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2.4 Ecology
Organism
Word
Definition
Organism
A single living individual
Ecosystem
All interacting communities of organisms and abiotic factors of the
environment within a defined area.
Environment
The sum total of all of the factors in the surroundings that influence an
organism
Abiotic factors
Non-living chemical and physical factors of the environment (e.g.
temperature, light, water, soil, nutrients).
Biotic factors
Includes factors such as food, organisms, competition. Predation,
parasitism
Climate
Weather conditions in a certain geographical area averaged over a
long period of time.
Micro-climate
local atmospheric zone where the climate differs from the surrounding
area
Weather
Rainfall, temperature average (or highs and lows), sunshine hours
and wind in a particular area at a particular time.
Adaptation
The feature that increases the chances that an organism will survive
and reproduce.
Structural; physical structure / feature of the organism
Behavioural; certain behaviour of an organism
Physiological; certain functioning of an organisms body
Habitat
The place where an organism lives
Niche
The way an organism makes it’s living; its role in the community
Fundamental niche
the full range of environmental conditions (biotic and abiotic) under
which the organism can survive
Realised Niche
The niche that the organism actually occupies.
Gause’s principle
THE COMPETITIVE EXCLUSION PRINCIPLE
If two species, with the same niche, coexist in the same ecosystem,
then one will be excluded from the community due to intense
competition.
Tolerance
An organisms ability to survive in a habitat with variation in
environmental conditions
Optimum range
A habitat that has environmental conditions where a species will
function at it’s best.
Stress
When the environmental conditions differ from the optimum range
Acclimation
When an organism can make adjustments to its tolerance levels over
time to environmental conditions
Liebigs’law of
minimum
It states that growth is controlled not by the total of resources
available, but by the scarcest resource
Limiting factors
A factor that controls a process, such as organism growth or species
population size or distribution.
It states that growth is
controlled not by the total of
resources available, but by
the scarcest resource
Liebigs’law of
minimum
A factor that controls a
process, such as organism
growth or species
population size or
distribution.
Limiting Factor
In the
Ecosystem
Affect each other
Organism
SJ Gaze
acclimatation
Optimum range
Organism
allow
To live in
A habitat that has
tolerance
environmental
conditions where a
species will function at
its best.
Relationship between tolerance levels and stress levels
death
death
Maximum stress
level
All together makes up one species
Tolerance limits
Gause’s Principle
If two species, with the same niche, coexist in the same ecosystem, then
one will be excluded from the community due to intense competition.
Optimum range
Environmental factor (eg temperature)
Physiological
stress
2.4 Ecology
Populations
Word
Definition
Organism
A single living individual
Population
All the organisms of a given species occupying a defined area
sampling
Counting a smaller number of organisms and calculating the estimated population size or density in a given
area.
Quadrat sampling
Population count of a individual taken within an area of defined size at selected points.
Transect sampling
Samples along a selected line (transect) through a community.
Capture /
Recapture
Lincoln Index
Total pop = No. of animals in 1st sample (marked) x No. of animals in 2nd sample
-------------------------------------------------------------------------------------------------------number of marked animals in 2nd sample (recaptured)
Population
number
The total number of individuals of a single species in a defined area
Density
Population density is total population size per unit of area.
Distribution
The way individuals in a population are spaced from each other
Clumped – focused around tolerance levels of niche
Spaced – often seen in territories
Random – not based on distribution of resources
Age structure
Defines the relative proportions of individuals of each age:
a. Pre-reproductive
b. Reproductive
c. Post-reproductive
Natality
Birth rate, usually expressed as live births per 1,000 persons per year
Mortality
Death rate
Survivorship
Survivorship is the chance of an organism staying alive at any given age.
Survivorship
curves
By plotting survivorship data on a log scale we can construct survivorship curves.
There are three main types of survivorship curves.
Type l - low mortality in the juvenile phase (humans)
Type ll – constant mortality rate through all ages (jellyfish, birds)
Type lll – high juvenile mortality (shellfish, plants)
J - curves
Exponential growth followed by a crash in numbers, overshooting the carrying capacity
Sigmoid growth
S – shaped growth curve in which numbers increase exponentially at first, followed by levelling off of growth
rate till numbers stabilize at carrying capacity.
Carrying capacity
The maximum numbers of individuals that can be supported by a given environment
Population growth
Population growth= Births – Deaths + Immigration - Emigration
R- Selected
population growth
Early reproduction, Short life span, High mortality rate, Little or no parental care, Large investment in producing
large numbers of offspring, Below carrying capacity
K-Selected
population growth
Late reproduction, Long life span, Low mortality rate, Extensive parental care, Greater investment in
maintenance and survival of adults, At or near carrying capacity
Population
regulation
Factors that control population growth; include density dependant and density independant
Environmental
Resistance
Decreases the birth rate, or increases death rate, related to environmental conditions, such as food & space.
Biotic Potential
maximum rate at which a population could grow given optimal conditions (food, water, space)
Density
dependant factors
Density
independent
factors
Factors that become more inhibiting of growth as the density increases ;Food, Water,
Shelter,Disease
Growth Factors that are not influenced by the current density of a population; weather extremes, climate
K= carrying capacity
3. Natality rate drops or
mortality rate increases
as carrying capacity
approached
4. The carrying capacity
of the environment is
reached. Natality equals
mortality.
1.
Population
low due to
lack of
breeding
individuals
2.
Exponential
growth with
few limiting
factors
Population
regulation
5. The
population
fluctuates in
response to
changing
environmental
factors, or
because of
immigration /
emigration
Density
dependent
If none then population
reaches biotic potential
Food, Water,
Shelter, Disease
time
Organism
Population
growth
Weather extremes,
climate
Density
independent
Number of individuals
in a defined area
Density
A single living individual
Population
number = 5
high
low
population
Distribution
All the organisms of a
given species occupying a
defined area
Age
Structure
P o s t – re p ro d u c tive s
O rganism s
have ceased to
breed because
of disease or old age
Birth
rate
per
1000
New generation
K-Selected
population
growth
Late reproduction, Long life
span, Low mortality rate,
Extensive parental care,
Greater investment in
maintenance and survival of
adults, At or near carrying
capacity
Clumped
Death
rate per
1000
Uniform
Survivorship curves
Rapid growth
slow growth
Number of survivors (log scale)
P re – re p ro d u c tive
Im m ature organism s
not yet
reproductively active
Mortality
Natality
R e p ro d u c tive s
Produce offspring
Random
zero growth
Type l - low mortality in the juvenile phase
Type ll – constant mortality rate through all ages
Type lll – high juvenile mortality
R-Selected
population
growth
Early reproduction, Short life
span, High mortality rate, Little
or no parental care, Large
investment in producing large
numbers of offspring, Below
carrying capacity
Percentage of maximum life span
SJ Gaze
Population
2.4 Ecology
Community
Word
Definition
Community
A area that contains populations of species interacting with each other – the
biotic components of an ecosystem
Environmental
heterogeneity
a range of resources in the natural habitat - allows one species to survive just
beyond the niche limits of the other competing species.
Zonation
A graduated range of Abiotic factors (environmental) in an area - examples a
rocky shore and altitudinal zonation up the side of a mountain.
Stratification
Stratification is caused by a vertical gradient of abiotic factors. This may be
seen in a forest where variation in light levels and quality, temperature, wind,
precipitation levels etc may determine the type of species found at each level
Succession
Changes in species distribution in time. Changing environmental conditions
(abiotic) and the effect of previous species (biotic) provide newly available
niches that new species can exploit.
Intraspecific
interactions
Interactions between members of the same species
Competition
When two species or individuals compete for limited resources causing harm
to both (or decreased benefits)
Predation
The killing of other organisms for food
Predator-prey
cycles
The fluctuation in population number of predator which lags behind the rise
and fall of prey – attributed to predation and environmental factors
Territoriality
Territoriality means the claiming of space – and the resulting resources found
within that space – food, water, nesting sites, even mating partners.
Home range
A home range is an area that an individual or group may occupy or be found at
various times of the year.
Interspecific
interactions
Relationships between members of different species.
Mutualism
Relationship between two species in which both species benefit – eg insect
pollination
Commensalism
Relationship between two species in which one species benefits and the other
is not affected.
Amensalism
The presence of one species harms another but it is not affected itself
Exploitation
Relationship between two species in which one species benefits at the
expense of another – Predation – predator kills prey, Herbivory – Herbivore
doesn’t kill plant, Parasitism – doesn’t kill it’s host
Antibiosis
Relationship between two species in which one benefits or is not affected
while the other one is harmed –eg penicillin mould.
Social organisation
Interactions within a group of individuals of the same species which benefit the
group as a whole – may not benefit certain individuals
Individual (the female male have dependant cubs with her) – eg, Polar bears
Family groups collect food and raise offspring together – eg, nesting birds
Extended Family groups often with a ranking of dominance (African hunting
dogs) most females are related – male is not
Networks of smaller groups joining together for food, security – eg rabbits,
Complex super organisations where there is a division of labour and niche –
the entire colony acts as an entire organism eg termites, ants
Changes in
species
distribution
in time
Community
Territory
Succession
Zonation
A graduated range of
Abiotic factors (in an area
Defending of space by a species
Stratification
a vertical gradient of
abiotic factors
Patterns
location
Community
Home range
Area an individual or group may
occupy
A area that contains populations of
species interacting with each other
Same species
Environmental
heterogeneity
a range of resources in the
natural habitat
Intraspecific
interactions
Interspecific
interactions
Different species
Exploitation
Species
B
Species
A
Ha rmed
Benefits
Parasitism
organism doesn't kill it’s
host
Species
A
Species
A
Benefits
Benefits
Beneficial relationships
Resource sharing – food, shelter
Offspring / juvenile rearing
Predation protection – warning,
safety in numbers
Mutualism
Species
B
Species
A
Benefits
Benefits
Herbivory
Consuming plants for food
Commensalism
Ha rmed
Species
A
Species
B
Predation
N ot a ffected
Benefits
killing of other organisms
for food
Amensalism
Species
A
Species
B
N ot a ffected
Ha rmed
Species
A
Predator-prey cycles
Species
A
Harmful relationships
Competition for resources – food,
space, light, nutrients, water, mates
Ha rmed
Social
organisation
SJ Gaze
Individual
Family Groups
Antibiosis
Species
A
Benefits or not a ffected
Species
B
Ha rm ed
Competition
Species
A
Ha rmed
Species
B
Ha rm ed
Extended Family Groups
Networks
Complex super organisations
2.4 Ecology
Ecosystem
Word
Definition
ecosystem
A community plus all the non-living matter in the area, e.g. a forest includes
not only the inhabitants but also the non-living parts of the soil.
Trophic level
Position of an organism in a food chain; plants occupy the first trophic level
and herbivores the second
Food chain
A series of organisms through which energy flows, the first link is always a
producer.
Food web
A series of food chains linked together showing the feeding relationships of all
species in a community.
Producer
Species occupying trophic level one, the plants and phytoplankton that convert
suns energy into food by the process of photosynthesis
Consumer
An organism that feeds off another organism, either plant or animal or fungi –
often killing them in the process
Decomposer
An organism that feeds of dead organic material returning nutrients into the
ecosystem
Energy
Entering the ecosystem from the sun, about 1% gets converted to chemical
energy but photosynthesis
Pyramids of energy
These show the proportion of energy stored at each trophic level,
approximately 10% get passed on to each successive trophic level.
Pyramids of
numbers
Showing the number of organisms at each level required to feed one top
carnivore.
Pyramids of
biomass
The total dry weight of organisms (standing crop) in a particular trophic level.
Organisms vary greatly in size, often being larger the further up the trophic
levels, so a pyramid of biomass more accurately reflects the transfer of
energy.
Heat energy
Pyramids of biomass decrease from one trophic level to the next. Energy, in
the form of heat energy is wasted at each step in a food chain. This is due to:
– respiration using up energy for movement and warmth;– energy (heat) lost
to the surroundings;– energy and materials lost in excretion
Biochemical cycles
Nutrients are continually recycled between the abiotic environment and the
biotic communities
Carbon Cycle
Carbon is circulated through the ecosystem from CO2 in the atmosphere to carbon in
organisms (via the photosynthesis process of plants). It is released back to CO 2 by
respiration, decomposition after death, transformation into fossil fuels (over millions of
years) and eventual combustion (burning)
Nitrogen Cycle
Nitrogen gas in the atmosphere is fixed into useable form by 1) nitrogen fixing bacteria
(in legumes) and nitrifying bacteria in nitrates or 2) lightning. The plants can take up
the nitrates through their roots and convert them to amino acids → then protein which
can be passed along the food chain to consumers. Bacteria can either decompose
organisms back into nitrates for plants or into N2 gas (denitrifying bacteria)
Phosphate cycle
Plants uptake phosphates from the soil through their roots. This is passed on to the
next trophic level through consumption. The phosphates are released back into the soil
by decomposers (bacterial or fungal)
Water cycle
The water or hydrologic cycle refers to the continuous circulation of moisture on earth,
particularly between the atmosphere and the earth’s surface. Solar radiation provides
the energy for the water cycle. Water changes between gaseous and liquid states
through the processes of transpiration, evaporation, and precipitation.
ONE WAY travel of energy through an ecosystem
Consumer
An organism that feeds off another
organism, either plant or animal or
fungi – often killing them in the
process
Light
energy
Decomposer
Energy lost
through
consumption
producer
Species occupying trophic
level one, the plants and
phytoplankton that convert
suns energy into food by the
process of photosynthesis
consumer
Producer
decomposer
Energy lost through respiration and heat
photosynthesis
An organism that feeds of dead organic
material returning nutrients into the
ecosystem
A series of organisms
through which energy
flows, the first link is
always a producer.
Role
Trophic level
2nd carnivore
4
1st carnivore
3
herbivore
2
producer
1
Trophic Levels
Ecosystem
Food chain
Position of an
organism in a
food chain
decomposer
Energy lost through death
Entering the ecosystem from the sun,
about 1% gets converted to chemical
energy but photosynthesis
Consumer,
producer or
decomposer
Ecosystem
Energy
Circular travel of nutrients
through an ecosystem
respiration
N2
Pyramid of energy
These show
the proportion
of energy
stored at each
trophic level
respiration
CO2
Carnivores
respiration
consumption
ammonification
Producers
Carbon
Nitrogen
NH4+
nitrification
SJ Gaze
fossilisation
assimilation
ammonium fixing bacteria
Showing the
number of
organisms at
each level
required to feed
one top
carnivore.
Fossil
fuels
death
C NO3-
Nitrates Decomposers
NO3decomposition
N2 CO2
10% passed on
to each level
Pyramid of numbers
combustion
Herbivores
photosynthesis
Pyramids
Nutrient cycles
The total dry
weight of
organisms
(standing crop)
in a particular
trophic level
Pyramid of biomass