2.5 Lesson 2 Summary
Module 1 ~ Lesson 2
About 10% of the energy at a given trophic level is transferred to the next energy level. The rest is used in cellular functions, lost as heat, or excreted. Feeding relationships can be represented as a pyramid of numbers, a pyramid of biomass, or pyramid of energy. Toxins that are passed through trophic levels are not excreted, and their concentration is amplified due to biomagnification and bioaccumulation.
conservationist: someone who advocates saving and/ or conserving natural resources
food chain: a diagram or model that uses a straight line to show how food (energy) transfers from producers to primary consumers to higher trophic levels
food web: a diagram or model that shows the connections among food chains (food/energy transfer) in an ecosystem
trophic level: describes the feeding level through which matter and energy are transferred; indicates an organism's position in the food chain (e.g., producer, primary consumer, secondary consumer)
biodiversity: a variety in the number and kind of species in a given area
biomagnification: the buildup of harmful chemicals in higher trophic levels (top predators)
Ecologists measure biomass in different ways. Some include previously living matter such as dead trees, bark, and carcasses, while others do not. The units used to record biomass also vary. This means that ecologists cannot be sure that they are making a fair comparison between ecosystems.
Use Figure 1.13 on page 20 of your textbook to describe how the higher trophic levels would be impacted by extreme drought. How would lower trophic levels be impacted by disease in the hawk population?
Drought would decrease the productivity of grasses. If there is less grass, it impacts the entire food web. The available food for all other trophic levels will decrease. If the hawk population is diseased, they will not prey on the lower levels. This will likely cause an increase in the number of snakes. More snakes will result in fewer mice since they will not be preyed on, which will result in overgrazing on the grass.
Explain how the same species can occupy more than one trophic level within the same food web. How might this enhance the stability of a food web? (page 30, #9)
Species have varied diets. For example, bears eat berries (producers), but also fish (primary or secondary consumers) which means they can occupy the second, third, or fourth trophic level. When an organism is not dependent on only one food source, the chances of it surviving a year where that food source was scarce is increased. When organisms can ensure survival, an ecosystem has greater stability.
Explain why the trophic structure of a grassland ecosystem results in an upright pyramid of numbers while the trophic structure of an aspen tree in the the northern boreal forest is inverted. (page 31, #16)
The relative number of producers that can support consumers is greater in a grassland due to the size of the producer; an aspen tree can support many primary consumers due to its size.