Populations and ecosystems Flashcards
What is ecology
The study of the inter-relationships between organisms and their environment
What are abiotic factors
Components of the non-living parts of an ecosystem
What are biotic factors
Components of the living parts of an ecosystem.
What is an ecosystem
An ecosystem consists of the living (biotic) and non-living (abiotic) components of an area and the interrelationships between them.
What are the two major processes we need to consider within an ecosystem
1) The flow of energy through the system
2) The cycling of elements within the system.
Define population
A population is a groups of individuals of one species that occupy the same habitat at the same time and are able to interbreed.
What is an ecosystems carrying capacity
The size of a population of a species that an ecosystem can support.
What two key things does the size of a population vary as a result of
1) The effect of abiotic factors
2) Interactions between organisms, for example intraspecific and interspecific competition and predation.
Define community
All the populations of different species living and interacting in a particular place and the same time.
What is a habitat
The physical place where an organism lives and the conditions that it lives in (abiotic factors)
What are microhabitats
Smaller units within a habitat that each have their own microclimate.
What is an ecological niche
- The specific position occupied by an organism in a particular ecosystem, dependant upon the resources it uses.
- It includes all the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population.
What is the competitive exclusion principle
No two species occupy exactly the same niche.
What type of growth curve do we plot when a population grows in size slowly over a period of time
A graph of numbers of individuals in a population against time.
Why can’t we plot a graph of numbers in a population against time for a population such as bacteria that grow rapidly over a short period of time
The graph will be an exponential that increases rapidly and makes it difficult to interpret as the graph will quickly run off the scale.
What type of growth curve do we plot for populations that increase in size rapidly such as bacterial populations
You plot time against log of bacterial population numbers.
List some factors that may slow the reproduction of bacterial colonies
- Mineral ions are consumed as the population becomes larger.
- The population becomes so large that the bacteria at the surface are recent light reaching those at deeper levels.
- Other species are introduced into the pond, carried by animals or the wind, and some of these species may use the bacteria as food or compete for light or minerals.
- Winter brings much lower temperatures and a much lower light intensity of shorter duration.
What is the carrying capacity of a population
The size of the population that can be sustained over a relatively long period
Name the four key abiotic conditions that determine the size of a population
1) Temperature
2) Light
3) PH
4) Water and humidity
Describe the effect of temperature not being optimum on the carrying capacity of cold-blooded animals and plants
- In plants and cold blooded animals, as temperature falls below the optimum, the enzymes work more slowly and their metabolic rate is reduced.
- Populations therefore have a smaller carrying capacity.
- At temperatures above the optimum, the enzymes work less efficiently because they gradually undergo denaturation.
- Again, this reduces the populations carrying capacity.
Describe the effect of the temperature not being optimum on warm blooded animals
- Warm blooded animals can maintain a relatively constant temperature regardless of the external temperature.
- However, the further the temperature of the external environment gets from their optimum temperature, the more energy the organisms expend in trying to maintain their normal body temperature.
- This leaves less energy for individual growth so they may mature more slowly and their reproductive rate slows.
- The carrying capacity of the population is therefore reduced.
Describe how light affects the carrying capacity of all organisms
- Light is the largest source of energy for most ecosystems.
- The rate of photosynthesis increases as light intensity increases.
- The greater the rate of photosynthesis, the faster plants grow and the more spores or seeds they produce.
- Their carrying capacity is therefore potentially greater.
- In turn, the carrying capacity of animals that feed on plants is potentially larger.
Describe how PH affects populations of organisms
- PH affects the action of enzymes.
- Each enzyme has an optimum PH at which is operated most effectively.
- A population of organisms is larger where the appropriate PH exists and smaller, or nonexistent, where the PH is different from the optimum.
Describe how humidity affects populations of organisms
- Humidity affects the transpiration rates in plants and the evaporator of water from the bodies of animals.
- Again in dry air conditions, the populations of species adapted to tolerate low humidity will be larger than those with no such adaptations.
What is intraspecific competition
Competition between members of the same species.
What is interspecific competition
Competition that arises between members of different species
What are some example of things that individuals may compete for
- Food
- Light
- Space
- Water
- Light
- breeding sites
What is the competitive exclusion principle
The competitive exclusion principle states that where two species are competing for limited resources, the one that uses these resources most effectively will ultimately eliminate the other: no two species can occupy the same niche indefinitely when resources are limiting.
What is predation
Predation occurs when one organism consumes another.
Why are the prey usually exterminated when a predator and its prey are brought together in a laboratory
The range and variety of the habitat is limited due to being in a lavatory so the prey is easily caught
Why do prey survive predators in the wild when they don’t in the laboratory
- The area over which the population can travel is far greater- the variety of the environment is much greater.
- This means there are many more potential refuges.
Explain the predator-prey relationship
- Predators each their prey, thereby reducing the population of prey.
- With fewer prey available the predators are in greater competition with each other for the prey that are left.
- The predator population is reduced as some individuals are unable to obtain enough prey for their survival or to reproduce.
- With fewer predators left, fewer prey are eaten so more survive and are able to reproduce.
- The prey population therefore increases.
- With more prey now available for food,
The predator population in turn increases.
What other factors cause cyclic fluctuations in populations aside from predator-prey relationships
Disease and climactic factors
Why are periodic population crashes important in evolution
- There is a selection pressure which means that those individuals who are able to escape predators or withstand disease are more likely to survive and reproduce.
- The population therefore evolved to be better adapted to the prevailing conditions.
What is abundance in ecology
The number of individuals of a species in a given space. It is often needed to study habitats.
What are two key sampling techniques used to study habitats
- Random sampling using frame quadrants or point quadrants
- Systematic sampling along a belt transect
Name the two types of frequently used quadrat
1) Point quadrat
2) Frame quadrat
Describe what a point quadrat is
- A point quadrat consists of a horizontal bar supported by two legs.
- At set intervals along the horizontal bar are ten holes, through each of which a long pin may be dropped.
- Each species that the pin touches is then recorded.
Describe what a frame quadrat is
- A frame quadrat is a square frame divided by string or wire into equally sized subdivisions.
- The quadrat is placed in different locations in the area being studied and the abundance of each species within the quadrat is then recorded.
List the three factors to consider when using quadrats
1) The size of quadrat to use
2) The number of sample quadrats to record within the study area.
3) The position of each quadrat within the study area.
Explain why the size of quadrat to use is important to consider
- The size of the quadrat depends on the size of the plants or animals being counted and how they are distributed in the area.
- Larger species require larger quadrats.
- Where a population of species is not evenly distributed through an area, a large number of small quadrats will give more representative results than a small number of large ones.
Explain why the number of sample quadrats to record within the study area is important to consider
- The larger the number of sample quadrats, the more reliable the results will be.
- As the recording of species within a quadrat is a time-consuming task a balance needs to be struck between the reliability of results and the time available.
- The greater the number of different species present in the area being studied, the greater the number of quadrats are required to produce reliable results for a valid conclusion.
Why is the position of each quadrat within the study area important to consider
To produce statistically significant results, a random sampling technique must be used.
Describe how to take a random sample with a quadrat
1) Lay out two long tape measures at right angles, along two sides of the study area
2) Obtain a series of coordinates by using random numbers taken from a table or generated by a computer.
3) Place a quadrat at the intersection of each pair of coordinates and record the species within it.
Describe how to carry out systematic sampling
- A belt transect can be made by stretching a string or tape across the ground in a straight line.
- A frame quadrat is laid down alongside the line and the species within it recorded.
- It is then moved it’s own length along the line and the process is repeated.
- This gives a record of species in a continuous belt.
Describe the two ways of measuring abundance of a species that doesn’t move (when using a quadrat)
1) Frequency: The likelihood of a particular species occurring in a quadrat. It is worked out as a percentage of the number of quadrats containing the species over the number of quadrats used.
2) Percentage cover: This is an estimate of the area within a quadrat that a particular plan species covers. It is useful where a species is particularly abundant or is difficult to count.
Describe the advantage and disadvantage of using percentage cover as a measure of abundance
- Advantage: Data can be collected rapidly and individual plants to do not need to be counted.
- Disadvantage: does not work where organisms occur in several overlapping layers.
What technique do we use to measure the abundance of moving species
Mark-release-recapture
Describe the technique of mark-release-recapture
- A known number of animals are caught, marked in some way, and then released back into the community.
- Some time later, a given number of individuals is collected randomly and the number of marked individuals is recorded.
- The size of the population is then calculated as follows : estimated population size= (total individuals in the first sample x total individuals in the second sample) / number of marked individuals recaptured.
Describe the assumptions that Mark-release-recapture relies on
- The proportion of marked to unmarked individuals is the same as the proportion in the population as a whole.
- The marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have sufficient time to do so.
- The population has a definite boundary so that there is no immigration into or emigration out of the population.
- There are few, if any, deaths and births within the population.
- The method of marking is not toxic to the individual nor does it make the individual more conspicuous and therefore more liable to predation.
- The mark or label is not lost or rubbed off during the investigation.
