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Ecology
Overview

Earth is home to trillions of different
organisms
◦ None can survive alone
All organisms must interact with the living
and nonliving things around them
 Ecology = the study of how organisms
interact with the living and nonliving
things that surround them.

Organisms and Their Environment

Just sitting here you are surrounded by and
interacting with the environment
◦ What are you interacting with right now?

The environment is every nonliving and
living thing surrounding you
Parts of an Ecosystem

Ecosystem is a short way of saying
“ecological system”
◦ Used to describe any portion of the
environment
◦ Made up of all living things:
 Bacteria, plants, animals
◦ These living things = biotic factors
◦ We also study nonliving things
 Soil, water, physical space, and energy
◦ These nonliving things = abiotic factors
Parts of an Ecosystem

There are many types of ecosystems.
◦ Decaying log, a pond, a field of corn, a fish tank

In every ecosystem, organisms interact
with both the biotic and abiotic parts of
the environment
◦ Example: Frogs in a pond are affected by
 Insects, fish, hawks, children
 Rainfall, acidity of the pond,
temperature, and amount of light
Parts of the Ecosystem

There are many different environments
that are available for organisms
◦ Some species may only live in one
environment
 Their “home”
◦ A specific environment for an organisms is
known as its habitat
 Example: Field, forests, oceans, streams, deserts
◦ The role an organism plays in an environment
= niche
Parts of the Ecosystem

All of the organisms of a species that live
in the same area make up a population
◦ Example: Ants in an anthill = one population

Different populations are combined to
form communities
Parts of the Ecosystem

All of the Earth’s ecosystems make up a
biosphere
◦ Biosphere = biologically inhabited portions of the
planet

The earth’s biosphere extends from the
deepest ocean troughs to the highest peaks
of mountains
◦ Includes all water, land, and air that organisms can
live in

Organisms interact and compete for vital
resources
◦ Food, space, shelter
Parts of the Ecosystem

The fundamental concept of ecology = all
living organisms are interdependent
◦ They interact with one another and with the
physical environment

The interactions result in a flow of energy
and a cycling of materials essential for life
Environmental Limits on Population
Size

The growth and survival of organisms
depends on the physical conditions and on
the resources available to an organism
◦ If there were unlimited resources, living things
could produce populations of infinite (unlimited)
size

In an ecosystem, resources are finite
(limited)
◦ Resources = oxygen, carbon dioxide, water,
nutrients, space, and sunlight

Because resources are finite, organisms must
compete for resources
Environmental Limits on Population
Size

Competition = struggle for resources
among organisms
◦ Competition keeps the size of the species
population in check (balanced)

Populations tend to increase or decrease
depending on the resources available at
the time
◦ It tends to follow a cycle
 May follow the seasons
◦ The size of population remains stable
Environmental Limits on Population
Size

Limiting factors = factors in the
environment that limit the size of the
population
◦ Some are abiotic, others biotic
 Abiotic factors = oxygen, sunlight, intensity of light,
temperature, water, minerals, type of rocks or soil,
acidity
◦ Biotic factors = predator vs prey relationship,
 Predator = hunter; prey = hunted
 Too many predators, not enough prey the
population of predators will start to starve…
Environmental Limits on Population
Size

The number of organisms of a single species
that an ecosystem can support = carrying
capacity
◦ Determined by available energy, water, oxygen,
and minerals, interactions with organisms
◦ Example: a fields carrying capacity of foxes is
affected by:
 Climate, number /kind of populations present (viruses,
prey),
◦ The population will increase until carrying
capacity is reached.
Types of Carrying Capacity

Natural Carrying Capacity
◦ Limited by the available biotic and abiotic
resources

Social Carrying Capacity
◦ Determined by the number of organisms
people want or will tolerate
Environmental Changes

Dynamic Equilibrium
◦ Constantly changing stable state where
populations fluxuate on either side of an
average

Biomass
◦ The amount of living material in a given time
 It can refer to one or several species
Population Interactions

Many species interact in an ecosystem
◦ Most occur when obtaining food

Populations are linked either directly or
indirectly with other populations
◦ Each population can have one or more
specific role in an ecosystem
 Maintaining diversity in the ecosystem is essential to
its stability
Roles in an Ecosystem

The role that each species plays in an
ecosystem = ecological niche
◦ Only one organism can occupy a particular
niche at a time
 If 2 species try to fill the same role in an ecosystem,
competition results
 One organism will be a better competitor than the
other/ better suited, it forces the other to move or
is eliminated
◦ Over time only one organism
will occupy each niche
Roles in an Ecosystem

It might appear as if different population
occupy the same niche but they are
indeed different
◦ Example: deer and moose. They live in the
same area and both eat plants.
 The plants they prefer are different though.
 There is only competition when food is scarce
◦ Example: Birds may all live in the same tree
and eat insects but each bird will live and eat
in a different part of the tree
Roles in an Ecosystem

Competition for a particular niche often
occurs when a foreign species enters an
area
◦ The new species may be more successful than
the native species
 The new species may not have an enemies to
control its population
 Humans often introduce many foreign species
 Example: zebra mussles in the great lakes, brought by cargo
ships, have become a big problem
Relationships in an Ecosystem

In ecosystems, populations of different
species are linked by complex webs of
interactions
◦ Sometimes the relationship is competitive;
sometimes they are cooperative
◦ Example: termites have uni-cellular organisms
in their intestinal tracts that digest their food
 The organism has a place to live (in the termite)
and plenty of food, and it helps the termite gain
nutrients
Relationships in an Ecosystem

Other relationships help one but have no
effect on the other
◦ Example: a shark attacks and eats its prey.
Small fish swim below the shark and eat up
the left-overs. The fish benefit but the shark is
unaffected
Food Chains
Predator-Prey
relationships are
the most common
relationships
 Food chains, show
the relationship
between predator
and prey
relationships

◦ It shows what eats
what
Food Chains

Organism’s niches are partly defined by
how they gather food
◦ Example: photosynthetic organisms make
their own food and store energy (from the
sun)
 These organisms = autotrophs (self-feeders) or
producers
◦ They provide food energy for almost all other
living things
Food Chains
Hetertrophs = acquire food by consuming
other organisms
 Herbivores = hetertrophs that survive on
plants
 Carnivores = hetertrophs that eat other
animals
 Hetertrophs are known as consumers

Food Chains
The wastes and dead bodies of organisms
are consumed by decomposers
 Decomposers recycle materials that can
then be reused by producers

Food Chains

There are two relationships that do not
fit the normal predator-prey relationship
◦ They feed on other organisms but do not kill
it to feed themselves

Scavengers = are consumers that eat dead
organisms (vultures)
◦ Nature’s clean-up crew, not decomposers
though
Food Chains

Dead bodies and wastes still have to be
broken down by decomposers
◦ Parasites are organisms that attack other live
organisms (host organisms)
 Rarely kill them
◦ Parasites usually live on or in the body of
their hosts
 Ticks live on a dog and feed on its blood
Food Chains
Food chains generally begin with
autotrophs and end with hetertrophs and
are eventually consumed by decomposers
 Food chains can be very simple or very
complex
 Decomposers may or may not be
included but we must remember they
break down the wastes and dead bodies
of all living organisms

Food Webs

Normally each organism feeds on more
than one kind of organism
◦ Organisms have more than one food source
 Food chains are oversimplified, food webs are food
chains connected together (more complex)
◦ Because organisms can eat many things,
ecosystems remain stable even when one
population shows a major decline in numbers
◦ Organisms that feed on declining populations
rely more heavily on other food choices until
the population recovers
Energy Flow Through an Ecosystem

Almost all organisms use the solar energy
stored in food to power their life processes
◦ The energy can’t remain in the organism forever
◦ An organism is constantly losing energy, it is
breaking bonds in food to use the energy to live
◦ The energy is used to make ATP then used in
cells.
◦ Lots of energy is used as heat and is lost to the
environment

This means each step in the food chain has
less energy than the previous organism
Energy Flow Through an Ecosystem
Most of the energy originally gained from
the sun is lost (used) by that organism.
 Only 10% of the original energy is passed
on to the next organisms

◦ Only 10% of the energy it gained is passed on
to the next organism
◦ This means food chains are normally quite
short
Energy Flow Through an Ecosystem

Energy Pyramid = a diagram that
illustrates the transfer of energy though a
food chain or web
◦ Each block represents the amount of energy
that was obtained from the organism below it
◦ Each level is smaller due to the loss of heat as
the organisms carry on their life activities
Energy Flow Through an Ecosystem

A continual input of energy (mostly from
sun) is required to start the process and
to keep it going
◦ Producer organisms capture this energy and
store it in chemical bonds of the food
molecules they make
◦ The flow of energy that accompanies the
transfer of food is essential to life
◦ Even though we are constantly losing energy,
the sun continues to provide more, continuing
life
Recycling and Reusing Materials
◦ Parts of dead organisms are not consumed
during any of the steps of a food chain.
Decomposers extract the last bit of
energy contained in the dead organisms
and energy in waste products to sustain
their life functions
 When they do this, the raw materials
contained in the once-living matter is
transferred to soil = decomposition

Recycling and Reusing Materials

Decomposers = bacteria and fungi
◦ Due to decomposers, atoms and molecules in
living things cycle through both nonliving and
living parts of the biosphere
◦ Through this they pass through the food chain
◦ Example: Plants use carbon dioxide and water
and store it as glucose, when the plant is eaten
the glucose is broken down and used within the
organism. The organism may release carbon
dioxide and water in respiration

Much of this cycling in the ecosystem is
done by decomposers
Energy Flow

Sunlight  plants  Primary consumer 
secondary consumer  tertiary consumer 
decomposers
◦ Or

Sunlight  autotrophs  heterotrophs 
decomposers
◦ Or

Sunlight  producers  herbivores/omnivores 
carnivores/omnivores decomposers

All start with _________ & end with
__________
Risks within Food Chains

Bioaccumulation – toxins accumulate in
greater concentrations as your progress
up a food chain
Relationships in Ecosystems

Producer – Consumer – Decomposer

Predator – Prey

Parasite – Host
◦ Pinworm, tapeworm, bot fly, leech, tick, mosquito,
lamprey, chigger, tomato worm wasp, fleas

Scavenger – Dead Things
Types of Relationships

Symbiotic Relationships
◦
◦
◦
◦
Clown fish and anemone
Birds and buffalo
Hummingbirds and flowers
Fig and wasp
Diversity Benefits Species and
Habitats

As a result of evolution, there is a great
diversity of species on Earth
◦ Each ecosystem is populated with many
species which occupy their own niche
◦ The relationships of these populations keep
the ecosystem stable and the diversity of
species increases the chance that at least
some organisms will survive in the face of
large environmental changes
Diversity Benefits Species and
Habitats

Biodiversity = measurement of the degree
to which species vary within an
ecosystem
◦ There is a connection between biodiversity
and stability of the ecosystem
◦ Example: a forest has many trees, if there is a
disease, it will not kill all the trees in one area.
Disease and insect infestation are resisted by
biodiversity.
Diversity Benefits Species and
Habitats

Interactions between organisms may
allow an ecosystem to remain stable for
thousands of years
◦ In ecosystems populations tend to increase
and decrease in size in a predictable pattern
◦ Overtime, the population size stays stable
 Example: Increase in predator or prey population
Diversity Benefits Species and
Habitats
The loss of biodiversity in an ecosystem
upsets its stability
 Removing species from an environment
often causes instability due to the loss of
organisms that were filling critical
ecological niches

Diversity Benefits Species and
Habitats

Many species may be lost when natural
disasters or human activities cause largescale destruction of habitats
◦ Example: Destruction of rain forests, some
organisms may be able to return to a
damaged ecosystem, others may not be able
to return
◦ The interactions between populations will be
lost
Diversity Benefits Species and
Habitats

Species can be lost when humans do not
consider their impact on the ecosystem
◦
◦
◦
◦
Example: Human hunting of mountain lions
Led to overpopulation of deer
Led to overgrazing of grass lands
Led to deer starving and soil erosion that
caused permanent environmental damage
Diversity Benefits Species and
Habitats

When land is cleared for agricultural
purposes, the loss of biodiversity may
cause an unstable ecosystem
◦ When plants are genetically similar it can lead
to problems with diseases and bugs

This is avoided with natural biodiversity
◦ Less likely one pest or disease would destroy
the environment
Biodiversity Benefits Humans
Biodiversity is a great resource for
humans as well
 It ensures the availability of a rich variety
of genetic material

◦ Some that could be valuable to humans

Genetic diversity found in rain forests
could provide humans with medicines,
insecticides, and other useful resources
◦ If we destroy these ecosystems, we could be
destroying solutions to our problems
Biodiversity Affected by Humans

Urban Sprawl
◦ Minimizing biodiversity by putting up
structures

Ecosystems are dynamic
◦ Always changing
◦ Does not balance out and reach a steady state
Environmental Changes
Many environments have few resources
that can provide home for living
organisms
 These environments will naturally change
over long periods of time to become
habitats with many diverse species

◦ The series of changes when one habitat
changed into another = ecological succession
Environmental Changes

In the process of ecological succession,
each community causes modification to
its environment
◦ Modifications result in changes that make it
more suitable for another community
◦ The original species that lived there may find
it harder to adapt to the changes while new
species may be more successful for the new
niche
Environmental Changes

As grasses grow in an area of shallow soil,
they add organic matter making the soil
deeper and more fertile
◦ Shrubs are then able to live there
◦ The shrubs will cause shade which will
eliminate the grasses and lead to trees
◦ This shallow soil may eventually change into a
stable forest to last thousands of years
Environmental Changes

Climatic changes, natural disasters, and
activities of animals (including humans)
can alter stable ecosystems
◦ Changes may be rapid (forest fire) or slow
(long-term drought / climate change)
◦ Altered environments undergo a slow series
of succession changes that return them to a
stable environment
◦ During this time, existing communities are
replaced with different communities
Environmental Changes

There are two observed patterns of
succession
◦ A community of bare rock gradually accumulate
soil, leading to progression of vegetation types
from grasses to shrubs and eventually a forest.
◦ A lake gradually accumulates sediments from
erosion and the buildup of organic debris from
plants and organisms. The lake fills up and
becomes shallow. After many years, it may
become a swamp. If the filling continues it will
mature into a forest
Keystone Species

Species that other species depend on or
suffer by their actions
◦ Elephants
◦ Beavers
◦ Humans
New Species
Introduced species are organisms not native to an
area that appear by accident, on purpose, or by
circumstance (on their own)
 Unlike native species the new species evolved away
from the community that they are now part of – as a
result, many do not have predators, disease, or other
form of natural check to keep them under control

◦ They may exploit prey or plants that have not evolved to
protect themselves from this new organism
◦ Most introduced species die shortly after being
introduced, but those who do not generally become a
huge environmental problem
 Example – zebra muscles, purple loosetriphe, round goby, ruffle,
water flea, Norway maple, Japanese barberry