Grade 12 Environmental Studies - Part 1 POPULATION ECOLOGY Flashcards
Textbook pages 1 - 8
Define Natality
Birth rate in animals or the production of seeds in plants
Define Mortality
Death rate
Define Immigration
Individuals move into a population and stay
Define Emigration
Individuals leave a population and do not return
Define Stable Population
One that fluctuates around the carrying capacity
What are the consequences of an Unstable Population?
Habitat deteriorates rapidly (Lowers carrying capacity)
Habitat eventually unable to support population, which may go extinct
Define Predation
Biological interaction in which one species, the Predator, kills and eats another species, the Prey.
Define population ecology
Study concerned with the fluctuation in the size of a population and the factors, physical and social, that regulates these fluctuations.
All the ecosystems on earth make up the ____________
biosphere
Define biosphere
the part of earth where living organisms are found
Define ecosystem
Made up of groups of different species of organisms that interact with each other and with the environment.
Define organism.
An individual form of life, such as bacterium, protest, fugus, plant or animal, composed of a single cell or a complex of cells that are capable of growing and reproducing.
Define community
A group of different species that inhabit and interact in a particular area
Define species
A group of closely related organism that are very similar to each other and are usually capable of independent existence.
Define individual.
A single organism capable of independent existence.
Define population.
A group of organisms of the same species that occupy the same area and can breed freely with each other.
Define demographics
The statistics such as the size, age distribution, growth rate, and density of a population.
What is the birth rate for humans?
The number of births per 1000 people in a year.
What is the death rate for humans?
The number of deaths per 1000 people per year.
What is a closed population?
Population with no immigration or emigration - the only parameters affecting any change in population numbers will be births, or deaths e.g. fish in fish pond.
List the dynamic parameters that affect the growth of a population:
- Natality
- Immigration
- Mortality
- Emmigration
How is the growth of a population regulated?
- Exponential = increasing more and more rapidly (populations will increase in unoccupied area where there is no shortage of food or other resources and no predators)
- As the number increases, demands are made on available resources
- This builds environmental resistance - which causes birth rate / immigration rate to decrease and death rate / emigration rate to increase.
- Environmental resistance = The total number of factors that stop a population from reproducing at its maximum rate.
- Eventually a balance is achieved - population stabilises at particular size or number.
- This is the carrying capacity of the ecostystem.
- Carrying capacity is the population density that the environment can support.
Define environmental resistance:
The total number of factors that stop a population from reproducing at its maximum rate.
Define carrying capacity.
Carrying capacity is the population density that the environment can support.
Population size is self-regulating. What does this mean?
Fluctuates seasonally and anually, depending on available resources.
All negative feedback mechanisms are examples of this self-regulation.
Di
Discuss the limiting factors that help to regulate population growth - buiding up environmental resistance:
Density independent factors - as a result of natural factors e.g physical factors (rainfall, tempererature, humidity, acidity, salinity) & catastrophic events (e.g. floods, fire, droughts, volcanic eruptions, tsunamis, earthquakes)
**Density dependent factors **- that have a greater effect when population is high - a) organisms compete for resources such as food, light, oxygen, water, space, shelter b) are more easily found by predators c) spread disease and parasites more readily.
Explain stable population:
One in which numbers decrease when its size exceeds the carrying capacity but increase again when numbers fall below the carrying capacity i.e. one that fluctuates around the carrying capacity.
Explain an unstable population:
- Develops if the population far exceeds the carrying capacity.
- This results in the habitat deteriorating rapidly, which leads to lower caraying capacity AND eventually not being able to support the population, which will decrease rapidly and possibly become extinct.
How is population size estimated?
- Direct method
- Mark-recapture method
Explain the direct method in estimating population size:
- Counting every single individual in a population = censure
* Can only be used for** populations of organisms that are large enough to be seen, where the area in which the animals are being counted is not too large.
Can be used when:
* animals are slow moving e.g. snails, tortoises etc.
* stationary e.g. plants
* usually stay fixed e.g. barnacles, mussels
How can direct method of estimating population be used for large areas?
- aerial photographs e.g. penguins, seals, species of large trees etc.
- **helicopters - for counting large animals e.g. elephant, buffalo in game reserves
How can the direct method for estimating population be used for humans?
Every 5 years in SA a population census - census forms can be filled in, accounting for everyone in a household.
How can population size be estimated by using the indirect method?
- Counting a sample number of the population
- then using the sample calculations to estimate the total size of the population
Explain the quadrat method of estimating population:
Involves counting the number of individuals in small measured areas (quadrats) and then using the nubmers to calculate the population size of the total area with the aid of the following formula:
Total population = (N)
N = numbers in sample x size of whoel habitat over the **size of quadrat **
The purpose is to enable comparable samples to be obtained from areas of consistent size and shape.
Discuss the** quadrat method** step by step:
- Measure the size of the total area
- use a wooden frame of known diamters as a quadrat - refer to same in each sample
- quadrats should be distributed at random
- count the individuals in each quadrat - take several samples
- using formula, calculate the size of the population
Why is random sampling NB?
- Distribution of individuals may not be uniform throughout the area
- NB to sample as quadrats the total area - true reflection
Explain the mark-recapture method of estimating a population size:
- A known number of individuals is caught and marked and then released.
- After a suitable time period another sample is captured and the nubmer of marked individuals are counted.
- A formula is used to calculate population size - based on principle that the RATIO OF THE UNMARKED TO MARKED INDIVIDUALS in a sample will be the same as the RATIO IN THE POPULATION as a WHOLE.
When is it suitable to use the MARK-RECAPTURE method to estimate population size?
- Mobile animals e.g. butterflies
- Not easily visble e.g. fish in a dam
Explain the Mark-recapture method of population estimation:
- Mark a well-defined area
- Capture as many individuals as possible and mark them e.g. metal tag, spot on plant
- Release the marked individuals - back into environment
- Allow them to mix with unmarked
- Recapture as many individuals as possible
- Count the total nubmer and count the marked ones amongst them.
- Calculate the total population size by using PETERSEN INDEX
-
P = M x C over R
(C = total number of animals caught in second sample, R = total number of marked animals in second sample i.e. recaptured)
See page 5 of your textbook.
What precautions must be taken for a reliable result when using the MARK-RECAPTURE method?
- Short time should pass between first and second sampling - no births and deaths in meantime
- Sampling should be repeated several times
- Marking must not damage the individual or affect environment
- marked animals must mix freely with rest of population
- No immigration or emigration is allowed
NB: Study page 6 - 7 of your textbook for a DEMONSTRATION of this method!!!
