Exam 15: Mutualism and Commensalism

Most wasps are carnivores, but one group feeds on pollen and nectar and pollinates the flowers they visit. Wasps are less efficient than bees at pollination because their bodies are not covered with fuzzy hairs and therefore, pollen is less likely to stick to them. But masarine wasps specialize in pollinating certain species, including beardtongues (Penstemon sp.). Given this information, how will the costs and benefits of masarine wasp-plant mutualisms likely compare to those of bee-plant mutualisms?

Refer to the figure. In the study illustrated in the figure, van der Heijden and colleagues compared the effects of differing numbers of mycorrhizal species (0?-14) on the same 15 plant species. They measured the effects of this mycorrhizal species diversity on net primary production (measured as shoot and root biomass) and on cycling of nutrients (measured as phosphorus content). Based on the figure, what can be concluded about the effect of mycorrhizal diversity on plant ecosystems?

A bacterium provides essential amino acids to an aphid, which in turn provides sugars to the bacterium. Assuming that each partner is benefiting from the interaction, this would be an example of which type of mutualism?

What is a "cheater" in a mutualistic relationship? Give an example. Under what circumstances would cheating be a benefit to the cheating party? How might the exploited partner respond?

Spider crabs live on the ocean floor in shallow areas and greenish-brown algae live on their backs. This provides the algae with a home and the algae's greenish-brown color helps the crab blend in and stay safe from predators. This association can be considered a mutualism because

What types of environmental factors can cause positive associations, including mutualism and commensalism, to vary in terms of their costs and benefits? Give several environmental conditions that might impact these associations.

Refer to the figures. The two figures represent the results of studies on a mutualism between the plant Medicago and its partner, a mycorrhizal fungus. The top figure shows the percentage of carbohydrate transferred from the plant to the fungus, depending on the amount of phosphorus the fungus supplies to the plant. The bottom figure shows the amount of fungal phosphorus incorporated by plant roots, depending on the amount of carbohydrate supplied to the fungus. Given the information in these two figures, does the mutualism appear to be under the control of the plant or the fungus, or do both partners exercise some control?

A coral reef ecosystem provides food and habitat for a variety of species. Discuss, with examples, how a coral reef might increase species diversity in the shallow ocean habitat.

Bromeliads and other tropical plants live in and on rainforest trees, obtaining food and living space from the trees but not helping or harming them. What type of association do trees and bromeliads have, and how much coevolution is occurring to maintain this relationship?

Forest fragmentation and habitat loss is increasing around the world. Many species living in forests are "forest specialists." These specialists can only survive in certain types of trees, or in certain microclimates found only in a particular forest type; that is, they have facultative mutualisms with certain species in the forests. One of these is the white-backed woodpecker, a rare European species found in old-growth deciduous forests. Others include more than 20,000 types of wood beetles, which require specific types of oaks as their habitat. Predict what will happen to these mutualisms, and to the distribution and abundance of species, as forest fragmentation and habitat loss continues.

A mycorrhizal-associated fungus grows between the cells of the root of a plant, forming a mantle around the exterior of the root. This is an example of which type of association?