1. Non-neutral species interactions can be classified into three broad categories according to fitness effects: mutualisms occur when both species benefit one another (+/+); exploitation happens when one species benefits while harming the other (+/-); and competition describes two species the harm one another (-/-).
Symbiosis corresponds to a different aspect of the species relationship, and so can apply to multiple kinds of the three categories (based on fitness effects) listed above.

A. List a single, specific example of a symbiosis based on two of the three possible interactions (i.e. mutualistic symbiosis, exploitation symbiosis, and competitive symbiosis), remembering to cite one reference each. Examples should include common and Latin names (e.g. humans (Homo sapiens); fruit flies (Drosophila melanogaster)) [~1-2 sentences per example]

B. What about the third category? Why might it be far more difficult (or even impossible) to find real-world examples of that kind of symbiosis? [~2-4 sentences]

2. Rhizosphere mutualisms are often critical for individual plants, species, and entire ecosystems. Interactions with animal mutualists (e.g. pollinators and seed dispersers) are also extremely important for many plants. However, one of these broad classes of mutualism has had a much greater direct effect on global biodiversity than the other. <This one is meant to be challenging.>

A. Which mutualism is more directly responsible for a greater share of biodiversity? [~1-2 sentences]

B. Provide evidence for your answer to 2A above with one (or at most two) properly credited figure(s) from a scholarly article, along with a brief verbal explanation of how the data in the figure support your argument. <Hint: dramatic changes in biodiversity can be seen over time (e.g. fossil record and/or molecular phylogenetics) or across space.> [~1-4 sentences total]

3. Mutualistic symbioses involving a single large and many small microbial partners (“hosts” and “symbionts”, respectively) acquired from the environment are often initiated and controlled by host adaptations, even though symbionts should evolve much more quickly.

Why might hosts be so much better-adapted to the symbiosis than their fast-evolving partners? Cite anything you find that helps you answer the question, but it might be possible to think through this based on class discussions and the information here. <Hint: imagine the environments faced by an ‘average’ member of the host population vs. an average member of the symbiont populations.> [~2-4 sentences]

1. Non-neutral species interactions can be classified into three br...