Biology- Unit 4- Populations

What is ecology?
Study of inter-relationships between organisms and their environments.
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Two components within an environment and their meanings?
Abiotic (non-living components) and biotic (living components)
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Examples of both?
abiotic- temperature and rainfall biotic- competition and predation.
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What is a ecosystem?
more or less self contained functional unit in ecology made up of all the abiotic and biotic factors in a specific area.
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What are the two main proccesses in an ecosystem we should consider?
Flow of energy through the system and cycling of elements within the system.
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What is a population?
Group of interbreeding organisms of one species in a habitat.
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What is a community?
all the populations of different organisms living and interacting in a particular place at a particular time.
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Place where a community of organisms live. also micro-habitats within these.
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What is a niche?
How an organism fits into the environment. So it refers to where the organisim lives and what it does there.
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What is abundance?
Number of individuals of a species in a given space.
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Why cant we count every organisim?
Time consuming and would certiantly damage the habitat being studied.
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What must the sample be in order for conclusions to be true of the entire population? How can this be achieved?
Representative- using random/systematic sampling and a large sample size.
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Factors to consider when using quadrats?
Size of quadrat ( consider the size of the organisim and their distribution eg: if not evenly distributed a large number of small is better then few large ones)
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Number of quadrats- Balance between time consuming and getting valid results. More species present= more quadrats needed. Also position (eg random)
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Why is random sampling important and how do we do it?
To avoid any bias in gaining results so therefore increase validity. 1) Lay out 2 tape measures at right angles to each other. Obtain a set of co-ords randomly using a computer and place quadrat at the intersection of these co-ords, same corner.
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Other method? When could it be better?
Systematic sampling- When a transition in the community could be taking place eg: more in one area then another.
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Belt and line transects?
Line- string or tape across the ground in straight line, any organisim over the line is recorded. Belt uses two parrell strips, counting species between the belt.
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Two methods of measuring abundance?
Frequency - Likelihood of a species occurring within a quadrant. Useful for ideas of general distrubution but doesn't count density.
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Percentage cover- estimation of the area within a quadrat which the species covers. Useful for abundant species or if they are hard to count but less accurate.
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Why does it not work with animals?
Because they are mobile and move away when approached or they hide and are difficult to identify.
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Name of a method which works with animals?
Mark-release- recapture techniques
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How does it work?
A known number of animals are caught, then marked and then released into the community. Later on a given number are collected randomly and the number of marked collected are counted.
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Estimated pop size = the total number in the first sample x the total number of individuals in the second sample/ the number of marked individuals recaptured.
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What does this method rely on?
Proportion of marked to unmarked in the second sample is the same in the population as a whole. Marked samples released distrubt themselves in the community evenly. No immigration/emmigration. Few deaths/birthds. Marking not toxic/disadvantagous/lost
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3 phases in a population growth curve?
Period of slow growth where a small number reproduce slowly. Then period of rapid growth as the ever-increasing number continue to reproduce. Pop size is doubling. Then a decline, finally becoming stable (with fluctuations)
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Abiotic factors that effect population?
Temperature- each species has an optimum- moving away from this decreases its chances of surviving. Plants and coldblooded animals enzymes can become denatured due to temperature changes, leading to slower reactions.
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What about warm blooded animals?
More energy must be used to provide this constant body temperature so less energy for growth and reproduction.
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Another factor?
Light- More photosynthesis so plants therefore get more energy (respiration) so more plants growth & animals then have more plants to eat.
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2 others?
Ph and water and humidity. pH agian effects enzymes while water and humidity affect transpiration rates.
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What is competition?
When two or more individuals share a resource and there is insufficient to satisfy them, there is competition.
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Type one? (Intra)
Intraspecific- members of the same species are in competition for a resource. Greater the avaliability of the resources, less competition, so more population growth.
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Interspecific- members of different species. One will increase while the other decreases. If this continues, one will eventually be wiped out (competitive exclusion principle).
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What does this principle mean?
When two species are competing for the same resource,the one that uses it the most effectively will elimate the other. So no two species can occupy the same niche if the resources are limiting.
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What does an increase in food supply cause?
Increase likelihood of species being able to survive so increases likelihood of producing offspring so therefore pop increase.
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What is a predator?
Organism that feeds on another organism known as its prey.
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What is predation?
When one organism is consumed by another.
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What is the effect of predator prey relationships on pop sizes?
Pred eat prety therefore reducing population of prety. With fewer prety the predators are in greater competition with each other so pred pop decreases as not all can get enough food. Fewer pred, fewer prey eaten so their population increases.
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In natural populations, is this relationship diffrent?
The fluctuations in pop sizes are far less severe because organisims often consume a wide range of foods, not just a single prey.
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What are two main events which lead to an explosion in human population?
Development of agriculture and the development of manufacturing and trade (industrial revolution)
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What does the human population graph not follow?
The sigmoid population growth curve- because wars, disease and famine only have caused temporal reversals of growth.
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Factors that affect growth and size of human populations?
Basic factors- birth and death rates but also affected by migration (immigration and emigration).
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Equation for population growth? Percentage population growth rate (in given period)?
(births + immigration) - (deaths + emigration) Pop change during period / pop at start of period x 100
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Name some factors that affect birth rates?
Economic factors, cultural and religious backgrounds, social pressures and conditions, birth control, political factors.
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Equation for birth rate?
Number of births per year/total population that year x1000
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Death rates?
life expectancy, food, medical care, safe drinking water, disasters/war
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Number of deaths per year/ total pop the same year x 1000
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what is a demographic transition?
Change in society- eg development has caused a shift from high birth rates but low life expectancy to now low birth rates but high life.
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What is a population pyramid?
Shows the percentages of males and females of each age group stacked agianst each other. (pg 22)
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What do the graphs look like?
Stable- birth rate and death rate are balanced so no sig change in pop size. Increasing- higher birth then death so we see more of younger ages and less of old. Decreasing pop has smaller base.
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Other cards in this set

Card 2


Two components within an environment and their meanings?


Abiotic (non-living components) and biotic (living components)

Card 3


Examples of both?


Preview of the front of card 3

Card 4


What is a ecosystem?


Preview of the front of card 4

Card 5


What are the two main proccesses in an ecosystem we should consider?


Preview of the front of card 5
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