Effect of seed predation on seed bank size and seedling recruitment of bush lupine (Lupinus arboreus) |
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Authors: | John L Maron Ellen L Simms |
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Institution: | (1) University of California, Bodega Marine Laboratory, Box 247, Bodega Bay, CA 94923, USA e-mail: jlmaron@ucdavis.edu; Fax: 707-875-2089, US;(2) Department of Ecology and Evolution, University of Chicago 1101 East 57 Street, Chicago, IL 60637, USA, US |
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Abstract: | Whether seed consumers affect plant establishment is an important unresolved question in plant population biology. Seed consumption
is ubiquitous; at issue is whether seedling recruitment is limited by safe-sites or seeds. If most seeds inhabit sites unsuitable
for germination, post-dispersal seed consumption primarily removes seeds that would otherwise never contribute to the population
and granivory has minimal impacts on plant abundance. Alternatively, if most seeds ultimately germinate before they lose viability,
there is greater potential for seed consumption to affect plant recruitment. Of the many studies on seed consumption, few
ask how seed loss affects seedling recruitment for species with long-lived seed banks. We examined post-dispersal seed predation
and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California. We followed the fate of seeds in paired experimental
seed plots that were either protected or exposed to rodent granivores in grassland and dune habitats. Significantly more seeds
were removed by rodents in dunes than grasslands. In dunes, where rodent granivory was greatest (65% and 86% of seeds removed
from plots by rodents in two successive years), there is a sparse seed bank (6.6 seeds m−2), and granivory significantly reduced seedling emergence (in the same two years, 18% and 19.4% fewer seedlings emerged from
exposed versus protected plots), suggesting seed rather than safe-site limited seedling recruitment. In contrast, rodents
removed an average of 6% and 56% of seeds from grassland plots during the same two years, and the grassland seed bank is 43-fold
that of the dunes (288 seeds m−2). Even high seed consumption in the second year of the study only marginally influenced recruitment because seeds that escaped
predation remained dormant. Burial of seeds in both habitats significantly reduced the percentage of seeds removed by rodents.
Results suggest that granivores exert strong but habitat-dependent effects on lupine seed survival and seedling emergence.
Received: 24 October 1996 / Accepted: 4 February 1997 |
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Keywords: | Bush lupine Granivory Seed bank dynamics Seedling recruitment |
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