10.3 - Changes in ecosystems

What is the definition of a population?

The number of a particular species living in one habitat

What are abiotic factors & give examples?

All the physical or non-living aspects to an ecosystem:

• Climatic factors (e.g. temperature, water/humidity, light/shade)

• Soil factors (e.g. soil pH, mineral supply, soil composition, moisture)

• Human factors (e.g. pollution)

• Catastrophes (e.g. floods & fires)

What is the difference between density-independent & density-dependent factors?

Density-independent factors (abiotic factors):

• the size of the effect is independent of the size of the population (e.g. low light intensity will limit plant growth regardless of the number of plants present)

Density-dependent factors (biotic factors):

• the size of the effect depends on the size of the population (e.g. bigger population = greater competition)

What are biotic factors?

All the living aspects of an ecosystem (e.g. food, competitors, predators, parasites & pathogens)

What is interspecific competition?

Competition for resources (e.g. food, space, water, light) between members of different species

• competition between species only occurs if they have the same niche

What is the competitive exclusion principle?

Two species cannot co-exist in the same habitat if they have the same niche; one species will out-compete the other 

What is intraspecific competition?

Competition for resources (e.g. food, water, space, light) between members of the same species

What is the relationship between predator & prey populations?

The populations of predators & their prey depend on each other, so they tend to show cyclical cycles 

What is the relationship between parasites/pathogens & their hosts’ populations?

Parasites/pathogens & their hosts have a close symbolic relationships, so their populations oscillate

When do abiotic & biotic factors govern who survives?

• Abiotic factors - in harsh environments

• Biotic factors - in mild environments (e.g. competition)

What is the definition of succession?

The gradual change in an ecosystem over time

What is the definition of a climax community?

A stable, mature community that undergoes little or no succession & where plants & animals have established equilibrium (e.g. oak or pine forest)

As succession proceeds, how does the habitat become less harsh & the abiotic factors less hostile?

• Daily temperature fluctuations decrease → due to shade

• Water is more easily available → retained in soil

• Nitrates increase → due to nitrogen fixation & decay

What is the difference between primary & secondary succession?

• Primary succession - occurs on newly formed or exposed land with no soil previously devoid of life

• Secondary succession - existing community has been removed, leaving soil intact but with no plant or animal species (e.g. forest fire)

What are lichens?

• The only species that can survive on bare rock with very little water & few available nutrients (start the process of succession)

• They have a mutualistic relation between algae & fungi

Describe primary succession

1. Begins with pioneer species (e.g. lichen) that survive harsh conditions & help form a thin layer of soil

2. Mosses & small plants grow, increasing soil depth & nutrient content

3. Over time, larger plants establish themselves, further changing the environment

4. Each new species alters the environment, making it less suitable for previous species, leading to out-competition

5. This ongoing change increases biodiversity & leads to a less hostile environment

6. The final, stable stage is called the climax community, typically dominated by trees

Describe secondary succession

1. Primary succession is disrupted & plants are destroyed

2. Succession starts again, but soil is already created → doesn’t start from bare rock

3. Species richness & number of organisms (i.e. biodiversity) increases

4. Larger plant species & animals start to colonise area

5. Food webs become more complex

What is plagioclimax community?

Human activity (e.g. ploughing, weeding, mowing, herbicides, burning) prevents succession in a habitat from reaching its natural climax community