Component 1: Populations Flashcards
Define ‘Population’
All the organisms, of a particular species, in a particular location at one time
Define ‘community’
All the organisms, of all species, living in one location at one time
Define ‘ecosystem’
A characteristic community of interdependent species ad their habitat
Define ‘habitat’
The location in which an organism lives
Define ‘niche’
The role of a particular species in its ecosystem, including its microhabitat, feeding and breeding behaviour etc
Define ‘ecology’
The study of how living organisms interact with each other and their environment
Define ‘environment’
The physical and biological conditions under which an organism lives
Define ‘biotic’
The biological components of an ecosystem
Define ‘abiotic’
The non-biological components in an ecosystem
What are some characteristics of ecosystems?
- they are dynamic (constantly changing)
- they vary in size
- energy flow, biological cycles, succession, species composition and population size are all subject to change within an ecosystem
What does the population number depend on?
- they fluctuate depending on birth rate, death rate, immigration into population and emigration from population
Population numbers will increase if…?
Birth rate + Immigration > Death rate + emigration
What is the birth rate term for when talking about yeast or bacteria?
REPRODUCTIVE RATE
What 2 factors influence the size of population in ecosystems?
- Availability of Light - more light will lead to an increase in population as there is more energy available
- Availability of Nutrients - increase the population as there is more energy available
Draw a population growth graph and label the 4 phases?
1 = lag phase 2 = log phase 3 = stationary phase 4 = death phase
Describe what is happening in the lag phase for animals?
- slow increase in population
- birth rate is only slightly greater than death rate
- there are very few organisms
- sexually reproducing organisms may be reaching sexual maturity and find a mate
- organisms are adapting to the environment
Describe what is happening in the lag phase for bacterium?
- slow increase in population
- reproductive rate is only slightly greater than death rate
- very few bacteria
- bacteria are adapting to the new culture/medium
- bacteria are synthesising enzymes and proteins
- replication of DNA and cells increase in size in bacteria
Describe what is happening in the log phase?
- rapid increase as reproductive rate is greater than the death rate
- resources are plentiful so there are very few limiting factors
- environmental resistance is low, food availability is high and nutrients are high
- bacterium: toxins are low
Describe what is happening in the stationary phase?
- rate of growth slows as organisms start to compete for resources (limiting factors)
- organisms are dying in equal numbers to those being reproduced (birth/reproductive rate = death rate)
- population has reached the carrying capacity
Describe what is happening in the death phase?
- death rate exceeds the reproductive rate
- population crash
- animals: caused by a natural disaster (floods/fires), disease or shortage of food
- bacteria: caused by competition for nutrients or accumulation of toxins
What is meant by limiting factors?
Aspects of the environment, either physical or biotic, which restricts population size (causes environmental resistance to population growth
What are some limiting factors?
predation, parasitism, disease, overcrowding, competition from other species for food, accumulation of toxic waste (bacteria) and climate
What are density dependent factors?
- the effect of these factors increases as the population density increases
- these lead to a slow down in population growth
What are some example of density dependent factors?
parasitism, food availability, nesting site availability, predation, disease, territory availability and shelter
- toxin accumulation for bacterium
What are density independent factors?
- the effects of these factors does not depend on population density
- all living organisms are affected regardless of the population size
- these can lead to a population crash
What are some examples of density independent factors?
soil pH, light, temperature, water pH, mineral nutrients, oxygen and any sudden/violent change in an abiotic factor (e.g. flood, fires, etc)
How does disease affect the population?
- biotic factor
- decreases the population
- the denser the population the more rapidly disease spreads and therefore the greater impact of disease
How does light intensity affect the population?
- abiotic factor
- increasing light intensity increases the population as more energy is available for producers and this makes more food available for consumers
- effect not dependent on population density
How does competition for food affect the population?
- biotic factor
- increasing the competition decreases the population
- the greater the population the greater the impact as there are more individuals competing for the same resources
How does the production of toxins affect the population?
- biotic factor
- population decreases as toxin concentration increases
- the greater the population the more rapidly toxins accumulate
How does predation affect the population?
- biotic factor
- as predation increases, the population decreases
- also density dependent
What is meant by ‘carrying capacity’?
The maximum population size that can be maintained over a period of time in a particular habitat/environment (or the maximum number around which a population fluctuates in a given environment)
Why does population size fluctuate?
- limiting factors change
- when food supply or predation changes the population changes
- if a herbivore population goes above the carrying capacity then it leads to overgrazing which would then lead to a population crash
- carrying capacity is theoretical
- a change in weather can result in a change in the numbers of a species that the environment can support
What do plants compete for?
Light, water, space and mineral ions
What do animals compete for?
Food, water, shelter, space and reproductive partners
What are the two type of competition?
Intraspecific and interspecific
What is intraspecific competition?
Competition between individuals of the same species
- it can be an important factor in limiting the size of a population
- it is a key factor in the evolution of a species by natural selection
What is interspecific competition?
Competition between individuals of different species as 2 species cannot occupy the same niche in a specific habitat
- niche overlap
- the more overlap the more competition will happen
When the niche overlaps the organisms may be competing for…?
food, oxygen, CO2, light, nutrient, nesting/dwelling sites
What happens to the numbers of 2 different bacteria when placed in the same culture?
- population will increase less rapidly than if they were grown alone as they compete for nutrients
- one bacterium will outcompete the other as they may be better adapted for this niche
- hence reproduces more rapidly and takes bulk of nutrients
- therefore no 2 species can occupy the same niche
Describe the snowshoe hare and lynx predator-prey cycle
- in seasons where there is favourable weather, lots of plant growth, increased food for hare, pop increases as many young survive
- the larger prey pop provides more food for the predators, more young predators survive, predator pop increases
- as predator pop increases, prey pop decreases as more are eaten
- later less prey is available as food, predator pop declined as intraspecific competition food (starvation)
Why will the prey population rise before the predator?
- prey may breed quickly (e.g. hares), food for predator increases, more survive and its pop can build
As the predator population rises, why does the prey population fall?
- a larger predator population, the greater predation pressure on the prey
- loss exceeds the ability to replace (mortality > natality)
What are some general points about predator-prey cycles?
- fluctuations in predator numbers are smaller than those numbers in prey
- fluctuations in predator numbers lag behind the fluctuations in numbers of prey
What is ‘measuring abundance’?
A measure of how many individuals exist in a habitat
How can plant abundance be measured?
Using a quadrat
How can animal abundance be measured?
- assessed by capture-mark-recapture experiments
- kick sampling in a stream and counting aquatic invertebrates
What is meant by ‘measuring distribution’?
distribution of a species describes the are in which its found
How do you measure the distribution of plants?
transect line with quadrats
How do you measure the distribution of animals?
- direct observation of nests or individuals
- faecal deposits
- marking on vegetation
What is the food chain?
- a diagram which shows a simple, unbranced, feeding relationship, usually with only one organism at each trophic level
- the source of energy for most food chains is sunlight
What do food chains not show?
- all the species at each trophic level, calculated efficiency will be low
- detritivores and decomposers which are often a greater biomass than other consumers
- omnivores or organisms feeding at several trophic levels
- food webs show all of these things
What are some sources of energy in ecosystems?
- the Sun is the source of energy for most ecosystems
- light is trapped as chemical energy by photosynthesis
- some ecosystems where energy comes from chemosynthesis (hydrothermal vents)
What factors contribute to environmental resistance?
Predation, competition for food, disease, food availability and climate
If environmental resistance increases, how would this affect the carrying capacity?
- increasing resistance, decreases the carrying capacity
- becomes more difficult for organisms to survive and breed
- therefore fewer organisms can be supported by the environment
Explain the lag phase for bacterium?
- Genes are being switched on for synthesis of enzymes/proteins
- Getting used to new medium
- Replication of DNA
- Cells increase in size
What is meant by exponential growth?
Population grows at an increasing rate
Reasons for decline phase in bacterium cultures?
- competition for nutrients
- accumulation of toxins
- carrying capacity has been exceeded
What does GPP stand for?
Gross Primary Prodcutivity
What is GPP?
- the rate of production of chemical energy in organic molecules by photosynthesis in a give area in a give time (kJ m^-2 y^-1)
- most gross production is released by the respiration of the plant
- on average GPP = 0.2% of the energy from the Sun hitting the Earth
What does NPP stand for?
Net Primary Production
What is NPP?
- Energy in the plant’s biomass which is available to primary consumers (kJ m^-2 y^-1)
- is the GPP minus the chemical energy generated in respiration nd used up by the metabolism of producers
How is NPP calculated?
NPP = GPP - R
- NPP represents the chemical energy available to heterotrophs in an ecosystem
- GPP = 1% and NPP = 0.5% (would be higher if plants have a high photosynthetic effciency
Difference between production and productivity?
Production (NPP) = quantity made
Productivity (GPP) = rate of production
What is biomass?
The mass of biological material living, or recently living, organisms
What is a trophic level?
Feeding level; the number of times that energy has been transferred between the Sun and successive organisms along a food chain
What is a saprobiont?
A micro-organism that obtains its food from the dead or decaying remains of other organisms
What do food chains show?
- energy in the food consumed is incorporated into the molecules of the consumer (energy passes to higher trophic levels as material is eaten)
- loss of energy from the ecosystem as it moves up
What is decomposition?
detritivores and decomposers recycle nutrients and energy remaining in organic compounds
What are detritivores?
- E.g. worms
- organisms that feed on small fragments of organic debris
- a saprobiont
What is a decomposer?
Microbes (bacteria and fungi) that obtain nutrients from dead organisms and animal waste (are saprobionts)
What is the general order of a food chain?
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