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Article 4

Effects of density versus size on grazing by a key exploited herbivore

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G. M. Martins, A. C. L. Prestes, A. I. Neto
CIIMAR / CIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Rua dos Bragas 289, P 4050-123 Porto, Portugal
CIRN & Grupo de Biologia Marinha, Departamento de Biologia, Universidade dos Açores, 9501-801 Ponta Delgada, Azores, Portugal
Corresponding author: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

ABSTRACT. – Fishing decreases the biomass of target species via reduction in the numbers and/or size of individuals. In natural systems, the strength of biological interactions, including predator-prey dynamics, are often density or size-dependent. Hence, changes in the numbers or size of key taxa may be expected to influence biological interactions but their effects do not need to be identical. Here we compare the effects of biomass reduction in populations of the exploited limpet Patella candei. Biomass removal was experimentally achieved by either removing individuals (density reduction) or by replacing large by small individuals (size reduction), while controlling for total limpet biomass in a laboratory-based experiment. At the experiment’s termination, biomass reduction led to proportional changes in area grazed. However, there was no difference whether this was achieved via changes in density or in size. Furthermore, no discernible effects of treatments were evident on different components of the algal assemblage. A field survey also revealed that P. candei biomass explained a greater proportion in variation in the area free of algae than density alone. Our results suggest that loss of biomass in populations of P. candei has quantitatively and qualitatively similar effects on algal cover regardless of whether it is caused by an equivalent (biomass) reduction in the numbers or size of individuals.

You are here: Volume 63 (2013) Issue 1 Article 4
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