Module 5, chapter 54 (communities)

What are species interactions?

What are the 4 major types of interactions?

• Commensalism

• Consumption

• Mutualism

• Competition

Define commensalism

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• One species benefits and the other is unaffected

• Can be parasitic or mutualistic

Define consumption, including the 3 sub-types.

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• One organism eats or absorbs nutrients from another, increasing the consumers fitness but decreasing the victims fitness

3 types:

Predation: predator kills all or most of prey

• Fatal to victim­– all or most of tissue consumed

• Predators ae typically carnivores, but seed predators consume and kill plant embryos (herbivory)

Herbivory: consumes plant/algae tissue such as leaves, stems, fruits, or roots, but typically not entire organism

• May or may not be fatal to victim depending on extent of damage; apical meristem facilitates recovery

Parasitism: organism lives in/on a host and takes its resources

• Usually not fatal because they tend to be small relative to host, but can decrease fitness

Define mutualism. Discuss the ant-acacia tree mutualism example and how it was disturbed.

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• Two species interact in a way that grants fitness to both

• Fitness benefits range from survival to reproductive related factors

• Depending on context, can become parasitic or commensal

  Ex. Ants live in acacia trees: the ants protect the tree, and the tree provides food for the ants

  The presence of the big-headed ants in Kenya disrupted this, which led to increased herbivory by elephants and increased landscape visibility. As a result, lions were less likely to kill zebras, and their prey species shifted from zebra to buffalo

Define competition, include the 2 sub-types.

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• Two species compete for the same resources, which lowers fitness for both

2 types:

Intraspecific competition: competition between members of same species

• Major cause of density dependent growth: competition increases as density increases

Interspecific competition: competition between members of different species

• Niche differentiation: two species with overlapping niches are able to coexist by  shifting niches such that they no longer overlap

• Character displacement: changes in a species’ traits that enable species to exploit different resources

List the mechanisms of defense used by prey.

• Mechanical defense: use physical structures to deter predators

• Chemical defense: produce toxins/noxious chemicals to ward off predators

• Aposematic coloration: bright warning colors signaling toxicity/danger

• Batesian mimicry: harmless species imitates warning signals of harmful one

• Mullerian mimicry: two harmful species evolve to look alike

• Cryptic coloration: Camouflage that helps organisms blend into their

Define species richness, its trends, and its pertinence to the tropics.

Define species evenness. What is the diversity stability hypothesis?

Define species composition.

Factors impacting diversity: discuss species and impact, specifically keystone species.

Factors impacting diversity: discuss disturbance.

What does the intermediate disturbance hypothesis say?

• Moderate levels of disturbance foster greater levels of diversity than do high or low levels

  • High disturbance: excludes many slow growing species

  • Low disturbance: allow competitively dominant species to exclude less competitive species

What does the Island biogeography model say?