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

Data from Fussmann et al. (2017) for main publication and manual supplement

Functional response data provided by Katarina Fussmann and colleagues (https://doi.org/10.1101/101675). “N0” is the initial prey density; “Nend” is the remaining prey density after the experiment; “Ndead” is the number of dead prey individuals after the experiment; "T" is the time in minutes, "P" is the number of predators in the experiment (0 == control). These data appear both in the main publication (D8) and are needed to perform examples in the supplemental "manual" published in MEE. Please also refer to the original publication (https://doi.org/10.1101/101675) if you use these data

Ecological stability in response to warming

That species' biological rates including metabolism, growth and feeding scale with temperature is well established from warming experiments(1). The interactive influence of these changes on population dynamics, however, remains uncertain. As a result, uncertainty about ecological stability in response under warming remains correspondingly high. In previous studies, severe consumer extinction waves in warmed microcosms(2) were explained in terms of warming-induced destabilization of population oscillations(3). Here, we show that warming stabilizes predator-prey dynamics at the risk of predator extinction. Our results are based on meta-analyses of a global database of temperature effects on metabolic and feeding rates and maximum population size that includes species of different phylogenetic groups and ecosystem types. To unravel population-level consequences we parameterized a bioenergetic predator-prey model(4) and simulated warming effects within ecological, non-evolutionary timescales. In contrast to previous studies(3), we find that warming stabilized population oscillations up to a threshold temperature, which is true for most of the possible parameter combinations. Beyond the threshold level, warming caused predator extinction due to starvation. Predictions were tested in a microbial predator-prey system. Together, our results indicate a major change in how we expect climate change to alter natural ecosystems: warming should increase population stability while undermining species diversity

Supplementary_data

Analyzed data file with the breakdown coefficients of cotton–strips (k cotton), green–tea (k green), rooibos–tea (k red), global litter decay rate (K) and the long–term carbon stabilization factor (S). Data file include standardized and raw covariates, temperature and pH

Data from: Comparing biotic drivers of litter breakdown across streams compartments

Litter breakdown in the streambed is an important pathway in organic carbon cycling and energy transfer in the biosphere that is mediated by a wide range of streambed organisms. However, most research on litter breakdown to date has focused on a small fraction of the taxa that drive it (e.g. microbial versus macroinvertebrate mediated breakdown) and has been limited to the benthic zone (BZ). Despite the importance of the hyporheic zone (HZ) as a bioreactor, little is known about what, or who, mediates litter breakdown in this compartment and whether breakdown rates differ between the BZ and HZ. Here we explore the relationship between litter breakdown and the variation in community structure of benthic and hyporheic communities by deploying two standardized bioassays (cotton–strips and two types of commercially available tea bags) in 30 UK streams that encompass a range of environmental conditions. Then, we modelled these assays as a response of the streambed compartment and the biological features of the streambed assemblage (Prokaryota, Protozoa and Eumetazoa invertebrates) to understand the generality and efficiency of litter processing across communities. Litter breakdown was much faster in the BZ compared with the HZ (around 5 time higher for cotton strips and 1.5 times faster for the tea leaves). However, differences in litter breakdown between the BZ and the HZ were mediated by the biological features of the benthos and the hyporheos. Biomass of all the studied biotic groups, α–diversity of Eumetazoa invertebrates and metabolic diversity of Prokaryota were important predictors that were positively related with breakdown coefficients demonstrating their importance in the functioning of the streambed ecosystem. Our study uses a novel multi–metric bioassay that is able to disentangle the contribution by Prokaryota, Protozoa and Eumetazoa invertebrates to litter breakdown. In doing so our study reveals new insights into how organic matter decomposition is partitioned across biota and streambed compartments

Ecological stability in response to warming

That species' biological rates including metabolism, growth and feeding scale with temperature is well established from warming experiments(1). The interactive influence of these changes on population dynamics, however, remains uncertain. As a result, uncertainty about ecological stability in response under warming remains correspondingly high. In previous studies, severe consumer extinction waves in warmed microcosms(2) were explained in terms of warming-induced destabilization of population oscillations(3). Here, we show that warming stabilizes predator-prey dynamics at the risk of predator extinction. Our results are based on meta-analyses of a global database of temperature effects on metabolic and feeding rates and maximum population size that includes species of different phylogenetic groups and ecosystem types. To unravel population-level consequences we parameterized a bioenergetic predator-prey model(4) and simulated warming effects within ecological, non-evolutionary timescales. In contrast to previous studies(3), we find that warming stabilized population oscillations up to a threshold temperature, which is true for most of the possible parameter combinations. Beyond the threshold level, warming caused predator extinction due to starvation. Predictions were tested in a microbial predator-prey system. Together, our results indicate a major change in how we expect climate change to alter natural ecosystems: warming should increase population stability while undermining species diversity