The genesis of size variability in plants and animals
Authored by CA Pfister, FR Stevens
Date Published: 2002
Sponsors:
Mellon Foundation
United States National Science Foundation (NSF)
Platforms:
No platforms listed
Model Documentation:
Other Narrative
Mathematical description
Model Code URLs:
Model code not found
Abstract
The changes in the size structure of a cohort of individuals through
time can have important population-level consequences, but the
determinants of patterns of variation in individual size are not well
understood. We use an individual-based simulation model to determine
what factors can lead to changes in the variability in size among
individuals through time, with attention paid to those factors that
increase variability. A pattern of increasing size variability over time
(i.e., growth depensation) has been documented in a variety of taxa.
Size-dependent growth has generally been advanced as the explanation for
its occurrence. We evaluated the independent and interactive effects of
size-dependent growth factors, positive temporal correlates in growth
(termed ``growth autocorrelation{''}), and environmental stochasticity
in generating growth depensation. In contrast to expectation, our
results indicate that size-dependent growth is not the major contributor
to changing variability patterns. Instead, our simulations indicate that
growth autocorrelation is often the major determinant causing growth
depensation. Data collected from the kelp Alaria nana and the whelk
Nucella canaliculata showed evidence for positive correlations in growth
(independent of size), while the tidepool sculpin Oligocottus maculosus
does not. The changes in size variability in these three species
(increasing size variability through time in A. nana only) were
consistent with model predictions. Our results emphasize a need to
disentangle size-related processes from other correlates of growth in
field populations and to document how these phenomena are affected by
environmental stressors and intraspecific interactions.
Tags
Competition
Dynamics
Life-history
Natural-populations
Prey
selection
Dependent growth
Frequency-distributions
Individual variation
Thaidid gastropods
Larval salamanders