The Roles of Humans in Alaskan Marine Food Webs

On October 20, Professor Jennifer A. Dunne of the Santa Fe Institute presented a summary of the complex food webs of Sanak Island. Dunne and her colleagues have compiled the most detailed marine species food web to date. Their data demonstrates the great influence the Aleut natives of Sanak Island had on the island.

Sanak Island is an island off the Western Gulf of Alaska. The island has a 6000 year-long record of human inhabitance, but there were no apparent extinctions throughout this time due to human subsistence. Because of such food web stability, Sanak Island is of interest to environmentalists.

Dunne and her colleagues used ecological observations, shell and bone middens, literature, and interviews of Aleut elders to compile their data. With these sources, Dunne compiled 235 different species and 1804 links within the food web. The program Network3d generated their complex food map and color coordinated the different organisms by species.

The Sanak food web contains a vast number of species, but this is not a result of the biodiversity of the location. Instead, the number and kinds of species recorded demonstrate the quality of the food web data collected.

Invertebrates leave very little evidence after decomposition and are harder to trace after time. As a result, invertebrates are often less represented, and food webs that contain a majority of invertebrates are of better quality. The Sanak food web is composed of 107 invertebrates.

The quality of a food web is measured by the number of species recorded, but the quality can be biased due to intensive concentration on one type of organism. This bias is eliminated by a process called trophic species aggregation where organisms that serve the same role in an environment are grouped together into nodes. After trophic species aggregation, the Sanak marine food web contained more nodes than any other marine food web.

The Sanak food web demonstrates the influence humans had on their environment through the Aleuts’ eating habits. The Aleuts directly fed on 30 percent of the intertidal food web and 24 percent of the marine food web. The Aleut natives are two path lengths away from 96 percent of the food web, so they were extremely connected to their environment. Although their positioning allows them to have great effect on their local diversity, there were no apparent extinctions due to the human subsistence.

The Aleut natives maintained a stable food web because of their consumption pattern. They focused on only a few prey species at a time and switched once a species became scarce. This type of consumption allowed populations in low abundance to recover. The Aleuts prey switched across habitats, seasons, and trophic levels and consequently maintained the stability of their food web.

Professor Jennifer A. Dunne is currently working with Messel Shale to compile a Cambrian food web. The Cambrian food web is currently the largest terrestrial food web complied with around 700 species and over 6000 links.