Populations and ecosystems Flashcards
Define population
A group of organisms of the same species, occupying a particular space at a particular time that can potentially interbreed
Define ‘gene pool’
All the alleles of all genes in a population
Define Community
All the populations of different species living in the same habitat at the same time
What are biotic conditions? Give examples
Living factors of an ecosystem.
e.g predation, disease, food supply.
What is a plagioclimax?
When human activities prevent succesion and stop a climax community forming. It is usually used for the conservation of a species (as it prevents them being out competed by a new environment)
Define ecosystem
The community of biotic and abiotic factors of an area and their interactions. It is said to be dynamic
State 5 features of an ecosystem
- Dynamic
- Can range in size from very small to very large
- Can range in complexity (e.g a desert is relatively smple, a tropical rainforest is very complex)
- Self-contained
- Flow of energy and nutirents within it
Why are ecosystems described as ‘dynamic’?
o Populations constantly rise and fall
o Any small change can have a large effect
o Biotic and abiotic factors may alter the condition of the ecosystem
What 4 factors affect population size and distribution?
- Interspecific Competition
- Intraspecific Competition
- Predation
- Abiotic Factors
What is interspecific competition?
Outline the process
When individuals of different species compete for the same resources such as food, light etc.
- Where populations of the two species share the same niche, one will normally have a competitive advantage over the other.
- The population of this species will eventually increase in size and the other will diminish.
- If these conditions continue this will lead to the compete removal of one species. This is known as the local extinction.
What is intraspecific competition? What is eventually reached as a result?
When individuals of the same species compete for the same resources such as food, light etc.
- This is competition for the same resources between individuals from the same species
- For example: When resources are plentiful, the population of species increases
- As the population increases, however, there are more individuals competing for these resources (e.g. food and shelter)
- At one point, the resources become limiting and the population can no longer grow in size – the carrying capacity has been reached
- The population may then decrease so the cycle starts again
Describe a predator-prey cycle (Lokta-Volterra model)
The prey population increases because there are not many predators to eat the prey
The predator population increases because there is plenty of prey for them to eat, so more survive and reproduce.
The prey population decreases because there are many predators eating the prey
The predator population decreases because there isn’t as many prey as animal s, so there is less food available for them to eat, so there is more intraspecific competition between predators.
Each cycle is approx. x years
What is meant by ‘carrying capacity’?
The maximum stable population size of a species that an ecosystem can support
Define the term ‘niche’
The role that an organism plays in a ecosystem, which is governed by adaptations to abiotic and biotic conditions
What is the competitive exclusion principle?
- A niche can only be occuped by one species, meaning that every individual species has its own unique niche
- Competition for food / named resource;
- If two species had identical nichces, one would go extinct
- The better adapted outcompetes the other species
What causes interspecific competition?
Overlap between the niches of different species
Population size and Carrying capacity
Label the graph
A B C K
A = lag phase. Few individuals still acclimatising to their habitat. Rate of reproduction is low.
B = 10 log phase/exponential phase.
Plentiful resources and suitable conditions. Reproduction rate is fast and exceeds the mortality rate.
C = stationary phase. Reached carrying capacity of the habitat. Rate of reproduction and mortality are equal. The habitat cannot support a large population.
Population remains stable.
K = carrying capacity. maximum size of a population an ecosystem can support
Why is sampling carried out?
To select a sample which is representative of the population
What are the 5 key factors to consider when carrying out an ecological study?
Large sample size
Removing bias
Seasonal differences
Choosing appropriate samples
Conclusions shown
Sampling can either be ______or ________
Sampling can either be random or systematic
Describe, in detail, how and why we use random sampling in an ecological study
1) Choose an area to sample - a small area within the area being investigated.
2) Samples should be random to avoid bias, e.g. if you were investigating a field you could pick random sample sites by dividing the field into a grid and using a random number generator to select coordinates.
3) Use an appropriate technique to take a sample of the population
4) Repeat the process, taking as many samples as possible. This will reduce the likelihood that your results are down to chance. Eliminates bias
5) The number of individuals for the whole area can then be estimated by taking the mean of the data collected in each sample and multiplying it by the size of the whole area.
How is systematic sampling different to random sampling?
- A similar grid is used, however samples are taken at regular intervals.
- Usually used to investigate environmental gradient.
How can we increase the reliability of data used in an ecological study? 6
- Increase repeats
- Calculate running mean
- When enough quadrats used, graph would level off
- Take enough readings to carry out statistical test
- Test a large number to make sure results are reliable
- Need to be sure work can be carried out in designated time
Why do we use random samples? [3]
- Avoids bias
- Data representative / Choice of X variable not influencing results
- Allows use of statistical tests
