14 Homework - Mutualism

How can coral reefs be highly productive despite being in nutrient-poor waters?

Corals have endosymbiotic algae (zooxanthellae) that produce carbohydrates via photosynthesis.

True or False: Species that exhibit a facultative mutualism can survive in the absence of their mutualistic partner.

True.

Which environmental conditions favor fungi that are less mutualistic and more parasitic?

High nutrient availability in the soil.

In low-nutrient soils, why do plants allocate more carbohydrates to mycorrhizal fungi?

The fungi provide essential nutrients (like phosphorus) that plants cannot easily obtain on their own.

Why might mycorrhizal fungi from fertilized soils be less beneficial to plants?

They evolved under conditions where nutrient exchange was less necessary, making them less efficient partners.

Under what evolutionary condition are mutualisms expected to evolve?

When the fitness of both mutualists exceeds that of non-mutualists and unsuccessful mutualists.

What results from Johnson (1993) support the idea that mycorrhizae benefit plants?

Increased shoot mass and lower root-to-shoot ratios in plants with fungi.

Which soil condition is most likely to produce the strongest mutualistic interaction between plants and mycorrhizae?

Low nutrient availability.

Why does nitrogen limitation promote carbon transfer from zooxanthellae to the coral host?

The zooxanthellae cannot use all the fixed carbon for their own growth due to lack of nitrogen, so they release the excess to the coral.

In a plant-mycorrhizae mutualism, what does each partner provide?

Plants provide carbohydrates; fungi provide nutrients.

What are the primary benefits in an ant-acacia mutualism?

Acacia thorns provide habitat/food for ants, and in return, acacias with ants grow faster and are protected from herbivores.