Predicted effects of behavioural movement and passive transport on individual growth and community size structure in marine ecosystems
Castle, MD and Blanchard, JL and Jennings, S, Predicted effects of behavioural movement and passive transport on individual growth and community size structure in marine ecosystems, Advances in Ecological Research, 45 pp. 41-66. ISSN 0065-2504 (2011) [Refereed Article]
We develop a spatially explicit, continuous, time-dependent model of size
spectra to predict how the active movement and passive transport
of individuals can influence individual growth and size spectra. Active movements
are ‘prey-seeking’ behaviour, with individuals moving locally towards
areas with high concentrations of favoured prey, and ‘predator-avoiding’
behaviour, with prey moving away from areas of high predator density.
Passive transport represents the effects of turbulent mixing on small individuals.
The model was used to explore the individual and community effects
of these biotic and abiotic processes and their interactions, and to predict
how energy from local sources of primary production is propagated through
the food web. Prey-seeking and predator-avoiding behaviour led to systematic
changes in the relative abundance of different-sized individuals in relation
to centres of primary production and associated changes in size-spectra
slopes. In areas of high phytoplankton abundance, community size-spectrum
slopes were shallower and larger individuals were present, whereas in low
production areas, slopes were steeper and size spectra truncated. Variations
in size-spectra slopes were much reduced by spatial aggregation across the
gradient of phytoplankton abundance, and regional slopes most closely
approximated the slopes close to centres of high primary production. Individual
growth was faster when closer to centres of production. The extent to
which stability is apparent in size spectra depended on the scale of aggregation.
This implied that sampling at relatively large space and time scales in
relation to those of phytoplankton ‘blooms’ was necessary to compare
emergent properties, such as size spectra, among regions or ecosystems.
Further, at larger scales, responses to human impacts will be clearer and
less likely to be masked by variability induced by smaller scale processes.