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Scaling relationships (where body size features as the independent variable) and power-law distributions are commonly reported in ecological systems. In this review we analyze scaling relationships related to energy acquisition and transformation and power-laws related to fluctuations in numbers. Our aim is to show how individual level attributes can help to explain and predict patterns at the level of populations that can propagate at upper levels of organization. We review similar relationships also appearing in the analysis of aquatic ecosystems (i.e. the biomass spectra) in the context of ecological invariant relationships (i.e. independent of size) such as the 'energetic equivalence rule' and the 'linear biomass hypothesis'. We also discuss some power-law distributions emerging in the analysis of numbers and fluctuations in ecological attributes as they point to regularities that are yet to be integrated with traditional scaling relationships and which we foresee as an exciting area of future research.

Species invasions are a principal component of global change, causing large losses in biodiversity as well as economic damage. Invasion theory attempts to understand and predict invasion success and patterns of spread. However, there is no consensus regarding which species or community attributes enhance invader success or explain spread dynamics. Experimental and theoretical studies suggest that regulation of spread dynamics is possible; however, the conditions for its existence have not yet been empirically demonstrated. If invasion spread is a regulated process, the structure that accounts for this regulation will be a main determinant of invasion dynamics. Here we explore the existence of regulation underlying changes in the rate of new site colonization. We employ concepts and analytical tools from the study of abundance dynamics and show that spread dynamics are, in fact, regulated processes and that the regulation structure is notably consistent among invasions occurring in widely different contexts. We base our conclusions on the analysis of the spread dynamics of 30 species invasions, including birds, amphibians, fish, invertebrates, plants, and a virus, all of which exhibited similar regulation structures. In contrast to current beliefs that species invasions are idiosyncratic phenomena, here we provide evidence that general patterns do indeed exist.conservation ͉ invasion ͉ population dynamics ͉ range expansion ͉ regulation

Ulrich Brose Body size is recognized as an important determinant of trophic structure as it affects individual energetic demands, population density, and the interaction between potential prey and predators. However, its relationship with trophic position remains unclear. It has been hypothesized that a positive relationship between body size and trophic position would be associated to some particular trophic structures, which would allow larger organisms to satisfy their energetic demand and sustain viable population sizes at higher trophic positions, where fewer resources are available. To test this hypothesis, we analyzed the diet of 619 killifishes from four species (Austrolebias cheradophilus, A. luteoflammulatus, A. viarius and Cynopoecilus melanotaenia), collected in temporary ponds occurring in the grasslands of Rocha, Uruguay. Trophic position, diet richness, number of energy sources, and evenness were estimated for 20 size classes, formed by consecutive groups of 31 individuals. Gape limitation and preference for the larger available prey were evaluated as explanations for observed patterns with an individual based model (IBM). In agreement with the hypothesis, killifishes presented a strong positive relationship between trophic position and body size (R2=0.86), associated with a trophic structure that could allow larger organisms to have access to more energy from the environment. This was reflected in a positive relationship between body size and 1) prey richness, 2) number of basal energy sources (i.e. plants, detritus, phytoplankton and terrestrial prey), and 3) evenness in prey use. IBM results showed that changes in trophic structure with body size are well explained by gape limitation, but not by size preferences. Our results suggest that the fulfilment of the greater energetic demands of larger organism will depend on community diversity, which typically increases with ecosystem size, indicating a novel connection between area, diversity, body size, and food chain length.