Lecture 13: Important/Keystone Species

What were the changes to the ecological community in Yellowstone National Park after the reintroduction of wolves?

Reintroduction of wolves in 1995/1996

• population size - wolves prey on elk (reduce population and change behaviors)

• plants eaten - With reduced feed pressure plants along rivers and streams began to recover. (Willow and aspen grew more robustly, creating habitats for various species.)

• height of plants - with fewer animals’ trees like willows, aspens, and cottonwoods were able to grow taller. and with behavior change : Wolves caused elk to avoid areas where they were more vulnerable, such as open riverbanks and valleys.

What are trophic cascades? How does the role of keystone species relate to trophic cascades?

trophic cascades: change in the dynamics of any one species population can cause cascading disaster to the whole community.

Keystone species: has a dramatic effect on an ecosystem and community disproportionate to its abundance. (usually top predators)

keystone species effect on a community and ecosystem via predation on intermediate trophic levels describes how certain species, often top predators, play a critical role in maintaining the structure, function, and diversity of an ecosystem by controlling populations of species at mid-levels in the food web.

Keystone Species' Role in Trophic Cascades

• Keystone species often initiate trophic cascades by directly or indirectly affecting species at multiple levels in the food web.

• Their removal can collapse ecosystems, as unchecked intermediate species can overconsume resources, leading to reduced biodiversity and ecological degradation.

• Their reintroduction or protection often restores balance, fostering resilience and biodiversity.

What is the role of ecosystem engineers? Identify a species in Kentucky that is an ecosystem engineer. What is its role. Find example of ecosystem engineers in a few other ecosystems.

ecosystem engineers: species can change communities by altering the environment. (Physically modify the environment)

Examples:

• beavers - build dams across rivers and streams

• ants - build complex underground tunnels

• prairie dogs - build underground tunnels and apartments

• Corals - build reef structures

What are invasive species? Why are some species invasive?

invasive species: threaten native biodiversity. non-native species that spreads widely and become dominant in a community. (major ecological effects)

Alien (exotic) species: non- native species from somewhere else enters a new community. (introduced deliberately or accidentally)

Examples:

• Introduced Norway rate in Aleutian Islands

  • rats reduce numbers of gulls and oystercatchers

  • gulls and oystercatchers feed on herbivores invertebrates: snail and barnacles

  • population increase

  • suppression of algae

  • rocky intertidal community altered from algae dominated community to invertebrate-dominated community

• invasive zebra mussels

  • Decreases:

    • Phytoplankton and zooplankton - plankton-eating fish and disrupt the base of the aquatic food web.

    • Native mussels - plankton-eating fish and disrupt the base of the aquatic food web.

    • Plankton-eating fish - reduction in plankton decreases food availability for fish species

  • Increases:

    • Aquatic plants - increase water clarity

    • Detritus - Zebra mussels produce waste (detritus), increasing food availability for decomposers

    • Decomposers and detritivores

    • Bottom-dwelling fish - With more decomposers and detritivores to feed on, fish that live near the bottom benefit from the increased food supply.