7-18/19 Evolution + Ecosystems Flashcards
What are the five causes of evolution?
Mutation Gene flow Non-random mating Isolation Natural selection
What is evolution caused by?
A change in the allele frequencies in a population
What causes a non-evolving population?
Very large population
No migration
No mutation
Random mating
What is stabilising selection?
Where there is no environmental change
This tends to eliminate the extremes of the phenotypes
What is directional selection?
When the environmental conditions change, the optimum has changed
One extreme is favoured over the other
This causes a shift in the mean phenotype
What is disruptive selection?
Where the extreme phenotypes are favoured over the mean ones
It occurs when the environmental factor takes two forms
What is speciation?
The evolution of new species from existing ones
This involves reproductive separation
What is adaptive radiation?
The variations of alleles in the gene pools of different populations of species leads to each population becoming adapted to the local environment
What is genetic drift?
Smaller populations have a lower genetic diversity
This means that there is not an equal chance of each being passed on
Those passed on will quickly affect the whole population
This makes speciation occur faster
What is allopatric speciation?
Where two populations become geographically separated
The difference in environmental conditions between locations leads to a difference in natural selection
What is ecology?
The study of the inter-relationships between organisms and their environment, including abiotic and biotic factors
What are the two major processes within an ecosysten?
The flow of energy
The cycling of elements
What is the carrying capacity?
The size of the population that the ecosystem can support
What affects the carrying capacity?
The effect of abiotic factors
Interactions between organisms e.g. competition and predation
How is the growth of a population expressed?
Through logarithms
What are the common abiotic factors?
Temperature
Light
PH
Water and humidity
What is a stable population?
Where the birth rate and death rate are in balance and so there is no increase or decrease in the population size
What is an increasing population?
Where there is a high birth rate, giving a wider base to the population pyramid and fewer old people, giving a narrower apex to the pyramid
This happens in economically less developed countries
What is a decreasing population?
Where there is a lower birth rate (narrower base) and a lower mortality rate leading to more elderly people (wider apex)
Occurs in economically more developed countries
What is intraspecific competition?
Competition which occurs between individuals of the same species
This occurs over food, water, breeding sites, etc
What is interspecific competition?
Competition between individuals of different species for food, light, water, etc
What is the rule about ecological niches?
Two species cannot occupy the same niche so the one that uses the resources most effectively will eliminate the other
What is an ecological niche?
Where an organism lives and what it does there
No two species occupy the same ecological niche
