Chapter 6: Changes in Ecosystem

Question 1

name two long term changes that affected the water cycle

Answer 1

reduced temperature
reduced evaporation rate
expansion of deserts
ice age
breaking up of Pangea

Question 2

why does Australia contain a great number of endemic species

Answer 2

due to Australia being isolated from all other land masses the organisms have all evolved over 100million years to differ from species around the world as they have to adapt to the conditions of Australia

Question 3

define ecological succession

Answer 3

the process of communities structure and composition changing, heading towards ecosystem stability

it includes the changes of both the biotic and abiotic factors

the changes in abiotic factors allows different species that are suited to the environment to come in

Question 4

explain what the end of a succession is marked by

Answer 4

climax community

this is when k-selected, slower growing and longer living species adapted to stable environments such as oaks and jarrahs become dominant.

Question 5

explain what primary succession is

Answer 5

primary succession occurs when a lifeless, soilless area becomes inhabited

these barren areas are caused by natural disasters such as tsunamis and earthquakes aka nudation

primary succession is usually in four stages:

1. Pioneer Species: pioneer species usually autotrophic plants such as lichen are introduced into an area which break down substrate and allow soil formation
2. Soil Formation: the decomposition of the pioneer species creates a thin layer of soil which allows new species such as mosses to move in. These new species increase nutrients in soil and allow other species such as grasses to move in which creates a simple ecosystem
3. R-selected species move in: plants that are suited to the hostile environment usually disperse seeds, grow and reproduce quickly. They capitalise on unused resources and their population grows rapidly but also decreases rapidly as competition is introduced
4. Immigrant species arrive: species such as insects and small invertebrates arrive and increase the food web and create a community. But they can only stay if their is enough resources
5. Biodiversity increases: over an extended period biodiversity will increase as new species arrive and adapt to the new environment

Question 6

explain secondary succesion

Answer 6

secondary succession is when a previously community is taken out and replaced by a new community

1. the wipe out is either caused by a natural or human event such as fire or logging
2. this leaves only soil and some organic matter so fast growing plants recolonise and small invertebrates rearise
3. slower growing trees stabilise the community and allow bigger omnivores to arrive
4. a climax community is eventually arrived at

Question 7

name 2 factors that prevent a community reaching climax

Answer 7

selective grazing

fires

Question 8

explain what prescribed burning is

Answer 8

it when burns are done purposely during none windy colder months such as June or May to reduce the severity of future unplanned fires

Question 9

what are 3 benefits of fires

Answer 9

dominant species are removed which opens up space for grasses to grow

mobile species such as birds and wallabies arrive

ash from fire increases the nutrients in the soil

Question 10

what does fire intensity depend on (2 factors)

Answer 10

weather

fuel load