Abstract
We study the temporal variation in the empirical relationships among body size (S), species richness (R), and abundance (A) in a shallow marine epibenthic faunal community in Coliumo Bay, Chile. We also extend previous analyses by calculating individual energy use (E) and test whether its bivariate and trivariate relationships with S and R are in agreement with expectations derived from the energetic equivalence rule. Carnivorous and scavenger species representing over 95% of sample abundance and biomass were studied. For each individual, body size (g) was measured and E was estimated following published allometric relationships. Data for each sample were tabulated into exponential body size bins, comparing species-averaged values with individual-based estimates which allow species to potentially occupy multiple size classes. For individual-based data, both the number of individuals and species across body size classes are fit by a Weibull function rather than by a power law scaling. Species richness is also a power law of the number of individuals. Energy use shows a piecewise scaling relationship with body size, with energetic equivalence holding true only for size classes above the modal abundance class. Species-based data showed either weak linear or no significant patterns, likely due to the decrease in the number of data points across body size classes. Hence, for individual-based size spectra, the SRA relationship seems to be general despite seasonal forcing and strong disturbances in Coliumo Bay. The unimodal abundance distribution results in a piecewise energy scaling relationship, with small individuals showing a positive scaling and large individuals showing energetic equivalence. Hence, strict energetic equivalence should not be expected for unimodal abundance distributions. On the other hand, while species-based data do not show unimodal SRA relationships, energy use across body size classes did not show significant trends, supporting energetic equivalence.
Highlights
Ecology and Evolution published by John Wiley & Sons Ltd
Different authors have tried to establish the generality of the predicted energetic equivalence across species of different sizes, with species-based data from local communities presenting much broader scatter in the bivariate relationship, which led to the suggestion that local size– density relationships (LSDR) may be better described by polygonal or quantile regressions (Damuth 1981; Maurer and Brown 1988; Marquet et al 1995; White et al 2007)
When we examined the scaling of total energy use across individual-based body size bins, we found that total energy use across all individuals could be well fit by a piecewise scaling relationship, rather than following a shallow, nonsignificant pattern as expected under the equivalence rule (EER)
Summary
Understanding how body size influences observed patterns in species abundance and diversity has been a longstanding area of research in ecology (Peters 1983; Calder 1984; Brown et al 2004; White et al 2007; Sibly et al 2012). A test of trivariate macroecological patterns a power law scaling relationship (Damuth 1981, 1987) This global size–density relationship (GSDR) showed a scaling exponent that is the inverse of the exponent of the relationship between body size and metabolic rate (Damuth 1981, 1987; White et al 2007), which implies that the energy flux per unit area in a given population, estimated as the product of metabolic rate and abundance, will be independent of body mass. These authors suggested that greater emphasis should be given to understanding the mechanisms underlying abundance–energy relationships and to consider alternative (i.e., nonenergetic) determinants of species abundance (Isaac et al 2013)
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