Ecosystems & Communities

Chap

ter 4

4.1 ClimateWeather 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 NorthernHemisphere, south facing sides of trees andbuildings receive moresunlight, and are often warmer and drier, thannorth-facing sides.Therefore - moss grows onthe north side of trees. These differences can bevery important to many organisms.

Microclimates

Lake Effect Snows

Climates of New Jersey

Factors That Affect Climate

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.

4.2 Niches and Community InteractionsEvery 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.

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.

NicheA 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.

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.

CompetitionCompetition 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.

CompetitionDirect 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

SymbiosesSymbiosis 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.

CommensalismCommensalism - 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 mammalsand 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 bloodThe 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 SuccessionEcological succession - a series of more-

or-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

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.

Before

Hurricane Katrina

After

Hurricane Katrina

Secondary Succession

After

Hurricane Hugo

Before Hurricane Hugo

Secondary SuccessionForest fires can kill some trees, other trees are spared, and fire can stimulate their seeds to germinate.

After Fire

Secondary SuccessionForest 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

After Fire – small grasses & underbrush return

Several years after the fire

flowers return

Secondary Succession

5-6 years after the fire small

pine trees return