Abstract |
- The intermittent upwelling hypothesis (IUH) predicts that the strength of
ecological subsidies, organismal growth responses, and species interactions will vary
unimodally along a gradient of upwelling from persistent downwelling to persistent upwelling,
with maximal levels at an intermediate or ‘‘intermittent’’ state of upwelling. To test this model,
we employed the comparative-experimental method to investigate these processes at 16–44
wave-exposed rocky intertidal sites in Oregon, California, and New Zealand, varying in
average upwelling and/or downwelling during spring–summer. As predicted by the IUH,
ecological subsidies (phytoplankton abundance, prey recruitment rates), prey responses
(barnacle colonization, mussel growth), and species interactions (competition rate, predation
rate and effects) were unimodally related to upwelling. On average, unimodal relationships
with upwelling magnitude explained ~50% of the variance in the various processes, and
unimodal and monotonic positive relationships against an index of intermittency explained
~37% of the variance. Regressions among the ecological subsidies and species interactions
were used to infer potential ecological linkages that underpinned these patterns. Abundance of
phytoplankton was associated with increases in rates of barnacle colonization, intensity of
competition and predation, and predation effects, and rates of barnacle recruitment were
associated with increases in mussel growth, barnacle colonization, and species interactions.
Positive effects on interactions were also seen for rates of colonization, competition,
predation, and predation effects. Several responses were saturating or exponential, suggestive
of threshold effects. These results suggest that the IUH has geographic generality and are also
consistent with earlier arguments that bottom-up effects and propagule subsidies are strongly
linked to the dynamics of higher trophic levels, or top-down effects, as well as to nontrophic
interactions. The ~50% of the variance not explained by upwelling is likely due to more
regional-to-local influences on the processes examined, and future efforts should focus on
incorporating such effects into the IUH.
- Keywords: rocky intertidal, bottom-up, predation, intermittent upwelling hypothesis, ecological subsidies, competition, meta-ecosystems, productivity, recruitment, upwelling/downwelling regime, top-down, Large Marine Ecosystems
|
Funding Statement (additional comments about funding) |
- B. A. Menge’s research has been funded by NSF (awards 0324867, 0726983, 1050694, and 1061233), the Andrew W. Mellon Foundation, the Wayne and Gladys Valley Foundation, the David and Lucile Packard Foundation, the Gordon and Betty Moore Foundation, and the Kingfisher Foundation. D. N. L. Menge acknowledges the Carbon Mitigation Initiative, with funding from British Petroleum and Ford, for support during this project. This is publication 427 from PISCO, the Partnership for Interdisciplinary Studies of Coastal Oceans, funded primarily by the David and Lucile Packard Foundation.
|