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OCR Biology A level 6.3.2 population and sustainability summary notes
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Summary notes for topic 6.3.2 Population and sustainability of OCR Biology A level Module 6. Detailed electronic notes with diagrams.
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Roots decomposed/acted on by decomposers/rot/decay Nitrogenous compounds released by decomposers
Formation of nitrate
Crop rotation:
Different crops have different nutrient requirements
Each year different demands on soil
in 4th/fallow year; no nutrients removed/used for grazing animals
Nutrient levels allowed to build up
Use legume in rotation
6.3.2 Populations and Sustainability
Population will not increase in size indefinitely because:
ANIMALS:
1. Population reaches carrying capacity
a. Maximum size of population that can be supported by the environment
b. Because there are limiting factors
2. Intraspecific competition between organisms of the same species
a. For food/nesting sites/named resource
3. Interspecific competition
a. With other named species
b. For named resource
4. Larger animal populations
a. Attract more predators
b. Pathogens/parasites/diseases spread more easily
PLANTS - rise because
1. Rise in temperature
a. Increased rate of metabolism
b. Enzymes work more efficiently
2. Greater light intensity
, a. Increased photosynthesis
3. Increased day length/more light
a. Increased photosynthesis
4. More minerals in water
a. From increased rate of decomposition
b. From agricultural run off/sewage
Fall because
1. Overshoot carrying capacity
2. Decreased photosynthesis
a. Shading / lack of light / colder
b. Minerals exhausted
3. Eaten by consumers
4. Build up of toxins
Carrying capacity:
The maximum population size
That can be supported by a particular habitat
Due to limiting factors
Habitat cannot support a larger population
Rates of reproduction and mortality are equa
Population size stays stable
Small fluctuations due to small variations in environmental conditions
Factors allowing a large population of animals to increase from just a few individuals in a newly colonised area
Animals are an introduced species
o Fill vacant niche
o Not reached carrying capacity
No/few predators
Plenty of food/space
o Breed successfully and rapidly
o More young survive
o Few die before breeding
o Birth rate greater than death rate
Animals may be restricted to an area e.g island
o Cannot emigrate so numbers build up
Predator–prey relationships and their possible effects on the population sizes of both the predator and the prey;
Typical prey-predator relationship:
Prey populations increase
o When conditions suitable/when predator
numbers are low/when few limiting factors
Provides plenty of food for predator population
o Begin to increase later (time delay)
Prey eaten by predators
o Both decline in numbers
Cycle repeated
Prey populations reach higher levels than predators
How stability maintained:
Limited food supply
Competition
Predation
Disease
Reached carrying capacity / death rate = birth rate
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