Scientists use different types of models to analyze the structure of ecosystems. which characteristic is seen in a biomass pyramid, but not in a numbers pyramid?
the total number of trophic levels in an ecosystem
living matter found at each trophic level in an ecosystem
energy available at each trophic level in an ecosystem
organisms found at each trophic level in an ecosystem

Which of the following statements is (are) true? i. free entry to a perfectly competitive industry results in the industry's firms earning zero economic profit in the long run, except for the most efficient producers, who may earn economic rent. ii. in a perfectly competitive market, long-run equilibrium is characterized by lmc < p < latc. iii. if a competitive industry is in long-run equilibrium, a decrease in demand causes firms to earn negative profit because the market price will fall below average total cost.

Experts are particularly concerned about four strategic metal resources that are important for the u.s. economy and military strength, and that must be imported. what percentage does the u.s. import? *

Utilization will always be lower than efficiency because: a. effective capacity is greater than design capacityb. expected output is less than actual output.c. effective capacity equals design capacity.d. effective capacity is less than design capacity.e. expected output is less than rated capacity.