CHAPTER 2:
ECOLOGY
2.1 Ecosystem Concept
i. Biotic components
ii. Abiotic components
iii. Interactions between/among biotic components
competition, parasitism, predation, commensalism and mutualism.
iv. Interactions between biotic and abiotic components.
i. Biotic Components
Communities of living organisms
Can be categorized as:
i. autotrophs / producers
ii. heterotrophy / consumers
-
herbivores, carnivores, omnivores, detritivores,
decomposers
i. Autotrophs / producers
Make their own organic compounds from inorganic materials obtained from the
environment
Do not eat or decompose other organisms
2 types:
i. photoautotrophs
e.g.: green plants, algae that perform photosynthesis ii. chemoautotrophs
e.g.: Nitrosomonas
(nitrifying bacteria) that perform chemosynthesis
ii. Heterotrophy / consumers
Cannot make their own food from inorganic materials
Require organic compounds produced by
other consumers or producers
Can be categorized as:
i. herbivores
(primary consumers that eat plants only)
ii. carnivores
(secondary or tertiary
consumers that eat other animals)
Can be categorized as:
iii. omnivores
(eat plants & other animals)
iv. detritivores
(feed on dead matter) v. Decomposer
v. Decomposers
Usually saprophytic organisms such as bacteria
& fungi
Decompose (break down) organic matter into inorganic materials
Inorganic materials will be restored in soil or water to be reused by the producers
bacteria
Fungi
ii. Abiotic Components
Non-living (physical & chemical) components of an ecosystem
(e.g.: temperature, light, water, nutrients) to which an organism is exposed.
Influence the growth & distribution of plant &
animal communities in that ecosystem
Can be divided into:
i. Atmosphere (air layer)
ii. Hydrosphere (freshwater & saltwater)
iii. Lithosphere
(land; especially the soil
& sediments)
Interactions between biotic components
• Living organisms interact in a variety of ways.
• No organism exists independent of other living things.
The producers, consumers and decomposers of a community interact with one another in a variety of complex ways and each forms associations with other organisms.
Interactions between biotic components
• Example of interactions:
– Competition – Parasitism – Predation
– Commensalisme – Mutualisme
Interactions between biotic components
Competition
• A relationship in which two or more individual strive to obtain the same limited resources.
• Occurs when 2 or more individuals compete for a same particular resource that is in short supply
• 2 types:
i. Intraspecific competition ii.Interspecific competition
i. Intraspecific competition (between individuals of same species)
E.g: between adult male panthers
ii. Interspecific competition (between individuals of different species)
E.g: between lions & panther, Paramecium
aurelia & P. caudatum
Interactions between biotic components
Parasitism
• A relationship in which one species benefit and the other/
host is adversely affected.
• Parasite gets its nutrients from another organism (its host)
• The host is harmed or at least loses some energy or materials
Commensalism
•A relationship in which one species/ commensal benefits while the other species remain unharmed.
•Looser association in
which one partner remains relatively unaffected.
•Remora fish – shark
–A slight loss in the streamline of the shark.
–Remora fish is dependent on the shark for scraps of food
Mutualism
• A relationship in which both species benefit.
• Symbiotic relationship that is beneficial to both species.
– Essential for the growth and survival of the participating organisms
• Lichen consists of the hyphae of fungus and the cells of
photosynthetic alga so closely associated that they function as a single unit.
– Fungus – structural support, absorbing water and mineral – Benefits – organic food materials are manufactured by alga
photossynthesis.
Predation
• A relationship in which one species/ predator eats another species/
prey.
• Occurs when a predator catches, kills & eats its prey
• Usually, the predator is larger than its prey
• Both predator & prey have certain adaptations
Predation
• Presence of predator lowers prey population size
• Eg: between Didinium (predator) & Paramecium (prey)
Interactions between biotic and abiotic components
Biotic factors
Abiotic factors
ORGANISMS
Human activities Competitors
Predators Symbionts (mutualism,
Commensalism, Parasites)
Solar energy
Relative humidity Atmospheric gases Temperature
Photoperiod Wind
Topography Fire
Soil texture Water
Minerals
Organic matter Soil pH
Wave action Salinity
Food Chain, Food Web and Trophic levels.
Food chain a series of groups of organisms (trophic levels) in which, there is repeated eating and eaten by so as to transfer food energy.
Base of the food chain is always formed by a plant (producer / autotroph), which is grazed on by a herbivore, which is predated over by a
carnivore, which may be eaten by another carnivore.
Trophic level the level of an organism in a food chain.
A food chain only follows just one path as animals find food.
Characteristic of Food Chain
repeated eating in which each group eats the
smaller one and is eaten by the larger one a nutritive interaction
unidirectional flow of energy from sun to
producers and then to a series of consumers of various types.
80 to 90% of potential energy is lost as heat at each transfer
4 or 5 trophic levels usually.
omnivores occupy more than one trophic level and, some organisms occupy different trophic positions in different food chains.
Food Web
Detrital Food Web Grazing
Food Web
- primary source of energy
- solar radiations - producers (green plants)
synthesize their plant
biomass by the process of photosynthesis.
- producers form the first trophic level, follow by herbivores.
- primary source of energy - dead organic matter
called „detritus‟ (fallen leaves,
plant or dead animal bodies).
- primary consumers are
'detritivores' e.g. protozoans,
bacteria, fungi.
- detritivores are inturn eaten by secondary consumers e.g.
insect larvae, and nematodes.
In nature, detritus food chains are indispensable as the dead organic matter of grazing food chain is acted upon by the
detritivores to recycle the inorganic elements into the ecosystem.
Grazing Food Chain:
Detrital Food Chain:
Ecological Pyramids
A geographical representation of an ecological parameter
number of individuals
amount of biomass
amount of energy
• present in various trophic levels of a food chain
• producer forming the base and top carnivores at the tip
Ecological pyramids
Pyramid of Numbers
Pyramid of Biomass
Pyramid of Energy
As you go up a food chain the size of the individual increases and the number of individual decreases.
Pyramid of Number
Number of individuals per unit area of various trophic levels.
Producers forming the base and carnivores the tip.
Width of the bars represent the numbers.
Shape of the pyramid of numbers vary
Pyramids of
number - simple easy method of
giving an overview;
good at comparing changes in
population numbers with time or season.
Disadvantage of
pyramids of number:
All organisms are included regardless of their size,
therefore a system say based on an oak tree would be inverted.
Pyramids of Biomass
Biomass present per unit area of different trophic levels.
Producers at the base and carnivores at the tip.
Biomass total amount of living or organic matter in an ecosystem at any time.
“Missing mass” (not eaten by consumers) – becomes detritus and is decomposed.
Disadvantage of
pyramids of biomass:
Only uses samples from populations, so it is
impossible to measure biomass exactly; and also the time of the year that biomass is
measured affects the result.
Pyramids of Energy
The amount of energy trapped per unit
time and area in different trophic level of a food chain.
Always upright.
Because at each transfer about 80 - 90%
of the energy available at lower trophic level is used up to overcome its entropy and to perform metabolic activities.
Only 10% of the energy is available to next trophic level.
Energy Flow in Ecosystem
Energy flow is not cyclic but a one way flow.
Energy input for an ecosystem is the sun.
Organism
Food chain Detritus Heat
100 % solar radiation
50 % reflected or absorbed
50 % reach earth surface
42 % lost as heat
8 % reach green plants
1-2 % for photosynthesis
6-7 % lost as heat
Lost in respiration NPP
GPP
During photosynthesis, light energy will be changed into chemical energy (GPP) in
the molecules of complex food e.g.
carbohydrate, fats, protein.
Part of the product of photosynthesis is used in plant respiration.
The rest of the photosynthetic products kept in plants and shown as growth
(NPP).
Net primary productivity (NPP) supplies the energy that can be used by organisms in the next trophic level.
Not all the energy able to be absorbed by primary consumer.
Some will be excreted, some lost to decomposers.
Those energy absorb by primary
consumer is used for respiration and growth.
The biomass produced is the secondary production.
The process of energy transfer will
continues until all the energy loss as heat.
Solar energy from the Sun is trapped by primary producers and converted into chemical energy. The chemical energy is transferred in the food web and finally as heat radiated into space.
Primary productivity - the amount of biomass produced through photosynthesis per unit area and time by plants.
Gross primary production (GPP) – the amount of light energy that is converted to chemical energy by producers through photosynthesis per unit of time.
Net primary production (NPP) – net gain in energy in producers after some energy is used for
respiration and is available to be transferred to organisms at next trophic level.
Secondary production - the net quantity of energy transferred and stored in the somatic and
reproductive tissues of heterotrophs over a period of time.
NPP = GPP – RS (energy used by autotrophs respiration)
2.3 BIOGEOCHEMICAL CYCLES
• Organisms require essential chemical elements (eg: C, H, O, N, P, S ) to build organic matter
• The chemical elements cycle within the biosphere
• Biogeochemical cycles describe the cycling &
changing of chemical elements in ecosystems that involve biotic & abiotic geological components
(Relation between biological and geological component and chemical changes)
Biogeochemical cycles are cycling of matter from the abiotic environment to organism and then back to the abiotic environment
BIOGEOCHEMICAL CYCLES
…BIOGEOCHEMICAL CYCLES
Two components of a biogeochemical cycle:
1. Reservoir pool
- those parts of the cycle where the chemical is held in large quantities for long periods of time
2. Exchange pool
- the chemical is held for only a short time.
• Reservoir pools: atmosphere ( CO2 ), fossil fuels, soils, sediments, limestone etc
• Atmospheric CO2 is usually taken by plants for photosynthesis ( to make organic materials )
• Animals assimilate organic carbon by eating the plants or other animals
• C is returned to atmosphere ( as CO2 ) through cellular respiration by organisms
• Dead organic matter may form fossils & burning of fossil fuels also releases CO2
CARBON CYCLE
Carbon cycle
Sources of Carbon:
- Major source of carbon CO2 (Atmosphere & ocean water).
- Carbonates of earth's crust derived from rocks, which by chemical reactions give rise to carbon dioxide.
- Fossil fuels like peat, coal and petroleum products.
- Oceans, where carbon remains stored as carbonates in the form of limestone and marble rocks.
Carbon Dioxide Utilisation
- Photosynthesis carbon fixed by the producers enters the food chain and is passed to herbivores, carnivores and decomposers.
Carbon Dioxide Production
- Respiration of producers and consumers
- Decomposition of organic wastes and dead bodies by the action of bacteria and fungi on decay.
- Burning of wood and fossil fuels
- Volcanic eruptions and weathering of carbonate rocks by the action of acids
NITROGEN CYCLE
Living organisms cannot pickup elemental gaseous nitrogen directly from the atmosphere (except nitrogen fixing bacteria). It has to be converted into nitrates to be utilized by plants.
Nitrogen Fixation
- Atmospheric nitrogen fixation: thunderstorms and lightning convert atmospheric gaseous nitrogen to oxides of nitrogen. They get dissolved in water forming nitrous acid and nitric acid, which inturn combine with other salts to produce nitrates.
Nitrogen (g) Nitrogen oxide nitrous & nitric acid nitrates
- Industrial production of fertilizers (Haber's process)
- Biological nitrogen fixation: transformation of gaseous nitrogen into nitrates by living organisms (bacteria). E.g.
rhizobium species in the root nodules of legumes;
Nostoc and Anabaena (cyanobacetria) in the coralloid roots of cycas; Actinomycetes in the root nodules of Alnus.
Nitrogen fixing Rhizobium Nitrogen (g)
Nitrates
Nitrogen fixing bacteria
Ammonification
- Decomposition of protein of dead plants and animals, and nitrogenous wastes like urea, uric acid, etc to ammonia, in the presence of ammonifying bacteria or putrifying bacteria. E.g.
Bascillus vulgaris and Bascillus mycoides.
Protein Amino acids Ammonia Ammonifying bacteria
Nitrification
- Oxidation of ammonia to nitrates through nitrites in the presence of nitrifying bacteria, which are also chemosynthetic autotrophs.
- Ammonia is converted into nitrites by Nitrosomonas and Nitrococcus bacteria.
- Nitrites are then converted into nitrates by Nitrobacter and Nitrocystis, which are now available for plant absorption.
Ammonia
Nitrosomonas
Nitrites Nitrates
Denitrification
- Ammonium compounds, nitrates and nitrites are reduced to molecular nitrogen in the presence of denitrifying bacteria such as Micrococcus denitrificans, Pseudomonas aeruginosa, and etc.
- Denitrification reduces soil fertility and is stimulated by water logging, poor drainage, lack of aeration and accumulation of organic matter in the soil.
Ammonium Nitrates
Nitrites
Nitrogen (g)
2.4 Conservation & management
SUSTAINABLE DEVELOPMENT
- Balancing the needs of humans with the
need to protect environment to ensure
the needs can be met not only in the
present but in the future as well.
SUSTAINABLE DEVELOPMENT
• Development may continue but must be planned / managed to minimise environmental damage
• E.g.:
i. sustainable forestry ii. sustainable agriculture iii. sustainable fisheries
Sustainable forestry
Reforestation- replanting native sp
Establish forest reserves- to maintain ecosystem
Retention of seed tree- to maintain high
biodiversity
Sustainable agriculture
Biological control- crop rotation
Row planting- plant different types of plants in different alternate rows
Contour farming and terracing farming
Sustainable fishery
Open and close seasons in fishing activities: eg: capture fishery
Capture fishery: amount of fish that can be
taken from a fishery on a continual basis
without causing it to become overfished or
reducing the stock biomass.
• the maximum
population growth that can possibly occur under ideal conditions
2.5 Population growth
BIOTIC POTENTIAL ( r )
Growth at biotic potential
Gives the maximum rate for population growth when
resources are plentiful
Resources include water, food and
spaces
Growth at biotic potential
BIOTIC POTENTIAL ( r )
ENVIRONMENTAL RESISTANCE
• Environmental conditions that prevent populations from achieving their biotic potential
• E.g. of environmental resistance:
– Limiting resources (food, light, shelter) – Accumulating toxic waste
– Predation
– Diseases
ENVIRONMENTAL RESISTANCE
• Growth rate may become zero
• Described by an S-shaped growth
curve
CARRYING CAPACITY
• „The maximum population size that can be supported by the available resources
(energy, shelters, soil nutrients, water and suitable nesting sites)
• Symbolized as K
CARRYING CAPACITY
• Carrying capacity is achieved when
population growth slows & maintains at a nearly steady level
• Described by the stable Stationary phase of
the S-shaped growth curve
NATALITY & MORTALITY
• Natality
–
‘birth rate’
– the number of offspring produced during a certain amount of time
• Mortality
– ‘death rate’
– the number of individuals dying during a
certain amount of time
NATALITY & MORTALITY
• If natality > mortality
• population size increases
• If mortality > natality,
• population size decreases
• If natality = mortality,
• population is stable
Population Growth Curves
Two patterns of population growth:
- Exponential growth
- Logistic growth / S-shaped (sigmoid) growth pattern
Population growth
0 200 400 600 800 1000 1200
0 2 4 6 8 10 12
time
numbers
population
Exponential Growth
• J-shaped curve
• Population increase in size
• Numbers of births > deaths
Logistic Growth
Population growth
0 5 10 15 2 0 2 5 3 0
0 5 10 15
tim e
population size
• S-shaped
/sigmoid curve
• Due to
environmental resistance
• 3 phases: lag, rapid growth, stable.
