Population Size and Ecosystems Flashcards
Population
A group of organisms of a single species interbreeding and occupying an area
Factors determining population size
Birth rate, death rate, immigration, and emigration
Fugitive species
Cannot tolerate competition. To increase, they reproduce rapidly and have effective spreading. They invade new environments fast. e.g. weeds.
Equilibrium species
Control population by competition. They have an S shaped one-step growth curve. e.g. rabbits.
Lag phase for bacteria
Bacteria adapt to new environment and prepare for growth
Log phase for bacteria
Bacterial cells replicate exponentially. No limiting factors.
Stationary phase for bacteria
Bacterial growth levels off as cell death = new cells. Factors such as nutrient supply become limiting and waste builds up.
Death phase for bacteria
Cell death exceeds cell division. Waste products have reached toxic levels that stop growth.
Abiotic factors
Non living factors e.g. temperature, light, pH, water
Biotic factors
Living factors e.g. competition, disease, predation
Carrying capacity
Maximum population size of a species that an environment can sustain.
Population crash
Sudden dramatic decrease in population, when a population greatly exceeds carrying capacity
Equation for population growth
B+I=E+D
Why is bacterial growth plotted on a log scale?
The numbers are too large for a linear scale
Density dependent factors
The effect of density dependent factors increases as the population increases.
Biotic factors - living
e.g. competition, predation, disease
Determine carrying capacity
Density independent factors
Abiotic factors - non living
Not linked to population density
e.g. earthquakes, tsunami, wildfires
Abundance
Number of individuals of same species in an area
Capture-mark-recapture
Organisms trapped and marked then release. The same sampling occurs a day later.
Pop size = day 1 total x day 2 total / marked in day 2
Random sampling
Using a quadrat to find density of organisms in an area
Systematic sampling
Using a transect to determine changes in percentage cover of species due to changes in abiotic factors e.g. light intensity
Niche
Its role in an ecosystem
Ecosystem
A characteristic community of interdependent species and their habitat
Producers
Trophic level 1
Autotrophic organisms which absorb light energy
Consumers
Heterotrophic organisms that ingest it or absorb from other organisms
Herbivores
Trophic level 2
Animals which feed on organic matter from producers
Carnivores
Feed on other animals at lower levels
Trophic level
Position in a food chain
Detritivores
Feed on dead organic matter e.g. earthworms
Decomposers
Break down organic compounds into simpler inorganic compounds to be absorbed by plant roots e.g. bacteria
How is energy lost?
Light is reflected from leaf surface
Wrong wavelength of light which cannot be absorbed by pigments
Light passes through leaf
How is most energy lost by producers?
Lost as heat from respiration
Why is a lot of energy from herbivores not used?
Cellulose in plant cell walls cannot be digested and is lost as waste for decomposers
GPP
Gross primary productivity
Rate of production of chemical energy in biological molecules by photosynthesis
Most used during respiration and some lost as heat
NPP
Net primary productivity
Energy in plant biomass which could pass to the primary consumers at level 2 at feeding
Calculating NPP
GPP - R = NPP
Secondary productivity
Rate at which heterotrophs accumulate energy in the form of new cells and tissues
Calculating the efficiency of energy transfer
Energy into biomass after transfer / energy available before transfer x 100
Ecological pyramids
Represent food chains: the base is primary producer, and the top is consumer
Succession
Sequence of changes in a community over time eventually leading to a stable climax community which has high biodiversity and productivity
Sere
Each stage of succession
Primary succession
Begins with bare rock. First organisms to colonise are pioneer species (lichens, mosses)
Pioneer species penetrate rock, forming cracks, allowing humus to build up, allows grasses and ferns to colonise
Grasses and ferns change rock as roots penetrate further and deeper, death and decay allows more soil and plants to invade
Increase biodiversity and stability
Climax community
Secondary succession
Begins with bare soil from wildfire
Achieved much faster as soil is already present, containing seeds and spores.
Human activity can prevent climax community e.g. farming of land, deforestation, soil erosion
Process of carbon cycle
CO2 from atmosphere fixed into carbohydrate by photosynthesis
Respiration releases CO2
Combustion releases carbon in form of CO2
Decomposition releases CO2 due to respiration
Deforestation increases CO2 in atmosphere
Ways human activity is disturbing carbon cycle
Deforestation, burning fossil fuels, increase in decomposition
What does increase CO2 lead to?
Enhanced greenhouse effect, global warming, driving climate change.
Melting ice caps, sea levels rising, increased extreme weather, desertification, soil erosion, extinction, dieases
Carbon footprint
Total amount of CO2 produced directly due to actions of an individual per year
How can we reduce carbon footprint?
Produce less meat - land resources and feed
Crops grown for humans not feed
Packaging reduced
Transport distances reduced
Food produced locally
Nitrogen cycle definition
Flow of inorganic and organic nitrogen in the abiotic and biotic elements of an ecosystem
Nitrogen fixing
Fixing atmospheric nitrogen into ammonia
Nitrification
Converting products of decay into nitrate ions
Azotobacter
Free-living bacteria in soil. Aerobic and fixes nitrogen gas to ammonium ions
Rhizobium
In root nodules of legumes and shares symbiotic relationship. Uses nitrogenase to fix gas into soluble ammonium
Nitrosomonas
Free living aerobic bacteria, convert ammonium to nitrite
Nitrobacter
Free living aerobic bacteria, converts nitrite to nitrate which is absorbed into plant root hair by active transport
Denitrification
Loss of soluble nitrate compounds
Process of nitrogen cycle
Decomposers break down molecules into ammonium
Nitrosomonas converts ammonia to nirite then nitrobacter converts it to nitrate - nitrification
Inorganic nitrogren sources converted to gas by pseudomonas - denitrification
Azotobacter and rhizobium fix gas to ammonia - nitrogen fixing
Nitrates absorbed by root hair by active transport, requires ATP
Human activities improving availability of nitrate
Adding chemical fertilisers (ammonium nitrate)
Adding manure (animal waste)
Adding treated sewage (human waste)
Planting legumes
Ploughing or draining to improve aeration
Human activity causing nitrogen pollution
Excess nitrates on grasslands leads to weeds, reduced biodiversity, competition
Draining wetlands destroys habitats
Nitrate pollution causes eutrophication
Eutrophication
Fertilisers washed into rivers, causes algal blooms to form, covering surface of water, reducing oxygen for organisms under, plants and animals die, encourages denitrifying bacteria to form, decreasing nitrate levels
