Bio 1b lec 19

Energy flow vs. matter cycling

Energy flows one way through ecosystems and is eventually dissipated as heat; matter such as carbon is recycled.

Photosynthesis and cellular respiration

Photosynthesis captures sunlight and stores energy in carbon bonds while taking in CO2; respiration releases usable energy and returns CO2.

Trophic levels

Feeding positions in a food chain: primary producers, primary consumers, secondary consumers, tertiary consumers, and quaternary consumers.

Energy transfer efficiency

The fraction of energy at one trophic level converted into biomass available to the next; approximately 10% on average.

Caterpillar energy budget

Of 200 J of plant material consumed, 100 J is lost as feces, 67 J is used in respiration, and 33 J becomes new biomass.

Why food chains are short

Energy is lost at each trophic transfer, leaving progressively less energy and biomass to support higher trophic levels.

Productivity and food chain length

Higher ecosystem productivity supplies more energy and can support longer food chains, as shown in the tree-hole experiment.

Food web

A network of interconnected food chains showing multiple feeding relationships and energy pathways.

Exclusive vs. non-exclusive consumers

Exclusive consumers feed at one trophic level; non-exclusive consumers feed across multiple trophic levels, as sea nettles do.

Dominant species

A species characterized by high abundance within its ecological community.

Keystone species and Pisaster

A species with a disproportionately large ecological impact; Pisaster sea stars prevent mussels from monopolizing space and reducing biodiversity.

Ecosystem engineers and beavers

Organisms that physically modify habitats; beaver dams create wetlands that support other species.

Bottom-up vs. top-down control

Bottom-up control begins with resource availability at lower trophic levels; top-down control begins with consumers regulating lower levels.

Trophic cascade and trout experiment

Predators indirectly affect organisms across at least three trophic levels; trout reduce grazing invertebrates, allowing algae to increase.

Lake Vesijärvi biomanipulation

Reducing zooplankton-eating fish allowed zooplankton to increase, algae to decrease, and lake water to become clearer.