C2. Variation in Population Size Flashcards
Populations
A population is____________________________________________. Populations of different species in a habitat make up a _______________.
Population size is ____________________________________________________________.
This number changes over time because of the effect of various factors. The maximum stable population size of a species that an ecosystem can support is called the ___________ ____________. Carrying capacity varies as a result of both ________and ________factors.
A population is all the organisms of one species in a habitat. Populations of different species in a habitat make up a community.
Population size is the total number of organisms of one species in a habitat.
This number changes over time because of the effect of various factors. The maximum stable population size of a species that an ecosystem can support is called the carrying capacity. Carrying capacity varies as a result of both abiotic and biotic factors.
Abiotic factors and population size
The population size of any species varies due to abiotic factors, e.g. the amount of _____, ________or _______available, or the _________________or the chemical composition of their surroundings. When abiotic conditions are ideal for a species, organisms can ______ _____ ________and _______________successfully.
When abiotic conditions aren’t ideal for a species, organisms can’t grow as fast or reproduce as successfully.
The population size of any species varies due to abiotic factors, e.g. the amount of light, water or space available, or the temperature or the chemical composition of their surroundings. When abiotic conditions are ideal for a species, organisms can grow more quickly and reproduce successfully.
When abiotic conditions aren’t ideal for a species, organisms can’t grow as fast or reproduce as successfully.
Biotic factors and population size - 1. Interspecific competition
Interspecific competition is when organisms of ________species compete with each other for the same ___________. This can mean that the resources available to both populations are __________, e.g. if they share the same source of food, there will be less available to both of them. This means both populations will be limited by a lower amount of food. They’ll have _____ _______for _______and _______________, so the population sizes will be lower for both species. If two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be ___-______________—it won’t be able to exist alongside the better adapted species.
- Interspecific competition
Interspecific competition is when organisms of different species compete with each other for the same resources. This can mean that the resources available to both populations are reduced, e.g. if they share the same source of food, there will be less available to both of them. This means both populations will be limited by a lower amount of food. They’ll have less energy for growth and reproduction, so the population sizes will be lower for both species. If two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed—it won’t be able to exist alongside the better adapted species.
Biotic factors and population size - 2. Intraspecific competition
Intraspecific competition is when organisms of the _____species compete with each other for the same resources. It can cause a cyclical change in population size around the ecosystem’s carrying capacity-where the population grows, shrinks, grows again and so on (see Figure 1). This is because the population of a species increases when resources are plentiful. As the population increases, there’ll be more organisms competing for the same amount of space and food. Eventually, these resources become limiting. If the population grows beyond the carrying capacity, there won’t be __________ ____________ for all the organisms and the population will begin to decline. A smaller population then means that there’s less competition for space and food, which is better for growth and reproduction-so the population starts to grow again. This cyclical pattern then continues…
Intraspecific competition is when organisms of the same species compete with each other for the same resources. It can cause a cyclical change in population size around the ecosystem’s carrying capacity-where the population grows, shrinks, grows again and so on (see Figure 1). This is because the population of a species increases when resources are plentiful. As the population increases, there’ll be more organisms competing for the same amount of space and food. Eventually, these resources become limiting. If the population grows beyond the carrying capacity, there won’t be enough resources for all the organisms and the population will begin to decline. A smaller population then means that there’s less competition for space and food, which is better for growth and reproduction-so the population starts to grow again. This cyclical pattern then continues…
Biotic factors and population size - 3. Predation
Predation is where an organism (the predator) kills and eats another organism (the prey), e.g. lions kill and eat (predate on) buffalo. The population sizes of predators and prey are interlinked - as the population of one changes, it causes the other population to change (see Figure 3 on the next page).
As the prey population increases, there’s more food for predators, so the predator population grows. As the predator population increases, more prey is eaten so the prey population then begins to _____. This means there’s less food for the predators, so their population _____________, and so on.
Predator-prey relationships are usually more complicated than this though because there are other factors involved, like availability of food for the prey. Eg, it’s thought that the population of snowshoe hare initially begins to decline because there’s too many of them for the amount of food available. This is then accelerated by predation from the lynx.
Predation is where an organism (the predator) kills and eats another organism (the prey), e.g. lions kill and eat (predate on) buffalo. The population sizes of predators and prey are interlinked - as the population of one changes, it causes the other population to change (see Figure 3 on the next page).
As the prey population increases, there’s more food for predators, so the predator population grows. As the predator population increases, more prey is eaten so the prey population then begins to fall. This means there’s less food for the predators, so their population decreases, and so on.
Tip: Don’t get inter- and intra-specific competition mixed up. If you’re struggling just remember-inter means __________ species, whereas intra means the ________species
Tip: Don’t get inter- and intra-specific competition mixed up. If you’re struggling just remember-inter means different species, whereas intra means the same species
Investigating population growth of bacteria
With enough food and space, the size of a population of microorganisms, e.g. bacteria, will grow at a steady rate. This can be investigated experimentally by growing bacteria in a liquid broth—a liquid containing the nutrients the bacteria need to grow. A liquid broth containing bacteria can be called a broth culture.
When light is passed through a sample of broth culture, some of it is scattered because bacteria are present-this reduces the amount of light passing through the culture. A machine called a spectrophotometer can measure the amount of light passing through a sample of the culture and produce an absorbance value. The more bacteria present in a culture, the less light will pass through to be detected by the spectrophometer, producing a higher absorbance value (see Figure 4). So a broth culture sample with a high absorbance has a high number of bacteria present and vice versa.
Investigating population growth of bacteria
With enough food and space, the size of a population of microorganisms, e.g. bacteria, will grow at a steady rate. This can be investigated experimentally by growing bacteria in a liquid broth—a liquid containing the nutrients the bacteria need to grow. A liquid broth containing bacteria can be called a broth culture.
When light is passed through a sample of broth culture, some of it is scattered because bacteria are present-this reduces the amount of light passing through the culture. A machine called a spectrophotometer can measure the amount of light passing through a sample of the culture and produce an absorbance value. The more bacteria present in a culture, the less light will pass through to be detected by the spectrophometer, producing a higher absorbance value (see Figure 4). So a broth culture sample with a high absorbance has a high number of bacteria present and vice versa.
