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Topics 2-8 complete notes
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IB ESS (Environmental Systems & Societies) topics 2,3,4,5,6,7,8 complete notes
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IBDP ENVIRONMENTAL SYSTEMS AND SOCIETIES TOPICS 2-8Topic 2: Ecosystems and ecology
2.1 Species and populations
Key terms
Ecosystem → a community of interdependent organisms (biotic) and their interactions with the physical
environment (abiotic) they inhabit.
Species → a group of organisms sharing common characteristics that can interbreed and produce offspring that
also produce young.
Habitat → an ecological area or environment in which a species lives, where an organism can find food, shelter,
protection, mates.
Niche → the set of biotic and abiotic conditions and resources that an organism or population responds to (not just
habitat, but how an organism interacts with others). No two species can have the same niche.
Fundamental Niche: full range of conditions/resources an organism can survive and reproduce in.
Realised Niche: actual conditions a species exists in due to biotic interactions.
→ different niches can still share the same habitat due to space, behaviour patterns etc.
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Abiotic Factors
The nonliving, physical factors that influence organisms and ecosystems. Eg. temperature, sunlight, pH,
precipitation, soil, landscape/topography.
Biotic Factors
The living biological factors that may influence and organism or ecosystem. Eg. Predation, parasitism, disease,
competition.
Population Interactions
Herbivory → primary consumers feed only on plant materials. The plants as a food source affect the carrying
capacity of the environment for the herbivore.
Relationship can be:
→ Beneficial: lemurs eating tamarind and spreading the seed.
→ Harmful: beetles eating leaves.
Predation → consumers kill and eat another organism. Relationships are controlled by negative feedback
mechanisms: as prey increases, after time so do predators. Increase in predators reduces number of prey.
Predation benefits prey - removes old/sick individuals, leaving a superior breeding pool.
Relationship is harmful to prey.
→ Crocodiles and wildebeest.
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,Parasitism → organisms benefit at the expense of another, the host. Endoparasites live inside hosts, ectoparasites
live on the surface of hosts.¡
Relationship is symbiotic (co-living) and harmful to the prey.
→ Jewel wasps lay eggs inside cockroaches.
→ Tapeworms (endoparasites) and ticks/mites (ectoparasites).
Mutualism → another form of symbiosis where species tend to co-evolve to benefit each other either through their
behaviour our life cycle.
Relationship is symbiotic and mutually beneficial.
→ Caterpillars feed ants in return for their protection.
→ Honeybees and flowers.
Competition → one or more individuals depend on the same limited environmental resources. It can be
intraspecific (within a species) or interspecific (between different species).
Relationship promotes evolution.
→ Giraffes compete for food and mates with their long necks.
→ Galápagos finches evolved with different beak shapes due to competition.
Disease → aka. pathogen - can be bacteria, virus, fungi. Reduces carrying capacity of infected organism.
→ Dutch elm disease, caused by fungus clogging vascular tissues in the tree, preventing water movement.
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Population Growth
Population → group of organisms in the same species living in the same area at the same time, capable of
interbreeding. Abundance of resources affects population structure over time.
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Limiting Factors → slow population growth as carrying capacity is reached
Density-Dependent Factors - lower birth rate/raise death rate as population grows
Density-Independent Factors - affect a population regardless of density, abiotic factors.
Interpreting population graphs:
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,S Population Curve (aka sigmoid curve)
Rapid initial growth, then slowing as carrying capacity is reached, where
population fluctuates around K. Divided into lag phase, exponential growth
phase, transitional phase, stationary phase
J Population Curve
Increasingly rapid exponential growth with no signs of slowing, exhibited by
organisms that produce rapidly. Controlled by favourable abiotic
components, results in a population crash
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, 2.2 Communities and ecosystems
Communities and Ecosystems
Community → all populations living and interacting in a common habitat at a specific time (only biotic). Involves
many interactions among species, communities with higher diversities are more stable and resilient to
disturbances.
Ecosystem → a community and the physical environment it interacts with (biotic interacting w/ abiotic). Divided
into terrestrial, marine, and freshwater, defined uniquely by various abiotic factors.
Photosynthesis and Respiration
→ all organisms respire, only producers photosynthesize
Photosynthesis → process by which a plant converts light energy from the Sun into usable chemical energy stored
in organic matter. Produces the raw material for biomass.
Inputs: sunlight as energy, CO2, H2O.
Outputs: glucose (foundation for other organic molecules).
Transformations: light energy → chemical energy stored in biomass.
carbon dioxide + water → glucose + oxygen
Diagram:
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Respiration → conversion of organic matter to carbon dioxide and water in all living organisms, releasing energy for
life processes. “Wasted” energy is lost as heat, increasing the entropy in the ecosystem while allowing organisms to
maintain low entropy.
Inputs: organic matter (glucose) and oxygen.
Outputs: release of energy to maintain order (counteract entropy) and heat.
Transformations: stored chemical energy → kinetic energy and heat energy.
glucose + oxygen → carbon dioxide + water
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