Ecosystems - biotic and abiotic factors

Define ecology:

the interrelationship between organisms and their environment, which determines the distribution of abundance of flora and fauna

What is an ecosystem?

the combination of all biotic factors living in a community and their interactions with abiotic factors

How do abiotic factors affect biotic factors?

abiotic factors create selection pressures that select for different types of organisms and hence affect biotic factors

What are the ecological levels of organisation?

1) individual

2) population - no. of individuals in a single specie

3) community - different populations living together (only biotic)

4) ecosystem - how biotic factors interact with each other and their environment

5) biome - large geographical area with similar biotic features

6) biosphere - all living things reacting with each other and the world

Examples of abiotic factors:

• salinity

• pH level

• soil texture

• temperature

Examples of biotic factors:

• terrestrial/aquatic predators

• human activity - foraging

• competition - intraspecific and interspecific

• mutualism, symbiosis

What is parasitism?

a symbiotic relationship where one organism benefits and the host is negatively affected

What is mutualism?

a symbiotic relationship where both organisms benefit from the relationship

What is commensalism?

one organism benefits and the other is unaffected

What is symbiosis?

a close and often long term relationship between one or more species. can be:

• obligate - needed for survival

• facultative - optional

What are adaptations?

characteristics that enable a species to survive in its environment

What are selection pressures?

A change in the environment that results in some resources being limited and increases competition for these resources

• drives natural selection

• biodiversity is essential for the survival of a population

Examples of selection pressures:

It can include abiotic factors such as temperature, light intensity, soil type, water availability. Also includes biotic factors such as interspecific/intraspecific competition for resources, predator and prey

What is distribution and abundance and how does selection pressures affect this?

The distribution of a species is where it is found, abundance of a species determines how many individuals of that species live throughout the ecosystem. Abiotic and biotic selection pressures affect the distribution and abundance of organisms by causing fluctuations in population numbers.

Examples of biotic factors that determine the distribution and abundance of a species:

• availability and abundance of food

• number of competitors

• number of mates

• number of predators

• number and variety of disease-causing organisms

What techniques are used to measure the abundance of plants?

• quadrats

• mark-release-recapture

How to calculate the estimated abundance using quadrats?

(total number of individuals counted x total area) divided by the area of each quadrat

How is the mark-release-recapture technique calculated?

abundance = no. captured x no. recaptured / number marked in recapture

What are the advantages and disadvantages of quadrat sampling?

(+) easy and inexpensive, minimal disturbance to environment

(-) only suited for plants and slow-moving animals

What are the advantages and disadvantages of mark-release-recapture?

(+) simple method that estimates the abundance of animals in large populations that are difficult to count

(-) only suitable for mobile animals, can be time consuming to capture and wait to recapture, can be disturbing to the environment

What are transects?

used to measure variation, can be line transect or belt transect

a transect is a narrow strip that cross the entire area being studied from one side to another, providing an accurate and easy method of representing an area

Cane toads:

• invasive species introduced for biological control

• lack of natural predator in Australia resulted in cane toads thriving as they have no selection pressure

• one female can lay 30,000 eggs at a time

Adaptations of the cane toads:

physiological - poisonous (neurotoxin), absorb water through their skin, can cope with brackish salt water

structural - dry warty skin, counter shading for camouflage in two directions, swollen parotid glands (produce toxins here)

behavioural - opportunistic eaters, nocturnal

Evidence that cane toads have acted as a selection pressure on the environment:

Red bellied snakes have evolved to have smaller heads so they aren’t able to eat the large toads, they receive smaller dose of poison which allow snakes to evolve an increase immunity for cane toad poison

What is spatial sorting? How is this seen in cane toads?

how over a distance, a population differs

Cane toads have evolved to have longer legs (faster, longer legs allow easy access to food), research shows that faster cane toads may develop spinal arthritis.

What is an ecological niche?

the role an organism plays in a community, and all the resources an organism uses including abiotic and biotic factors