Question

1. the saguaro is a common cactus in the deserts of the southwestern united states. the gila woodpecker eats insects that damage saguaros. the bird pecks at the cactus to remove the insects. as it pecks, it removes damaged cactus tissue. it also makes a nesting cavity for itself. the nesting cavity does not negatively affect the saguaro. any nesting cavity of a saguaro not being used by woodpeckers is available for use by lizards, rodents, and other birds.

a. why would the saguaro be considered a keystone species in its ecosystem? (1 point)
b name examples of predation, mutualism, and commensalism that involve the saguaro. (3 points)

Explanation:

a. The saguaro is a keystone species as it provides nesting cavities used by multiple other species (lizards, rodents, other birds) and its well - being is tied to the presence of the Gila woodpecker which controls insect pests. Its removal would have a large impact on the ecosystem.
b.

• Predation: Insects damaging the saguaro (insects are predators to the saguaro).
• Mutualism: The Gila woodpecker eats insects that damage the saguaro. The woodpecker gets food and the saguaro is protected from insect damage.
• Commensalism: Lizards, rodents, and other birds using the nesting cavities made by woodpeckers in the saguaro. The saguaro is not affected while the other species benefit.

Answer:

a. It provides nesting cavities for multiple species and its health is related to pest - controlling woodpeckers, so its removal would greatly impact the ecosystem.
b. Predation: Insects preying on saguaro. Mutualism: Saguaro and Gila woodpecker. Commensalism: Lizards/rodents/other birds using saguaro nesting cavities.