Consumer pressure, seed versus safe-site limitation, and plant population dynamics |
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Authors: | J L Maron S N Gardner |
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Institution: | (1) Botany Department, Box 355325, University of Washington, Seattle, WA 98195, USA e-mail: jmaron@u.washington.edu Tel.: +1-206-5438917, Fax: +1-206-6851728, US;(2) Biology and Biotechnology Research Program, Lawrence Livermore National Laboratory, P.O. Box 808, L-452, Livermore, CA 94551-0452, USA, US |
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Abstract: | Plants often suffer reductions in fecundity due to insect herbivory. Whether this loss of seeds has population-level consequences
is much debated and often unknown. For many plants, particularly those with long-lived seedbanks, it is frequently asserted
that herbivores have minimal impacts on plant abundance because safe-site availability rather than absolute seed number determines
the magnitude of future plant recruitment and hence population abundance. However, empirical tests of this assertion are generally
lacking and the interplay between herbivory, spatio-temporal variability in seed- or safe-site-limited recruitment, and seedbank
dynamics is likely to be complex. Here we use a stochastic simulation model to explore how changes in the spatial and temporal
frequency of seed-limited recruitment, the strength of density-dependent seedling survival, and longevity of seeds in the
soil influence the population response to herbivory. Model output reveals several surprising results. First, given a seedbank,
herbivores can have substantial effects on mean population abundance even if recruitment is primarily safe-site-limited in
either time or space. Second, increasing seedbank longevity increases the population effects of herbivory, because annual
reductions in seed input due to herbivory are accumulated in the seedbank. Third, population impacts of herbivory are robust
even in the face of moderately strong density-dependent seedling mortality. These results imply that the conditions under
which herbivores influence plant population dynamics may be more widespread than heretofore expected. Experiments are now
needed to test these predictions.
Received: 3 November 1999 / Accepted: 15 February 2000 |
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Keywords: | Herbivory Plant population dynamics Seed- versus safe-site-limited recruitment Seedbank Simulation model |
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