Transcript Ecosystems

Ecosystems
Science 10
Biosphere

This is the title given to the area of the earth
where life exists.

It is about 20km thick, from the bottom of the
oceans to the highest point in the atmosphere
where life can be found.

The biosphere can be divided into biomes.
Biomes

These are divided according to the type of vegetation
which can be found in its midst.

There are three main types:
 Terrestrial
 Freshwater
 Marine

Each of these biomes can be divided into a wide
variety of ecosystems.
Ecosystems

This includes all the organisms in an area that interact
with each other and with their environment.

The fuel for ecosystems is the sun.

Sunlight is captured by green plants for
photosynthesis and stored as carbohydrate energy.

This energy then gets passed on as herbivores eat
plants and carnivores eat the herbivores.
Two main factors in an
ecosystem

Abiotic factors- these are all of the nonliving
aspects of the ecosystem that affects the
organism.


These include water, carbon dioxide, minerals,
light, temperature, wind, space, etc…
Biotic factors- these are all of the living
organisms in an ecosystem
Modes of Nutrition


Autotrophs

Capture sunlight or chemical energy

Producers
Heterotrophs

Extract energy from other organisms or organic
wastes

Consumers, decomposers, detritivores
Simple
Ecosystem
Model
energy
input from
sun
PHOTOAUTOTROPHS
(plants, other producers)
nutrient
cycling
HETEROTROPHS
(consumers, decomposers)
energy output (mainly heat)
Consumers

Herbivores

Carnivores

Parasites

Omnivores

Decomposers
SPRING
fruits
insects
rodents,
rabbits
birds
SUMMER
fruits
rodents,
rabbits
insects
birds

Detritivores
Seasonal variation in the diet of an
omnivore (red fox)

Does one ecosystem hold more energy than
another?

How is energy stored and transferred within an
ecosystem?

How does it leave an ecosystem?

These types of questions are important because
the energy that is captured by plants through
photosynthesis determines the amount of
energy that is available for all other organisms
in the ecosystem.

Human survival depends on the amount of
energy that is stored in agricultural ecosystems

Compared with animals, green plants produce more
energy per unit land area. (see results from graph
exercise)

Thus, most of the energy in an agricultural ecosystem
is found in the crops, such as the field of corn.

Only a portion of this energy is transferred to
livestock that eat the plants.

As a result, animals and animal products contain less
energy than plant and plant products that are raised on
the same amount of land.

This begs the question; Why is only some of
the original energy transferred to the plant
eaters?

What happens to it?

Why is some lost from level to level?
Trophic Levels

Ecosystems can be thought of as being made
up of several feeding levels, or Trophic levels

All the organisms at a trophic level are the
same number of steps away from the energy
input into the system
Trophic Levels

Producers (autotrophs) make up the first trophic level.

Primary consumers (heterotrophs) feed at the second
trophic level.

Secondary consumers (heterotrophs) feed at the third
trophic level and so on.

All the organisms at a trophic level are the same
number of steps away from the energy input into the
system

Most of the energy that enters each trophic level is used by the
organisms at this level just to stay alive.

The organisms need energy to move from place to place, grow,
reproduce, and carry out other activities.

Some of the energy cannot be used and passes out of the
organisms as waste.

Only a small percentage of the energy remains stored in each
organism as body tissues.

It is this energy that is available as potential food for
consumers in the next trophic level.
Food Chain
MARSH
HAWK

A straight line sequence
of who eats whom

Simple food chains are
UPLAND
SANDPIPER
rare in nature
GARTER SNAKE
CUTWORM
Food
Web
Many organisms eat a
variety of foods and
consume organisms
from many different
trophic levels.
The complex
relationship is
demonstrated via a
food web.
Decomposer Food Chains



Organisms that receive energy from dead plant and
animal material
Make up majority of food chains
Scavengers eat the remaining energy in large dead
organisms


Ex: Vultures eat the carcasses of dead animals
Decomposers – types of organisms that break down
cells to extract remaining energy

Ex: fungi and bacteria
Grazing Food Web
Detrital Food Web
Two Types of Food Webs
Producers
(photosynthesizers)
Producers
(photosynthesizers)
herbivores
decomposers
carnivores
detritivores
decomposers
ENERGY OUTPUT
ENERGY OUTPUT
Primary Productivity

Gross primary productivity is
ecosystem’s total rate of photosynthesis

Net primary productivity is rate at which
producers store energy in tissues in
excess of their aerobic respiration
Primary Productivity Varies

Seasonal variation

Variation by habitat

The harsher the environment, the
slower plant growth, the lower the
primary productivity
Pyramids



Pyramid of Numbers – shows how the greatest
number of organisms is in the first trophic level, least
number on top of the trophic level
Pyramid of Biomass –shows the relative mass of the
organisms at each trophic level
Pyramid of Energy Flow – shows how the energy
available at each trophic level is greatest at the
bottom of the food chain and least at the top
Pyramid of Biomass


Aquatic ecosystem in Florida
Site of a long-term study of a grazing food web
Biomass
pyramid
decomposers,
detritivores
5
(bacteria,
crayfish)
third-level carnivores
(gar, large-mouth bass)
1.5
1.1
second-level consumers
(fishes, invertebrates)
37
first-level consumers
(herbivorous fishes,
turtles, invertebrates)
809
primary producers (algae,
eelgrass, rooted plants)
Pyramid of Energy Flow


Primary producers trapped about 1.2 percent of
the solar energy that entered the ecosystem
About 10% passed on to next level
top carnivores
21
carnivores
herbivores
383
decomposers
3,368
producers
20,810 kilocalories/square meter/year
detritivores
All Heat in the End

At each trophic level, the bulk of the energy
received from the previous level is used in
metabolism

This energy is released as heat energy and lost
to the ecosystem

Eventually, all energy is released as heat

Work on questions 1-4 page 274

Work on questions 5-10 pages 275-276.

Complete “Going with the Flow” worksheet
Feeding levels




First trophic level – always plants
Second trophic level – primary consumers
Third trophic level – secondary consumers
Energy flows through the food chain but only about
10% of the energy is passed on from one trophic level
to the next.

Ex: Plant has 100kJ, caterpillar uses 10% for life processes,
90% is lost as heat or waste
Carrying Capacity
Can any population of organisms keep growing
forever? What might limit its numbers?
The largest number of individuals in a species that
an environment can support is called the carrying
capacity.
4 factors that determine carrying capacity



1.
2.
3.
4.
Materials/energy –limited by the amount of usable
energy, water, carbon
Food Chains- population sizes at each trophic level
(predators, herbivores)
Competition – Intraspecific (same species)/Interspecific
(between species)
Density – how many organisms occupy a given space at a
given time
Factors which can limit the growth
of a population include:





predation
shortage of food
disease
lack of water
lack of space
Factors That Affect the Size of a
Population

Density Dependent: (overcrowding,)

If population density increases it can cause a decrease in
the population




Increased stress = spread of disease and parasites
Increased aggression = neglect of offspring
These factors decrease the population numbers
Density Independent

Events that can decrease population numbers that are not
dependent on the size of the population (ie. Forest fire)

Please work on questions 1-4 page 290

Finish for homework