11 Bio - Mod 3 (1)

Effects of the environment on organisms

Ecosystem

• Combination of biotic (living) and abiotic (non-living) factors living in a community (group of different populations)

• Abiotic and biotic factors create selection pressures that affect the rate of reproductive and survival in an organism

• Competition for resources occurs between organisms

• The successful species will have a range of favourable traits (adaptations) which are passed down through offspring as these organisms are more likely to survive and reproduce.

Selection pressures

• Drives natural selection (evolutionary process) and biodiversity

• Individuals within a population have variations that helps them adapt better to their environment

• Includes abiotic factors (sunlight, water availability, temperature, soil) and biotic factors (reproduction, prey, predators, competition for resources), these usually determine the abundance and distribution of a species

Ecology

• Study of interrelationships between the environment and the organisms within it

• Ecologists obtain information on the abundance and distribution of species within an environment to record any changes

Measuring abundance

• Plants: sampling techniques (one or more samples are randomly taken), quadrants (1m x 1m squares are analysed for the percentage coverage of a specific plant)

• Animals: mark-release-recapture (animals are captured, marked and then released, provided with time to mix with other animals to notice the abundance of animals in the area)

Population trends

• These trends provide information into which abiotic and biotic factors are most suitable for an organism

Changes in populations

• Members of the population with advantageous traits survive and reproduce in their habitat, caused by selection pressures

• e.g the peppered and black moths were in England. the peppered moths were more abundant as the trees were lighter and these moths camouflaged, whereas the black moths were an easier prey for predators. during the Industrial Revolution, the soot created covered the trees and camoflauged the black moths, making the peppered moths easier to see for predators. after promoting a change in environmental conditions, the soot in the air reduced allowing for the number of peppered moths to increase and the number of black moths decrease again.

Cane toads

• Native to South and Central America

• Introduced to Queensland in 1935 to control cane beetles eating sugarcane crop

• These toads did not eat the cane beetles but instead ate native species

• They produce a toxin, poisoning animals when they attempt to eat them

• They spread towards NSW and NT, the ‘invasion frontline’ entering WA at a speed of 50km/h

• The toads are cannibals but have no other predators

• Females lay 30,000 eggs at a time, significantly increasing their population

• These toads created a selection pressure within the Australian ecosystem as some animals developed resistance against this toxin, the traits becoming common in the species as it is passed down to offspring

• e.g red-bellied black snakes which have a smaller head size compared to body length are more likely to survive as they cannot open their jaws wide enough to eat the toad. the population declined, however the advantageous trait was found after a small number survived eating cane toads and passed it down

• e.g northern quoll suffered declined populations after the introduction of cane toads. quolls have stopped eating these toads, scientists determined it might be a behavioural adaptation that stops them. toads acted as a selection pressure stimulating genetic diversity

Spatial sorting of cane toads

• The fastest toads near the ‘invasion frontline’ have reproduced offspring with the same

• The toads have been proven to have longer legs and a thinner pelvis which allows for them to travel at a faster speed than those toads closer to QLD

• The speed cane toads are moving has increased from 10-15 km/h to 60 km/h.

Prickly pear

• Initially introduced to Australia due to the conflict within Spain

• Spain used this plant to create red dye, introduced to start a dye industry

• It was introduced in the 1800s also to be used a an alternative source of food for livestock

• There was a lack of selection pressures for prickly pear, leading to a lack in diversity and high population

• When the ‘pads’ of this plant are detached and come in contact with soil they regrow forming a new plant

• These plants became a pest as they would not stop growing

• Pesticides and burning methods did not work to minimise the number of prickly pear, significantly increasing the population

• The cactoblastis moth was introduced in Australia as a biological control for this plant, the larvae of this moth ate through the cactus and significantly reduced numbers

• This form of biological control worked as the larvae did not eat or harm any of the native Australian plants only eating prickly pear