1. Populations Flashcards
Suggest an explanation for the change in the percentage of deaths due to cancer shown in the diagram
- Decrease in percentage of population dying from infectious diseases
- Therefore greater proportion of those remaining die of cancer
- Greater survival to old age so cancer more likely
- Because of accumulated genetic error/ exposure to mutagens/ reduced immune response
What would an age pyramid look like for a population that had a life expectancy at birth of 70 years
Narrow based population pyramid
Explain how two changes in social conditions could have reduced the death rate
- Better food supply so fewer deaths by starvation
- Cleaner water supply so less disease transmission.
Give two possible reasons for fluctuating death rate
- Epidemics/ outbreaks of disease
- Limited/changing food supply
Suggest three reasons why the rapid increase in human population has resulted in the reduction of populations of many other species
- Predation of other species/ eat more of other species
- Interspecific competition/ disruption of food chain
- Destruction of habitat/damage by pollution
- Niche not present
- Competition for named abiotic resource
Give examples of abiotic and biotic factors.
Abiotic:
- temperature
- rainfall
Biotic:
- Competition
- Predation
Define an ecosystem.
-Made up of all the interacting biotic and abiotic factors in a specific area. Very often a self contained, self functioning unit
Define biome.
a large naturally occurring community of flora and fauna occupying a major habitat, e.g. forest or tundra.
Define a population.
A group of interbreeding organisms of a particular species in a habitat.
Define a community.
All the populations of different organisms living and interacting in a particular place at the same time.
Define a habitat.
The place where a community of organisms lives
What is a microhabitat?
A smaller unit within a habitat with its own microclimate.
What is an ecological niche?
A niche describes how an organism fits into the environment- where it lives and what it does there.
What are the three factors to consider when using quadrats to sample an area?
- SIZE of quadrats to use- depends on size of species being counted and how they are distributed
- NUMBER of sample quadrats to record within the study area- larger numbers means more reliable results
- POSITION of quadrats within the study area- random sampling must be used to produce statistically significant results.
Why is random sampling important?
- Avoids bias
- Ensures data obtained are valid
How do we make sampling random?
- Make a grid by laying out two tape measures perpendicular to eachother
- Obtain coordinates using a random number generator (generated by a computer or using a random number table)
- Place a quadrat at the intersections of coordinates and sample at that point
Why would systematic sampling along a transect be used instead of using a quadrat to randomly sample?
-When you want to measure the abundance and distribution systematically when some form of transition in the organisms takes place- for example, measuring the stages of zonation.
What are the two ways abundance can be measured?
- FREQUENCY- counting whether a species is present in a quadrat or not
- PERCENTAGE COVER- estimate of area within a quadrat that a particular plant species covers