Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory
Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory
Date
2008-11-09
Authors
Knight, Tiffany M.
Caswell, Hal
Kalisz, Susan
Caswell, Hal
Kalisz, Susan
Linked Authors
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Keywords
Demography
Elasticity analysis
Extinction risk
Interspecific interactions
Matrix model
Tolerance
Elasticity analysis
Extinction risk
Interspecific interactions
Matrix model
Tolerance
Abstract
Overabundant white-tailed deer (Odocoileus virginianus) are a significant management
problem in North America that exert unprecedented herbivory pressure on native understory
forest communities. Conserving understory plant populations requires quantifying a sustainable
level of deer herbivory. To date, most population projection models consider only deer presence
and absence. To estimate population growth rate along a gradient of herbivory, we focused on
Trillium grandiflorum because it is a common understory species and a bellwether of deer effects
and forest decline. We used matrix population models, and employed both prospective and
retrospective analyses using a regression life table response experiment (LTRE).
Deer affect size, stage and population dynamics of T. grandiflorum. Because deer target
flowering and large non-flowering stages of T. grandiflorum, these individuals do not produce
seed in the year they are browsed and are more likely to regress in stage and size in the following
growing season relative to non-browsed plants. Importantly, sustained high browse levels result
in populations dominated by small, non-flowering individuals. Our LTRE revealed a significant
negative and decelerating relationship between herbivory and λ. This non-linearity occurs at the
highest herbivory levels because highly browsed populations become dominated by stages that
deer do not consume and are thus buffered from rapid decline. However, population extinction is
expected when herbivory is greater than the pivotal value of ~15%. Our study demonstrates that
levels of deer herbivory commonly experienced by forest understory perennials are sufficient to
cause the loss of T. grandiflorum and likely other co-occurring palatable species.
Description
Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Forest Ecology and Management 257 (2009): 1095-1103, doi:10.1016/j.foreco.2008.11.018.