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ECOLOGY chapter 50
Ecology: Study of interactions between
organisms and their environment.
Environment includes both abiotic (nonliving) and biotic (living) components.
Abiotic: light, water, nutrients, chemicals,
rocks, weather, etc.
Biotic: organisms.
Organisms compete with, parasitize, eat or
are eaten by and change the environment for
other organisms.
Ecology explores a wide range of questions
about what factors control the distribution,
abundance and behavior of organisms.
For example, Red Kangaroos occur
primarily in the Australian interior in
semiarid regions.
Distribution of Kangaroos suggests an abiotic
factor (precipitation) influences it, but perhaps
populations also influenced indirectly by biotic
factors such as competitors, predators, food
availability and parasites.
Ecologists have to consider multiple factors to
explain patterns of abundance and distribution.
Ecology has many subfields of study ranging from
ecology of individual organisms to dynamics of
landscapes
Organismal Ecology
Population Ecology
Community Ecology
Ecosystem Ecology
Landscape Ecology
We will explore these sequentially
Distribution of species
Biogeography: study of the broad patterns
of distribution of organisms across the
globe.
Patterns strongly influenced by historical
factors such as continental drift (see chapter
26) and barriers including mountain ranges
and seas.
For example, Australia populated by marsupial
mammals (e.g. kangaroos, wombats, koalas)
because placental mammals did not colonize it
before it separated from other landmasses.
Tapirs found only in southeast Asia and South
America. Ancestral populations separated when
land masses diverged.
Role of dispersal in distribution
Ability to cross barriers affects distribution.
Thus, species of birds often more widely
distributed than mammals.
However, inability to reach an area not only
factor that limits distribution. Ability to
survive in new area is critical.
To survive and thrive species must be able
to cope with both biotic and abiotic factors.
Biotic factors
The presence of competitors or predators
may limit an organisms ability to establish
itself.
For example, algae are eaten by sea urchins
and limpets, which limits the ability of
seaweeds to establish themselves on rocks
Biotic factors
Conversely, absence of predators and competitors
has allowed many organisms introduced into new
areas to increase so much they become pests.
E.g. Japanese beetles (from Asia), zebra mussels
and purple loosestrife from Europe) (Melaleuca
(Eucalyptus trees from Australia) and many other
invasive species have spread widely in the U.S.
Abiotic factors
The major factor affecting distribution of
terrestrial organisms is climate, which
incorporates temperature, sunlight, wind
and precipitation.
Abiotic factors
Climate is determined by global factors
such as inputs of solar energy and the
movement of the earth through space.
Study discussion of climate patterns pages
1088 and 1089
Climate
Local factors such as the presence of mountains
and large bodies of water also affect climate.
Mountains force up moist air moving across them.
As the air cools the water condenses and falls as
rain. The result is that one side of the mountain
range is wet and the other side is drier (and
perhaps a desert [e.g. Mojave and Gobi Deserts.])
Climate
Large bodies of water moderate climate.
Land heats faster than water and warm air
rises.
Cooler air over water moves in and replaces
the warm air.
The warm air that was over land cools at
high altitude and sinks over water.
Results is steady flow of cool air over land.
Terrestrial Biomes
Biomes are major types of ecosystems that
cover large areas of the earth and are
classified by their dominant vegetation
types.
(an ecosystem is the community of
organisms in an area and their physical
environment)
Each biome also is populated by a diverse
array of animals, fungi and microorganisms
adapted to that environment.
Major terrestrial biomes include
Tropical forest
Desert
Temperate Grassland
Savanna
Temperate broadleaf forest
Coniferous forest (Taiga)
Tundra
(see descriptions pages 1100-1104)
Savannah
Terrestrial biomes
Terrestrial biomes often vertically
stratified. Layers defined by different size
plants
(e.g. in forests there is an upper canopy of
tall trees, low tree layer, shrub layer, ground
layer of herbaceous plants, litter layer and
root zone).
Stratification provides multiple different
habitats for animals which occupy
specialized feeding niches.
Convergent evolution
Actual species in a biome differ from one
area to another but they possess similar
adaptations.
This is convergent evolution (development
of same evolutionary solutions to ecological
problems)
Convergent evolution
For example vegetation in all deserts
worldwide characterized by extensive root
systems, long-term water storage capability,
thick waxy coverings to reduce water loss,
and extremely small (if any) leaves
Biomes often maintained by disturbance.
Wildfires are an essential factor in
maintaining many biomes (e.g. grasslands,
savannahs, some coniferous forests). Fire
favors trees such as longleaf pine whose
bark resists fire and grasses, which recover
quickly after burning.
Aquatic biomes
Aquatic biomes less influenced by climate
than terrestrial biomes
Why?
Aquatic biomes
Water is more thermally stable.
It takes a lot of heat to change the
temperature of a body of water.
Major aquatic biomes
Lakes
Rivers
Estuaries
Intertidal zone
Marine pelagic zone
Coral reefs
Marine benthic zone (benthic zone is
sea/lakefloor)
See pages 1094-1097.
Aquatic biomes often stratified by light and
temperature.
Light intensity decreases with depth. Upper
(photic) zone supports photosynthesis.
In ocean photic zone narrow but contains
most organisms.
Aphotic zone sparsely populated.
Benthic zone (bottom) organisms often
depend on rain of dead organic matter
(detritus) from above.
Thermal stratification of lakes
In temperate areas lakes are thermally stratified in
summer and winter.
Water densest at 4ºC so water at this temperature
sinks through colder or warmer water.
Thus, in spring and fall all water in lake mixes
which redistributes nutrients throughout the lake.