Range limits and geographic patterns of abundance of the rocky intertidal owl limpet, Lottia gigantea

Authors

  • Phillip B. Fenberg,

    Corresponding author
    1. Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA
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  • Marcelo M. Rivadeneira

    1. Centro de Estudios Avanzados en Zonas Aridas (CEAZA) & Facultad de Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, 1781421 Coquimbo, Chile
    2. Departamento de Ecología, Facultad de Ciencias Biológicas, Center for Advanced Studies in Ecology and Biodiversity (CASEB), P. Universidad Católica de Chile, Alameda 340, Santiago, Chile
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Phillip B. Fenberg, Department of Zoology, Oregon State University, 3029 Cordley Hall, Corvallis, OR 97331, USA.
E-mail: fenbergp@science.oregonstate.edu; pfenberg@gmail.com

Abstract

Aim  We evaluate the stability of the range limits of the rocky intertidal limpet, Lottia gigantea, over the last c. 140 years, test the validity of the abundant centre hypothesis, and test indirectly the roles played by recruitment limitation and habitat availability in controlling the range limits. Because this species is size-selectively harvested, our results also allow us to assess conservation implications.

Location  The Pacific coast of North America, from northern California to southern Baja California (41.74° N–23.37° N), encompassing the entire range of L. gigantea.

Methods  The historical and modern distributions of L. gigantea were established using museum data and field observations. Overall and juvenile abundances of local populations were estimated at 25 field sites. The spatial distribution of abundance was evaluated statistically against the predictions of five hypothetical models. The availability of habitat was estimated by measuring the percentage of unavailable sandy beach within cumulative bins of coast across the range of L. gigantea.

Results  The northern limit of L. gigantea has contracted by c. 2.4° of latitude over recent decades (after 1963), while the southern limit has remained stable. The highest abundances of L. gigantea occur in the centre of its geographic range. Habitat availability is ample in the centre and northern portions of its range, but is generally lacking in the southern range. The northern range is only sparsely populated by adults, with sharp declines occurring north of Monterey Bay (36.80° N). In the southern range, abundance drops precipitously south of Punta Eugenia (27.82° N), coinciding with the region where suitable habitat becomes sparse.

Main conclusions  Support for the abundant centre hypothesis was found for L. gigantea. Northern populations are characterized as being recruitment-limited, demographically unstable and prone to local extinctions, while southern populations are suggested to be habitat-limited. The abundant centre is suggested to result partly from a combination of the indirect effects of human harvesting, generating denser populations of smaller individuals, and larval recruitment from well-protected offshore rocky islands primarily found in the range centre.

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