Study notes for a 7 in IB ESS Topic 2: Ecosystems and Ecology
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IB Environmental Systems and Societies SL
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ECOSYSTEMS AND ECOLOGY, Topic 2
2.1 SPECIES AND POPULATIONS
Species: group of organisms sharing similar characteristics that can interbreed to produce
fertile offspring
Habitat: environment in which species normally live
Niche: describes the set of biotic and abiotic conditions and resources in which a population
can potentially survive (fundamental) or where it actually lives (realized)
Biotic factors: living part of the environment
Abiotic factors: non-living parts of the environment
There are upper and lower levels beyond which a population cannot survive (tolerance
range) and a range in which a specie thrives (optimum range)
Predation: occurs when one animal or plant hunts and eats another organism
- Predatory-prey relationships are controlled by negative feedback loops
- Herbivory: interactions where animals feed on plant
Parasitism: an organism (parasite) benefits and lives at the expenses of another (host). Can
either be a ectoparasite (outside) or endoparasite (inside)
Symbiosis: mutualism relationship in which two organisms live together and they both
benefit from it. (ex. rhinos and oxpecker, eats parasites off the skin of rhino)
Disease: organism causing a disease is a pathogen, reduces the carrying capacity
Competition: when resources are limited, species compete to survive. Can be intraspecific
(same species) or interspecific (between different species, occurs when niches overlap, the
degree to which they overlap determines the degree of competition). No one benefits from
it, although the best competitor suffers less and survives.
Population growth:
- S-curve: begins with lag phase where population and births are low exponential
growth, favourable biotic and abiotic conditions boost population transitional
phase, population growth slows as carrying capacity of the environment is reached
stationary phase: population oscillates about the carrying capacity
- J curve: population grows exponentially due to favourable conditions and plentiful
resource, species that produce many offspring without much parental care. At some
point the population numbers crash once factors/resources become limiting
Limiting factors:
- Plants: light, nutrients, water, CO2, temperature
- Animals: space, food, mates, nesting sites, water
Carrying capacity: maximum number of individuals that can be sustained by the
environment. Population size at which factors becoming limiting to further population growth.
, 2.2 COMMUNITIES AND ECOSYSTEMS
Community: many species living together
Population: organisms belonging to the same species living together
Ecosystem: community of interdependent organisms (biotic) and the environment they
inhabit (abiotic)
Photosynthesis: process by which green plants convert light energy from the sun into usable
chemical energy stored in organic matter
- CO2 + H2O Glucose + O2
- Inputs: sunlight, carbon dioxide and water
- Outputs: glucose (energy source for growth/build organic molecules) and oxygen
- Transformations: energy changes from light to chemically stored in organic matter.
Chlorophyll is need to capture certain wavelengths of sunlight to do so
Respiration: release energy from glucose and other organic molecules in all living cells.
Beings anaerobically in cytoplasm and is continued aerobically in mitochondria.
- Glucose + O2 CO2 + H2O
- Inputs: organic matter (glucose) and oxygen
- Outputs: release of energy for work
- Transformations: energy from chemical to kinetic and heat
Feeding relationships
- Producers: convert abiotic components into living matter, they support the ecosystem
by constant energy input and new biomass (autotrophs) (energy from light:
photoautotrophs)
- Consumers: eat other organisms to obtain energy and matter (herbivores, carnivores,
omnivores)
- Decomposers: obtain food and nutrients from the breakdown of organic material and
release nutrients contributing to soil formation. Essential for cycling matter in
ecosystems. Feed on dead matter at each trophic level
Food chain: describes the flow of energy and matter between organisms, driven by feeding
relationships
Food web: an ecosystem contains many interconnected food chain
Pyramids: graphical models of the quantitative differences that exist between the different
trophic levels of an ecosystem, in a given area and time
- Pyramid of numbers: record the number of individuals at each trophic level coexisting
in an ecosystem (simple and easy, good for comparisons BUT size is not considered)
- Pyramid of biomass: represent the biological mass or energy of the standing stock at
each trophic level [gm-2/Jm-2] (use samples, impossible to measure biomass
accurately as organisms should be killed)
- Pyramid of productivity: shows the flow of energy through each trophic level of a food
chain in a period of time [gm-2y-1/Jm-2y-1]
Top carnivores are in trouble: pollutants in pesticides bioaccumulate in tissues of organism
and biomagnify along the food chain until they reach top predators which risk intoxication.
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