distribution of species, and (iv) changing functional roles and niches by affecting activity patterns. Using an allometric-trophic network model, we then test how a shift in temporal activity patterns for diurnal, nocturnal, and crepuscular species impacts food web stability. The results indicate that diel niche shifts can severely impact community persistence by altering the temporal overlap between species, which leads to changes in interaction strengths and rewiring of networks. ALAN can thereby lead to biodiversity loss through the homogenization of temporal niches. This integrative framework aims to advance a predictive understanding of community-level and ecological-network consequences of ALAN and their cascading effects on ecosystem functioning.This article is part of the theme issue ‘Light pollution in complex ecological systems’

Collection of studies included in the review from How artificial light at night may rewire ecological networks: concepts and models

Artificial light at night (ALAN) is eroding natural light cycles thereby changing species distributions and activity patterns. Yet, little is known about how ecological interaction networks respond to this global change driver. Here, we assess the scientific basis of the current understanding of community-wide ALAN impacts. Based on current knowledge, we conceptualize and review four major pathways by which ALAN may affect ecological interaction networks by (i) impacting primary production, (ii) acting as an environmental filter affecting species survival, (iii) driving the movement and distribution of species, and (iv) changing functional roles and niches by affecting activity patterns. Using an allometric-trophic network model, we then test how a shift in temporal activity patterns for diurnal, nocturnal, and crepuscular species impacts food web stability. The results indicate that diel niche shifts can severely impact community persistence by altering the temporal overlap between species, which leads to changes in interaction strengths and rewiring of networks. ALAN can thereby lead to biodiversity loss through the homogenization of temporal niches. This integrative framework aims to advance a predictive understanding of community-level and ecological-network consequences of ALAN and their cascading effects on ecosystem functioning.This article is part of the theme issue ‘Light pollution in complex ecological systems’