13.1 & 2 Investigating populations & Succession
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Describe the process of succession [6]
• (Colonisation by) [named] pioneer species; • Pioneers cause change in environmental abiotic / biotic factors (give an example); • Pioneers make the environment less hostile for new species; • New species change/make conditions less suitable for previous species; • Change/increase in diversity/biodiversity; • Stability increases [population/richness/abiotic factors]; • Climax community [represented by…..];
Explain how succession results in a wide variety of fish living on coral reefs. [2]
• Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity • Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;
Describe random sampling [estimation of population density] [5]
• Use a grid / split area into squares/sections OR Map the area • Method of obtaining random coordinates / numbers, e.g. random number generator; • Count number/frequency of plants in a quadrat; • Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section); • Valid method of calculating total number of … e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in area;
Describe systematic sampling [3]
• Transect / line/tape measure (from one side of the dune to the other); • Place quadrats at regular intervals along the line; • Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
Which type of sampling would you choose? On a beach
RANDOM
Which type of sampling would you choose? Along a beach
SYSTEMATIC
Which type of sampling would you choose? In a wooded habitat
RANDOM
Which type of sampling would you choose? On a coral reef
RANDOM
Which type of sampling would you choose? Investigate how the distribution of species changes across a sandune away from the sea.
SYSTEMATIC
Describe how you would determine the mean percentage cover for beach grass on a sand dune. [3]
• Method of randomly determining position (of quadrats) e.g. random numbers table/generator; • Large number/sample of quadrats; (min 20) • Divide total percentage by number of quadrats/samples/readings;
Describe the mark, release, recapture technique [4]
• Capture sample, mark and release; • Appropriate method of marking suggested / method of marking does not harm fish; • Take second sample and count marked organisms; • No in No in Population = (No in sample 1 X No in sample 2) divided by Number marked (recaptured) in sample 2;
The mark-release-recapture method can be used to estimate the size of a fish population. Explain how. [4]
• Capture/collect sample, mark and release; • Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish); • Allow (time for) fish to (randomly) distribute back into population before collecting a second sample; • (Population) = (number in first sample 1X number in second sample) divided by number of marked fish in second sample/number recaptured;
Suggest why the mark-release-recapture method can produce unreliable results in very large lakes [2]
• Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly; • Fish may remain in one area OR fish may congregate
Describe how you would determine how many quadrats to use when investigating a habitat. [5]
• Calculate running mean/description of running mean; • When enough quadrats, this shows little change/levels out (if plotted as a graph); • Enough to carry out a statistical test; • A large number to make sure results are reliable and representative; • Need to make sure work can be carried out in the time available;
What is meant by carrying capacity?
• Maximum number of individuals of each species an ecosystem can support.
Suggest two reasons for conserving rainforests.
• Conserve/protect species/plants/animals/organisms OR For (bio)diversity; • Conserve/protect habitats/niches OR Provides/many habitats/niches; or conserve land for indigenous communities; • Reduces climate change; • Source of medicines/drugs/wood; • Reduces erosion/eutrophication; • (For) tourism;
Define: POPULATION
A group (of organisms) of the same species in the same area at the same time, that can interbreed to produce fertile offspring.
Define: Community
All the individuals of all the different species within the same area at the same time.
Define: Species richness.
The number of different species in a specific area at a specific time. (that make up a community) Reject: Number of individuals of each species
What are the features of a CLIMAX COMMUNITY?
• Stable populations of all species (unless environment changes) • Stable species richness (composition may change due to competition) • Stable Abiotic factors (unless environment changes) • Stable Biotic factors (unless invasive species introduced) • Wide variety of niches / habitats • Some fluctuations in birth / death rate due to change in dominant species • Stable NPP
Describe the process of succession [5]
• (Colonisation by) pioneer species; • Pioneers cause change in environmental abiotic / biotic factors (give an example); • Pioneers make the environment less hostile for new species; • New species change/make conditions less suitable for previous species; • Change/increase in diversity/biodiversity; • Stability increases [population/richness/abiotic factors]; • Climax community;
Fill in the missing words: An ecosystem supports a certain size of population of a species, called the (1) capacity. There are often numerous habitats within an ecosystem. Within a habitat, a species occupies a (2) governed by an adaption to both (3) and biotic conditions. Populations of different species form a (4).
(1) carrying (2) niche (3) abiotic (4) community;;
In northern India, there is a conflict of interests between farmers of livestock (eg cows) and people trying to conserve ibex (a type of wild goat). When livestock are given extra food, their populations can grow too large and compete with ibex.
Interspecific (competition);
Different species occupy different ecological niches. Explain the advantage of species occupying different niches.
(Less) competition for food/resource; Accept: space/named resource.