Environmental Systems and Societies for the IB Diploma Revision Guide
Detailed notes for the whole ESS syllabus in the International Baccalaureate. These notes cover all studied units and basically replace your book in a short and summarised form.
Ecosystems and Ecology
2.1 Species and populations
What is a species? Group of organisms that share common characteristics and
that interbreed to produce fertile offspring. Species: biggest gene pool possible
under natural conditions.
What is a habitat? Ecological or environmental area in which a species lives.
Place where it can find food, shelter, protection and mates for reproduction
What is a niche? Particular set of abiotic and biotic conditions and resources to
which an organism or population responds
Describes the full range of conditions in which a species could survive
and reproduce
Niche includes behavior, nutrition, activity (night or day)
Every species faces competition: direct form of competition is
interspecific competition
Abiotic Factors: non-living, physical factors that influence the organism and
ecosystems. Temperature, sunlight, pH, precipitation
there are also limiting factors within the abiotic factors (e.g. low annual
average temperature restricts growth of trees, bc subsoil is permanently
frozen (common to the Arctic)
Biotic Factors: interactions between organisms: predation, herbivory,
parasitism, mutualism, disease and competition
Predation: one species feeds on another
Herbivory: form of predation- the act of eating plants (herbivores play
important role in ecology of any area, influencing plant communities and
individual plant growth
Parasitism: host provides habitat and food for bacteria, in return, bacteria
cause disease in host. Example of parasitism where the symbiont
, (bacteria) benefits and host is harmed. Note: not all parasites have to
cause disease
Mutualism: type of symbiotic relationship- both benefit from it
Disease: abnormal condition, disorder of structure or function (affects
part or all of an organism)
Competition: relationship between species that attempt to use the same
limited resource (e.g. trees competing for sunlight at top of canopy)
Commensalism: one species receives benefit from another, which
enhances fitness of one species, and has no effect on other
Symbiosis: species live together which can include any of the above
Population: collection of individual organisms of the same species that occupy
specific area. Population dynamics- refer to how the number of individuals in a
population changes over time
Density-dependent factors: factors that lower birth rate or raise death rate
as population grows in size. They are negative feedback mechanisms
leading to stability or regulation of the population.
o When prey increases, so does predator, but then prey decrease and
then again predator decrease, causing prey to increase again
Density-independent factors: affect a population irrespective of
population density: notably environmental change. Abiotic factors are
density independent factors- droughts, fires, hurricanes and long-term
climate change. Impact: can lower birth rate and increase death rate
Factors regulating population size:
o Internal: fertility rates, territory size
o External: predation, pressure, parasitism
Ways humans can cause population growth:
o Increase available resources
o Reduce competition
, o Reduce pressure prom predators
o Introduce animals to new areas
Ways humans can decline population growth
o Change environment, cause habitat disruption
o Change biological environment by introducing new species
o Cause secondary extinctions
o Overkill
Population growth curves: S and J curves
Describe a generalized response of populations to a particular set of
conditions (abiotic and biotic factors)
J curve: hits its carrying capacity and just continues causing a population
explosion and competition for resources. Exponential growth
S curve: when population abundance is low, exponential growth. When
pop. Size increases, resources become limited, so pop growth rate slows
and curve flattens
2.2 Communities and Ecosystems
What is a community? Group of populations living and interacting with each
other in a common habitat.
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