Module 7- Populations in ecosystems Flashcards
5 marks
Changes in ecosystems can lead to speciation. In Southern California 10 000 years ago a number of interconnecting lakes contained a single species of pupfish.
Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a number of different species of pupfish. Explain how these different species evolved.
- Geographical isolation
- Variation due to mutation
- Different environmental conditions / selection pressures
- Organisms with beneficial allele survive and reproduce
- Leads to change in allele frequency
4 marks
Succession occurs in natural ecosystems. Describe and explain how succession occurs
- Colonisation by pioneer species
- Pioneers species change the environment conditions e.g. produces thin layer of soil called humus
- Environment becomes less hostile for other/new species, which enable other species to colonise
- Increase in biodiversity
- To climax community
1 mark
Explain why it would be more appropriate to use a transect rather than random quadrats when investigating this succession.
Ensures sampling of each community
3 marks
Many species in the pioneer community are xerophytes. Suggest and explain how having sunken stomata is an advantage to these plants.
- Sand has a low water retention
- Sunken stomata reduce transpiration
- as pocket pf saturated air trapped near stomatal pore
- This reduces diffusion / water potential gradient
Define succession
The change in an ecological community overtime
Define pioneer species
The first species that colonise bare rock. Can withstand hostile abiotic factors
e.g. lichen
Define primary succession
Starts with a pioneer species colonising bare rock or sand
Define secondary succession
Succession is disrupted and plants are destroyed.
Succession starts again, but soil is already created (doesnt start from bare rock)
Define climax community
The final stage of succession. The animals/ plants/ species remain constant and exist in balance with the environment
2 marks
Algae are green protoctists. Lichens consist of a fungus and an alga living together in a relationship where both organisms benefit. Suggest how the relationship between the alga and the fungus allows the lichen to survive on an inorganic surface such as a wall.
- Algae photosynthesise and produce carbohydrates
- Funus absorbs water and mineral ions which is available to the algae
4 marks
Explain colonisation
- Lichens able to survive hostile environment
- Death of lichen makes the habitat less hostile
- E.g. Produces thin layer of soil called humus
- Slow growth limits spread of lichen, other plants grow faster
5 marks
Explain what limits the size of populations in a climax community
- Number of producers providing energy
- Light intensity affecting the rate of photosynthesis
- Space for niches
- Birth rate balancing death rate
- Competition for limited resources e.g. food
- Predation
Reasons for conserving woodlands
- Conserving / protecting habitats / niches
- Conserving / protecting endangered species / increases biodiversity
- Reduces global warming
- Source of medicines / chemicals / wood
- Reduces erosion / eutrophication
Describe how you would investigate the distribution of marram grass from one side of the dune to the other
Line transects from one side of the dune to the other
Place quadrats at regular intervals along the line
Work out % cover of marram grass for each quadrat
Define community
All the species
