Transcript Ecology Powerpoint - Ms Martin`s Grade 10 Science

UNIT 1
Dynamics of
Ecosystems
In this unit, you will examine the complex
relationships present in ecosystems in order to
further investigate issues of sustainability. The
large scale cycling of elements in
biogeochemical cycles and the
bioaccumulation of toxins in food chains are
studied. Population dynamics are examined in
the context of the carrying capacity and
limiting factors of ecosystems. The concepts
and implications of species biodiversity are
explored as well. With the knowledge you have
gained, you will investigate how human
activities affect an ecosystem and use the
decision-making model to propose a course of
action to enhance its sustainability.
What is an Ecosystem?



All life on earth is found in a thin layer known
as the biosphere. The biosphere, in turn, is
made of many smaller parts called
ecosystems, or biomes.
Organisms inhabit these ecosystems - on land,
in the soil, in the oceans, and even within the
atmosphere, where tiny spores and bacteria
can be found. These are large areas of the
earth with similar climate, vegetation, soils,
and life forms.
Several examples are the tundra, boreal
forest, deciduous forest, or grassland
ecosystems
 Ecosystems
are made of non-living or
abiotic things, and living or biotic things.
ecology is the branch of science that
studies how the biotic and abiotic factors
interact with each other.
Cycles of Matter
 While
energy flows in a one-way direction
through an ecosystem, nutrients are recycled
over and over again. Biogeochemical cycles
are the processes by which nutrients move
through organisms and the environment. The
important nutrients that are recycled are
carbon, oxygen, and nitrogen.
The Carbon Cycle

Carbon is the key element for living things. Carbon can
be found in the atmosphere and dissolved in the
oceans as part of the inorganic carbon dioxide (CO2)
molecule. The carbon in carbon dioxide is recycled into
more complex organic substances through
photosynthesis.

Photosynthesis – process by which green plants make
their own food from water, carbon dioxide, and light
energy, producing sugar (stored energy) and oxygen
(a by-product).

For this process to take place, chlorophyll must be
present (found in green plants).
 The
general equation for photosynthesis is:
6CO2 + 6H20 C6H12O6 + 6O2
 Cellular
respiration – process in which living things
release the energy that is stored in their food (in
the form of sugars)
- takes place in cells, in an organelle called the
mitochondrion.
 The
general equation for cellular respiration is:
C6H12O6 + 6O26CO2 + 6H20 + energy
 Photosynthesis
and cellular respiration are
part of the cycling of matter and the
transfer of energy in ecosystems.
The Carbon-Oxygen Cycle




These two atoms are so intertwined in life’s
biogeochemical cycles that they are considered
as part of one large cycle.
Plants consume carbon dioxide and convert it
through photosynthesis to glucose, cellulose, and
other complex molecules that build the plant.
As plants use water molecules, they are split into
hydrogen and oxygen.
The oxygen released makes up 21% of our
atmospheric gases, and supports all life on earth.
 Notice
in the following diagram below that all
plants and animals are dependent on each
other. The gases that are produced by
photosynthesis are required by animals, and
the waste gases of animals are needed by
the plants.
Carbon Reserves
There are 4 main reservoirs through which carbon can be
found.

The Atmosphere: The atmosphere plays a central role in
the carbon cycle. Here, carbon is found as carbon
dioxide. Atmospheric carbon dioxide enters terrestrial
food chains through plants when they perform
photosynthesis.

The Oceans: Oceans play a major role in determining
carbon dioxide levels in the atmosphere. Carbon
dioxide dissolves in ocean water and returns to the
atmosphere when it spontaneously comes out of
solution. Carbon leaves the water when it enters
aquatic food chains via photosynthesis. The carbon is
returned to the water when aquatic organisms respire.

The Earth’s Crust: Carbon can be trapped in rock for
millions of years until geological conditions bring it
back to the surface. The burning of fossil fuels releases
carbon dioxide from carbon stores long-buried in the
earth. This adds to the levels of carbon dioxide in the
atmosphere, increasing the greenhouse effect, and
contributing to global warming.

Living Organisms: Some of the carbon picked up by
plants returns to the atmosphere as carbon dioxide
when plants respire (breath). The rest of the carbon is
used to build plant tissues. The carbon then either
moves through the food chain beginning with
herbivores when they eat plants, or to decomposers,
when plants die. Animals and decomposers return the
carbon to the atmosphere as carbon dioxide when
they respire.
Disturbing the Carbon Cycle



Humans have had a direct impact on this
cycle in several ways. We have produced
more carbon than ever before as a result of
burning fossil fuels (carbon monoxide and
carbon dioxide).
We have cleared forests for farmland, cities,
and highways.
Although CO2 makes up only 3/100 of 1% of
the earth’s atmosphere, it is a cause for
concern because it is known as a greenhouse
gas since it helps to trap heat in the earth’s
atmosphere, contributing to global warming.
Natural Events
The cycling of carbon can be disturbed by
natural events.
1. Forest Fires - the combustion or burning of
plant material, such as wood, releases large
amounts of carbon dioxide into the
atmosphere. Similarly, the burning of leaves
and stubble in the fall increases the amount
of carbon dioxide in the atmosphere.
2. Volcanoes - volcanic activity can break
down rocks containing carbon
compounds and release carbon dioxide
into the atmosphere. The ash generated
from a volcano can also block sunlight
from reaching the Earth's surface. This
may reduce the amount of
photosynthesis done by plants, causing
the amount of carbon dioxide in the
atmosphere to increase.
Human Impact
The cycling of carbon can be disturbed by
human activities.
1. Deforestation – cutting down forests has
reduced the amount of plants available
for photosynthesis, which means that less
CO2 can be removed from the
atmosphere.
2. Burning (combustion) of fossil fuels –
gasoline, coal, and natural gas contain
carbon and when burned, they release
CO2 into the Earth’s lower atmosphere.
There is concern that the increase in CO2
will lead to global warming.
Video
The Oxygen Cycle




The oxygen cycle, which moves oxygen through an
ecosystem, is closely linked to the carbon cycle.
Plants use water during photosynthesis and release
oxygen gas into the atmosphere. The chemical
formula for oxygen gas is 02.
Organisms then use the oxygen gas during cellular
respiration and release water into the atmosphere.
The cycle continues as plants produce oxygen
during photosynthesis, which is then used by
organisms in cellular respiration.
 The
diagram below illustrates the cycling of
carbon and oxygen in a farm ecosystem. Notice
how the processes of photosynthesis and
respiration link the carbon and oxygen cycles
together.
The Nitrogen Cycle
 All
plants and animals need nitrogen. They
use it to make proteins, an essential
molecule for building healthy cells and
tissues.
 However, nitrogen gas, which makes up
78% of the atmosphere, is usable.
 It must be converted to other forms of
nitrogen.
The nitrogen cycle has five main steps.
1) When a plant or animal dies or excretes waste,
or when leaves fall from a tree, nitrogen
compounds pass into the soil or water.
2) Bacteria in the soil or water break down these
nitrogen compounds into ammonia, which is a
toxic substance.
3) Some ammonia is converted by bacteria into
ammonium ions (NH4), which some plants can
use directly.
4) Nitrifying bacteria in the soil convert ammonium
ions into nitrite ions, which are taken up by certain
plants.
5) Nitrite ions are converted into nitrate ions,
dissolved in water, and taken up by plant roots.
 Farmers
regularly add soluble nitrates to their soil
when they apply fertilizer, or even animal
manure.
 This greatly enhances plant growth and increases
the yield of grain, fruit, or vegetables needed to
feed a hungry world.
 When fields are cropped year after year without
adding fertilizer, the productivity of the soil is
greatly reduced, because there is very little of
the plant matter remaining in the field after
harvest, so the soil bacteria have little or nothing
to work on to convert to nitrates.
 Atmospheric
nitrogen can sometimes enter
plants directly.
 This is called nitrogen fixation.
 Certain plants, such as alfalfa, clover and peas
(the legume family), have tiny bacteria living in
their root system.
 These bacteria can absorb nitrogen directly out
of air spaces in the soil, and convert them for
direct absorption by the plant.
 In return, the bacteria obtain oxygen and sugars
from the plant.
 Nitrogen
Fixation – process of changing
nitrogen (N2) into ammonia (NH3) and
nitrates (NO3) which are soluble in water.
 Nitrification
– converting toxic ammonia to
less harmful nitrates.
There are three ways in which nitrogen can
be fixed into the environment.
1) Legumes (clover, alfalfa, beans, and peas)
 bacteria (rhizobia and cyanobacteria) that
grows on the roots of legumes can change
N2 into NO3 and NH3
 nitrates and ammonia are absorbed into
the roots of the legumes
 plants then convert these molecules into a
variety of proteins
2) Lightning
 energy from the lightning causes nitrogen
gas to react with oxygen in the air,
producing nitrates
3) Industrial Production
 industrial nitrogen fixation produces fertilizer
that farmers use to grow better crops
Denitrification – process in which bacteria
convert nitrates and ammonia into nitrogen gas
nitrogen
legume
(nitrogen fixation)
lightning
factory
(industrial production)
bacteria
(denitrification)
animal waste
animal
nitrate and ammonia
Plant
(nitrogen in
tissue
How Farmers Maintain Nitrate Levels
 Crop
Rotation
 Practice of moving different crops on the same
land.
 Rotation is between plants that need nitrogen
and legumes.
 Legumes are rotated with vegetable crops in
order to keep a proper amount of nitrogen in
the soil.
 Fertilizers
 material
used to restore nitrogen levels and
increase production from land
 Summer
Fallow
 Cropland that is purposely kept out of
production during a regular growing season.
 Resting the ground in this manner allows one
crop to be grown using the moisture and
nutrients of more than one crop cycle.
 Provides additional time for crop residues to
break down and return nutrients to the soil for
the subsequent crop.
Too Much of a Good Thing
An excess of nitrates and ammonia can lead to
an overabundance of plants. This can have a
progressively harmful effect on lakes and rivers.
Bodies of water containing an excess of nitrates
and ammonia have frequent algal blooms
(Grand Beach) and excessive weed beds along
the shoreline. The blooms can produce
dangerous toxins, which can harm fish and
wildlife.
Eventually the algal blooms "crash" and the
algae begin to die. The decomposing weeds
and algae deplete oxygen from the water
which causes fish to die due to a lack of
oxygen.
Human Impact
The cycling of nitrogen can be disturbed by
human activities.
1. Agricultural industry - a major source of
the nitrate and ammonia production.
Livestock operations produce large
quantities of animal feces (manure). The
disposal of manure is monitored so that
large amounts of manure are not
washed off the land (runoff) and into
lakes and rivers during the spring
snowmelt or heavy rainstorm
2. Excessive use of fertilizers on cropland soil may erode and fertilizers may wash
off farmland. The ammonia and nitrates
can also seep into the groundwater. The
ingestion of nitrates from well water can
cause in children a blood disorder called
anemia.
3. Septic fields and holding tanks leakage, releasing wastewater and
sewage into the ground. These materials
can seep into the earth, enter
groundwater, and end up in people's
drinking water.
4. Water-treatment plants - malfunctions
can occur, releasing raw sewage into
lakes and rivers. A heavy rainstorm may
overwhelm the capacity of a watertreatment plant, requiring the release of
partially treated wastewater into a lake
or river.
Video
Roles in Ecosystems
Let’s take a closer look at the interactions
among organisms in an ecosystem. Since all
living things require energy to live, the
ultimate source of that energy is the Sun.
Food Chain
 a simple linear relationship that
demonstrates the transfer of energy in an
ecosystem.
Video: Decomposers & Detritus Feeders
Video: Producers & Consumers
Food Web
 a diagram
representing the
eating habits of
an ecosystem
and consists of
interlocking
food chains.
Trophic Level
 each step in the series of feeding relationships in
a food chain/web.
Niche
 the place and role occupied by an organism in
an ecosystem, determined by its nutritional
requirements, habit, etc.
Consumers
 heterotrophic organisms who receive energy by
ingesting other organisms.
Omnivores
 are consumers who feed on both producers and
consumers.
Top Carnivore
o Last link in food chain/web.
o Animal who is not preyed upon
Ex.) wolves
Detritivores
o Heterotrophs that
consume organic
waste and remains.
Include scavengers
and decomposers.
Ex.) vultures, dung
beetles, maggots, fungi.
Decomposers
o Break down
dead organisms
and animal
waste.
Ex.) fungi
TERTIARY
Consumers
SECONDARY
Consumers
Heterotrophs who consume other
carnivores.
Ex.) sharks, hawks
Heterotrophs who consume lower
consumers.
Ex.) carnivores – fish, cats
PRIMARY
Consumers
Heterotroph
o organism that is incapable
of making its own food
Heterotrophs who consume
producers. Ex.) herbivores –
deer, rabbits, butterflies
PRODUCERS
Autotrophic organisms who receive
their energy from the Sun. Ex.)
Plants
Scavenger
o An organism that feeds on
dead plant and animal remains
Ex.) vulture
Autotroph
o uses energy to
make its own food
Video: Bill Nye’s Food Webs
Energy Pyramids
When a producer undergoes photosynthesis
it converts the Sun’s energy into a chemical
form that it can use. When a consumer
(herbivore) comes along and eats the plant
it does not get all the energy that the plant
produced. Most of the energy a plant
produces through photosynthesis is used by
the animal to grow and carry on life
activities. In fact, only 10% of the energy is
available to be passed on to the consumer
that eats it. This is referred to as the Ten
Percent Law.
Sun
Grass
Caterpillar
Robin
Hawk
1000 J
100 J
10 J
1J
To find 10% of something,
simply multiply the number by 0.10.
For this reason there must be a large
amount of producers in an ecosystem to
support very few top carnivores. As you
move up the food chain fewer and fewer
animals can be supported by the trophic
level below them on the food chain. This
variation in numbers or mass can be shown
by using energy pyramids instead of food
chains.
Biomass Pyramid
Related to the energy pyramid is the
biomass pyramid. This pyramid shows the
total amount of living material available at
each trophic level. The area at the bottom
of the biomass pyramid corresponds to the
producer level. This represents the greatest
amount of living material. You should note
that a pyramid of biomass does not follow
the 10% rule that the energy pyramid
follows.
Relationships among organisms in an
ecosystem are complex. Food chains consist
of producers and consumers, which are
connected into food webs. Energy flows
through ecosystems from one trophic level
to the next.
Food Chains Song
Bioaccumulation
Biodegradable – substance that is broken down
naturally in the environment. Examples include
sewage, food scraps, and dead organisms.
Non-biodegradable – substance that is broken
down very slowly or not broken down at all by
natural processes. Examples include the pesticide
DDT, PCB’s (polychlorinated biphenyls), mercury,
glass, and certain types of plastics.
Once pollutants enter an ecosystem, they will
remain there forever. A pollutant becomes a
toxin when it adversely affects living organisms.
Examples of toxins include DDT and mercury.
Government of Canada - DDT Video
Bioaccumulation
 When
producers take in the water they
require for photosynthesis, they may also
absorb small amounts of toxins. These
toxins are then stored inside the plants.
 When
herbivores eat the plants, they
begin to store the toxins in their fat. Many
producers must be eaten to keep one
herbivore alive, so the amount of toxin
inside one herbivore is much higher than
that of the individual producers it
consumed.
 The
stored toxins continue to be passed
up the food chain. This process is known
as biomagnification.
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
DDT
At each trophic level, the amount of toxin inside
the organisms increases. This process is known as
bioaccumulation or bioamplification. Eventually
the levels of the toxin become high enough
inside the secondary or tertiary consumers that
their health is affected. They may be poisoned
and die, or weakened and more susceptible to
disease or predators.
Interactions in Ecosystems
There are three basic ecological relationships
that occur.
1. Predator – Prey Relationship
 drives food chains / webs. Involves the
predator (in search of food) and prey
(potential meal)
2. Mating
 organisms have evolved to produce as
many offspring as possible to ensure the
survival of the species.
3. Competition
 caused by an organisms desire to survive and
produce offspring
 organisms will compete for natural resources
(food, shelter, territory, mates, water).
 there are two types of competition
i. Interspecific Competition
 between
2 similar species for a resource.
 Deer and elk for grass
ii. Intraspecific Competition
 between
members of the same species for a
resource
 Two rams for one ewe
Biodiversity
The variety of organisms found within an
ecosystem is known as its biodiversity. The
biodiversity of an ecosystem is an indicator
of its stability and health. Stable and healthy
ecosystems will have a large number and
variety of species present.
Different types of ecosystems have differing
numbers and types of organisms present.
The producers, consumers, and
decomposers in Brazil's tropical rainforest
are quite different from those in Canada's
tundra. The biodiversity of an ecosystem
may also appear to change through the
year.
Video: Why Biodiversity Matters
Video: The Threat to Biodiversity
Sustainability
Stable and healthy ecosystems are
sustainable; they are renewable and can
continue without the addition of new
materials. They rely on the undisturbed
cycling of nutrients and the natural
biodiversity of the area to maintain
predator-prey relationships.
Natural Prairie Grassland
 greater biodiversity
 different plants, including those that can "fix"
nitrogen
 biodiversity helps protect it from predators
 Example:
o Grasshoppers consume grasses; their
population is kept in check by predators such
as red-wing blackbirds.
o Other plant species may not be harmed by
grasshoppers, and will continue to grow.
Lawn
 monoculture - Only one type of plant (grass) is present
 grasses cannot "fix" nitrogen
 a lawn ecosystem can only be sustained with the addition
of fertilizer on a regular basis.
 large concentration of a small number of species, means
they are more vulnerable to attack
 a lawn requires the addition of herbicides to keep it
weed-free, and insecticides to reduce the damage
caused by insects.
Effects of Extinction
Organisms are linked together in complex
food webs. Should one species in an
ecosystem go extinct, the entire food web
may be jeopardized. A species is
considered to be extinct when it is no
longer found anywhere on our planet.
Extinction disturbs predator-prey
relationships.
Removing one
species from the
following food web
would affect the
other species.
1. How would the removal of wild rice affect the
primary consumers in the Lake Winnipeg
ecosystem?
Wild rice is a producer. It is an important food
source for primary consumers (minnows,
blackbirds). A lack of wild rice could create a
food shortage for these primary consumers
causing their populations to decline.
2. What would happen to the secondary consumers?
As the primary consumer population declines,
there would be less food for secondary
consumers. This would cause the secondary
consumer population to also decrease.
3. What would happen to the tertiary consumers?
The tertiary consumer population would also be
reduced because of the food shortage.
The removal of one species can have a large
impact on an ecosystem.
It can lead to a domino effect:
One event can cause a large chain reaction.
Classification Description
Example
extinct
a species that is no
longer found
anywhere
Blue Walleye
Last seen in Lake
Erie in 1965
endangered
a species that is close
to extinction in all
parts of Canada or in
a significantly large
location
Eastern Cougar
extirpated
any species that no
longer exists in one
part of Canada, but
can be found in others
Grizzly Bear
No longer in MB and
SK but still in AB and
BC
threatened any species that is likely to
become endangered if
factors that make it
vulnerable are not
reversed
vulnerable any species that is at risk
because of low or
declining numbers at the
fringe of its range or in
some restricted area
Wood Bison
Grey Fox
Invasive Species
Introduced species are considered invasive
if they cause native species in associated
habitats to decline. Invasive species thrive
in their adopted habitat because they lack
natural predators. They often disrupt
ecological functioning and cause severe
aesthetic, cultural and economic damage.
In North America, the Asian Long-horn
Beetle threatens eastern forests, Asian carps
destroy aquatic ecosystems and kudzu
smothers native plants.
In the past, we often did not concern
ourselves with the importance of
biodiversity to our planet. As our
knowledge of ecology has grown, we have
become more aware of the need for
biodiversity in maintaining and preserving
ecosystems, including the survival of our
species.
Video 1: Invasive Species
Video 2: Invasive Species
Population Growth
Population
 is a group of organisms that belong to the
same species living in a particular area at
a particular time.
Community
 a collection of all the populations in a
particular area at a specific time.
Population Growth
 Populations
can only grow to a certain
size. If the population has too many
people, there will not be enough space,
food, resources to support that population
Exponential Population Growth
 The
graph is shaped liked a “J”
 When conditions are “ideal” (perfect)
o
o
Population will increase rapidly in size
The larger a population gets, the faster
it increases
Population
The larger the
population gets,
the faster the
population grows.
Population is growing slowly
Time
Logistic Growth Curve
 The
graph is shaped like an “S”
 The environment cannot support the
population growth
o There is not enough resources such as
food and water for all of the population
o The rate of population begins to slow
Population
Population rate decreases
The larger the
population gets, the less
resources there are. The
population cannot
increase anymore.
Population rate increases
Time
Limits on Populations
Biotic Potential
 the maximum number of offspring that a
species could produce, if resources were
unlimited.
Population Growth Patterns



Changes in population size in a community occur
when individuals are added to or removed from a
population.
If natality (the birth rate) increases while other
factors remain constant, the population will
increase. The population will also increase with
immigration (moving into a population).
If mortality (the death rate) increases, the
population will decrease. The population will also
decrease with emigration (moving out of a
population).
 In
populations in open ecosystems, all four
factors influence population size, with natality
and mortality generally having the greatest
effect.
 Population growth can be represented
mathematically by the formula:
Population growth = (births + immigration) – (deaths + emigration)
In mature ecosystems, where resources tend to be constant
or available in predictable patterns, populations remain
relatively stable over the long term (population growth = 0).
This balance is referred to as dynamic equilibrium, or a
steady state.
Open & Closed Populations
 In
most natural ecosystems all four factors
are acting on the population of each
organism. These populations are said to
be open populations. However,
immigration and emigration do not
happen in laboratory settings and in some
game reserves, so these populations are
considered closed populations.
Biotic Potential: maximum number of offspring that a
species could produce, if resources were unlimited.
Biotic potential is regulated by 4 factors:
1. Birth potential

maximum number of offspring per birth.
Ex.)
Bear = 1-2 cubs
Fish = 1000+
2. Capacity for survival

the number of offspring that reach reproductive age.
Ex.)
Sea turtles lay many eggs, but few
reach maturity.
3. Procreation
 the number of times a species reproduces
each year.
Ex.) Elk = 1/year mice = 1/6 weeks
bacteria = several times a day
4. Length of reproductive life
 the age of sexual maturity and the number
of years the individual can reproduce.
Ex.) humans ~ 40 years
Limiting Factors
 The
environment provides factors that
prevent populations from attaining their
biotic potential. Any resource that is in
short supply is a limiting factor such as
food, water, territory, and the presence of
pollutants.
Abiotic
Factors that cause a
population to increase
Factors that cause a
population to decrease
o favourable light
o favourable
temperature
o favourable chemical
environment
o too much or too little
light
o too cold or too warm
o unfavourable chemical
environment
Biotic
Factors that cause a
population to increase
Factors that cause a
population to decrease
o sufficient food
o low number or low
effectiveness of
predators
o few or weak diseases
and parasites ability to
compete for resources
o insufficient food
o high number or high
effectiveness of
predators
o many or strong diseases
and parasites
o inability to successfully
compete for resources
Carrying Capacity
Carrying Capacity
 the maximum number of individuals of a species
that can be supported indefinitely by an
ecosystem.
The population can fluctuate over time.
 Sometimes there is lots of resources available, the
population can increase
 Sometimes there is not many resources available,
the population can decreases
 When
a population exceeds its carrying
capacity, mortality increases, reproduction
declines, and as a result, productivity is lower.
The population declines until it falls below its
carrying capacity. When conditions become
favorable once again, such as new growth
occurring in a cutover, then the birth rate will
increase, and mortality and emigration will
decrease. Thus the population changes in a
cyclical manner.
Once the carrying capacity has been
reached, the population size will increase
and decrease around that limit.
Carrying
capacity
Drawing a line through the
middle of the fluctuations
(changes) represents the
carrying capacity for that
species.
Limits on Populations
There are four factors that determine carrying capacity.
1. Materials and Energy
 Populations are limited by the amount of usable
energy from the sun, as well as the supply of water,
carbon, nitrogen and other essential elements.
2. Food Chains
 Population sizes at any level are influenced by the
size of the populations at lower trophic levels.
Populations are also related to higher trophic levels
(ex. predator – prey relationships)
3. Competition
 Both interspecific competition and
intraspecific competition.
4. Density
 Depending of their size, environment and the
way of life, different species have different
needs for space. The need for space can
determine an organism’s population density,
which is the amount of individuals living in an
area at any one time.
 If
a population increases beyond a suitable level,
it produces conditions that limit further growth in
numbers. For example, overcrowding increases
stress level and promotes the spread of disease
or parasites which may cause increased
aggression and neglect of offspring. This would
lead to an increase in death rate and a
decrease in birth rate, which causes the
population to decrease.
Density Dependent and
Independent Factors
1. Density-dependent factors
 affect a population because of the density or
size of the population. They increase in
significance as the population increases. These
factors include competition, predation, disease,
and stress and act to decrease the size of a
population by increasing the death rate and
decreasing the birth rate.
Ex.) food shortage, disease
2. Density-independent factors
 affect a population regardless of the population
density. They will affect a population regardless
of its size. These factors include natural
occurrences and human activity and also act to
decrease the size of a population by increasing
the death rate and decreasing the birth rate.
Ex.) volcanic eruptions, drought, flooding, war