The searching trajectories of different animals can be described with a broad class of flight length (l j) distributions with P(lj) ؍ lj ؊ . Theoretical studies have shown that changes in these distributions (i.e., different values) are key to optimizing the long-term encounter statistics under certain searcher-resource scenarios. In particular, they predict the advantage of Lé vy searching ( Ϸ 2) over Brownian motion ( > 3) for low-prey-density scenarios. Here, we present experimental evidence of predicted optimal changes in the flight-time distribution of a predator's walk in response to gradual density changes of its moving prey. Flight times of the dinoflagellate Oxyrrhis marina switched from an exponential to an inverse square power-law distribution when the prey (Rhodomonas sp.) decreased in abundance. Concomitantly, amplitude and frequency of the short-term helical path increased. The specific biological mechanisms involved in these searching behavioral changes are discussed. We suggest that, in a threedimensional environment, a stronger helical component combined with a Lé vy walk searching strategy enhances predator's encounter rates. Our results support the idea of universality of the statistical laws in optimal searching processes despite variations in the biological details of the organisms. R andom walks based on Lévy flight distributions P(l j ) ϭ l j Ϫ in concrete ''Lévy walks'' with Ϸ 2, are the optimal searching strategy for scarce fixed targets that are randomly located (1). A Lévy walk could be more efficient than the usual Gaussian (i.e., Brownian) motion as suggested by early works on microzooplankton (2-4), although Brownian motion is generally assumed in reaction-diffusion predator-prey models. Recently, ecological examples of Lévy walks have been provided for a wide range of animal species (5-10). However, the theoretical study of more complex scenarios has shown that the advantage of Lévy searching over other types of motion is restricted to a set of prey densities, and mobility and size of the predator relative to the prey (11-13). Therefore, natural selection should favor flexible behaviors, combining different searching strategies (i.e., searching statistics) under different conditions. Here, we present experimental evidence that changes occur in both the short-and long-term searching statistics of a predator (Oxyrrhis marina), coinciding with density changes of its moving prey (Rhodomonas sp.). The specific biological mechanisms involved are also identified.The marine heterotrophic dinoflagellate O. marina has two flagella, one transversal and one longitudinal, providing three types of movement: rotation, translation, and sudden directional changes (14, 15). The flagellar apparatus of O. marina has been well studied at both the cellular (15) and the ultrastructural (16) level. Continuous flagellar movements are responsible for simultaneous rotation and translation of organisms, giving rise to a helical path during movement. Normal helical motion is interrupted by sudden (60-100 ms)...
Why does the neutral theory, which is based on unrealistic assumptions, predict diversity patterns so accurately? Answering questions like this requires a radical change in the way we tackle them. The large number of degrees of freedom of ecosystems pose a fundamental obstacle to mechanistic modelling. However, there are tools of statistical physics, such as the maximum entropy formalism (MaxEnt), that allow transcending particular models to simultaneously work with immense families of models with different rules and parameters, sharing only well-established features. We applied MaxEnt allowing species to be ecologically idiosyncratic, instead of constraining them to be equivalent as the neutral theory does. The answer we found is that neutral models are just a subset of the majority of plausible models that lead to the same patterns. Small variations in these patterns naturally lead to the main classical species abundance distributions, which are thus unified in a single framework.
Increasing evidence-synthesized in this paper-shows that economic growth contributes to biodiversity loss via greater resource consumption and higher emissions.Nonetheless, a review of international biodiversity and sustainability policies shows that the majority advocate economic growth. Since improvements in resource use efficiency have so far not allowed for absolute global reductions in resource use and pollution, we question the support for economic growth in these policies, where inadequate attention is paid to the question of how growth can be decoupled from biodiversity loss. Drawing on the literature about alternatives to economic growth, we explore this contradiction and suggest ways forward to halt global biodiversity decline. These include policy proposals to move beyond the growth paradigm while enhancing overall prosperity, which can be implemented by combining top-down and bottom-up governance across scales. Finally, we call the attention of researchers and policy makers to two immediate steps: acknowledge the conflict between economic growth and biodiversity conservation in future policies; and explore socioeconomic trajectories beyond economic growth in the next generation of biodiversity scenarios.
Pueyo, S. 2006. Diversity: between neutrality and structure. Á/ Oikos 112: 392 Á/405.Here I present an integrated framework for species abundance distributions (SADs) that goes beyond the neutral theory without relying on complex mechanistic models. I give some general mathematical results on the relationship between SADs and their underlying dynamics, and analyse an extensive set of marine phytoplankton data in order to test the neutral theory against this broader framework.The main theoretical and empirical results are: (i) the logseries, which is the SAD produced by simple neutral models without migration, is quite robust in response to additional factors, including some forms of niche segregation; (ii) when there is a small but significant deviation from a logseries, the SAD will generally have the form of a power law, regardless of the specific mechanisms; (iii) when the deviation is moderate, the SAD will generally have the form of a lognormal, regardless of the specific mechanisms; (iv) although in a wide range of situations neutral and non-neutral dynamics cannot be distinguished from the SAD alone, some empirical SADs do have the fingerprint of non-neutrality: this is the case of marine dinoflagellates, in contrast to marine diatoms, which adjust to neutral theory predictions. The results for marine phytoplankton illustrate that both neutral and non-neutral mechanisms coexist in nature, and seem to have different weights in different groups of organisms.In addition to the above findings, I discuss several related contributions and point out some important pitfalls in the literature.
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