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Abiotic conditions that influence the size of a population
Factor Explanation + Effect
Temperature Each species has a different optimum temperature at which it
is best able to survive. The further away from this optimum,
the smaller the population that can be supported. Far below
the optimum temperature, the slower enzyme activity is and
so metabolic rate is reduced. Populations therefore grow more
slowly. Temperatures above the optimum cause denaturation
so population grow more slowly. Warm-blooded mammals can
maintain a relatively constant body temperature, regardless of
the external temperature. The further away from the optimum
these organisms are, the more energy they use trying to
maintain normal body temperature less energy for individual
growth. The animals therefore mature slower and their
reproductive rate is reduced. The population size gets smaller.
Light The ultimate source of energy for ecosystems, the basic
necessity of life. The rate of photosynthesis increases as light
intensity increases. The greater the rate of photosynthesis, the
faster the plants grow and the more spores or seeds they
produce. Their population growth and size is therefore greater.
In turn, the population of animals that feed on plants is
PH PH affects enzyme activity. Each enzyme has an optimum PH
at which it operates most effectively. A population of
organisms is larger where an appropriate PH exists, smaller or
non-existent where the PH is very different from the optimum.
Water and Humidity Where water is scare, populations are small and consist of
species that are well adapted to living in dry conditions.
Humidity affects transpiration rates in plants and the
evaporation of water from the bodies of animals. In dry air
conditions, populations of a species adapted to tolerate low
humidity will be larger than those with no such adaptations.