Interactions in the Environment

© Lisa Michalek

POPULATIONS & COMMUNITIES POPULATION

– All the organisms of one species that live in one place at a particular time.

– No population ever lives alone. COMMUNITY

– All the populations that interact with each other in a particular place.

– The amount of variety in a community is called species diversity or BIODIVERSITY.

few species = low biodiversity many species = high biodiversity

PROPERTIES OF A POPULATION

DENSITY: The size of a population in a given area.

DISTRIBUTION: How the population is spread in a given habitat.

GROWTH RATE: The increase or decrease in the density of a population over a specific period of time.

CARRYING CAPACITY The size of a population that can be

supported by an ecosystem. The population density has reached a

maximum for the particular habitat. Population growth slows and may reach a

stage of zero growth as the population density comes close to an area’s carrying capacity.– Zero growth means that the size of the

population is no longer increasing.– The birth and death rate are about equal.

CARRYING CAPACITY

In food relationships, nutrients (food) are transferred from one

organism to another.

Nutritionally, Organisms are either:

Autotrophs– Can make their own food from inorganic

compounds.– Also called PRODUCERS.– Example: Green Plants

Heterotrophs– Cannot make their own food.– Also called CONSUMERS.– Must obtain their nutrients from the environment.– They are classified according to the type of food

they eat.

Nutritionally, Organisms are either:

HERBIVORES

Animals that feed on plants and plant materials.

Examples: Cows, Horses, and Sheep

CARNIVORES

Animals that feed on other animals. Examples: Wolves, Lions, and Tigers

– PREDATORS: Carnivores that kill and consume their prey. (Owls and Wolves)

– SCAVENGERS: Carnivores that feed on dead animals they find. (Buzzards and Vultures)

OMNIVORES

Animals that feed on both plants and animals. Example: Humans

DECOMPOSERS

Feed on dead and decaying organisms Also called Saprophytes. Examples: Bacteria and Fungi

SYMBIOTIC RELATIONSHIPS

SYMBIOSIS: – Organisms of different species live together in

close association.– At least one member of the association benefits

(gains) by the association. Mutualism, Commensalism Parasitism

MUTUALISM A relationship in which both

organisms benefit.– nitrogen-fixing bacteria

A type of bacteria that lives in little knobs on the roots of peas and clover plants.

These bacteria make important nitrogen compounds that are used by the plant and the plant supplies moisture and organic nutrients to the bacteria.

COMMENSALISM Two organisms of different species live in a

relationship that is beneficial to one and the other is not affected.– The remora (little fish) attaches itself to the shark’s

body with little suction cups. – The remora gets scraps of uneaten food from the

shark, the shark is not harmed bythe relationship.

PARASITISM One organism (the parasite) benefits and the

other organism (the host) is harmed.– Athlete’s foot fungus (parasite) feeds on the host

organism (humans). – The host is harmed by the relationship and the

parasite benefits.

COMPETITION Competition occurs when there is a struggle

among organisms living in the same habitat (environment) for the same limited resources.

Some of these resources are food, space, water, light, oxygen, and minerals.

When two species compete intensely for the same resource, one species usually wins.

Competition may result in the elimination of one species in the ecosystem.

Competing species tend to reduce their use of common resources.

FOOD CHAINS Food passes through an ecosystem in a certain path

known as Food Chain. Food chains involve the transfer of food materials from

producer to primary consumer to secondary consumer to tertiary consumer.

Each level on a food chain is a Tropic Level.

Producer – green plants and other photosynthetic organisms. Producers change the energy of sunlight into the chemical energy of food.

Primary Consumer – are always herbivores because they are the animals that eat green plants.

Secondary Consumers – are animals that eat other animals (carnivores). These include predators and scavengers.

Higher-Level Consumers – are organisms that eat secondary consumers.

Decomposers – break down all organisms into chemical materials that are returned to the environment for use by other living organisms.

Tropic Levels

FOOD WEBS In a natural community,

there are many interconnecting food chains.

Most organisms eat more than one type of food.

Most organisms are consumed (eaten) by more than one species of organism.

The flow of energy and materials is much more complicated than a simple food chain.

SEASHORE FOOD WEB

The interconnecting food chains of an ecosystem form a FOOD WEB.

PYRAMID OF ENERGY At each step on the food web, energy is transferred to

the next higher level. Energy is “lost” at each food level, because much of

the food energy taken in by a consumer is used in the process of metabolism.

Less energy is available to the higher levels on the food chain.

PYRAMID OF ENERGY

PYRAMID OF BIOMASS The amount of organic matter in an ecosystem is its

biomass. This pyramid shows that the total biomass an

ecosystem can support decreases at each higher feeding level.

This is because there is less energy available at each level.

The greatest amount of biomass is found at the producer level, and degreases with each higher feeding level.

MATERIAL CYCLES

In a self-supporting ecosystem, materials must be recycled between the living and nonliving environment so they can be reused.

There are three major material cycles.– The Carbon-Oxygen Cycle– The Water Cycle– The Nitrogen Cycle

CARBON-OXYGEN CYCLE Involves the process of

cellular respiration and photosynthesis.

Oxygen is released as a byproduct of photosynthesis.

Carbon Dioxide is released as a byproduct of respiration.

During EVAPORATION, water is changed into water vapor and during CONDENSATION water vapor is changed back into water.

WATER CYCLE

Nitrogenous wastes and the remains of dead organisms are converted by decomposers and soil bacteria into compounds that can be used by autotrophs (producers).

NITROGEN CYCLE

ECOLOGICAL SUCCESSION The gradual replacement of one community by

another. Ecological succession eventually leads to the

formation of a stable community. Each community slowly changes the

environment. The changed environment often is more suitable for new types of organisms and less suitable for the existing organisms.

Ecological succession occurs in step stages. A stable community is called a

CLIMAX COMMUNITY.

SUCCESSION

Primary Succession– Occurs in an area that

has no existing life.– Must begin with the

formation of soil.– Example: a bare rock,

rocky cliffs, sand dunes, newly formed volcanic island, newly exposed land areas.

Secondary Succession– Occurs in an area where an

existing community has been partially destroyed and its balance is upset.

– Example: Forest Fire, Tornado, Hurricane

First Stage– Can begin with bare rock.– Lichens are usually one of the first organisms to

appear because they can live on bare rock.– The first organisms are called PIONEER

ORGANISMS.– Pioneer organisms are able to survive in harsh

conditions with few nutrients.

PRIMARY SUCCESSION

Second Stage– Grasses

ECOLOGICAL SUCCESSION

Third Stage– Shrubs and

Small Trees

Fourth Stage— Sun Trees

Fifth Stage— Shade Trees

ECOLOGICAL SUCCESSION

CLIMAX COMMUNITIES If environmental conditions in an ecosystem remain

stable over long periods of time, the same species of plants and animals that make up that ecosystem continue to live and interact together.

These permanent plant and animal species make up a stable or climax community.

There is a balance within the population and the environment.

A Climax Community remains until a drastic environmental change occurs.– Storm, Forest Fire, Flood, Volcanic Eruption

The type of climax community is determined by the abiotic factors of the area.

ECOSYSTEM STABILITY Under stable environmental conditions, the

number of organisms in naturally occurring populations remains constant (the same), with only small periodic changes.

A stable ecosystem will be able to resist invasion by potential competitors.

A stable ecosystem will be able to resist change in the face of disturbance.

A more diverse ecosystem will be more stable.