19.2 Variation in population size Flashcards
What is a population
What is population size
A group of individuals in the same species that occupy the habitat at the same time
The number of individuals in a population
How do you plot graphs of population size and time
Why do we use a logarithmic scale
It is an exponential shaped graph
We use a logarithmic scale eg in bacteria because it will originally double each hour, but the numbers will get too high and there isn’t a set timescale
So get the logarithm numbers of bacteria, and plot them against time so all points can be represented on the graph
Why would a bacterial cell originally growing in perfect conditions in a pond have a slowing growth rate
Give any possible reasons for why a population doesn’t grow indefinitely
. Mineral ions are consumed as the population becomes larger
. So population gets so large that the bacteria at the surface prevent light reaching those at deeper levels
. Other species are introduced to the pond, carried by animals or wind so will use bacteria as food or compete for light and minerals with them
. Winter brings colder temperatures and lower light intensity
Give examples that effect growth rate of a population
. Availability of food, light, shelter, water, oxygen, disease, toxic waste
so every population has a carrying capacity which is the maximum number that can be reached by the population
How does the abiotic factor temperature influence the size of a population of cold blooded animals or plants
. Each species has a different optimum temperature at which it is best able to survive
. The further away from this optimum, the fewer individuals in a population are able to survive, and the smaller is the population that can be supported
In plants and cold blooded animals, if temp falls below optimum, the enzymes work more slowly so their metabolic rate is reduced
At high temperatures, above optimum, the enzymes work less efficiently because they gradually undergo denaturation
So the carrying capacity of that population is reduced
How does abiotic factor temperature affect the size of a population of warm blooded animals
. Warm blooded animals can maintain a relatively constant body temperature regardless of external temperature.
So you may think their carrying capacity is unaffected by temperature
However the further the temperature of the external environment gets from the optimum temperature, the more energy those organisms need to maintain this temperature
So this leaves less energy for growth so they mature more slowly and reproductive rate slows
So carrying capacity of that population is reduced
How does abiotic factor light affect carrying capacity of plants.
How does this affect animals
. Light is ultimate source of energy for most ecosystems
. As light intensity increases, rate of photosynthesis increases so plants grow faster and produce more seeds and spores.
Their carrying capacity is therefore potentially greater , and for animals there is more food for them to feed on so the carrying capacity for animals is potentially bigger also
How does abiotic factor PH affect carrying capacity of a species
. It affects the action of enzymes
. Each enzyme has an optimum PH at which it operates at most effectively
. A population is larger where the appropriate PH exists, and is smaller where there is a PH different from the optimum
How does abiotic factor water and humidity affect carrying capacity of a species
Where water is scarce, populations are small and only consist of species that are well adapted to living in dry conditions
Humidity affects transpiration rates of plants, and the evaporation of water from the bodies of animals
So population size depends on how the species is adapted to those conditions , eg in dry conditions the populations of species adapted to tolerate low humidity will be larger than those without.
