7C: Populations in Ecosystems

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  • Created by: DBaruch
  • Created on: 26-01-17 17:39

What is an ecosystem

  • An ecosystem is all the organisms living in a community plus all the non-living (abiotic) conditions in which they live. Ecosystems include both biotic and abiotic conditions. Biotic conditions are the living features of an ecosystem, for example the presence of predators or food. Abitoic conditions are the non-living features of an ecosystem, such as the temperature and soil.
  • Ecosystems vary in size- they can be small (pond) or large (an ocean). the place where an organism lives within an ecosystem is known as its habitat.
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What is a niche

  • A niche is the role of a species within its habitat, for example what it eats, and where and when it feeds. The niche a species occupies includes: its biotic interactions (organisms it eats and those eaten by) and its abiotic interactions(temperature range an organism can live in). Every species has its own unique niche and a niche can only be occupied by one species.
  • If 2 species try to occupy the same niche, they will compete with each other. 1 species will be more succesful than the other until 1 species is left
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Adaptations

  • An adaptation is a feature that members of a species have that increases their chance of survival and reproduction. These features can be physiological, behavioural or anatomical. Organisms with better adaptations are more likely to survive, reproduce and pass on advantageous alleles that determine these adaptations. The frequency of these alleles in the population increases meaning they become more common. This is called natural selection.
  • Every species is adapated to use an ecosystem, each species has its own niche. For example anteaters can only break into ants nest to reach the ants. Organisms are adapted to both the abiotic conditions and the biotic conditions in their ecosystem
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Populations

  • A population is all the organisms of 1 species in a habitat. Populations of different species in a habitat make up a community. Population size is the total number of 1 species in a habitat. The maximum stable population size of a species that an ecosystem can support is called the carrying capacity. This varies depending on abiotic and biotic factors
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Abiotic factors and population size

  • The population size of any species varies due to abiotic factors (light, water, space ETC.) When abiotic conditions are ideal for a species, organisms can grow more quickly and reproduce succesfully.
  • When abiotic conditions aren't ideal for a species, organisms can't grow as fast or reproduce as successfully
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Biotic factors and population size

  • Interspecific competition- is when organisms of different species compete with each other for the same resources in an ecosystem. If one is better adapted then it will survive and out-compete the other and will survive
  • Intraspecific competition- is when organisms of the same species in an ecosystem compete with each other for limited resources. It can cause a change in population size and change the ecosystems carrying capacity
  • Predation- is when an organism kills and eats another organism. The population sizes of predators and prey are interlinked, as the population of one changes it causes the other population to change.
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Abundance and distribution

  • Abundance- is the number of individuals of 1 species in a particular area. Abundance can be estimated by counting the number of individuals in samples taken. However frequency and percentage cover can also be used
  • Distribution- is where a particular species is within the area you are investigating
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Methods for investigating populations

  • There are lots of different methods for studying populations of organisms, choosing the right one depends on the type of organism and habitat. Quadrats and transects can be used for studying non-motile organisms, for motile organisms nets and traps are better
  • Quadrats- they are placed on the ground at different points within an area. The % cover can be measured by counting how much of the quadrat is covered by the species
  • Transects- you can use lines called transects to help find out how organisms are distributed across an area. Belt transects- quadrats are placed next to each other along the transect to work out species frequency and % cover. Interrupted belt transect- you take measurements using a quadrat placed at regular intervals, it makes it easier to cover a large distance
  • Capturing motile organisms- for flying insects you'd use a sweep net. For aquatic animals you'd use a net. For ground insects you'd use a pitfall trap thats sunk into the ground
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Mark-release-recapture

  • It is a method used to measure the abundance of more mobile species. Capture a sample of species and count them. Mark them in a harmless way. Release them back into their habitat. Wait a week, then take a 2nd sample from the sample population. Count how many of the second sample are marked. 
  • Image result for mark release recapture equation P= total population size, M= number caught in 1st sample, C= number caught in 2nd sample, R= number marked in 2nd sample
  • There are a few assumptions that are made when using the method: the marked sample has had enough time to mix back with the population, the marking has affected survival, there are no changes in population size due to births, deaths and migration during the period of study
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What is Succession

  • Succession is the process by which an ecosystem changes over time. Succesion happens in a series of stages. At each stage, the plant and animal communities in an area slowly change the environmental condition, making the conditions more suitable for other species with different adaptations. This means that biotic conditions changes as abiotic conditions change, causing one community of organisms to be succeeded (replaced) by another. There are 2 types of succession, primary and secondary
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Primary succession

  • It occurs on land that has been newly formed or exposed.
  • Pioneer stage- it starts when a species colonise a new land surface. Wind dispersed seeds begin to grow. They can grow because they are adapted to the conditions. When they die they change the abiotic conditions, they decompose and form basic soil. The next organsisms do the same until eventually larger plants and animals can live there.
  • Later stages of succession- at each stage, different plants and animals are better adapted for the improved conditions move in, and out-compete the plants and animals that are already there, and become the dominant species in the ecosystem. As succession goes on the ecosystem becomes more complex and new species move in alongside existing species, increasing biodiversity. Eventually these changes result in a climax community- the ecosystem is supporting the largest it can and won't change much more
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Secondary Succession

  • Secondary succession occurs on land that's been cleared of all the plants but where soil remains (forest fire etc.) It can occur at any stage after the pioneer stage.
  • The process of secondary succession is similar to primary succession but because there is already a layer of soil, secondary succession starts later and the pioneer species are larger plants (shrubs)
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Human impact and climatic climax

  • Human activites can prevent succession, stopping a climax community from developing. When succession is stopped artificially like this, the climax community is called a plagioclimax
  • Which species make up the climax community depends on what the climate's like in an ecosystem. The climax community for a particular climate is called its climatic climax (temperate climates will contain large trees as conditions dont change too much)
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What is conservation

  • Conservation is the protection and management of species and habitats in a sustainable way. Sustainable means that enough resources are taken to meet the needs of people today, without reducing the ability of people in the future to meet their own needs. It is a dynamic process as methods need to be adapted to the constant changes that occur within an ecosystem.
  • Not everyone agrees with every conservation method, so careful management is needed to find a balance between human needs and conservation
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Conservation methods

  • Management of succession- human activites can interrupt the process of succession. Conservation frequently involves preventing succession in order to preserve an ecosystem in its current stage of succession.
  • Seed banks- stores lots of seeds from lots of different species, they act as a backup for the conservation of plant species in the wild
  • Captive breeding- it involves breeding animals in a controlled environment. Often the animals are endangered or are extinct in the wild, it can help to increae their numbers. Animals breed this way can be reintroduced into the wild to increase numbers.
  • Fishing quotas- they limit the amount of certain fish species fishermen can catch. They help to conserve fish species by reducing the numbers that are caught and killed, it aims to stop a situation in which fish population reaches such low numbers they become extinct.
  • Protected areas- preserve natural areas and restrict urban and industrial development
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Conflicting conservation evidence

  • The evidence from 1 study alone usually wont be enough to conclude theres a link between the presence of 1 species on another species. If studies came to the same conclusion, the conclusion would become increasingly accepted. Sometimes studies come up with conflicting evidence that leads to different conclusions
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