2.1.4 Population Interaction

In this section, we will look into different interactions between species. These are:

Competition
Herbivory and predation
Symbiosis
Disease

Part 1: Competition

Competition may take place when two individuals complete for...

Space
Food
Mate
Other resources

Key: these are the niche. No 2 species can occupy the same niche in an ecosystem.

Two types of competition are:

Interspecific competition

the competition between different species for shared resources such as space, food and nesting sites during the breeding season and also for roosting sites during the non-breeding season (Dhondt, 2011)

intraspecific competition

a competition between individuals from the same species

Species A has an overlapping niche with B compared to C. A and B will have interspecific competition more than A and C

Factors affecting growth:

Density-dependent factors operate as negative feedback mechanisms regulating the population and leading to stability.
- Predator–prey relationships are a good example of density-dependent control.
Density-independent factors are generally abiotic. The most important ones are extremes of weather (drought, fire, hurricanes) and long-term climate change. Others include geophysical and geological events such as earthquakes and volcanic eruptions and the tsunamis that can result from them. Their impacts include an increase in the death rate and a reduction in the birth rate, especially of smaller individuals.
- The response depends, in part, on the frequency and severity of the event. Density-independent factors can operate alongside density-dependent factors.
- Density-independent factors may have significant influence on population size, but it is the density-dependent factors that tend to regulate the population around the carrying capacity. In addition to competition for limited resources, these factors include the increased risk of predation and the transfer of pathogens in dense populations

If two species having the same niche live in separate habitat

If two species having the same niche live in the same habitat

Part 2: Herbivory & Predation

Herbivory

Herbivory is an important ecosystem interaction because it allows energy to flow up the food chain from producers (plants) to primary consumers (herbivores & omnivores). However, herbivory is not typically considered a symbiotic relationship

Predation

Predation is when one animal hunts and eats another animal as food. Although this is not always considered a type of symbiotic relationship

Fun Fact:

Hippopotamuses spend the day in rivers so they do not overheat
The carrying capacity of a herbivore’s environment is affected by the quantity of the plant it feeds on. An area with more abundant plant resources has a higher carrying capacity than an area that has less plant material available as food for the herbivore

Part 3: Symbiosis

Parasitism

Win - Lose

Rafflesia have the largest flowers in the world but have no leaves. Without leaves, these plants cannot photosynthesise, so they grow close by South-east Asian vines (Tetrastigma spp.) from which they draw the sugars they need for growth

Commensalism

Win - Unharmed

two species in which one species obtains food or other benefits from the other without either harming or benefiting the latter

Mutualism

Win - Win

Corals provide the zooxanthellae with a protected environment, and the coral polyp cells produce carbon dioxide and water that the zooxanthellae need for photosynthesis. The zooxanthellae use energy from the sun to turn the carbon dioxide and water into oxygen and help the coral to remove waste

Part 4: Other Interactions

An organism that causes disease is known as a pathogen
Pathogens are...

bacteria, viruses, fungi and single-celled animals called protozoa.

The disease-causing species may reduce the carrying capacity of the organism it is infecting.
Changes in disease can also cause populations to increase and decrease around the carrying capacity

Dutch elm disease is caused by fungus (Ascomycota) that affects elm trees. The elm bark beetle spreads the fungus

Exercise

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