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problem, I don't see any fatal inconsistencies with our hypothesis," says Estes.
Many scientists have difficulty believing that predation could play such an important role in the structure of marine food webs, but the authors show that the timing of events; information on the abundance, diet and foraging behavior of both predators and prey; and feasibility analyses based on demographic and energetic modeling, are all consistent with this hypothesis. Dr. Robert Paine, of the University of Washington agrees, "It's a plausible and unifying explanation for the sequential collapse. In a multiple causation world, this is likely one of the main causes."
Traditionally, little attention has been paid to the role of predation in structuring open ocean ecosystems (i.e. top down effects). For the last 30 years most scientists have focused on bottom up influences such as changes in the physical oceanic environment and food shortages. These researchers are convinced that the power of predation is much greater than previously realized - if animals are forced to switch food sources, the ripple effects through an ecosystem can be profound.
One of the most striking implications of this work is the complex interconnections between changes in open ocean populations and coastal environments. This is most apparent in Estes' study sites throughout the Aleutian Archipelago where he and his team have studied kelp forests for over thirty years. "What we've seen is that the kelp forest ecosystem in South Western Alaska went from being robust to being ... gone. It's staggering that it occurred over such a large area in such a short time - just a few years," says Estes. "The food web interconnectivity - that urchin explosions could be linked to whaling 50 years ago - is amazing."
"We may take well intended actions to protect species like sea otters - but that may not be enough if we've unwittingly set in motion other disturbances that eventually impact different animals in different places," says Jeremy Jackson, of Scripps Institution of Oceanography. Jackson was the lead author on a widely cited paper in Science that first demonstrated pervasive impacts of historic disturbances on ocean ecosystems. "This is the most dramatic example to date," says Jackson. "It's so counterintuitive - and reaches back beyond memory and across the entire North Pacific Ocean."
"The message," says Springer, "is that overfishing and massive extraction can lead to food web impacts that are unexpected and unintended."
The authors feel that the importance of predation in structuring food webs needs to be more fully appreciated and understood - and humans are the ultimate predators. This points to the need for caution in managing fisheries today. The kind of extraction that happened with whales fifty years ago still goes on with other species, wearing away the resilience of the system.
"To me it very much is an overfishing problem - same damn thing - but fifty years ago whales were the fish," says Estes.
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