Ecological Succession Questions Flashcards
A climax community is more stable than a pioneer community. Explain what makes this the most stable community (2)
More species present
More complex food webs
Change in one species will have little effect on others
Alternative food sources
Explain why it would be more appropriate to use a transect rather than random quadrants when investigating succession (1)
Series of changes over a distance
Ensure sampling of each community
Succession occurs in natural ecosystems. Describe and explain how succession occurs (5)
Colonisation by pioneer species
Change in environment
Enables other species to colonise
Change in diversity
Stability increases
Climax community
Land exposed by a shrinking glacier in Alaska became covered by dense forest. Explain how succession resulted in the formation of the forest (4)
Pioneers colonised land
Change in environment
Enables change in species
Conditions change further to favour tress
In areas where the soil is waterlogged the climax community is bog dominated by the moss. Explain why bog is described as the climax community (1)
Stable community/no further succession
Waterlogged soils lack oxygen. Suggest why trees are unable to survive in waterlogged soils (2)
Roots unable to respire aerobically
Active transport of minerals stops
A farmer stopped using a field for growing crops. Scientists studied succession in that field over the next 30 years. The number of Hemiptera (an order of insects) increased. Explain why (3)
More species diversity in the field
More niches/habitats
More feeding opportunities
In a lake;
Stage 1 - microscopic plants and animals
Stage 2 - layers of mud and organic matter settles on the bottom. Submerged plants appear.
Stage 3 - plants growing on surface and edges of pond. Submerged plants dies out.
Stage 4 - build up of mud and organic matter forms a marsh.
Stage 5 - community of land plants.
Explain how this illustrates the features of an ecological succession (6)
Colonisation
Microscopic plants at start
Death/decomposition
Increase in organic matter
New species colonise once there is a change
Increase in number of species
Increase in total amount of living material
Increase in nutrient availability
More stability
Several small rivers flow into a lake. These rivers flow through forested areas. Explain how deforestation might affect the process of succession in the lake. (2)
Direct result - leaching/soil erosion
Specific effect - more sediment/nutrients
Explain what limits the side of populations in a climax community (5)
Nutrient availability
Numbers of producers providing energy
Light intensity affecting the rate of photosynthesis
Disease killing members of species
Space for niches
Completion e.g. for food/light
Predation
Ecologists investigated succession in some abandoned crop fields. They recorded that the level of soil nitrates increased over a 60 year period. Explain why (2)
Increase in dead organisms/decomposition
Leading to increase in nitrification
Increase in nitrogen fixation
A pioneer plant had seeds that germinate better when the temperature fluctuates. Explain the advantage of this to the pioneer plants (2)
Bare soil temperatures fluctuate
More bare soil at start of succession
Explain the advantage to a plant that colonises after 50 years of having a high rate of photosynthesis at low light intensities (1)
Plants will grow/survive in shade/ when overshadowed
The increase in the index of diversity is one indication that a biological succession is taking place in the area. Describe those features of a succession that would bring about an increase in the index of diversity (3)
Initial environment hostile/few organisms adapted
These organisms change the environment
More niches/habitats
Allowing other organisms to be established
Explain what is meant by succession (2)
Change in community over time
Due to environmental factors/change in species present
