Topic 4 Ecology: Ecological Selection

Question 1

• Ecological succession is the change in composition of species, organisms and vegetation over time. It describes how one community is gradually replaced by another group of species. As succession progresses, the diversity (number of species in a community) and total biomass (total mass of all living organisms) increase. A final successional stage of constant species composition (climax community) is attained and unchanged until destroyed by some catastrophic event (blowout). Succession has a factor of randomness that makes it hard to predict. Successional stages may not occur in an expected order. Some species are established randomly due to influences of climate, season, or due to which species arrived first. Sometimes, a stable climax community is never achieved due to frequent disturbances (e.g., fires).

Answer 1

Note

Question 2

Resident species can change a habitat, which can affect succession by altering the conditions that make the habitat favorable:

Answer 2

Note

Question 3

• The substrate texture may change from solid rock, to fertile soil, to sand or others

Answer 3

1. Substrate Texture

Question 4

• May decrease due to decomposition of organic matter such as acidic leaves

Answer 4

2. Soil pH

Question 5

• The ability of the soil to retain water. The potential changes as soil texture changes

Answer 5

3. Soil water potential

Question 6

• May change from full sunlight, to shady, to darkness as trees become established

Answer 6

4. Light availability

Question 7

• Increases with population growth, and may be unsuitable to certain species

Answer 7

5. Crowding

Question 8

• These are the plants and animals that are the first to colonize a newly exposed habitat. Pioneer species are usually opportunistic, r-selected species that can tolerate harsh conditions. Lichens and mosses are examples of pioneer species because they grow fast and produce many progeny rapidly
• As soil, water, and light changes, r- selected species will be replaced by stable k-selected species. The k- selected species live longer, so their environmental effects slow down the rate of succession and reach climax where it remains for hundreds of years

Answer 8

6. Pioneer Species

Question 9

• Occurs on substrates that have never previously supported living things, such as volcanic islands, lava flows, or rock left behind by retreating glaciers. One of the essential prowesses for primary succession is soil building.
• Example - Primary succession could occur on rock or lava. First, lichens establish themselves and hold moisture and secrete acids to erode rock into soil. Soil then accumulates, and bacteria, protists, mosses, and fungi all appear. Insects then start to appear. The new soil is nutrient deficient, so nitrogen- fixing bacteria appear early. Grasses, herbs, weeds (all r- selected species) then become established. Eventually, depending on climate conditions, r- selected species are replaced by k- selected species, which include species like perennial shrubs and trees

Answer 9

Primary Succession

Question 10

• Begins in habitats where communities were entirely or partially destroyed by damaging events, such as fire, flood, insect devastation, overgrazing, forest clearing, construction sites, etc. The habitat previously supported life, so unlike primary, secondary succession begins on substrates that already bear soil. Examples:
• Secondary succession can occur on abandoned cropland. Germination of r- selected species occurs from seeds already in the soil. Later, trees will follow
• Ecological succession can happen with a pond. Note however, that this would only be secondary if there was a disruption of a pre-existing community. First, plants such as algae and pondweed and animals such as protozoa, insects, and fish colonize the pond. Next, plants such as reeds, cattails, and water lilies grow and make the pond shallower. As the pond becomes a moist marsh, grasses, herbs, shrubs, willow trees, frogs, and snakes start to exist at this habitat. Finally, the pond has become a woodland with trees as its climax species, such as pine or oak

Answer 10

Secondary Succession

Question 11

• Is the species in a community that is the most abundant or collectively has the highest biomass.

Answer 11

Dominant Species

Question 12

• Are not usually abundant but exert a strong control on their community structure not by their high quantity, but through their pivotal ecological role.

Answer 12

Keystone Species

Question 13

• a.k.a. foundation species, dramatically alter their physical environment.

Answer 13

Ecosystem engineers

Question 14

• Sits at the top of the food chain and no other creatures predate it.

Answer 14

Apex predator