Geoscience Reference
In-Depth Information
individual demands for resources, the amount of available resources, and the
reduction in population numbers by consumers, all dependent on body size,
will determine mean and maximum population density.
The range of patterns expected from the ecological theory ismuch richer than
a single power-law relationship, with aggregations and discontinuities, discrete
changes in slopes and intercepts, as well as non-linear relationships all being
predicted by theory and described empirically. The statistics used to analyse the
DMRmust have the power to detect this wide range of patterns.ML estimation
of parameters in frequency distributions and other techniques that avoid the
transformation of data in bivariate relationships have been favoured in com-
parative analysis here and elsewhere (
Packard et al., 2010; White et al.,2008
).
The consideration of alternatives toOLS regression (
Reuman et al., 2009; Zuur
et al.,2009
), the use of segmented regressions and model selection criterions,
has the potential to change the frequently invoked power law with exponent
close to
1 as the best description of the DMR.
The report of just one of the five DMRs in most studies, summed to the use
of parameters estimated with statistics that have a poor performance, is a
limitation for a proper synthesis in this area. The metacommunity data we
analysed exhibited a wide range of DMRs depending on the scale of analysis,
the pattern considered, and the statistics employed. At the metacommunity
and community level, a weak and positive mass-abundance relationship was
observed when values for different species or population were considered.
However, frequency distribution of individuals and species suggested a clear
scaling trend, with different regimes for different size classes. The cross-
community pattern was congruent with an energetic constraint. In this
sense, the different DMRs should be considered as alternative approaches
which reflect different, yet interrelated, attributes of energy distribution and
flux among individuals and species of different sizes.
0.75 or
ACKNOWLEDGEMENTS
We thank J. M. Pi˜ eiro and N. Vidal for their help. Authors thank PRO-
BIDES and Establecimiento Barra Grande for field assistance. This work
was supported by the grant Fondo Clemente Estable 2007-054 to M. A. M.
A. acknowledges support from FONDAPFONDECYT1501-0001.
REFERENCES
Ackerman, J.L., Bellwood, D.R., and Brown, J.H. (2004). The contribution of small
individuals to density-body size relationships: Examination of energetic equiva-
lence in reef fishes. Oecologia
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, 568-571.
