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Ecology
Part 2
• Ecology is the study of the
relationship of organisms to their
environment. Ecosystems are
physically distinct, selfsupporting systems of interacting
organisms & their
environment. Ecosystems are
composed of communities of
organisms & the abiotic, or
nonliving, factors in the
environment, such as sunlight,
soil, & water.
• Within an ecosystem, an organism occupies a
physical region called its habitat. It also has a
specific niche, or way of life.
• Abiotic factors play an
important role in
determining where
organisms live. Organisms
depend upon a continuous
supply of recycled
nutrients, such as nitrogen
& carbon. Organisms can
be carnivores, herbivores,
or omnivores.
• All organisms occupy a
trophic level, & all are
members of a specific food
chain. Permanent, close
relationships between
different species are called
symbiosis. Organisms
respond to regularly
occurring phenomena in
patterns called Circadian
Rhythms.
IMPORTANT TERMS for
ECOSYSTEMS
• Biotic factors – living components
Abiotic factors – nonliving components
Communities – several populations interacting
• Populations- group of individuals of the same
species
Habitats – where an organism lives
Niches- the specific role of the organism in its
habitat
BIOTIC RELATIONSHIPS
• Competition –
2 or more organisms striving for the same
resources
• Predators – captures & feeds on other (prey)
• Symbiosis –relationship in which 2 organisms live
closely together
1)Mutualism – both benefit
2)Commensalism – one benefits, the
other is neither harmed nor helped
3)Parasitism –
one benefits, the other is harmed
• Circadian Rhythm – cycle
of sleep & wakefulness
• Diurnal – day-active
• Nocturnal – night-active
• Hibernation – dormant in
the winter
Estivation – dormant in
the summer
Community Ecology
• Limiting factor – any abiotic factor that
restricts the numbers, reproduction, or
distribution of organisms – ex. = water, light,
phosphorus
• Range of tolerance – optimal range of
conditions for organisms – ex. = temperature,
sunlight, pH
SUCCESSION & BIOMES
• The biological communities of the world are
constantly changing. Many of these changes
involve ecological succession, or the
replacement of 1 group of species by another
group that is more adapted to life in a given
area.
IMPORTANT TERMS
for ECOLOGICAL SUCCESSION
• Seral community – intermediate community – prevents
its own regeneration
Climax Community –
stable, permanent community
• Primary succession –
life has not been there before (bare rock)
• Pioneer species –
1st organism to an area (usually lichens)
• Eutrophication –
adding nutrients to an ecosystem
• Secondary succession –
changes in a community where life has been before (old
field succession – soil is usually intact)
Two types of ecological succession
• Primary succession takes place where no
community existed before. Secondary
succession takes place on land that has
previously supported communities. During
succession land is occupied by a number of
seral communities before a climax community
finally becomes established.
• Large areas of similar
climate & vegetation are
called biomes. Tundra,
boreal forests, deciduous
forests, grasslands, tropical
rain forests, & deserts are
the major terrestrial
biomes. Two biomes make
up the aquatic world: the
marine &
freshwater. Estuaries are
special aquatic
communities.
Effects of latitude & climate
• Latitude & climate are the 2 primary factors
that determine the type of ecosystem present.
Winds, ocean currents, & the greenhouse
effect can affect the type of climate present in
an area.
TERRESTRIAL BIOMES
Biome –
area of similar climate, & vegetation
Tundra
Boreal (Coniferous) Forest or Taiga
Temperate Deciduous Forest
Chaparral
Temperate Grasslands
Savanna
Desert
Tropical Dry Forest
Tropical Rain Forest
AQUATIC ORGANISMS
Plankton: floaters - Phytoplankton
(plant), Zooplankton (animal),
Ultraplankton/nanoplankton
(photosynthetic bacteria)
Nekton: swimmers - fish, turtles,
whales
Benthos: bottom dwellers (octopus,
oysters)
Decomposers: breakdown organic
compounds (mostly bacteria)
Freshwater Zones
Littoral zone (near shore, shallow, with rooted
plants - lots of biodiversity)
Limnetic zone (open, offshore area, sunlit - main
p.s. portion of lake - lots of O2)
Profundal zone (deep, open water, too dark for
photosynthesis - low O2)
Benthic zone (bottom of lake, nourished by
dead matter - lots of decomposers).
Oligotrophic –
little nutrients in the water
Eutrophic – lots of nutrients in the water
Estuary – where rivers meet the oceans
Marine Zones
Intertidal Zone – between high & low tide
Coastal zone (from shore to continental shelf contains 90% of all oceanic species)
Open sea a) euphotic zone - low nutrients, high p.s., high
O2
b) bathyal zone - no p.s. - lots of migration c)
abyssal zone - dark, lots of nutrients, low O2
Open Sea zone – between continents
POPULATIONS IN ECOSYSTEMS
Populations are composed of individuals of
the same species living in the same area. The
maximum rate of reproduction for a
population is its biotic potential. A population
allowed to reach its biotic potential would
soon cover the earth. The growth of
populations is regulated by the environment’s
limiting factors such as rainfall, light, food,
space.
When a population establishes itself in a new
area, it grows slowly at first. The population
then enters an exponential phase of growth in
which its number doubles at decreasing
intervals. Exponential growth ceases when
the carrying capacity of the environment is
reached. The carrying capacity is determined
by limiting factors that restrict population
growth. Some limiting factors depend on the
population’s density; some are independent of
density.
Changes in populations are calculated by
subtracting the number of deaths &
emigrants from the number of births &
immigrants. Population crashes & explosions
are dramatic changes in the size of
populations.
Growth = (Births + immigrants) – (Deaths + emigrants)
The human population is currently in its
exponential phase of growth. The number of
humans now doubles about every 35
years. Providing for this growing population is
one of the major problems facing the modern
world.
IMPORTANT TERMS
for POPULATION GROWTH
Biotic potential – maximum growth rate
Lag phase – period of slow growth
Exponential Growth – the number of
individuals repeatedly doubles
Exponential Phase – period during which the
population doubles
J-Curve – combination of exponential growth
& lag phases
Stabilization Phase – population size levels off
Carrying Capacity – maximum number of
individuals the environment can support
S-Curve – combination of lag, exponential, &
stabilizing phases
Limiting factors –environmental elements
that stabilize population size & keeps species
from reaching their biotic potential
Population Density – number of individuals in
a given area
Density-Independent Factors –
elements that affect population size that are
not affected by the number of individuals in
the population (tornadoes, floods, hurricanes)
Density –Dependent Factors –
elements that affect population size that ARE
affected by the number of individuals in the
population (space, food, diseases)
Saw-Tooth Curve –
pattern formed by periodic growth & decline
in a population
Birth Rate –number of births per year
Death Rate –
number of deaths per year
Growth Rate – rate at which population
changes
What are age-structure pyramids?
 Diagram that
shows the
percentage of the
population at
each age level in a
population
Demographic transition – as countries become
industrialized, they have a decline in death
rates followed by declines in birth rates