Scaling in stream communities

Abstract

Scaling relationships between population density (N) and body size (W ), and of their underlying size distributions, can contribute to an understanding of how species use resources as a function of size. In an attempt to resolve the controversy over the form of scaling relationships, an extensive dataset, comprising 602 invertebrate species, was obtained from two geographically separate stream communities (Seebach in Austria and Mynach in Wales). We analysed the temporal consistency of the N-W relationship, which was subjected to ordinary least squares (OLS), bisector (OLS BIS ) and quantile regressions, and speciessize spectra with seasonally collated data. Slopes of seasonal OLS BIS regressions did not depart from Ϫ1 in either community, indicating a seasonally convergent scaling relationship, which is not energetically constrained. Species-size spectra may scale with habitat complexity, providing an alternative explanation for the observed body-size scaling. In contrast to the right-skewed species-size frequency distributions of single-species assemblages, the size spectra of these benthic communities exhibited 'central tendencies', reflecting their phyletic constitution. The shape of species body-mass spectra differed between the two communities, with a bimodal and seasonally convergent pattern in the Seebach community and a seasonally shifting unimodality in the Mynach community. The body-size spectra of large, mostly insect, species (greater than or equal to 1 mm) scaled to seasonal variations in habitat complexity (i.e. fractal D), suggesting that habitat structure constrains the community organization of stream benthos.

Measuring the Surface Roughness of Stream Stones

“…Fractal methods have been used to describe textural differences in constructed substrates with a checkerboard arrangement of heights (Taniguchi & Tokeshi, 2004), estimate the fractal dimension of riverbed topography (Robson et al, 2002), and describe the substrate-water interface of streambeds (Schmid et al, 2002). Fractal geometry has also been used in marine benthic studies (e.g.…”

The body-size structure of macrobenthos changes predictably along gradients of hydrodynamic stress and organic enrichment

“…In benthic environments, however, organisms can find refuge among the fronds of macroalgae or in sediment interstices, and therefore, environmental factors such as habitat architecture and substrate composition strongly affect the size structure of benthic communities (Strayer 1991;Holling 1992;Schmid 2000;Tokeshi and Arakaki 2012). In fact, the availability of shelters of different dimensions influences the size of crabs (Beck 1995), and different morphologies of macroalgae as well as different levels of habitat complexity determine the size spectra of amphipods (Hacker and Steneck 1990), gastropods (Pennings 1990), epifaunal (Gee and Warwick 1994) and infaunal assemblages (Schmid et al 2002).…”

Changes in body size spectra of benthic caridean shrimps (Decapoda: Caridea) and snails (Gastropoda) as response to seasonal variability

“…Aquatic ecologists, for example, have usually analyzed the frequency distribution of body sizes regardless the species to which organisms belong, or body size spectra, and studies conducted in small water bodies have reported scaling exponents that largely deviate from the expected value of -3/4 (Boix, Sala, Quintana, & Moreno-Amich, 2004;Schmid, Tokeshi, & Schmid-Araya, 2000, 2002. Indeed, recent studies on benthic macroinvertebrates from Mediterranean lagoons have shown that local body size-abundance relationships can be polygonal in shape, with the highest population density per size class increasing with average individual body size of 0.25 mg and decreasing beyond this threshold (Barbone, Rosati, Pinna, & Basset, 2007;Basset et al, 2008).…”