E6 Summary

Stage 2 Biology – Ecosystems Notes

 

E6. Communities are continually undergoing change

 

·         Organisms occupy specific habitats because their needs are met and they have appropriate adaptations

·         Succession = gradual process by which species composition of a community changes

o   Can be brought about by modification of the habitat caused by organisms living there

o   Provide food or shelter for others

o   Change soil structure by causing breakdown of rock or increasing organic matter in soil

o   Decompose dead material and make nutrients available to others

·         Succession is often studied in places where there is no life and colonisation occurs from scratch

o   Hardy species that have special adaptations enable them to survive

o   Lichens are often the first species to be established on rock

o   They break down rock, and decomposers act on lichen remains – first traces of soil

o   Mosses can then survive

o   Further breakdown and decomposition – conditions supportive of grasslands and shrubs

o   Succession continues – one type of community is replaced with another

o   As the ecosystem matures, it is dominated by slower growing species with less reproductive effort

·         Primary succession

o   Organisms establish themselves in a new environment (sand dune/volcanic island)

·         Secondary succession

o   Changes occur in an environment that has been exposed to damage or disaster (fire/logging)

·         Studying sand dunes

o   Typical changes in a community from the coastal sand dune back to the woodlands

o   Sand dunes are inhospitable for plant species – high temperatures/wind/little water/low nutrients

o   Moving further away, the layer of organic material increases which allows new plants and animals to survive

·         Succession is a competition between organisms              

o   In disturbed habitats, species with higher reproductive effort have an advantage, but as the ecosystem stabilises, those with low reproductive effort and longer life span overtake

o   Fire example

§  Fire clears out overgrown grasses and herbs

§  Stimulus for germination of acacia / wattle species

§  Many plants show adaptations to fire

·         Secondary succession is faster than primary succession as there is more soil and a greater mix of species of plants and animals available to re-colonise

Biodiversity

·         Variety of life forms that are found in the biosphere, different set of genes they contain and variety of ecosystems in different habitats (genetic/species/ecosystem diversity)

o   Australia has been geographically isolated – leads to endemic species of flora/fauna

o   Unique adaptations

o   Acacias and eucalypts dominate as they are adapted to most habitats

o   Main groups of mammals – monotremes (egg laying), marsupials (pouch) and placentals (live birth)

o   Many birds, reptiles and amphibians not found elsewhere

·         Different types of ecosystems are required to maintain balance in the atmosphere

·         Each species is not an isolated unit – important in its own right and forms relationships with others that are necessary for a healthy ecosystem

·         Co-evolution

o   Animals and plants living in the same area with unique interactions

o   Evolution of two species occurs together or in tandem so that the two depend on each other

·         Ecosystems are constantly changing and populations and communities are being shaped by forces of evolution

·         Genetic variation is essential to ensure survival of species in changing environments

·         With biodiversity at the genetic level, individual organisms in the population differ leading to natural selection

Natural selection

·         Individuals that are most suited to conditions are more likely to survive and pass on their genes

·         If there is little diversity, the population may be more susceptible to extinction