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Basic Ecological Concepts
What is ecology?
A branch of biology that involves…
“The study of the
relationships between
organisms and their
environment”
Biotic factors: living part of the ecosystem, all
the organisms living there
Abiotic factors: non-living part of the
ecosystem, all the physical and chemical
factors like temperature, pH, light, etc.
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Population Ecology
Deals with populations, which are groups
of individuals of the same species living in
the same area
Concentrates mainly on factors that affect
a population’s
Size
Population density
Growth
Structure
Examples of population ecology
How to develop sustainable fisheries
Increase populations of organisms we
wish to harvest
How to control pests and pathogens
Save populations of organisms threatened
with extinction
Human population growth
Review: How populations grow: Modes of reproduction
Asexual
Gen.1
Gen.2
Only 1 parent
Individual can
grow isolated and
still reproduce
Gen.3
Sexual
Gen.4
No genetic variability
New individuals
are clones of the
parent
2 parents needed
Asexual
Genetic variability
ensured by meiosis &
sexual reproduction
Good mutations are
passed more efficiently
in clones
New individuals
are not equal to
parents
No energy is used in
finding a mate… boring!
Useful when the
individual is well adapted
to the environment
Sexual
Less offspring in the
same time
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Example: Dinoflagellates
Occasionally they undergo dramatic population explosions by asexual reproduction
“Blooms”
Some of them related to “red tides”
But the population does not grow
forever… why?
Many factors affect the way
populations growth
Red tide
How populations grow: Reproductive capacity or biotic potential
Theoretical maximum rate of reproduction
Generally, several times larger than the number of offspring needed to maintain
the population
Population size limitations
Carrying capacity
Maximum number of individuals that the
Environmental resistance
environment can sustain in a given area
Availability of raw materials and energy
Production and disposal of waste
Interaction with other organisms
Diseases
Predators
Limited space
Population size
Limiting factors
Interspecific competition
Intraspecific competition
Time
3
The population growth curve
Describes the change in population
“IN” factors are in a sort of
equilibrium with “OUT” factors
size over time considering both
reproductive capacity and
environmental pressure
“IN” factors
always exceeds
“OUT”
IN OUT
•Natality: N/1000
•Mortality: N/1000
•Emigration
•Immigration
•Predation
•Competition
•Parasitism
•Diseases
New environment:
Natality and mortality are low
Plenty of resources
Community Ecology
Is about interactions between two different organisms
1) Harmful / Beneficial
PREDATION: One animal is food for the other.
The one that is food is killed
chameleon
cheetah
predators
preys
PARASITISM: One animal is food for the other!
The one that is food is alive while serving as food
Lamprey (parasite)
tapeworms
The host is in general
Fish (host)
weakened and more
susceptible to predation
or diseases
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2) Beneficial / The other is not affected
COMMENSALISM:
e.g. epiphytes, plants
that use trees as support to
reach the sunlight
e.g. remora living
attached to sharks
3) Beneficial / Beneficial
MUTUALISM:
e.g. bacteria that eat cellulose in the guts of
herbivores
butterflies eating nectar from flowers and
transporting pollen from one flower to
another
e.g. lichens: algae + fungi
4) Harmful / Harmful
COMPETITION
Interspecific: between
individuals of different species
Intraspecific: between
individuals of the same species
Both individuals are harmed to some extent
Occurs when both organisms need a vital
vultures
resource that is in short supply
More similar the requirements more
intense the competition is
Sp 1
Extinction
Evolution
Migration
Number of individuals
Competitive exclusion principle
Sp 1
Niche variable (e.g.food)
Sp 2
Sp 2
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Ecosystem Ecology
Ecosystem ecology:
Deals with energy flow in the system,
A community’s trophic structure
(feeding relationships) determines the
passage of energy and nutrients from plants
and other photosynthetic organisms to
herbivores, and then to predators
species
populations
communities
ecosystem
Environment: anything that
surrounds and affects an organism
during its lifetime
(Biotic and abiotic factors)
Living:
Other organisms
Nonliving:
•Temperature
•WaterRainfall
•Sunlight
Food chain: Linear representation or sequence of organisms feeding on one another
Trophic level: each stage or step in the food chain
4th consumers = carnivores
3rd consumers = carnivores
Omnivores
organisms like
humans do not fit
in a linear
representation of a
food chain
eat both animals
and plants
2nd consumers = carnivores
1st consumers = herbivores
Neither do
Decomposers
organisms like
fungi and bacteria
eventually return
nutrients to the soil
producers = autotrophs
(photosynthetic organisms:
plants, algae, cyanobacteria)
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Community interactions
Several food chains may exist
at each community
The same organisms can
be part of several food
chains
Food web
several food chains
interwoven
This is what really happens
in nature
Communities that make
food webs are stable and
will naturally fluctuate only
in response to changes in
the environment
Energy organization in ecosystems
3rd
Why the pyramid structure?
The broad energetic base is
necessary to support the upper
levels
Energy is “lost” from one level
to another as heat: approx. 90%
Capture and processing of food
more energy is “lost”
2nd
1st
Developed
countries:
3rd level present
Undeveloped countries:
Mostly 1st and 2nd level present
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The microbial loop
Explains how micro-organisms integrate into the classical food chain
The basic idea of a food chain is that minerals flow upwards from primary producers
through increasingly large organisms (herbivores first, then a chain of predators)
Without microbes
The energy in
the DOM
would go
mostly unused
50% of the
primary
production
depends on
the microbial
loops
Bacteria were originally assumed to have a decomposing role that helped to partially
recover and recycle minerals from material that was lost to the chain
Including microbes greatly increases the complexity of food webs
Bacteria, picopytoplankton, protozoans
Types of marine communities
Plant-like (photosynthetic)
Plankton
Drifting
organisms
Phytoplankton
Animal or animal-like (ingestive)
Zooplankton
Nekton
Active
swimming
organisms
Mostly fish
Mammals
Reptiles
Mollusks
Benthos
Organisms living in the ocean floor
Demersal
Living in close
relation with the
bottom and
depending on it.
Example: hakes,
cods, lobsters,
shrimps are
demersal
resources
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Types of marine ecosystems
Estuaries
Places were freshwater
and marine water meet
Coral reefs
Continental shelf
The “rain forests” of the
oceans
(coastal, above continental shelf)
Pelagic
Open waters
Epipelagic
(oceanic, above
deep sea
waters)
Intertidal
Area on the
shore which is
between the
low tide and
high tide
marks
Deep Sea & Mesopelagic
Mesopelagic: Depth 200-1000m
Deep sea: Depth more than 1000m
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