Chapter 4
Ecosystems & Communities
4.1 Climate
Weather and Climate
Weather - the condition of Earth’s
atmosphere at a particular time and place.
Climate - the average condition of
temperature and precipitation in a region
over long periods.
– Climate can vary over short distances.
– These variations produce microclimates.
Microclimates
In the Northern
Hemisphere, south
facing sides of trees and
buildings receive more
sunlight, and are often
warmer and drier, than
north-facing sides.
Therefore - moss grows on
the north side of trees.
These differences can be
very important to many
organisms.
Microclimates
Lake Effect Snows
Climates of New Jersey
Climate is affected by solar energy trapped in the
biosphere, by latitude, and by the transport of heat by
winds and ocean currents.
Factors That Affect Climate
Climate is affected by solar energy
trapped in the biosphere
(Greenhouse Effect)
Factors That Affect Climate
Temperature on Earth stays within a range suitable for
life due to the greenhouse effect. The greenhouse
effect is the trapping of heat by gases in the
atmosphere.
Factors That Affect Climate
Latitude and Solar Energy
Earth’s curvature causes
different latitudes to receive
less or more intense solar
energy. The unequal
distribution of the sun’s heat
on Earth’s surface results in
three main climate zones:
polar, temperate, and tropical.
Factors That Affect Climate
Heat Transport in the Biosphere
Unequal heating of Earth’s
surface also causes winds and
ocean currents.
Winds and currents move heat
and moisture through the
biosphere.
Factors That Affect Climate
Heat Transport in the Biosphere
Air that is heated by warm
areas of Earth’s surface—
such as near the equator—
rises, expands, and
spreads north and south,
losing heat along the way.
As the warm air cools, it
sinks.
Factors That Affect Climate
Heat Transport in the Biosphere
In cooler regions, near the
poles, chilled air sinks
toward Earth’s surface,
pushing air at the surface
outward.
This air warms as it travels
over the surface and rises.
Factors That Affect Climate
Heat Transport in the Biosphere
These upward and downward movements
of air create winds.
Winds transport heat from regions of
rising warmer air to regions of sinking
cooler air.
Earth’s rotation causes winds to
blow generally from west to east over the
temperate zones and from east to west
over the tropics and the poles.
Factors That Affect Climate
Heat Transport in the Biosphere
Similar patterns of heating and cooling occur in the oceans.
Surface water is pushed by winds.
Ocean currents, like air currents, transport enormous amounts of
heat.
Factors That Affect Climate
4.2 Niches and Community Interactions
Every species has its own tolerance, or a
range of conditions under which it can grow
and reproduce.
A species’ tolerance determines its habitat,
the place where it lives.
Tolerance
When an environmental condition, such as temperature, extends
in either direction beyond an organism’s optimum range, the
organism experiences stress.
The organism must expend more energy to maintain homeostasis,
and so has less energy left for growth and reproduction.
Niche
A niche consists of all the physical and biological
conditions in which a species lives and the way the
species obtains what it needs to survive and
reproduce.
An organism’s niche must contain all of the resources an
organism needs to survive.
A resource is any necessity of life.
– For plants, resources can include sunlight, water,
and soil nutrients.
– For animals, resources can include nesting space,
shelter, types of food, and places to feed.
Physical Aspects of the Niche
– Part of an organism’s
niche involves the
abiotic factors it
requires for survival.
– Most amphibians, for
example, lose and
absorb water through
their skin, so they
must live in moist
places.
– If an area is too hot
and dry, or too cold for
too long, most
amphibians cannot
survive.
Biological Aspects of the Niche
– Biological aspects of an
organism’s niche involve the
biotic factors it requires for
survival, such as when and
how it reproduces, the food it
eats, and the way in which it
obtains that food.
–
Birds on Christmas Island in
the Indian Ocean, for
example, all live in the same
habitat but they prey on fish
of different sizes and feed in
different places.
–
Thus, each species
occupies a distinct niche.
Competition
Competition occurs when organisms try to use
the same limited resources.
• Direct competition between species often
results in one species dying out.
• This is the basis of the competitive exclusion
principle.
– This principle states that no two species can
occupy exactly the same niche in exactly the same
habitat at the same time.
Competition
Direct competition between different species
almost always produces a winner and a loser—
and the losing species dies out.
Competition helps to determine the number
and type of species in a community.
Competition - Dividing Resources
Instead of competing for
similar resources,
species usually divide
them.
For example,
– the three species of
North American
warblers shown all
live in the same trees
and feed on insects.
– But one species feeds
on high branches;
another feeds on low
branches, and
another feeds in the
middle.
Predation, Herbivory, and Keystone Species
Predator-prey and herbivore-plant interactions
help shape communities.
Predation occurs when one organism (the
predator) captures and eats another (the
prey).
Predator-Prey Relationships
Predators can affect the
size of prey populations
in a community and
determine the places
prey can live and feed.
Birds of prey can play
an important role in
regulating the
population sizes of
mice, voles, and other
small mammals
Predator-Prey Relationships
This graph shows an idealized computer model of
changes in predator and prey populations over
time.
Herbivore-Plant Relationships
An interaction in which one animal
(the herbivore) feeds on producers
(such as plants) is called herbivory.
Herbivores can affect both the size
and distribution of plant populations
in a community and determine the
places that certain plants can survive
and grow.
For example, very dense populations
of white-tailed deer are eliminating
their favorite food plants from many
places across the United States.
Keystone Species
Sometimes changes in the population of a single species, often
called a keystone species, can cause dramatic changes in the
structure of a community.
In the cold waters off the Pacific coast of North America, sea otters
devour large quantities of sea urchins.
Sea urchins are herbivores whose favorite food is kelp, giant algae
that grow in undersea “forests.”
Sea Otter is a Keystone Species
Symbioses
Symbiosis occurs when two species live closely together
in one of three ways: mutualism, commensalism, or
parasitism.
•Mutualism - both species benefit from the relationship.
•Commensalism - one species benefits and the other is
neither helped nor harmed.
•Parasitism - one species benefits by living in or on the
other and the other is harmed.
Mutualism
Mutualism - both species benefit
from the relationship.
Clownfish are the only fish that do not get stung by the tentacles of the sea
anemone. Clownfish have a slimy mucus covering that protects them from the
sea anemone. However, if this covering is wiped off of a clownfish, it will get
stung and possibly be killed when it returns home to the anemone. The clownfish
and the sea anemone help each other survive in the ocean. The clownfish, while
being provided with food, cleans away fish and algae leftovers from the
anemone. In addition, the sea anemones are given better water circulation
because the clownfish fan their fins while swimming about.
Commensalism
Commensalism - one species benefits and the other is
neither helped nor harmed.
Barnacles often
attach themselves
to a whale’s skin.
They perform no
known service to the
whale, nor do they
harm it. Yet the
barnacles benefit
from the constant
movement of water
—that is full of food
particles—past the swimming whale.
Parasitism
Parasitism - one species
benefits by living in
or on the other and
the other is harmed.
Tapeworms live in the intestines
of mammals, where they absorb
large amounts of their hosts’ food.
Parasitism
Parasitism - one species
benefits by living in or on
the other and the other is
harmed.
Fleas, ticks, lice, and
the leech shown,
live on the bodies
of mammals
and feed on
their blood
and skin.
Leech
Parasitism
Parasitism - one species benefits by living in or on the
other and the other is harmed.
Tick on human skin after sucking blood
The parasite obtains
all or part of its
nutritional needs
from the host
organism.
Generally, parasites
weaken but do not
kill their host, which
is usually larger
than the parasite
4.3 Succession
Ecological succession - a series of moreor-less predictable changes that occur in a
community over time.
– Ecosystems change over time, especially
after disturbances, as some species die out
and new species move in.
– Over the course of succession, the number of
different species present typically increases.
Primary Succession
Succession that begins in an area with
no remnants of an older community is called
primary succession.
Primary Succession
Volcanic explosions can create new land or sterilize existing areas.
Primary Succession
on a lava flow
Primary Succession
Retreating glaciers can have the same
effect, leaving only exposed bare rock
behind them.
Secondary Succession
Before
Hurricane
Katrina
After
Hurricane
Katrina
Secondary succession
often follows a wildfire,
hurricane, or other natural
disturbance.
We think of these events
as disasters, but many
species are adapted to
them.
Secondary Succession
Before
Hurricane
Hugo
After
Hurricane
Hugo
Secondary Succession
Forest fires can kill
some trees, other
trees are spared, and
fire can stimulate their
seeds to germinate.
After Fire
Secondary Succession
Forest fires can kill some trees, other trees are spared,
and fire can stimulate seeds to germinate.
After Fire – seed cone
opened up from heat
After Fire – seedlings
begin to grow
Several years
after the fire
flowers return
After Fire – small grasses
& underbrush return
Secondary Succession
5-6 years after
the fire small
pine trees return