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2. Ecosystems and Ecology

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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.

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  • June 26, 2019
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  • 2018/2019
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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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