Chapter 15

What is required for a mutualism to evolve? With this in mind, what might cause a mutualism to end or shift? Which type of interaction (facultative or obligate) is this most likely to happen with?

-If one partner's needs are no longer being met and it is not benefitting, it will leave. -if environmental conditions change, and benefit is reduced or cost increased for either partner, the outcome may change, particularly for facultative interactions.

What are the two types of positive interactions?

-Mutualism: mutually beneficial interaction between individuals of two species (+/+ relationship) -Commensalism: individuals of one species benefit while the other does not, but neither are harmed. (+/0 relationship)

How is performance measured in plants? What comparisons of performance are used to look at interactions? What is relative neighbor effect (RNE)? In the study that focused on RNE, how did elevation affect the effect that neighbors had on target species? What does this suggest about interactions in stressful environments?

-Positive interactions are more common in stressful environments (high elevation, intertidal zones, wetlands, etc.) -Relative neighbor effect (RNE): target species' performance with neighbors present minus its performance with neighbors removed. -areas of high elevation always show more benefits with neighbors increasing growth.

What are trophic, habitat, and service mutualisms? Give an example of each.

-Trophic mutualism: mutualist receives energy or nutrients from its partner. (leaf cutter ants and fungus, mycorrihizae) -Habitat mutualism: one partner provides the other with shelter, living space, or favorable habitat (pistol shrimp dig burrows they share with the goby fish that in turn serves as a 'seeing eye fish' while also getting refuge) -Service mutualism: one partner performs an ecological service for the other. (pollination, dispersal, and defenses against herbivores, predators, or parasites)

How can the presence of a mutualist affect the distribution and community composition of an area? How might a mutualistic interaction affect competition?

-certain interactions can lead to more abundance for a species (ant and acacia mutualism increases the abundance of both species) -in the rocky intertidal zone the environmental condition is better under seaweed where starfish, urchins, and snails live to survive. -in coral reefs cleaner fish remove parasites from larger fish. -competition can affect mutualism becasue in areas of low stress competition prevails.

How might a positive interaction be used as a dispersal mechanism? Why are these interactions normally considered sporadic and facultative? Is this always the case?

-deer can move seeds long distances becasue they consume the seeds and don't digest them as they poop them out all over town. -example of facultative commensalism because it is optional and the deer doesn't benefit.

What are cheaters? What happens to mutualist interactions when one partner begins to cheat? What types of penalties might a partner use to discourage cheating?

Cheaters are individuals that increase offspring production by overexploiting their mutualistic partner. -the interaction won't persist once this happens. -Moths use yucca to collect pollen and lay their eggs and the larvae consume the seeds. Cheating can occur if moths lay too many eggs and the larvae consume too many seeds. The penalty is the yuccas can selectively abort flowers with two many eggs before the larvae hatch.

True or false. In positive interactions, the interaction does not cost either organism anything. Explain.

False, sometimes there is a cost to one or both partners, but the net effect is positive.

What is a facultative interaction? Are these types of relationships normally species-specific? Have these organisms coevolved? What is a nurse plant?

The interaction is optional. -few signs of coevolution -commensalism is always facultative for the species that does not benefit. -in deserts, the shade of adult plants creates cooler, moister conditions. Seeds of many plants can only germinate in this condition. The adult is called a NURSE PLANT.

How can interaction outcomes change with time? What types of factors are important in determining this?

When interactions no longer provide a net benefit, they cease to exist. -take in to account space and time.

What are zooxanthellae? Describe their relationship with coral.

Zooxanthellae are algae that that have a mutualistic relationship with coral. -the coral provides the algae with a home, nutrients, and access to sunlight. The algae provides carbohydrates from photosynthesis for the coral.

How can mutualism arise from a host-parasite interaction?

due to evolution, the parasite can no longer be harmful to its host and can instead both become dependent on each other.

What are mycorrhizae, and how are they an example of mutualism? What are the two types?

Mycorrihizae: symbiotic associations between the roots and various fungi. -the fungi increase the surface area for the plant to take up water and soil nutrients while the plants supply the fungi with carbohydrates. -Ectomycorrihizae: the fungus grows between root cels and forms a mantle around the root. -Arbuscular mycorrihizae: the fungus penetrates the cell walls of some root cells, forming a branched network called an arbuscule.

Why is a mutualism not considered altruistic? (Hint: Do these organisms really care about the growth, survival, and reproduction of the other partner?)

Not altruistic because they are in it for their own benefit.

What is a positive interaction? Give some examples. How did this type of relationship help with the colonization of land by plants?

Positive interactions are those in which one or both species benefits and neither is harmed. -corals forming a mutualism with zooxanthellae. -bacteria in a cow'a rumen gut that help digest plants. -lichens that grow on trees.

What are the three types of symbioses? Define each. What does symbiosis mean specifically?

Symbiosis: two species live in close physiological contact with each other. -includes parasitism (+/-), mutualism (+/+), and commensalism (+/0) -all have a positive net effect.

Describe the relationship between leaf cutter ants and their fungi? What kind of relationship is this? What is the name of the structure that the fungus produces for ants to feed on?

The ants nourish, protect, and eat the fungal species they grow, forming a relationship that benefits both and neither can survive without the other (mutualism)

What does it means when an interaction is obligate? Give an example.

The interaction is NOT optional for either species. -show clear signs of coevolution -common among mutualistic relationships. -ex) the leaf cutter ants and fungus can't live without each other and both have evolved unique features that benefit the other species.