Variation in population size


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1.3 Variation in population size

Population growth curves

1) a period of slow growth as the initally small number of individuals reproduce to slowly build up their numbers.

2) a period of rapid growth where the ever-increasing number of indibiduals continue to reproduce.  The population size doubles  during each interbal of time, as seen by the gradient of the curve which becomes increasingly steep. 

3) a period when the population growth declines until its size remains more or less stable. The decline may be due to food supply limiting numbers or to increased predation. The graph therefore levels out with only cyclic fluctuations due to variations in factors such as food supply or the population size of predators.  

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Population Size

Limiting factors 

- Abiotic factors, non-living part of the environment

- Biotic factors, acivities of organisms and include, competition and predation. 

Abiotic factors

- Temperature, the lower the temp the more slowly the population grows because there is a slower metabolic rate.  at a high temp enzymes can denature and work less efficiently.  

- light, ultimate source of energy for ecosystems, photosynthesis increases as light intensity increases, the greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce. 

-pH,action of enzymes 

- water and humidity, populations are small where water is scarce. Humidity affects transpiration rates in plants. 

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