Dynamics of Ecosystems · 2018-09-10 · Dynamics of Ecosystems In this unit, you will examine the complex relationships present in ecosystems in order to further investigate issues

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.

Gr. 10 Science Page 2 Dynamics of Ecosystems

Specific Learning Outcomes

Illustrate and explain how carbon, nitrogen, and oxygen are cycle through an

ecosystem.

Discuss factors that may disturb biogeochemical cycles.

Include: natural events, human activities.

Describe bioaccumulation and explain its potential impact on consumers.

Examples: bioaccumulations of DDT, lead, dioxins, PCBs, mercury...

Describe the carrying capacity of an ecosystem.

Investigate and discuss various limiting factors that influence population

dynamics.

Include: density-dependent and density-independent factors.

Construct and interpret graphs of population dynamics.

Describe potential consequences of introducing new species and species extinction

on an ecosystem.

Observe and document a range of organisms that illustrate the biodiversity within

a local or regional ecosystem.

Explain how the biodiversity of an ecosystem contributes to its sustainability.

Investigate how human activities affect an ecosystem and use the decision-making

process to propose a course of action to enhance its sustainability.

Include: impact on biogeochemical cycling, population dynamics, and biodiversity.


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 appear the way they do because of temperature, precipitation, and

distance from the equator.

Major Ecosystems of the Earth


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 + 6H2O Light→ 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 + 6H2O + energy

Photosynthesis and cellular respiration are part of the cycling of matter and the

transfer of energy in ecosystems.

carbon dioxide + water sugar + oxygen

sugar + oxygen carbon dioxide + water


Biogeochemical Cycles

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 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.

1. The Atmosphere

o 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.

2. The Oceans:

o 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.

3. The Earth’s Crust

o 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.


4. Living Organisms

o 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.


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.


Carbon-Oxygen Cycle


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)

o bacteria (rhizobia and cyanobacteria) that grows on the roots of legumes

can change N2 into NO3 and NH3

o nitrates and ammonia are absorbed into the roots of the legumes

o plants then convert these molecules into a variety of proteins

2. Lightning

o energy from the lightning causes nitrogen gas to react with oxygen in the

air, producing nitrates

3. Industrial Production

o industrial nitrogen fixation produces fertilizer that farmers use to grow

better crops

Denitrification – process in which bacteria convert nitrates and ammonia into

nitrogen gas

Plant

(nitrogen in

tissue

lightning

legume

(nitrogen fixation)

animal

animal waste

nitrogen

factory

(industrial production)

nitrate and ammonia

bacteria

(denitrification)


How Farmers Maintain Nitrate Levels

1. Crop Rotation

o Practice of moving different crops on the same land.

o Rotation is between plants that need nitrogen and legumes.

o Legumes are rotated with vegetable crops in order to keep a proper amount

of nitrogen in the soil.

2. Fertilizers

o material used to restore nitrogen levels and increase production from land

3. Summer Fallow

o Cropland that is purposely kept out of production during a regular growing

season.

o Resting the ground in this manner allows one crop to be grown using the

moisture and nutrients of more than one crop cycle.

o Provides additional time for crop residues to break down and return

nutrients to the soil for the subsequent crop.

http://simple.wikipedia.org/wiki/Crop

http://simple.wikipedia.org/wiki/Land


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 algae 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 waste (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

rainstorms.

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 water-

treatment plant, requiring the release of

partially treated wastewater into a lake or

river.


Nitrogen Cycle


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.

Food Web – a diagram representing the eating habits of an ecosystem and consists

of interlocking food chains.


Roles in Ecosystems

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.

PRODUCERS

PRIMARY

Consumers

SECONDARY

Consumers

TERTIARY

Consumers

Autotrophic organisms who receive their energy from the Sun. Ex.) Plants

Heterotrophs who consume producers. Ex.) herbivores – deer, rabbits, butterflies

Autotroph o uses energy

to make its own food

Heterotroph o organism that is

incapable of making its own food Decomposers

o Break down dead organisms and animal waste.

Ex.) fungi

Scavenger

o An organism that feeds on dead plant and animal remains

Ex.) vulture

Heterotrophs who consume lower consumers. Ex.) carnivores – fish, cats

Heterotrophs who consume other carnivores. Ex.) sharks, hawks

Detritivores o Heterotrophs that

consume organic waste and remains. Include scavengers and decomposers.

Ex.) vultures, dung beetles, maggots, fungi.

Top Carnivore o Last link in food chain/web. o Animal who is not preyed upon

Ex.) wolves



Food Chains and Food Webs

Clues to Chains and Webs

The clues below are related to terms about food chains and food webs. Identify the

terms described in the clues and write the terms on the answer lines at the left. Use

the word list on the board. Words may be used more than once!

____________________ 1. Process in which green plants use light to make sugar.

____________________ 2. Set of eating interactions within an ecosystem.

____________________ 3. Organisms that manufacture food.

____________________ 4. Consumers that eat producers.

____________________ 5. Consumers that feed on primary consumers.

____________________ 6. Consumers that feed on secondary consumers.

____________________ 7. Food chains that overlap.

____________________ 8. Organism that feeds only on plants.

____________________ 9. Organism that consumes both plants and animals.

____________________ 10. Organism that breaks down dead organisms and animal waste.

____________________ 11. Animals that feed on dead organisms.

____________________ 12. Substance needed by all organisms for making protein.

____________________ 13. Process in which nitrogen is released into the air.

____________________ 14. Organisms that add nitrogen to the soil.

____________________ 15. Substance that organisms make with nitrogen.

____________________ 16. Example of a first-order consumer.

____________________ 17. Any organism that does not produce its own food.

____________________ 18. Example of a herbivore

____________________ 19. Example of a carnivore

____________________ 20. Example of an omnivore


Making a Food Web

The table below indicates the relationships among eleven different organisms. Use

this information to correctly place each organism in the food web diagram under the

table. Write the names of the organisms on the lines provided.

Organism Eats Is Eaten By

bird spider fox, owl, snake

fox bird, mouse, rabbit

grass grasshopper, mouse, rabbit

grasshopper grass spider, toad

mouse grass fox,, owl, snake

owl bird, mouse, snake

rabbit grass fox

snake bird, mouse, toad owl

spider grasshopper bird, toad

toad grasshopper, spider snake

1.

2. 3.

8.

4.

6.

7.

9.

10.

5.


Feeding Relationships

Consider the sequence of organisms below. Then answer the questions that follow.

1. Which trophic level does the first organism occupy? __________________________________

2. Which organism is the primary consumer? __________________________________________

3. Which organism is the tertiary consumer? __________________________________________

4. Which organism is the top carnivore? _____________________________________________

5. Which organism is not a consumer? _______________________________________________

6. What are two ecological roles for the snake? ________________________________________

7. The fact that a grasshopper eats grass and may be food for a sparrow describes its __________

within this ecosystem.

8. Forests and grasslands are examples of __________________________________ ecosystems.

9. The linear relationship above is referred to as a _____________________________________.

10. You unpack your lunch. You have a chicken sandwich, an apple, and some juice. You eat everything.

Based on what you have eaten, you are best described as a/an ___________________________.

grain grasshopper sparrow snake fox wolf



Ecological Pyramids

Energy Pyramid

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.

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.

Sun Grass (1000J) Caterpillar (100J) Robin (10J) Hawk (1J)


Ecological Pyramids

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.


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 these 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.

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.

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.


Bioaccumulation


Interactions in Ecosystems

There are three basic ecological relationships that occur.

1. Predator – Prey Relationship

o drives food chains / webs. Involves the predator (in search of food) and

prey (potential meal)

2. Mating

o organisms have evolved to produce as many offspring as possible to ensure

the survival of the species.

3. Competition

o caused by an organisms desire to survive and produce offspring

o organisms will compete for natural resources (food, shelter, territory,

mates, water).

o 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

http://www.google.ca/imgres?q=interspecific+competition&um=1&sa=N&hl=en&rlz=1T4GGNI_en-GBCA520CA521&biw=685&bih=601&tbm=isch&tbnid=L2-q2GIJG3j9xM:&imgrefurl=http://moodle.rockyview.ab.ca/mod/book/view.php?id=56696&chapterid=20565&docid=BtsamnB_43yOQM&imgurl=http://resource.rockyview.ab.ca/t4t/bio20/images/m3/004_zebra.jpg&w=305&h=214&ei=iezvUb21AovoqAHHiYCgBA&zoom=1&ved=1t:3588,r:7,s:0,i:109&iact=rc&page=2&tbnh=171&tbnw=244&start=6&ndsp=11&tx=75&ty=53

http://www.google.ca/imgres?q=interspecific+competition&um=1&sa=N&hl=en&rlz=1T4GGNI_en-GBCA520CA521&biw=685&bih=601&tbm=isch&tbnid=Ac1JDIZq7QcirM:&imgrefurl=http://www.glogster.com/old/view?nickname=bbryyanna&title=false/&docid=-S1NRPvZIslseM&imgurl=http://c85c7a.medialib.glogster.com/media/a8/a866dd96f179b7d0f866c3debdc74c006d2c50d7a840d55573c23f5ed7cba1fe/competition-hirschkampf-743015-jpg.jpg&w=700&h=466&ei=iezvUb21AovoqAHHiYCgBA&zoom=1&ved=1t:3588,r:8,s:0,i:112&iact=rc&page=2&tbnh=183&tbnw=275&start=6&ndsp=11&tx=150&ty=101


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.

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.

Let’s compare the sustainability of a natural prairie grassland to that of a lawn.

Natural Prairie Grassland Lawn

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.

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.


Biodiversity

The food chain below is followed by a series of questions. Study the food chain and

then answer each question by circling “increase” or “decrease” as appropriate to the

right of each question.

1. If the grass is destroyed by fire, what will happen to the

rabbit birth rate?

increase decrease


rabbit death rate?

increase decrease


lynx population?

increase decrease

4. If the lynx birth and survival rate increases, what will

happen to the rabbit population?

increase decrease


happen to the amount of grass?

increase decrease


happen to the rate of disease among rabbits?

increase decrease

7. If additional predators of rabbits immigrate into the area,

what will happen to the lynx population?

increase decrease

8. If the lynx population is destroyed by unlimited hunting,

what will happen to the amount of grass?

increase decrease

grass rabbit lynx


The food chain below is followed by a series of questions. Answer each question by

circling the correct organism to the right of each question.

1. Which organism is a producer? grain mouse snake hawk

2. Which organism is a first-order consumer? grain mouse snake hawk

3. Which organism is a third-order consumer? grain mouse snake hawk

4. Which organism is necessary in the largest

amount in order to support this food chain?

grain mouse snake hawk

5. The snake is predator to which organism? grain mouse snake hawk

6. The snake is prey to which organism? grain mouse snake hawk

7. Which animal receives only about 1/1000 of

the energy produced in the grain?




Biodiversity

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.


Biodiversity

1. How would the removal of wild rice affect the primary consumers in the Lake

Winnipeg ecosystem?

2. What would happen to the secondary consumers?

3. What would happen to the tertiary consumers?

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.


Biodiversity

Classifying Species at Risk

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

Manitoba, Saskatchewan,

but still in Alberta & BC

threatened any species that is likely to become

endangered if factors that make it

vulnerable are not reversed Wood Bison

vulnerable any species that is at risk because

of low or declining numbers at the

fringe of its range or in some

restricted area

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.


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 Population will increase rapidly in size

o The larger a population gets, the faster it increases

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

Popu

lati

on

Time

Popu

lati

on

Time

The larger the population gets, the

faster the population grows.

Population is growing slowly.

Population rate decreases.

The larger the population gets, the

fewer resources there are. The

population cannot increase anymore.

Population increases.


Population Growth Patterns

Changes in population size in a community occur when individuals are added to or

removed from a population.

o 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).

o 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:

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 and 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.

Population growth = (births + immigration) – (deaths + emigration)


Limits on Populations

Biotic Potential – the 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+ eggs

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-1/6weeks 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.

Factors that cause a population to increase

Factors that cause a population to decrease

Abiotic

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

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 We saw that the Woodland Caribou population grew by 10%. However, in any

ecosystem, no population can sustain unlimited growth. There is only so much food,

water, and space to go around. The number of organisms that can be supported by the

community is called its 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.

o Sometimes there is lots of resources available, the population can increase

o 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.

The following population growth curve best represents what happens to a population

over time.

Once the carrying capacity has been reached, the

population size will increase and decrease around the limit

Draw a line through the middle of the fluctuations

(changes) represents the carrying capacity for that

species.


A classic example of population cycles is demonstrated by the snowshoe hare and

lynx. Historical records to pelts traded by the Hudson’s Bay Company shows us that

both the hare and lynx have gone through cyclical fluctuations on the basis of a 9-10

year cycle. Peak populations of lynx occur shortly after the peak populations of hares.



There are four factors that determine carrying capacity.

1. Materials and Energy

o 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

o 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

o Both interspecific competition and intraspecific competition.

4. Density

o 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 There are 2 broad types of factors that limit population growth.

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 erruptions, drought, flooding, war)


Compare Relation Frame: Compare and Contrast Make the distinction between:

Biotic Environment and Abiotic Environment

Biotic Environment Abiotic Environment

Write a summary statement:


Population Dynamics

A Predator-Prey Relationship

Let's take a closer look at the relationship between predators and prey. One example

is that of the lynx and its primary prey, the snowshoe hare. People have long been

aware that the populations of both the hare and the lynx fluctuated on a cyclical

basis. A team of wildlife biologists decided to study these fluctuations. The team

monitored the populations of both lynx and snowshoe hare over a number of years,

and recorded their observations. The data they gathered is found in the table below.

Year of Study

Lynx Population

Hare Population

Other Observations

1 30 50

2 5 25 low lynx birth rate

3 5 50 lynx eating mice – unusual

4 10 70 food is plentiful for hares

5 25 100

6 45 150 high lynx birth rate

7 65 175 winter food scarce for hares

8 95 160 hares are starving

9 115 100 many hares eaten by lynx

10 100 60

11 80 40

12 40 20 lynx are starving

13 5 50 lynx leave the area

14 5 75

15 10 120 high hare birth rate

16 30 160

17 60 180 greatest number of hares seen

18 100 150 trees and shrubs badly chewed

19 120 70 greatest number of lynx seen

20 90 45 many young hares die


Population Dynamics

Your role is that of wildlife management consultant. You must examine the data the

team has gathered, create a graph showing the changes in the sizes of the lynx and

hare populations, and interpret the information.

1. Examine the above data. Do you notice any trends:

a. in the changes in the hare population?

b. in the changes in the lynx population?

c. between the changes in the lynx and hare populations?


Population Dynamics 2. On the following graph, plot the fluctuations in the lynx and hare populations for

the 20-year study period.

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20

Num

ber

of H

are a

nd L

ynx

Year of Study

Hare and Lynx Populations


Population Dynamics

3. Examine the biologists' other observations and your graph to answer the following

questions.

a. Suggest possible reasons why the hare population was so high in Year 16 of

the study.

b. Suggest possible reasons why the lynx population was so low in Year 14 of

the study.

c. Suggest possible reasons why the hare population declined from Year 8 to

Year 11 of the study.


Population Dynamics

d. Suggest possible reasons why the lynx population rose from Year 4 to Year

8 of the study.

e. Predict the size of the hare population in Year 26 of the study. Explain how

you arrived at your prediction.

f. Predict the size of the lynx population in Year 26 of the study. Explain how

you arrived at your prediction.

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Dynamics of Ecosystems · 2018-09-10 · Dynamics of Ecosystems In this unit, you will examine the complex relationships present in ecosystems in order to further investigate issues