Pairwise interactions in tropical ant communities

Ecological communities are structured by competitive, predatory, mutualistic and parasitic interactions combined with chance events. Separating deterministic from stochastic processes is possible, but finding statistical evidence for specific biological interactions is challenging. We attempt to solve this problem for ant communities nesting in epiphytic bird’s nest ferns (Asplenium nidus) in Borneo’s lowland rainforest. By recording the frequencies with which each and every single ant species occurred together, we were able to test statistically for patterns associated with interspecific competition. We found evidence for competition, but the resulting co-occurrence pattern was the opposite of what we expected. Rather than detecting species segregation—the classical hallmark of competition—we found species aggregation. Moreover, our approach of testing individual pairwise interactions mostly revealed spatially positive rather than negative associations. Significant negative interactions were only detected among large ants, and among species of the subfamily Ponerinae. Remarkably, the results from this study, and from a corroborating analysis of ant communities known to be structured by competition, suggest that competition within the ants leads to species aggregation rather than segregation. We believe this unexpected result is linked with the displacement of species following asymmetric competition. We conclude that analysing co-occurrence frequencies across complete species assemblages, separately for each species, and for each unique pairwise combination of species, represents a subtle yet powerful way of detecting structure and compartmentalisation in ecological communities.We acknowledge support from the University of Cambridge, NERC, The Royal Society South East Asia Rainforest Research Programme, Yayasan Sabah, Danum Valley Management Committee, and the Economic Planning Unit in Kuala Lumpur. TMF was supported by the Czech Science Foundation (14-32302S, 16-09427S), and the Australian Research Council (DP140101541).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Elsevie

Can natural enemy diversity ensure stable biological control in the future?

Natural enemy diversity generally strengthens biological control, but individual studies have found anything from positive to negative effects. However, most studies investigating the impacts of natural enemy diversity on pest suppression have focused on short term effects, while ignoring the stability in pest suppression across time and space. Theory predicts that a high diversity of redundant species (i.e., species currently doing the same job) should stabilize ecosystem functioning, since different species are likely to be important during different environmental conditions. This implies that a high natural enemy diversity should provide an insurance against global environmental change. We will here present how generalist predators contribute to stability of aphid biological control in Swedish barley fields under varying landscape complexity and climate change. We have found that ground dwelling predators such as spiders and carabids can reduce aphid pest damage with 50% in such fields, and that the level of aphid biological control is higher in more complex landscapes (Rusch et al. 2013). In recent work, exploring feeding preferences of the most common carabid and spider species on over ten prey types with molecular gut content analysis we have confirmed that these species are highly generalistic and that a high diversity of predators contribute to aphid biological control (Roubinet et al. 2017). Our preliminary analyses suggest that the level of redundancy in aphid predation increases with landscape complexity, suggesting that barley fields in complex landscapes not only currently has more effective aphid biological control but that the stability of aphid control is likely to be higher in such landscapes. We are currently investigating the climate niches of different predators in relation to temperature and rainfall. These niches will be combined into climate niches for predator communities in different types of landscapes and we will test if the level of climate resilience (Kühsel and Blüthgen 2015) in predator communities is higher in complex landscapes. Finally, we will conduct mesocosm experiments under different climate scenarios to test if predator communities with different levels of redundancy and climate resilience really contribute to more stable biological control of aphids. (1) Rusch, A., Bommarco, R., Jonsson, M., Smith, H.G. & Ekbom, B. 2013. Flow and stability of natural pest control services depend on landscape complexity and crop rotation in the landscape. J Appl Ecol 50, 345-354. (2) Roubinet, E., Birkhofer, K., Malsher, G., Staudacher, K., Ekbom, B., Traugott, M. & Jonsson, M. 2017. Diet of generalist predators reflects effects of cropping period and farming system on extra- and intraguild prey. Ecol Appl 27, 1167-1177. (3) Kühsel, S. & Blüthgen N. 2015 High diversity stabilizes the thermal resilience of pollinator communities in intensively managed grasslands. Nature Comm 2015. 6: p. 7989.peerReviewe

Studying the Complex Communities of Ants and Their Symbionts Using Ecological Network Analysis

Ant colonies provide well-protected and resource-rich environments for a plethora of symbionts. Historically, most studies of ants and their symbionts have had a narrow taxonomic scope, often focusing on a single ant or symbiont species. Here we discuss the prospects of studying these assemblies in a community ecology context using the framework of ecological network analysis. We introduce three basic network metrics that we consider particularly relevant for improving our knowledge of ant-symbiont communities: interaction specificity, network modularity, and phylogenetic signal. We then discuss army ant symbionts as examples of large and primarily parasitic communities, and symbiotic sternorrhynchans as examples of generally smaller and primarily mutualistic communities in the context of these network analyses. We argue that this approach will provide new and complementary insights into the evolutionary and ecological dynamics between ants and their many associates, and will facilitate comparisons across different ant-symbiont assemblages as well as across different types of ecological networks

Present and historical landscape structure shapes current species richness in Central European grasslands

Context Current diversity and species composition of ecological communities can often not exclusively be explained by present land use and landscape structure. Historical land use may have considerably influenced ecosystems and their properties for decades and centuries. Objectives We analysed the effects of present and historical landscape structure on plant and arthropod species richness in temperate grasslands, using data from comprehensive plant and arthropod assessments across three regions in Germany and maps of current and historical land cover from three time periods between 1820 and 2016. Methods We calculated local, grassland class and landscape scale metrics for 150 grassland plots. Class and landscape scale metrics were calculated in buffer zones of 100 to 2000 m around the plots. We considered effects on total species richness as well as on the richness of species subsets determined by taxonomy and functional traits related to habitat use, dispersal and feeding. Results Overall, models containing a combination of present and historical landscape metrics showed the best fit for several functional groups. Comparing three historical time periods, data from the 1820/50s was among the most frequent significant time periods in our models (29.7% of all significant variables). Conclusions Our results suggest that the historical landscape structure is an important predictor of current species richness across different taxa and functional groups. This needs to be considered to better identify priority sites for conservation and to design biodiversity-friendly land use practices that will affect landscape structure in the future.Projekt DEAL; DFG [324399761]; Deutsche Forschungsgemeinschaft (DFG) [405945293]Open Access funding enabled and organized by Projekt DEAL. The work has been (partly) funded by the DFG Priority Program 1374 Infrastructure-Biodiversity-Exploratories (Project Number 324399761). CW was funded by the Deutsche Forschungsgemeinschaft (DFG) (Project Number 405945293)

Animal-Mediated Ecosystem Process Rates in Forests and Grasslands are Affected by Climatic Conditions and Land-Use Intensity

Decomposition, vegetation regeneration, and biological control are essential ecosystem functions, and animals are involved in the underlying processes, such as dung removal, seed removal, herbivory, and predation. Despite evidence for declines of animal diversity and abundance due to climate change and land-use intensification, we poorly understand how animal-mediated processes respond to these global change drivers. We experimentally measured rates of four ecosystem processes in 134 grassland and 149 forest plots in Germany and tested their response to climatic conditions and land-use intensity, that is, grazing, mowing, and fertilization in grasslands and the proportion of harvested wood, non-natural trees, and deadwood origin in forests. For both climate and land use, we distinguished between short-term effects during the survey period and medium-term effects during the preceding years. Forests had significantly higher process rates than grasslands. In grasslands, the climatic effects on the process rates were similar or stronger than land-use effects, except for predation; land-use intensity negatively affected several process rates. In forests, the land-use effects were more pronounced than the climatic effects on all processes except for predation. The proportion of non-natural trees had the greatest impact on the process rates in forests. The proportion of harvested wood had negative effects, whereas the proportion of anthropogenic deadwood had positive effects on some processes. The effects of climatic conditions and land-use intensity on process rates mirror climatic and habitat effects on animal abundance, activity, and resource quality. Our study demonstrates that land-use changes and interventions affecting climatic conditions will have substantial impacts on animal-mediated ecosystem processes.Projekt DEAL; Deutsche Forschungsgemeinschaft (DFG) Priority Program 1374 Infrastructure-Biodiversity-ExploratoriesGerman Research Foundation (DFG) [DFG-WE 3081/21-1]; Swiss National Science FoundationSwiss National Science Foundation (SNSF)European Commission [310030E-173542/1]Open Access funding provided by Projekt DEAL. We thank Kevin Frank, Kathrin Ziegler, Andreas Kerner, Tewannakit Mermagen, Annika Keil, Joanna Lim, Pierre Fauve, Corinna Herrmann, Nicole Prehn, Jessica Schneider, Thorsten Meene, Andrea Hilpert, Hannah Berner, Nadia Bianco, Ralph Bolliger, Viona Ernst, Marco Haberli, Nico Heer, Judith Hinderling, Arthur Knecht, Aron Muller, Ulf Pommer, Judith Reusser, Barbara Schmitt, Cecile Vollenweider, Deborah Werlen, and Pascal Wyss, who contributed to the fieldwork and labwork, and especially Katja Gruschwitz who also helped with the identification of the predator marks. We thank Christian Imholt for providing information about the rodent outbreak in 2017. We thank the managers of the Exploratories in three study regions, Kirsten Reichel-Jung, Juliane Vogt, and Miriam Teuscher, as well as all former managers for their work in maintaining the plot and project infrastructure. Thanks to Christiane Fischer for giving support through the central office, Andreas Ostrowski for managing the central data base, Juliane Vogt, Niclas Otto, and Ralf Lauterbach for providing detailed information about land-use data collection, Judith Hinderling, Torsten Meene, and Verena Busch for providing detailed information about exclosures used for the herbivory measurements, Falk Hansel and Stephan Wollauer for helping with the climate data preparation, and Markus Fischer, Eduard Linsenmair, Dominik Hessenmoller, Daniel Prati, Ingo Schoning, Francois Buscot, Ernst-Detlef Schulze, and the late Elisabeth Kalko for their role in setting up the Biodiversity Exploratories project. The work has been funded by the Deutsche Forschungsgemeinschaft (DFG) Priority Program 1374 Infrastructure-Biodiversity-Exploratories (DFG-WE 3081/21-1.) and the Swiss National Science Foundation (310030E-173542/1). Fieldwork permits were issued by the responsible state environmental offices of Baden-Wurttemberg, Thuringen, and Brandenburg (according to 72 BbgNatSchG).WOS:0005566844000022-s2.0-85089081818PubMed: 3477677

Interannual variation in land-use intensity enhances grassland multidiversity

Although temporal heterogeneity is a well-accepted driver of biodiversity, effects of interannual variation in land-use intensity (LUI) have not been addressed yet. Additionally, responses to land use can differ greatly among different organisms; therefore, overall effects of land-use on total local biodiversity are hardly known. To test for effects of LUI (quantified as the combined intensity of fertilization, grazing, and mowing) and interannual variation in LUI (SD in LUI across time), we introduce a unique measure of whole-ecosystem biodiversity, multidiversity. This synthesizes individual diversity measures across up to 49 taxonomic groups of plants, animals, fungi, and bacteria from 150 grasslands. Multidiversity declined with increasing LUI among grasslands, particularly for rarer species and aboveground organisms, whereas common species and belowground groups were less sensitive. However, a high level of interannual variation in LUI increased overall multidiversity at low LUI and was even more beneficial for rarer species because it slowed the rate at which the multidiversity of rare species declined with increasing LUI. In more intensively managed grasslands, the diversity of rarer species was, on average, 18% of the maximum diversity across all grasslands when LUI was static over time but increased to 31% of the maximum when LUI changed maximally over time. In addition to decreasing overall LUI, we suggest varying LUI across years as a complementary strategy to promote biodiversity conservation

Theoretical and experimental investigation on laminar boundary layer under cnoidal wave motion

Land-use intensification is a major driver of biodiversity loss. However, understanding how different components of land use drive biodiversity loss requires the investigation of multiple trophic levels across spatial scales. Using data from 150 agricultural grasslands in central Europe, we assess the influence of multiple components of local- and landscape-level land use on more than 4,000 above- and belowground taxa, spanning 20 trophic groups. Plot-level land-use intensity is strongly and negatively associated with aboveground trophic groups, but positively or not associated with belowground trophic groups. Meanwhile, both above- and belowground trophic groups respond to landscape-level land use, but to different drivers: aboveground diversity of grasslands is promoted by diverse surrounding land-cover, while belowground diversity is positively related to a high permanent forest cover in the surrounding landscape. These results highlight a role of landscape-level land use in shaping belowground communities, and suggest that revised agroecosystem management strategies are needed to conserve whole-ecosystem biodiversity. Land use intensification is a major driver of biodiversity change. Here the authors measure diversity across multiple trophic levels in agricultural grassland landscapes of varying management, finding decoupled responses of above- and belowground taxa to local factors and a strong impact of landscape-level land use