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No Omnivore’s Dilemma for Alaskan Hunter-Gatherers
19 February 2012 5:26 pm
VANCOUVER, CANADA—For most of the past 5000 years, the hunter-gatherers known as the Aleuts have lived on Sanak Island off the southern coast of Alaska, surviving on the local fish and marine mammals they caught as well as clams and mussels collected in the intertidal zone around their island. Now after constructing some of the most elaborate food webs ever built, a research team has begun to reveal how the Aleuts fit in as a top predator in the island ecosystem. In short, the Aleuts weren’t picky eaters, consuming about one-quarter of the different species on and around Sanak Island. But by being such “supergeneralists”, the research team suggests, they were likely able to keep the ecosystem stable because they would switch prey when a particular species became endangered, and thus harder to catch or collect.
“This is our first detailed picture of how humans fit into food webs,” ecologist Jennifer Dunne of the Santa Fe Institute in New Mexico said here yesterday at a symposium on the topic at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW). “It is the first time that the roles of humans as predators are explicitly compared to the roles of other predators in food webs.”
As part of a National Science Foundation-funded research effort known as the Sanak Biocomplexity Project, Dunne and her colleagues have collected and analyzed a wide variety of data on Sanak Island’s ecology and its human inhabitants, including archaeological and written evidence on the Aleuts. For example, ancient middens, essentially preserved dumps of food waste such as bones and shells, were studied to glean the historical diets of the Aleuts. The researchers ultimately determined what each species was eating, and what was eating it, linking individual food chains together into an overall food web.
Dunne and her colleagues have created two such food webs, one limited to species connected to the intertidal zone (above left) and a broader one, which includes birds and additional fish, looking at the whole marine ecosystem (above right). In the intertidal food web, for example, the Aleuts ate the highest number of different prey, 50 of 171 species, with a sea fish and marine crab taking the next slots, consuming 39 and 37 species respectively. In the marine food web, however, the Pacific cod takes the top spot, munching on 124 of the 513 species, although the Aleuts aren’t far behind with a diet encompassing 122 species. Dunne noted that 96% of the species in the Sanak Island marine food web they’ve built are within two feeding links to the Aleuts. They “were very tightly connected to nearly all the species in the marine ecosystem,” she says. “The Aleuts were positioned to have great effects on local diversity.”
Despite that, there’s no evidence that predation by the Aleuts drove any species to extinction, which Dunne attributes to their penchant for regularly switching food sources depending on the season, weather, and availability of various prey. Pointing out that the human appetite for bluefin tuna is currently driving the species to extinction, Dunne notes that the Aleutian way is a sharp contrast to much of the world today where rarity of a food increases its value and, consequently, demand for it.
The analysis by Dunne and her colleagues is rare and valuable in that it “puts people in the food web,” says fisheries expert Andrew Trites of the University of British Columbia in Vancouver, who also participated in the AAAS symposium.