Trophics Archives | JuneauNature

Who eats who?

Green-winged teal diet by season, From Martin Zim & Nelson, 1951. Hatched portion is plant diet, given as percentage below: mostly seeds of freshwater aquatic species. White portion is animal prey, mostly beetles and aquatic larvae. Passing through Southeast, especially in fall, teal and other dabblers rely heavily on the massive seed production of Lyngbye sedge. Absence of hatching in summer is due to low sample size. Perhaps even in 1951 it was considered poor taste to shot ducks in breeding season?

Southeast food pyramids

When you catch a fish, do you open its stomach to learn about its last few meals? If you hunt grouse or mallards, do you examine crops? Before enjoying the first tenderloin from guwakaan, the peace keeper (Sitka black-tailed deer), do you search for plant fragments on the back of its tongue, or open the rumen—that magic sack that converts the mostly-humanly-inedible flora of our bioregion into the tastiest meat on the planet?

I assembled this saltmarsh-foodweb back in 1992 for the first edition of Nature of Southeast Alaska. The layout takes a moment to absorb. At top are terrestrial species who move down into the tidal marsh to forage. At bottom are marine species who either come up from the depths when tides flood the marsh, or benefit by detritus wash-down, or by preying on species who in turn fed in the marsh. Central grey bar has mostly ‘resident’ flora and fauna of the salt marsh. Finally, birds in the 2-headed arrow band are migrants—who target the salt marsh on their way north and south in spring and fall. The salt marsh—and adjacent mudflats and uplift meadows—has to be the most ‘generous’ of our ‘exporting communities.’ For more on salt-marsh ecology, see Nature>Habitats>Coastal>Estuaries>Salt marsh.

One of the oldest books in my natural history library is American wildlife & plants: A guide to wildlife food habits. Martin, Zim & Nelson, 1951. The reason it remains relevant 65 years later, while other ecological works of the period have been supplanted, is that nowadays people look askance at shooting a couple hundred herons just to see what’s in their stomachs: 43% non-game fish, 25% “useful species,” 8% each of insects & crayfish, 5% mice & shrews, 4% herps. (Another thing ecologists rarely do anymore—applied entomologists perhaps excepted—is classify species as “useful,” which would sort of beg the question as to who is non-useful.)

Savannah sparrows are probably the most abundant nesters in high marsh and adjacent uplift meadow, in Southeast estuaries. They’re primarily seed eaters except in summer, when, like many vegans, they switch to hunting insects for their nestlings. See above chart for symbology.

This trophic diagram shows why salt marshes—constituting less than 1% of our land mass—are so essential to resident and migratory species from land and sea. Dashed arrow lines lead from eaten to eater. For more background on salt marsh trophics, see pages 80 to 85 in the 3rd edition of Nature of Southeast Alaska.