Predation and Food Webs - Freshwater Ecology: Concepts and Environmental Applications - page 397

A

Predators

4

2

Primary consumers

0

Fine particles

Periphyton

-2

Tree leaves

-4

-32 -30 -28 -26 -24 -22 -20

Fish

B 10

8

Copepod

6

Carex

4

Phytoplankton

2

Periphyton

-35 -33 -31 -29 -27 -25 -23 -21

δ 13

FIGURE 19.3 Stable isotope signatures of components of the food web in Lookout Creek,
Oregon (A), and Toolik Lake, Alaska (B). Errors plotted as standard error where data were
available. Note that the use of both isotopes allows for clearer separation of the food web
components. The primary consumers in the stream probably rely on periphyton, but those in
the lake likely rely on phytoplankton (data from Fry, 1991).

FIGURE 19.4 Daphnia lumholtzi, an invasive species in the central United States with large
spines that protect it from predation. This specimen is about 1.5 mm long (photograph cour-
tesy of Randy Bernot).