🔑🪨Section Five: Keystone Species and Other Types of Effects🌟🐠

🌟🐠Keystone species

A species whose effect on community structure is disproportionate to its abundance.

🌟🐠Paine 1974 sea star experiment

When sea stars (which eat mussels, barnacles, limpets and snails) were removed, mussels monopolized the space and richness crashed from about 18 to 1–2 species.

🌟🐠Why sea stars maintain diversity

They eat the dominant competitor (mussels), which frees up space for other species.

🌟🐠Direct effect

One species affects another through a direct interaction, such as predation.

🌟🐠Indirect effect

One species affects another through an intermediate species.

🌟🐠Density-mediated indirect effect

An indirect effect caused by changing the number (density) of an intermediate species.

🌟🐠Knight et al. 2005 trophic cascade

Fish eat larval dragonflies, so fewer adult dragonflies eat pollinators. Shrubs near ponds with fish got about 3.5 pollinator visits per 20 minutes vs. nearly 0 without fish.

🌟🐠Trophic cascade

Effects of a predator that pass down through multiple trophic levels.

🌟🐠Trait-mediated indirect effect

An indirect effect caused by changing the behavior or traits of an intermediate species.

🌟🐠Beckerman et al. 1997 spider experiment

Grasshoppers alone caused about 58% herbivory. With a lethal spider it dropped to about 17%, and with a nonlethal spider (mouthparts glued) also about 17%, so the effect came from grasshopper behavior, not from being eaten.

🌟🐠Bottom-up control

Abundance is controlled by resources at the bottom of the food chain; more producers mean more at every level above.

🌟🐠Top-down control

Abundance is controlled by predators at the top; effects alternate going down (more top predators, fewer secondary consumers, more primary consumers, fewer producers).

🌟🐠Trophic levels

Producers, primary consumers, secondary consumers and tertiary consumers.