A Level Biology - Populations

A Level Biology - Populations
Covers:
Definitions,
Population growth curve,
Environmental resistance,
Competition,
Sampling techniques.

Transcript

1. Populations
2. Important definitions • Abiotic – part of the environment that is non-living (temperature, oxygen availability…) • Biotic – part of the environment that is living (pathogens, disease…) • Carrying capacity – maximum number around which a population fluctuates in a given environment (the limit to the number of individuals an area can support sustainably) • Equilibrium species – species that controls populations by competition instead of reproduction and dispersal • Environmental resistance – the environment factors that slow down or limit population growth • Immigration – the movement of individuals into a population of the same species • Mortality rate – number of deaths over a given period (usually a year) divided by the number of adults in the population • Natality rate – reproduction capacity of a population, number of new individuals derived from reproduction per unit time
3. Important definitions cont. • Niche – a species role in the ecosystem • Population – an interbreeding group of individuals of the same species occupying a certain habitat
4. Population growth curve Time Lag phase > Period of adaptation for growth, initially slow as the number of individuals are few to start with Exponential growth/log phase > More individuals are able to reproduce so birth rate is higher than death rate, mammals are born, birds hatch from eggs, bacteria undergo binary fission and flowing plants develop from seeds Stationary phase > Birth rate is equal to death rate, population has reached it’s maximum size and carrying capacity has been reached Death/decline phase > Death rate is higher than birth rate Log number of individuals
5. Environmental resistance Abiotic factors – not-living • Temperature • Oxygen availability • Water availability Biotic factors – living • Parasites • Diseases • Predators Density dependent factors – population size influences impact • Toxic waste accumulation • Disease • Parasitism • Depletion of food supply Density independent factors – population size has no influence on impact • Violent change in a abiotic factor • Sudden freezing • Flooding • Natural disaster
6. Competition Intraspecific competition • Between individuals of the same species • Density dependent • The best adapted have a greater chance of survival Interspecific competition • Between individuals of different species • 2 species cannot occupy the same niche in the same habitat • Species with greater chance depends on the advantageous condition • Smaller species need less food so survive when food is scarce Occurs when a lot of organisms are competing for some sort of limited resource (food, water, nesting site…)
7. Sampling techniques Systematic sampling • When investigating distribution of organisms along a gradient or change in land etc • Place a tape measure along the area • Place a quadrat at regular intervals • Count the number of {organism} in each quadrat • Consider if it would be applicable to the question to say “at regular intervals” or “repeat in different areas” Random sampling • Lay out 2 tape measures to form a grid • Generate coordinates using a random number generator • Place quadrat so top left corner is at the coordinate • Count the number of {organism} in each quadrat • This avoids bias and gives a better representation of the whole area