10.5061/DRYAD.GTHT76HHT
Mutz, Jessie
0000-0003-3956-7760
Florida State University
Underwood, Nora
Florida State University
Inouye, Brian
Florida State University
Integrating top-down and bottom-up effects of local density across scales
and a complex life cycle
Dryad
dataset
2020
2021-05-22T00:00:00Z
2021-05-22T00:00:00Z
en
65221 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Effects of group size (local conspecific density) on individual
performance can be substantial, yet it is unclear how these translate to
larger-scale and longer-term outcomes. Effects of group size can be
mediated by both top-down and bottom-up interactions, can change in type
or direction across the life cycle, and can depend on the spatial scale at
which group size is assessed. Only by determining how these different
processes combine can we make predictions about how selection operates on
group size or link hierarchical patterns of density-dependence with
population dynamics. We manipulated the density of a leaf beetle,
Leptinotarsa juncta, at three nested spatial scales (patch, plant within a
patch, and leaf within plant) to investigate how conspecific density
affects predator-mediated survival and resource-mediated growth during
different life stages and across multiple spatial scales. We then used
data from field predation experiments to assess how L. juncta densities at
hierarchical scales affect different aspects of predation. Finally, we
incorporated predator- and resource-mediated effects of density in a model
to explore how changes in group size due to density-dependent predation
might affect mass at pupation for survivors. The effects of L. juncta
density on predation risk differed among scales. Per capita predation risk
of both eggs and late-instar larvae was lowest at high patch-scale
densities, but increased with plant-scale density. The final mass of
late-instar larvae declined with increasing plant-scale larval density,
potentially due to truncated development of high-density larvae. Predation
incidence (i.e., group attack rate) increased with larval density at all
spatial scales. A high coefficient of variation (i.e., greater
aggregation) of L. juncta density was associated with lower predation
incidence at some scales. Our model suggested that predator- and
resource-mediated effects of density interact: lower survival at high
larval density is mitigated by high final mass of larvae in the resulting
smaller groups. Our results emphasize the importance of spatial scale and
demonstrate that effects of top-down and bottom-up interactions are not
necessarily independent. To understand how group size influences fitness,
predator- and resource-mediated effects of density should be measured in
their demographic and spatial context, and not in isolation.
README.txt file describes data files and variable names.