4.1.2 Ecosystem Dynamics

Question 1

Niche

Answer 1

The part of the ecosystem that a species occupies
A/biotic factors: active time of day, food, habitat and interspecies interaction

Question 2

Realised niche

Answer 2

The niche an organism occupies in reality (adaptation), as the ideal niche has restrictions placed on it by abiotic or biotic factors (e.g. competition - another species successfully performed competitive exclusion to prevent one species from accessing a food source)

Example:
Abiotic factors are suitable for koalas to have widespread distribution along the east coast of Australia. But this distribution is not realised due to predation by dogs, cats and the impacts of fire, disease and drought. Thus, their realised niche is more localised.

Question 3

Ideal niche

Answer 3

The niche a species would occupy if there were no predators, parasites, or competition

Question 4

Resources partitioning

Answer 4

Within a habitat, species occupy a microhabitat (realised niche), allowing multiple species to share resources. Usually based on time and location

E.g.
- In the same forest, spine-tailed swifts may hunt in the canopy while ground thrushes hunt near the forest floor, partitioning the availability of food by altitude

Question 5

Effects of predation

Answer 5

Affects distribution and abundance of prey
- Predator population echoes the prey population
(prey^ predator^; prey v predator v; prey^ etc.)

Question 6

Factors affecting predation

7

Answer 6

• Interspecific competition for prey
• Availability of the prey’s food
• Reproduction rate (age of maturity, fertility, fecundity, number of reproductive cycles in a lifetime)
• Death rate
• Size of the ecosystem for supporting the predator and prey numbers
• Movement between ecosystems (migration)
• Number of shelter sites

Question 7

Competition

Answer 7

Intraspecific - between members of the same species. E.g. mating, territory.

Interspecific - competitive exclusion
- Short term: decreased population in one/both species
- In most instances, one population drops significantly because the species is unable to effectively access resources → increase in deaths + decrease in reproduction rates
- This trend may continue/reverse, depending on the success of each species in obtaining resources + the ability of the ‘losing’ species to adapt by occupying a different niche.
- Long term: can result in the elimination of the population, or even extinction.

Question 8

Consequences of symbiosis

Answer 8

• Increase biodiversity (e.g. symbiotic relationship of corals and photosynthetic algae produces coral reefs, which offer unique habitats for marine organisms like fish, increasing biodiversity)
• Develop new species through symbiogenesis, the integration of genetic material from different species
• Produce new capabilities for different organisms → enhance evolutionary fitness

Question 9

Consequences of disease

Answer 9

• Can decrease population size
• Spread of disease through population can be limited by genetic variation. More genetic diversity = higher likelihood that there are individuals who are resistant to the disease and survive to reproduce

Case Study example: Devil facial tumour disease (DFTD)
- Contagious nature of DFTD threatens extinction for Tasmanian devils because it causes suffocation or starvation
- Driven by chromothripsis, in which chromosomes are shattered and rearranged
- Insurance population of devils kept in captivity. Will be returned to the wild for repopulation if devils go extinct in the wild
- For the captive breeding program to be successful, insurance devils must retain at least 95% of the genetic variation of wild populations, so that the insurance population can be resilient against new diseases or environmental changes in the wild