ENV200H1 Chapter Notes - Chapter 4: Terrestrial Ecosystem, Ecosystem Ecology, Marine Ecosystem
Unit 4: Ecosystem
Ecology is the scientific study of relationships in the natural world
It includes relationships between organisms and their physical environments
between organisms of the same species (population ecology);
between organisms of different species (community ecology);
and between organisms and the fluxes of matter and energy through biological systems
Applied ecology uses information about these relationships to address issues such as
developing effective vaccination strategies, managing fisheries without over-harvesting,
designing land and marine conservation reserves for threatened species, and modeling
how natural ecosystems may respond to global climate change.
Section 2: Major Terrestrial and Aquatic Biomes
Geography has a profound impact on ecosystems because global circulation patterns
and climate zones set basic physical conditions for the organisms that inhabit a given
The most important factors are temperature ranges, moisture availability, light, and
Earth is divided into distinct climate zones that are created by global circulation patterns
The tropics are the warmest, wettest regions of the globe
subtropical high-pressure zones create dry zones at about 30° latitude north and south.
Temperatures and precipitation are lowest at the poles
These conditions create biomes—broad geographic zones whose plants and animals are
adapted to different climate patterns.
Since temperature and precipitation vary by latitude, Earth's major terrestrial biomes are
broad zones that stretch around the globe
Each biome contains many ecosystems (smaller communities) made up of organisms
adapted for life in their specific settings.
Another way to visualize major land biomes is to compare them based on their average
temperature ranges and rainfall levels
Land biomes are typically named for their characteristic types of vegetation, which in turn
influence what kinds of animals will live there
Soil characteristics also vary
Acidic, low in
Diverse (up to 100
-30 to 30°C
Fertile, high in
3-4 tree species/km2
40-100 cm/year, mostly
Thin, low in nutrients,
Aquatic biomes (marine and freshwater) cover three-quarters of the Earth's surface and
include rivers, lakes, coral reefs, estuaries, and open ocean
Ocean’s surface waters are warmest and contain most of the available light, but depend
on mixing to bring up nutrients from deeper levels
Marine and freshwater biomes change daily or seasonally.
During the winter months lakes and ponds can freeze over, and wetlands that are
covered with water in late winter and spring can dry out during the summer months.
There are important differences between marine and freshwater biomes.
freshwater habitats vary in size from small ponds to lakes
As a result, organisms that live in isolated and temporary freshwater environments must
be adapted to a wide range of conditions and able to disperse between habitats when
their conditions change or disappear.
Since biomes represent consistent sets of conditions for life, they will support similar
kinds of organisms wherever they exist, although the species in the communities in
different places may not be taxonomically related.
Species are not uniformly spread among Earth's biomes.
Tropical areas generally have more plant and animal biodiversity than high latitudes,
measured in species richness (the total number of species present)
This pattern, known as the latitudinal biodiversity gradient, exists in marine, freshwater,
and terrestrial ecosystems in both hemispheres
Why is biodiversity distributed in this way?
Higher productivity in the tropics allows for more species
The tropics were not severely affected by glaciation and thus have had more time for species
to develop and adapt
Environments are more stable and predictable in the tropics, with fairly constant
temperatures and rainfall levels year-round
More predators and pathogens limit competition in the tropics, which allows more species to
Disturbances occur in the tropics at frequencies that promote high successional diversity
both tropical ecosystems on land and deep sea marine ecosystems—which are subject
to much less physical fluctuation than other marine ecosystems => have high species
Predators that seek out specific target species may also play a role in maintaining
species richness in the tropics
Section 3: Energy Flow Through Ecosystems
Ecosystems maintain themselves by cycling energy and nutrients obtained from external
At the first trophic level, primary producers (plants, algae, and some bacteria) use solar
energy to produce organic plant material through photosynthesis
Herbivores—animals that feed solely on plants—make up the second trophic level.
Predators that eat herbivores comprise the third trophic level
if larger predators are present, they represent still higher trophic levels.
Organisms that feed at several trophic levels are classified at the highest of the trophic
levels at which they feed
Decomposers, which include bacteria, fungi, molds, worms, and insects, break down
wastes and dead organisms and return nutrients to the soil.
On average about 10 percent of net energy production at one trophic level is passed on
to the next level.
Processes that reduce the energy transferred between trophic levels include respiration,
growth and reproduction, defecation, and nonpredatory death (organisms that die but are