Stability and Change Flashcards

Ecosystem Stability: an ecosystem’s ability to maintain its structure & function over time despite disturbances

• In a healthy ecosystem, after disturbances: typical structures & functions are restored

• humans increase the magnitude of disturbances on ecosystems

Resistance: ability of the ecosystem to withstand or resist changes caused by disturbances

Resilience: ability of an ecosystem to recover from disturbances

• stable ecosystems have resistance & resilience which allows them to maintain stability despite disturbances

4 Factors that contribute to ecosystem stability:

1. Supply of Energy: ecosystems need a steady supply of energy to maintain stability

   • producer diversity (lots of species of plants) maximizes an ecosystem’s ability to harness the energy & maintain stability

2. Recycling of Nutrients: nutrients flow/transfer through the food web —> they’re returned to the soil as organic matter decomposes

3. Biodiversity: variety/diversity of life in a specific area —> higher biodiversity = more stable ecosystem

4. Climatic Factors: extreme weather & climate change create a less stable ecosystem

   • climate changes decrease species diversity bc as temps rise, abiotic factors move closer to zone of intolerance/stress

   • species can’t survive in their new climate

Keystone Species: have a disproportionately large impact on the community compared to their abundance or biomass

• their presence/absence has a significant impact on their ecosystem’s stability

• EX: wolves in Yellowstone

Describe how an organism that exhibits top-down control on the ecosystem is a type of keystone species

• many keystone species exhibit top-down control on the ecosystem & cause a trophic cascade

• EX: sharks in marine ecosystems

• EX: Grey wolves in Yellowstone

• EX: Parrot fish in coral reefs: eat bad algae that would coat/harm the coral —> they keep the algae level low so coral can flourish

NOT JUST apex predators can be keystone species

• many are, but any species on any trophic level can be a keystone species

  • EX: bees facilitate the reproduction of about 80% of the global plant population

• because of their significant impact on overall ecosystem health, the removal of a keystone species would disrupt the balance w/in the food web & would cause ecosystem collapse (unstable)

• Keystone species will modify their habitat —> loss of them can impact habitat structure

  • EX: Beavers & dams

  • EX: Elephants and falling trees

Ecological Succession: natural progression of changes in species composition & community structure over time

• predictable pattern of changes

• caused by disrupting existing vegetation & communities

3 Causes of Ecological Succession:

1. Natural Disturbances: wildfires, volcanic eruptions, hurricanes, floods, etc.

2. Human Activities: deforestation, agriculture, urbanization, mining

3. Changes in Environmental Conditions: natural or anthropogenic

   • shifts in temperature, precipitation patterns, soil fertility, introduction of new species

Primary Succession

Primary Succession: process of ecological change that occurs in an area that’s barren and/or wasn’t previously colonized

• EX: newly formed volcanic rock

• EX: retreating glacier

Pioneer Species: the first species to colonize barren land —> break down rock to create soil

• small & hardy organisms

• EX: lichens & mosses

Outline the process of primary succession:

1. After soil is formed, herbaceous plants can arrive (grass, wildflowers, ferns)

   • deeper root system stabilizes soil, eventually providing habitats for small animals

2. Shrubs & small trees arrive —> even deeper root system

   • enrich soil by providing organic matter to break down

   • provide habitat for more animals

3. Establishment of forest canopy (top layer of trees/forest)

   • as the small trees grow, they form the dense forest canopy

   • creates a diversity in microhaitats & provides shelter for more organisms

Climax Community: stage of relative stability —> characterized by mature & diverse community of plants/animals

• created at the end of succession

• can take hundreds or thousands of years to reach climax community after primary succession

Secondary Succession

Secondary Succession: process of ecological change that occurs in an area that has been previously colonized by living organisms

• the area has experienced a disturbance that disrupted the existing community —> there’s still soil present & organisms weren’t completely wiped out

Distinguish between primary & secondary succession:

• Unlike primary succession, secondary succession begins w/ pre-exisiting soil & sometimes remnant species —> secondary succession proceeds a lot faster

Process of secondary succession:

1. Begins w/ fast growing pioneer species

2. Plant species that were previously there quickly reestablish themselves & biodiversity increases

3. Natural community continues to develop until a climax community is established

Describe an example of an ecosystem that requires cyclical succession to maintain ecosystem health:

• this means they require periodic disturbances to happen —> disturbances are natural & critical for ecosystem stability

• EX: plants in the Chaparral biome in California are adapted to period wildfires & it’s become a natural part of that ecosystem

• now, because of human involvement, there are bigger & more out-of-control wildfires

  • these disturbances are more abundant than ecosystems need

  • Arrested Disturbance

Arrested Succession: occurs when the succession process is disrupted & sometimes prevents a climax community from being achieved

• stopped or slowed

• Caused by:

  • repeated disturbances (too frequent)

  • changes in environmental conditions

  • presence of persistent stressors