| Abstract |
- Ecosystems are shaped by processes occurring and interacting over multiple
temporal and spatial scales. Theory suggests such complexity can be simplified by focusing on
processes sharing the same scale as the pattern of interest. This scale-dependent approach to
studying communities has been challenged by multiscale meta-ecosystem theory, which
recognizes that systems are interconnected by the movement of ‘‘ecological subsidies’’ and
suggests that cross-scale feedbacks between local and regional processes can be equally
important for understanding community structure. We reconcile these two perspectives by
developing and testing a hierarchical meta-ecosystem model. The model predicts local
community responses to connectivity over multiple oceanographic spatial scales, defined as
macro- (100s of km), meso- (10s of km), and local scale (100s of m). It assumes that local
communities occur in distinct regions and that connectivity effects are strongest among local
sites. Predictions are that if macroscale processes dominate, then regardless of mesoscale
differences, (1) local communities will be similar, and (2) will be even more so with increased
connectivity. With dominance of mesoscale (i.e., regional) processes, (3) local structure will be
similar within but distinct between regions, and (4) with increased connectivity similar both
within and among regions. With dominance of local-scale processes, (5) local communities will
differ both within and among regions, and (6) with increased connectivity be similar within
but not between regions. We tested the model by evaluating rocky intertidal community
structure patterns with variation in ecological subsidies and environmental conditions at 13
sites spanning 725 km of the northern California Current system. External factors operating at
meso- and local scales had strong effects, explaining 52% and 27% of the variance,
respectively, in community structure. Sessile invertebrate and predator dominance was
associated with weaker upwelling, higher phytoplankton abundance, and higher recruitment,
and the opposite was true for macrophyte dominance. Overall, our results support the theory
that meta-ecosystems are organized hierarchically, with environmental processes dominating
at meso- to macroscales and ecological processes playing a more important role at local scales,
but with important bidirectional cross-scale interactions.
- Keywords: variation partitioning, coastal ecosystems, ecological subsidies, ecosystem dynamics, rocky intertidal communities, meta-ecosystems, oceanographic conditions, northern California Current large marine ecosystem, spatial scale, relative importance
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