Bio Exam 3: Ecosystem Part 1:

Green World Hypothesis- Why don’t herbivores eat everything --- why is the world green?

Green World Hypothesis explains why plants are still abundant despite being eaten by herbivores.

“The world stays green because herbivore feeding is limited by predators, disease, plant defenses, competition and environmental conditions”

What are the two factors which are correlated with species diversity?

The two factors correlated are location and area

Species Diversity:

the variety of different kinds of organisms that make up a community

Species Richness:

The total number of different species in a community

Relative Abundance:

The proportion of individuals represented by each species

What is evapotranspiration?

The amount of water that evaporates from soil and other surfaces plus the water transpired by plants

How does evapotranspiration relate to species diversity?

High evapotranspiration = high species diversity because warm, wet conditions support more plant growth. Low evapotranspiration = low species diversity because cold or dry conditions limit plant growth.

Three important species types:

dominant, foundation, and keystone species

What is a dominant species:

The most abundant species in a community- Ex: A grass species that covers a grassland

What is a foundation species:

Species that creates or modifies the environment, allowing other species to inhabit an area - Ex: Beavers create dams that create ponds = habitat

What is a keystone species:

Species with disproportionately large influence on its community - Ex: Sea otters keep urban populations in check

Other species: 

Endangered: At risk of extinction

Threatened: Likely to become endangered in the near future

Rare: Has a very small population, naturally or due to human activities

Non-Native: Occurs outside its natural geographic range because it has been introduced

Invasive: A non-native species that spreads and causes ecological, economic, or other harm

Indicator: Its presence, absence, or condition provides information about environmental health

Umbrella: A species selected for conservation to protect others that depend on its habitat

What is a disturbance?

A disturbance is an event that changes a community, removes organisms, and alters resource availability.

Natural Disturbances versus Human

Natural

- Storms

- Fires

- Floods

- Droughts

Human:

- Logging

- Urbanization

- Agriculture

- Overgrazing

What is Ecological Succession?

The process by which the species composition of a community changes over time, often following a disturbance or the creation of a new habitat.

What are the two types of succession?

Primary, Secondary

What is primary succession?

Begins in almost lifeless area where soil is absent or has been removed - Ex: Newly exposed rock after a volcanic eruption

What is secondary succession?

Begins after a disturbance removes some or all organisms but leaves the soil intact - Ex: A forest regrowing after a fire

Ecological Succession: two types? 

Early Colonizing Species Later Successional Species

Early Colonizing Species:

Arrive early in succession, Often tolerate harsh conditions, May grow and reproduce rapidly, Can help modify the environment

Later Successional Species:

Established after earlier stages, Often compete effectively under established conditions, May grow more slowly and live longer, May become more abundant as the community develops

Ecological Sussension:

Facilitation, Tolerance, Inhibition

Facilitation

Early species make the environment more suitable for later species

- Ex: Lichens contribute to breaking down rock and forming soil, helping other plants establish

Tolerance:

- Later species can establish and survive without being significantly helped or hindered by earlier species - Ex: Tree seedlings establish beneath existing vegetation

Inhibition:

- Existing species prevent or hinder other species from establishing or growing - Ex: Established plants block sunlight or occupy space, preventing other plants from growing