Biology Unit 3.5 - Population Size and Ecosystems Flashcards
What is a population?
A group of organisms of a single species interbreeding and occupying a particular area or habitat
How do dynamic factors affect population growth?
- Energy flow through an ecosystem can change
- Biological cycles may vary mineral availability
- Habitats change over time due to succession or human activity
- New species arrive and others are no longer present
Describe birth rate/cell division…
Measure of all the new births per unit time in a give population
Rate of cell division is used to describe the rate of asexual reproduction in single celled organisms
Describe death rate…
Measure of the number of organism deaths per unit time
If it exceeds birth rate/cell division the population will decrease
Describe immigration…
Measure of the number of individuals entering a population from another area
Net immigration will cause the population to increase
Descibe emigration…
Measure of the number of individuals leaving a population to another area
Net emigration will cause a population decrease
What are fugitive species?
Species that are poor at competition, but reproduce rapidly and have effective disspersal mechanisms, meaning they can invade new environments rapidly
What are equilibrium species?
Species that control their population by competition, causing them to have a sigmoidal (S-shape) growth curve called the one-step growth curve
What is the lag phase?
Period of adaptation or preparation for growth, with intense metabolic activity, notably enzyme synthesis
What is the exponential phase?
No factor limiting growth, so cells divide at a constant rate with the population doubling per unit time
What is the stationary phase?
Reproductive/growth rate of new individuals is equal to the death rate of older ones, with factors such as nutrient supply and build-up of waste becoming limiting
What is the death phase?
Death rate is greater than reproductive/growth rate, and where nutrients are completely depleted
Explain predator prey interactions…
The abundance of prey limits the number of predators and the number of predators controls the number of prey, causing their populations to oscillate, which is regulated by negative feedback
What is carrying capacity?
Maximum population size of a species that an environment can sustain, and is noted on a graph as a dashed line
What is a population crash?
A sudden dramatic decrease in population number, which occurs when population greatly exceeds its carrying capacity
How do you calculate population increase from a graph?
Subtract the population at the beginning of the exponential phase from the end, and then divide by the timespan of the exponential phase
What are density dependent factors?
Biotic factors whose effect increases as population increases:
* Competition
* Predation
* Disease
* Parasitism
Determine carrying capacity and weaken individuals and make them less likely to reproduce successfully
What are density independent factors?
Abiotic factors whose effect does not depend on population density:
* Earthquakes
* Tsunami
* Extreme weather
* Fires
Can decimate populations
What is interspecific competition?
Competition between members of different species within the same community, where each species occupies its own niche
What is intraspecific competition?
Competition for resources between member of the same population or species
What are ecosystems?
Characteristic community of interdependent species and their habitat, which is dynamic
How does energy flow through ecosystems?
Energy passes form producers at trophic level 1 to herbivores at trophic level 2, and then to carnivores at trophic levels 3 to 5, where energy will eventually leave the chain as heat
What occurs after an organism dies?
Detritivores break up organic matter, increasing the surface area for decomposition by decomposers, which releases essential nutrients
What is a food chain?
Illustrates energy transfer between organisms, from producer to apex predator
What is a trophic level?
Describes the position of an organism in a food chain, where trophic level 1 contains the most energy and supports other trophic levels
What is a producer?
Autotroph, usually plant or alga, that can convert simple inorganic molecules into complex organic compounds, by photosynthesis
What is a herbivore?
Animal which only eats plants and feeds on organisms at trophic level 1
What is a carnivore?
Animal which feeds on other animals at lower trophic level, and is found at trophic level 3 or above
What is a detritivore?
Animals such as earthworms, woodlice, and maggots which feed on dead organic matter, increasing its surface area to facilitate decomposition by decomposers
What is a decomposer?
Organisms, such as bacteria and fungi, which break down complex organic compounds into simpler inorganic compounds and ions, which are soluble and available for absorption by plant cells
What is a habitat?
Place where organisms lives
What is a community?
The species that occur together in a given space and time
What affects food chain length?
- The more energy that enters the food chain, the more energy fixed in photosynthesis, the longer the chain
- More efficient energy transfer between trophic levels, causes a longer chain
- Predator and prey populations flucuate and their relative abundance affect length of chain
- Larger ecosystems support longer chains
- Three dimensional environments have longer food chains
What is photosynthetic efficiency?
Measure of how well a plant converts light energy into chemical energy; can also be described as the % light captured by the plant
60% of light is not absorbed and isn’t fixed into carbohydrate due to:
* The wrong wavelength
* Reflected
* Transmitted straight through the leaf
What is gross primary productivity (GPP)?
Rate of production of chemical energy in organic molecules by photosynthesis in a given area, in a given time, so its units are kJ m-2 y-1
Substantial amount is used in respiration
What is net primary productivity (NPP)?
Chemical energy left after respiration, which represents the food available to primary consumers
What is secondary productivity?
Rate at which consumers accumulate energy in the form of cells and tissues
Occurs in heterotrophs:
- Herbivores have a lower secondary productivity
- Carnivores are more efficient at energy conversion
How is energy lost between consumers?
Energy is lost in molecules that are egested, as heat fuelled by respiration, while some remains in molecules in parts of an animal that are not eaten
What are the advantages/disadvantages of pyramids of numbers?
Advantage:
- Easy to construct
Disadvantage:
- Doesn’t take size of organism into account
- Doesn’t recognise differences between juvenile and adult organisms
- Range of numbers may make drawing the pyramid difficult
- May be inverted
What are the advantages/disadvantages of pyramids of biomass?
Advantages:
- Closely related to the energy passing through the system
Disadvantage:
- Difficult to measure accurately
- May be inverted
- Some trophic levels may seem like they contribute more to the next trophic level than they actually do
What are pyramids of energy?
Most accurate way of representing feeding relationships that provides a quantitative account of feeding relationships in a community by showing the quantity of energy transferred from one trophic level to the next
What is succession?
Sequence of changes in communities over time that leads to the development of stable climax communities
What is primary succession?
Occurs from a starting point of bare rock or site of, which are then colonised by pioneer species that penetrate the rock and form humus
Pioneer species are then outcompeted, and death and decay over generations contributes to the accumulation of soil
Soil is then taken advantage of, increasing diversity until a climax community is established
What is secondary succession?
Evolution of an ecosystem from existing bare soil, where more plant species colonise the area
Organs of vegetative reproduction remain in the soil, where they are dispersed, assisting the colonisation process
How does human interference affect succession?
Prevent the natural development of a climax community through grazing sheep, farming of land, deforestation and soil erosion, etc
How does migration affect succession?
Arrival of spores, seeds and animals is vital for succession to progress, where immigrating non-native species may spread, altering the community and the soil
What is the competitive exclusion principle?
When two species occur in the same habitat, one will outcompete the other; two species cannot occupy the same niche
What is faciliation?
Positive interaction between individuals of a different species that becomes increasingly important as succession progresses
What is mutualism?
Interaction between species that is beneficial to both species
What is commensalism?
Loose interaction between organisms of two species in which one benefits and the other is unaffected e.g., nurse plants make a canopy that protects individuals of other species
Why are nutrients recycled?
Chemical elements are available in limited amounts
How are fossil fuels formed?
Remains of dead plants and animals form coal, oil and other fossil fuels - trapping carbon within them, which are then released through combustion, contributing to the enhanced greenhouse effect
How do humans impact the carbon cycle?
Reduced photosynthesis - less carbon dioxide absorbed by the plant so concentration of carbon dioxide in atmosphere increases
Increase in combustion - increases carbon dioxide emissions, increasing carbon dioxide content in the atmosphere
Increase in decay - carbon dioxide absorbed by plants is released at a greater rate
What is climate change?
Change in regional and global climate patterns due to rise in atmospheric carbon dioxide due to increased combustion of fossil fuels and deforestation
What is carbon footprint?
The equivalent amount of carbon dioxide generated by an individual, a product or a service in a year
What is the nitrogen cycle?
Flow of organic and inorganic nitrogen within an ecosystem, where they are absorbed as nitrates which are used to make amino acids, proteins and nucleic acids, which are then passed to animals through food chains and food webs
What is nitrogen fixation?
Fixing of nitrates directly into nitrogen compounds using nitrogen fixing bacteria:
Azotobacter - free living aerobic bacteria that fix nitrogen into soluble ammonia absorbed through plant roots
Rhizobium - symbiotic anaerobic bacteria found in root nodules that convert nitrogen gas into soluble ammonia or ammonium ions using nitrogenase
How does rhizobium achieve symbiosis?
Lives in nodules found on roots of some legume plants and fixes nitrogen gas into soluble ammonia and ammonium using nitrogenase, which is inhibited by oxygen
Bacterium is surrounded by leghaemoglobin that prevents oxygen from reaching the anaerobic bacteria
Legume receives a soluble nitrogen source, while the bacterium receives glucose and other products of photosynthesis
What is putrefaction?
Decomposition of large organic molecules derived from dead plants, animals and waste products, forming ammonium ions
What is nitrification?
Two-step process:
Nitrosomonas converts ammonium into nitrite
Nitrobacter converts nitrite into nitrate
What is denitrification?
Reduction of nitrate and ammonium ions back to nitrogen using pseudomonas
What is eutrophication?
- Nitrates from chemical fertilisers or sewage waste are washed into a lake
- Causes an increase in growth of algae and small plants
- Algal bloom forms, which voers the lake
- Some algae dies due to lack of light
- Dead algae sink to the bottom of the lake and are decomposed by microbes, whcih increase in number
- Microbes are aerobic and use oxygen dissolved in the water
- Fish and other organisms die due to lack of oxygen
