Fish and their Scales: On the Power Laws of Aggregation, Size Distribution and Trophic Interaction

Abstract

Power law relationships are ubiquitous in ecology, and complex systems in general, and
can be used as metrics to describe many aspects of ecosystem structure and function.
While ecological interactions and processes predominantly occur at the individual level
of biological organisation, currently, most ecological studies aim to estimate “typical”
ecosystem behaviour over large spatial and temporal scales. This disconnect results
in the under- appreciation of ecosystem dynamics that are potentially important for
developing ecological theory and ecosystem modelling. The research presented herein
aims to estimate within-ecosystem dynamics, as quantified by power law relationships,
to test whether expected ecological dynamics can be captured effectively at smaller scales.
I show that Taylor’s power law, a metric of aggregation, varies systematically, both
spatially and temporally within the North Sea fish community, with the abiotic environment
when populations were considered as cohorts of individual body sizes. By combining
estimates of the power law distribution of body size in fish with stable isotopes that can be
used to infer trophic interactions, I show that seasonal trends in fish movement patterns
and the incorporation of pulsed phytoplankton production can be quantified in a highly
dynamic estuarine environment. Estimates of the in situ community predator-prey mass
ratio, which describes trophic behaviour, and the apparent trophic transfer efficiency are
then derived and shown to exhibit strong seasonal variation, indicative of an estuarine
food web that is temporally variable. Finally, I quantify the degree of individual specialisation,
a mechanism by which intraspecific competition is modulated, in the diet of a commercially
important but over-exploited fish species to inform conservation efforts.
This work shows that ecological dynamics can be captured by a range of ecosystem
metrics and that, therefore, small scale behaviours can be tested for empirically to direct ecosystem models and theory.

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Identifiers

ORCID for Matthew, Robert David Cobain: orcid.org/0000-0003-1701-3986

ORCID for Clive Trueman: orcid.org/0000-0002-4995-736X

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