Abstract
Marine reserves that prohibit fishing often result in greater densities of individuals and more species than adjacent fished areas. However, simple conclusions about their effects on species richness are confounded, because more species are expected to occur wherever there are more individuals. Here, there is an important distinction between the number of species per sampling unit (species density), and species richness measured as the number of species per given number of individuals. When conservation of species richness is an important goal, analyses need to discriminate between the alternative explanations for differences in the number of species. We used rarefaction to test whether species richness was higher in two ‘no-take’ marine reserves after controlling for differences in the density of individuals. We surveyed each reserve in three different years. There was a higher density of individuals and species in each reserve than in adjacent fished areas. However, rarefaction analyses indicated that effects on species richness were weak after controlling for the number of individuals: slightly higher species richness was recorded inside each reserve in one of three surveys, but the difference was small, and was apparent only when the maximum number of individuals was approached. Our results therefore indicate that patterns in species density were not reflected by patterns in species richness—the application of rarefaction methods is needed to determine the responses of species richness to protection elsewhere. The distinction between species density and species richness will not be important in all situations, but when it is important, inferences about species richness cannot be reliably deduced from measurements of species density.
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Acknowledgments
We thank the Rottnest Island Authority and the Western Australian Department of Conservation and Environment for logistical support and research permits, and numerous assistants for their help with the surveys. F. Tuya and S. Wilson provided comments that helped improve the manuscript. This research was partially supported by the Strategic Research Fund for the Marine Environment, the Western Australian Marine Science Institution and the Australian Research Council.
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Communicated by Craig Osenberg.
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Vanderklift, M.A., Babcock, R.C. & Cook, K. The effects of protection from fishing on species richness: distinguishing between alternative explanations. Oecologia 171, 309–315 (2013). https://doi.org/10.1007/s00442-012-2408-7
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DOI: https://doi.org/10.1007/s00442-012-2408-7