Exercises: Energy flow

Define trophic level and construct a four-link food chain typical of a Mediterranean holm oak forest, indicating which level each link belongs to and the type of feeding of each organism.

Explain, using the concept of ecological efficiency, why ecosystem food chains rarely have more than four or five levels.

In a meadow, producers fix $20\,000\ \text{kcal/m}^2$ per year and herbivores assimilate $2\,000\ \text{kcal/m}^2$ over the same period. Calculate the ecological efficiency of this transfer, expressed as a percentage.

An aquatic ecosystem shows these annual energy values per level: producers, $50\,000\ \text{kJ}$; herbivores, $4\,800\ \text{kJ}$; carnivores, $450\ \text{kJ}$. Calculate the efficiency of each transfer and comment on whether they comply with the $10\ \%$ rule.

Differentiate between ecological pyramids of energy, biomass, and numbers. Explain in which situation a biomass pyramid can appear inverted (give a marine example) and why an energy pyramid is never inverted.

Look at the energy pyramid in the diagram:

1. a) Identify which trophic level each tier (A, B, C, and D) occupies.
2. b) Calculate the missing value at level D ($?$) assuming that all transfers have the same efficiency as the first one.

A holm oak forest and an open ocean area far from the coast have very different net primary productivities. Explain what net primary productivity is and explain the abiotic factors that limit it in each of these two ecosystems.

Overfishing eliminates large predatory fish from a coastal area. Predict what will happen to the immediately lower trophic levels and explain how this 'trophic cascade' can end up affecting even the seabed algae.

Assuming an ecological efficiency of $10\ \%$ in each transfer, calculate how many kilograms of producers are needed to generate $1\ \text{kg}$ of biomass of a predator situated at the fourth trophic level of a chain. Comment on what the result implies for the conservation of large predators.