In this Letter we give specific examples of ZNZN LotkaaVolterra competition models leading to the formation of string networks. We show that, in order to promote coexistence, the species may arrange ...themselves around regions with a high number density of empty sites generated by predator-prey interactions between competing species. These configurations extend into the third dimension giving rise to string networks. We investigate the corresponding dynamics using both stochastic and mean field theory simulations, showing that the coarsening of these string networks follows a scaling law which is analogous to that found in other physical systems in condensed matter and cosmology.
1. Competition for resources has long been considered a prevalent force in structuring plant communities and natural selection, yet our understanding of the mechanisms that underlie resource ...competition is still developing. 2. The complexity of resource competition is derived not only from the variability of resource limitation in space and time and among species, but also from the complexity of the resources themselves. Nutrients, water and light each differ in their properties, which generates unique ways that plants compete for these resources. 3. Here, we discuss the roles of supply pre-emption and availability reduction in competition for the three resources when supplied evenly in space and time. Plants compete for nutrients by pre-empting nutrient supplies from coming into contact with neighbours, which requires maximizing root length. Although water is also a soil resource, competition for water is generally considered to occur by availability reduction, favouring plants that can withstand the lowest water potential. Because light is supplied from above plants, individuals that situate their leaves above those of neighbours benefit directly from increased photosynthetic rates and indirectly by reducing the growth of those neighbours via shade. In communities where juveniles recruit in the shade of adults, traits of the most competitive species are biased towards those that confer greater survivorship and growth at the juvenile stage, even if those traits come at the expense of adult performance. 4. Understanding the mechanisms of competition also reveals how competition has influenced the evolution of plant species. For example, nutrient competition has selected for plants to maintain higher root length and light competition plants that are taller, with deeper, flatter canopies than would be optimal in the absence of competition. 5. In all, while more research is needed on competition for heterogeneous resource supplies as well as for water, understanding the mechanisms of competition increases the predictability of interspecific interactions and reveals how competition has altered the evolution of plants.
Introduction Costamagna, Francesco
European papers (Online. periodico),
01/2019, Letnik:
4, Številka:
1
Journal Article
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The Special Section investigates, from a multidisciplinary perspective, foundations, tools and implications of regulatory competition in the EU legal order. The analysis takes the view that ...regulatory competition is not just an inevitable corollary of the creation of the internal market, but it is the result of political choices made to pursue specific policy objectives. Moving from different analytical angles, it sheds more light on the dangers that the choice to promote regulatory competition poses for the constitutional identity of the EU. The Special Section is composed by two main parts. The first one offers an in-depth examination of the complex relationship between the European integration process and regulatory competition, exploring its historical and conceptual foundations, as well as critically engaging with its implications on the EU constitutional architecture. The second one builds on these analytical findings and, in particular, on the idea that regulatory competition is the by-product of political choices made by supranational institutions. These choices, and the institutional dynamics underneath, vary from sector to sector. The Articles composing this second part look both at fields where EU law acted as a facilitator of regulatory competition and at fields where it functioned as a buttress against it or, at least, some of its most heinous effects.
Competition is ubiquitous in plant communities with various effects on plant fitness and community structure. A long‐standing debate about different approaches to explain competition is the ...controversy between David Tilman and Philip Grime. Grime stated that the importance of competition relative to the impact of the environment increases along a productivity gradient, while Tilman argued that the intensity of competition is independent of productivity. To revisit this controversy, we assumed that the effects of plant–plant interactions are additive and applied the new competition indices by Díaz‐Sierra et al. (2017) in a field experiment along a productivity gradient in S‐Germany, using the rare arable plant Arnoseris minima as a study species. The ‘target technique' was applied, to separate the effects of root and shoot competition. The study plants were exposed to five competition treatments with three replicates in 18 sites, respectively. We investigated the expectation that root competition is more intense in unproductive sites than shoot competition. Additionally, we predicted survival to be less affected by competition than growth‐related plant parameters. Using the biomass of individuals without competition as a proxy for site productivity there was a positive relationship with competition importance but no relationship with competition intensity when plants experienced full competition. Survival of the target plants was unaffected by competition. Root competition was the main mechanism determining the performance of the target plants, whereas the effect of shoot competition was relatively low albeit increasing with productivity. We conclude that when considering plant–plant interactions additive both Grime's and Tilman's theories can be supported.
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