Succession exam questions

A small, permanent pond is the habitat for a climax community of producers (aquatic plants and algae) and consumers (bacteria, protoctista, worms, snails, arthropods and small vertebrates like newts and fish).

Why might ecologists call this a ‘climax community’?

Pond community is stable and not subject to further succession

The protoctist Paramecium caudatum is usually between 200 and 300 μm in length. An accurate measurement would help in the correct identification of a specimen from this pond.

What laboratory equipment would you select to make an accurate measurement of the length of Paramecium caudatum?

Light microscope and eyepiece graticule

An animal fell into the pond. It drowned and decayed. Within a year the biological compounds in its body had been completely recycled.

What nitrogenous excretory molecule from the decomposers would pass to the next stage of the nitrogen cycle?

Ammonia

Compare the plant and animal species that make up the climax and the pioneer communities.

Pioneer community

Plants

• Small species, e.g. mosses and lichens

• Shorter life-cycle / fast growing

• Seeds / spores produced in large quantities, dispersed long distances, germinate rapidly

• Self pollinating / asexual reproduction

• Tolerate extreme environments - xerophytic

Animals

• Few species, mostly small

Climax community

Plants

• More species, larger species e.g. trees

• Do not tolerate extreme environments

• Require soil with ample water and minerals

• Dominant species

• Slow-growing

Animals

• Larger species

• More herbivore species

• Carnivores present

• Longer food chains

Succession involves changes in the species that live in an area over time.

State one other change that takes place in the same area over the same time.

Change in soil / substrate, increased humus

Suggest what was present in the area that is now occupied by mixed woodland before the pioneer community arrived.

Bare ground / rock

Outline the process of primary succession and explain why heather moorland is an example of deflected succession

Pioneer community - begins with bare rock, arrival as seeds or spores, nitrogen-fixation

Intermediate community - herbs, including grasses, followed by shrubs and trees

Climax community - dominance by a few tree species, little change over time

Serial stages, community and decomposition, changed composition of soil, increased organic / nitrate content

Heather moorland is deflected succession because a climax community is prevented from developing - plagioclimax, heather shrubs

Suggest how the scientist could achieve the following during their investigation:

Sample all stages of succession in the habitat

Minimise sampling bias

Sample insect biodiversity

Belt / line transect, stratified sampling

Random selection of transect sites

Systematic sampling / place quadrants at pre-determined intervals

Random sampling using quadrants in strata

Pooter / sweep nets / pitfall traps

Suggest the units the scientist should use to measure primary production in woodland and lake habitats

Woodland - kg m^-2 yr^-1

Lake- kg m^-3 yr^-1

Characteristics of a pioneer community (3)

species produce large numbers of wind-carried seeds or spores

biomass is low

many species are lichens and mosses

Describe the differences between a pioneer community and a climax community

Pioneers arrive before climax, pioneer communities subject to more change, pioneer community has less biodiversity and is less stable, lower biomass

Choose and describe sampling techniques that would show how the distribution and abundance of native and introduced grasses change across the two zones. (7)

• Lay string in a line across zones from sea to post-pioneer boundary

• Perform belt / line transect

• Frame quadrat placed systematically along intervals

• Use a key, identify species present

• Estimate percentage cover

• Repeat sampling over time and in one area

What is a plagioclimax?

Human intervention prevents the expected climax community from forming- stable but would not have occurred without human intervention, e.g. heathland.