Populations Flashcards
(38 cards)
Name the two major processes to consider within an ecosystem
- the flow of energy through the system
- the cycle of elements within the system
Provide an example of an ecosystem and describe the interactions within it
A fresh water pond or lake.
It has its own community if plants to collect the necessary sunlight energy to supply organisms with it.
Nutrients such as Nitrates and Phosphates are recycled within the pond/lake.
Define a population
A population is a group of interbreeding organisms of one species in a habitat
Define a community
A community is all the populations of different organisms living and interacting at the same place at the same time.
Define a habitat
A habitat is the place where a community of organisms lives.
Define a microhabitat
Groups of smaller habitats forming the makeup of a habitat
Define an ecological niche
A niche describes how an organism fits into the environment (i.e. It’s role)
A niche refers to where an organism lives and what it does there. It includes all the biotic and abiotic conditions required for an organism to survive, reproduce and maintain a viable population
Name and explain the three factors to consider when using a quadrat
1) The size of the quadrat to use (this depends upon the size and distribution of the plants or animals being counted in that area)
2) The number of sample quadrats to record within the study area (the larger the number of sample quadrats the more reliable the results)
3) The position of each quadrat within the study area (statistically significant results require random sampling to be used)
Describe the importance of using random sampling
It is important that sampling is random to avoid any bias in collecting data. Avoiding bias ensures that the data obtained is valid.
Describe a method of producing random sampling
1) Lay out two long tape measures at right angle, along two sides of the study area
2) Obtain a series of coordinates by using random numbers taken from a table or generated from a computer
3) Place a quadrat at the intersection of each pair of coordinates and record the species within it
Describe a method for systematic sampling along a transect to measure the abundance and distribution of a species
Place a tape measure or string along the study area, and record the number and type of different species within a quadrat places at regular intervals along the transect
Give two methods for measuring abundance and give pros and cons for each method
Frequency (the likelihood of a particular species occurring in a quadrat)
-Pro : useful when a species is hard to count (e.g. grass)
-Con : doesn’t provide information on density or detail distribution
Percentage cover (an estimate of how much of a quadrat a plant species covers)
-Pro : useful where individual plants are hard to count
-Con : less useful where organisms occur in overlapping layers
Explain why it is necessary to ensure the sample size is large
Because the larger the number of samples, the more representative of the community as a whole will be the results
Name and describe a method for recording the abundance of animals
Mark-release-recapture
A known number of animals are caught, marked and released back into the community. Another random sample of a given number is recorded and the number or marked animals is recorded.
Population size = (No. in 1st × No. in 2nd) ÷ No. of marked in 2nd
Give examples of some ethical considerations that should be regarded when carrying out fieldwork
- Organisms should be studied in situ. The frequency of moving an organism should be minimal
- Any organism removed should be returned ASAP (inc. dead)
- A sufficient time should be left before site is used for studies again
- Disturbance and damage to the habitat should be avoided. Damaged can adversely affect habitats
Suggest a reason why even dead organisms should be returned to the habitat from which they came
They can be eaten by other organisms and so provide energy and nutrients to the ecosystem
Suggest why it is beneficial to a habitat that further investigations are not carried out too soon after an initial study
It allows the habitat to recover from any disturbances/removal of organisms.
The results of a further study carried out out too soon after may result in data that is not typical of the habitat under ‘normal’ conditions
In a study of a seashore, students turn over large stones to record the numbers of different organisms on their underside. Suggest reasons why it is important that these stones are replaced the same way up as they were originally
The organisms live under the stone so they remain moist when not covered by the tide. If the stone is left upside down the organism may be come desiccated and die.
Name and describe the 3 phases of a population growth curve
1) Slow growth - the initially small number of individuals reproduce slowly to slowly build up their numbers
2) Rapid growth - the number of individuals continue to reproduce. The population size doubles during each interval time
3) Stable state - no growth except small fluctuations due to changes in biotic and abiotic factors
Give examples of Abiotic factors and how they affect a population size
1) Temperature - enzyme denaturation slows metabolic activity meaning more energy is needed for homeostasis than growth
2) Light - increases the rate of photosynthesis
3) pH - affects enzymatic action.
4) Water and humidity - where water is scarce, populations are small and consist only of species adapted for dry conditions
Explain the difference between Intraspecific and Interspecific competition
Intraspecific - competition between individuals of the same species
(Availability determines population size)
Interspecific - competition between individuals of different species
(Where populations of two species occupy the same niche, one will normally have a competitive advantage and grow in size.
Define an ecosystem
An ecosystem is made up of all the interacting biotic and abiotic features in a specific area.
State the equation that should be used to determine estimated population size from mark-release-recapture data
Estimated Population Size = (No. of individuals in first sample X No. of individuals in second sample) / number of marked recaptured individuals
Describe some assumptions made about data for Mark-release-recapture techniques
- marked individuals distribute themselves evenly amongst the remaining population (and have sufficient time to do so)
- population has a finite boundary (no migration in or out)
- there are very few deaths or “births” within the population
- the method of marking isn’t toxic and doesn’t make the individual more liable to predation
- the mark or label is not rubbed of during investigation
