UNIT D: CHANGES IN LIVING SYSTEMS

Matter cycles and energy dissipates through the biosphere and its component ecosystems. The concept of an ecosystem is used to

explain energy flow and nutrient recycling and to quantify large-scale and long-term processes. Students will study habitat destruction,

ecological succession and changes to populations, focusing on the need to balance the interests of a growing human population with

sustainable ecosystems.

OBJECTIVES:

UNIT D: OUTCOMES

● analyze ecosystems and ecological succession in the local area and describe the relationships and interactions among subsystems and components

● analyze and investigate the cycling of matter and the flow of energy through the biosphere and ecosystems as well as the interrelationship of society and the environment

● analyze and describe the adaptation of organisms to their environments, factors limiting natural populations, and evolutionary change in an ecological context.

OBJECTIVES:

Water: An Essential Abiotic Factor

● investigate and analyze an aquatic or a terrestrial local ecosystem, distinguish between biotic and abiotic factors, describe how these factors affect population size and

• infer the abiotic effects on life; e.g., light, nutrients, water, temperature• infer biotic interactions; e.g., predator-prey relationships, competition,

symbiotic relationships• infer the influence of biota on the local environment; e.g., microclimates, soil,

nutrients

● describe the potential impact of habitat destruction on an ecosystem

Abiotic vs. Biotic Factors In any part of the biosphere, there are abiotic

and biotic factors:Abiotic factors are physical, non-living parts of

an ecosystem.Biotic factors are living organisms found an

ecosystem.NOTE: “abiotic” is not the same as “dead.” Dead

things were once living and are therefore still considered biotic parts of an ecosystem.

Abiotic vs. Biotic FactorsAbiotic Biotic

Wind

Water

Temperature

Nutrients found in soil

Sunlight

Mammals

Trees

Fish

Plants/ flowers

insects

Ecosystems An ecosystem is a broad definition that refers

to all the organisms in an area as well as the abiotic factors with which they interact.It is IMPORTANT to remember that an ecosystem

is more than just animals and plants. It includes many abiotic factors that have a VERY STRONG influence on the success and health of an ecosystem.

Ecosystems vary in size: a fallen tree in a forest can support an ecosystem, our bodies are ecosystems, the boreal forest is an ecosystem.

Ecosystems This is the MOST IMPORTANT fact:

All life is connected.Organisms are connected to each other and the

abiotic factors they rely on or interact with. Therefore, ecosystems are what connects all life. Ecosystems are connected by the organisms that

leave or enter them and by the abiotic factors that leave or enter them.

Everything on Earth exists in a closed system.

Habitat Habitat is all the biotic and abiotic factors present

in an area that encourage the reproduction and survival of an organism.

Every organism has a preferred habitat. Every living thing has certain biotic and abiotic

requirements of its habitat. If those minimum requirements are not met, the organism will struggle to survive.

Nutrients are some abiotic examples of these requirements .they are any element or compound that an organism needs for growth or other functioning.

Water: An Essential Abiotic Factor Water is perhaps the most important abiotic factor in any

ecosystem. A few facts about water:

75-90% of all cells are made up of water.Somewhere between 70-75% if the Earth’s surface is covered

in water.Pure water (only H2O(l)) has a pH of 7 and is neither acidic

nor basic.The same water that existed on the earth millions of years ago

is still present today.Of all the water on the earth, humans can used only use about

three tenths of a percent of this water. Such usable water is found in groundwater aquifers, rivers, and freshwater lakes.

Water: An Essential Abiotic Factor Water is the solvent for life. Many ionic

components are dissolved in water and are transported between living cells in fluids such as blood and tree sap.

Water is a finite resource. There is only a certain amount that is useable to use as humans.When we remove water from the environment (an

ecosystem), it is no longer available to other organisms for their use. This is becoming a major problem in the world.

OBJECTIVES:

Biotic Factors: The Influence of Living Things

● investigate and analyze an aquatic or a terrestrial local ecosystem, distinguish between biotic and abiotic factors, describe how these factors affect population size and

• infer the abiotic effects on life; e.g., light, nutrients, water, temperature• infer biotic interactions; e.g., predator-prey relationships, competition,

symbiotic relationships• infer the influence of biota on the local environment; e.g., microclimates, soil,

nutrients

● describe the potential impact of habitat destruction on an ecosystem

Ecology If ecosystems are built on the interactions of

biotic and abiotic factors in an area, then ecology is the study of those interactions.

Ecologists are scientists who specialize in the study of interactions within ecosystems.

The study of ecology takes on many forms and is a difficult and challenging discipline.Remember, organisms interact with each other and

the abiotic factors that surround them. This forms a complex web of connections between all components of an ecosystem.

It is an ecologist’s job to make sense of that web.

Ecosystems

We have mentioned that ecosystems, are based on the complex interactions between all the biotic and abiotic factors within an area.

As a rule, ecosystems cover a larger geographic area than do communities.

For ecologist, studying an entire ecosystem is difficult – they are made up of many communities that first need to be studied before a more complete picture of the ecosystem is made.

Biomass Biomass is the dry mass of all the living

things occupying a habitat or ecosystem. It is generally accepted that biomass is a

good measure as to how many of each organism are present in a habitat or ecosystem.

Organization of Biotic Factors

Within ecosystems, it is possible to organize biotic factors (living things) into categories.

PopulationsA group of organisms, all of the same species,

which interbreed and live in the same area at the same time.

For example, all the deer mice occupying a particular meadow in the month of June are a population.

Ecologists often study ecosystems at the population level in order to better understand that organism’s role in the ecosystem.

Organization of Biotic Factors

CommunitiesA community is more complex than a population. It is

the interacting populations living in a certain area at a certain time.

Therefore, a community is made up of more than one group of organisms that interact with each other.

For example, a meadow in the month of June could be considered a community. There are plants, insects, birds and mammals that all interact with each other.

Studying communities is much more difficult to do. Ecologists struggle with the complexity of the connections between all the populations within that community.

Interactions in Ecosystems –Symbiosis Symbiosis is a type of interaction between

biotic factors in an ecosystem.Symbiosis is a long-lasting, ecological

relationship that benefits at least one organism of two different species that live in close contact.

One of the important things to remember about symbiosis is that it NEEDS to be long-lasting. If the interaction is momentary (like a bear attacking something) then it is not symbiosis.

There are three types of symbiosis that are recognized by ecologists.

Interactions in Ecosystems –Symbiosis Mutualism

This is a type of symbiosis where both organisms involved benefit from the relationship.

Nitrogen-fixing bacteria on the roots of some plants use the nutrients in the roots to sustain themselves (a benefit). The roots benefit from the relationship because the bacteria provide roots with a good source of nitrogen

Commensalism This is a type of symbiosis where one organism benefits and the other

is neither benefitted nor harmed. For example, brown-headed cowbirds follow herds of bison around.

The cowbirds eat flies that harass the bison (a benefit) and the bison are largely unaffected by the interaction.

Interactions in Ecosystems –Symbiosis Parasitism

This type of symbiosis involves one organism that benefits from the relationship and another which is harmed.

For example, yellow-bellied sapsuckers (a woodpecker) create small, square-shaped holes in the sides of trees. Sap leaks out of those holes, attracting ants which get caught in the sap. The sapsucker benefit by feeding on the trapped ants, the tree, however is harmed by the interaction (it loses sap).

Interactions in Ecosystems –Predator-Prey Interactions A predator is an organism that hunts another

organism for the purpose of killing and eating it. A prey animal is an organism that is hunted by a

predator. A predator-prey relationship is an

interaction between two organisms

where one organism (the predator) hunts, kills and eats the other organism (the prey). Predator-prey relationships are common in all

ecosystems. It is important, however, to note that parasitism is NOT predation, nor is a consumer eating a plant (there is no hunting taking place)

Interactions in Ecosystems –Competition The interesting thing about ecosystems is that

resources are limited. A prey species is not usually a prey species for only ONE organism.In many cases competition for resources (for

example a prey species) is a significant problem for organisms to overcome in order to be successful.○ If an organism isn’t well-suited to compete for a

resource, then it will struggle to survive.The resources that organisms compete for can be

either biotic factors (plants, meat, etc.) or abiotic factors (water, air, sunlight, etc.)

In many cases, competition for resources drives evolution.

OBJECTIVES:

The Web of Life

● analyze and describe how energy flows in an ecosystem, using the concepts of conservation of energy (second law of thermodynamics); energy input and output through trophic levels, food webs, chains and pyramids; and specific examples of autotrophs and heterotrophs

● explain why population size and biomass are both directly related to the trophic level of the species and explain how trophic levels can be described in terms of pyramids of numbers, biomass or energy.

Ecological Niches Within an ecosystem, each organism plays a

particular role. Some organisms may fill a number of niches depending on how they are connected to the ecosystem.

An ecological niche is a specific role an organism plays in its ecosystem.

American Ecologist Eugene Odum used the analogy that, “ If an organisms habitat is it’s “address”, the niche is the organism’s “profession”.

Ecological Niches Producer: an organism that uses light energy to

synthesize sugars and other organic compounds through the process of photosynthesis[ the conversion of light energy to chemical energy in the forms of sugars and organic molecules] (in most ecosystems, these are plants).

Consumer: a broad definition referring to any organism that uses other organisms as a source of energy (i.e. they eat other organisms).Primary consumer (herbivore): an organism that east green

plants, algae or phytoplanktons.Secondary consumer: an organism that eats herbivores.Tertiary consumer: an organism that eats secondary

consumers.

Ecological Niches Carnivore: an organism that kills and eats

other animals. Omnivore: an organism that eats both

plants and animals. Scavenger: a bird or animal that feeds on

dead and decaying animals that it did not kill itself.

Decomposer: (or detritivore) an organism that breaks down complex organic molecules into simpler molecules.

Energy Flow in Ecosystems Ecosystems are all about energy and matter. As you will

learn, energy flows and matter cycles. Energy flow starts with the ultimate source of energy in our

solar system – the Sun. From the Sun, energy flows through the producers and into the consumers at different levels.

Energy flows in steps and each step in the energy pathway is referred to as a trophic level:

Trophic comes from the greek word Trophikos, which means “to nourish”. A tropic level is the division of species within an ecosystem based

upon its energy source. Producers are the lowest trophic level, followed by primary

consumers, secondary consumers, etc. Energy is lost as we move up trophic levels.

Energy Flow in Ecosystems The reason that energy is lost as we move up

in trophic levels of the energy pyramid is because the higher up you go the more energy is used to survive, thus less is passed on.

There are numerous ways we can represent the flow of energy in ecosystems. We’ll explore a few of these:Pyramids of numbers, energy and biomass.Food chainsFood webs

Pyramid of Energy Amount of energy at each

trophic level can be represented by a pyramid of energy.

Tertiary consumers have a larger mass and expend large amounts of energy hunting, which is why the energy levels drop significantly.

Each level will obtain 1/10 or 10% of the energy their prey started out with.

Pyramid of Numbers Represents the number of organisms at each

trophic level. The pyramid is not always the same,

producers can be very large, while others are small.

What if we had a largenumber of top-levelconsumers and asmall number of producers?

Pyramid of Biomass Represents the biomass of each

trophic level in an ecosystem. Ex. Rainforest ecosystem would

store large amounts of solar energy and would contains lots of organic matter = large amount of biomass

Tundra gets a lot less energy and would contain less organic matter = smaller amount of biomass

The Pyramids Pyramids are a great way to represent the

flow of energy in an ecosystem (as well as, in some cases the numbers of individuals of each species in the population). The problem is that they are often difficult to construct:The pyramid of energy requires us to measure the

energy stored by plants and then what is passed on to the next trophic level – a difficult task.

The pyramid of biomass requires us to take the dry mass of all organisms (or at least a portion of them) in order to get the masses correct.

Food Chains Food Chain - a diagram of “who eats who”

in the ecosystem, with one organism at each trophic level.This is a very simple representation of the flow of

energy in an ecosystem. We trace energy from when it enters the ecosystem through the producer and as it passes from one trophic level to the next.

Food Chain

12 3

45

12

3

4 5

Food Webs Food webs – a diagram made up of

interconnecting food chains with many organisms at each trophic levelMore accurate because organisms eat more than

1 kind of food and can occupy more than one trophic level

Food webs are quite complex, but give a more complete picture of how energy flows within an ecosystem.

Food Webs

Food Chains and Food Webs You’ll notice that the food chains and food

webs both have arrows. Those arrows represent the flow of energy.For example, energy flows from the fish to the

osprey when the osprey eats the fish.THIS IS IMPORTANT TO REMEMBER!

OBJECTIVES:

The Recycling of Matter● outline the biogeochemical cycles of nitrogen, carbon, oxygen

and water and, in general terms, describe their interconnectedness, building on knowledge of the hydrologic cycle from Science 10, Unit D

● describe artificial and natural factors that affect the biogeochemical cycles:

• nitrogen cycle; e.g., automobile, agricultural and industrial contributions to NOx combining with water to produce nitric acid, nitrogen in manure and fertilizers

• carbon cycle; e.g., emissions of carbon oxides from extraction, distribution and combustion of fossil fuels, releases associated with deforestation and cement industries

• water cycle; e.g., extraction of ground water, dams for hydro-electricity and irrigation

Matter Cycles In the last lesson, we described that energy flows

through ecosystems. It originates with the sun (in most cases) and flows up the trophic levels.

In ecosystems, matter does the opposite: it cycles.

Matter cycles because the Earth is a closed system – energy is allowed to enter and leave, but matter is not.Therefore, we have a finite amount of matter to use in

our biosphere, therefore it must be cycled (think recycling).

The Biogeochemical Cycles Matter within our biosphere cycles through

biogeochemical cycles.“Bio” means living, therefore these cycles are

connected to living things.“Geo” means Earth or rock, therefore these

cycles are also connected to the rock/Earth.“Chemical” is obvious – these cycles are linked

with chemical reactions. Each cycle has a living, Earth and chemical

reaction connection.

Hydrological (Water) Cycle Involves the cycling of water in the

atmosphere and on the surface of the earth. driven by solar energy

evaporationcondensationprecipitation

Purposes of the Hydrological Cycle serves to stabilize the temperature of the

surrounding air and land due to the high latent heat of vaporization required for evaporation and the latent heat of fusion for freezing

serves as a purification process as the water percolates through the soil, it is

filtered “distillation” process – when water evaporates, it

leaves potentially harmful substances behind.

Hydrological Cycle

Carbon and Oxygen Cycles

Involves the cycling of carbon (usually in CO2(g) form) and oxygen in the atmosphere or as a part of organisms or the land.

photosynthesis and cellular respiration maintain a balance of concentrations of carbon and oxygen in the atmosphere 6 CO2(g) + 6 H2O(l) C6H12O6(s) + 6 O2(g) (Photosynthesis)

C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(l) (Cellular respiration)

Atmospheric concentrations of oxygen and CO2(g) O2 – 20.95%

CO2 – 0.033%

Oceans and forests serve as a sink for CO2 either absorbing or releasing CO2 to the atmosphere

What if CO2/O2 isn’t balanced?

What would happen if, for some reason, the equilibrium maintained by cellular respiration and photosynthesis is disrupted?

Carbon Cycle When carbon is not in its organic form it is

stored in 3 main areas: the atmosphere (gas), the ocean in sediments, and the Earth’s crust.

Under some conditions carbon is converted to rocks and fossils (coal, petroleum, natural gas) rather than going into immediate circulation.

Organic carbon is also stored in bogs. There is little oxygen in bogs, decomposition is

very slow, and carbon atoms become locked away (formation of coal).

Carbon Cycle

Oxygen Cycle The oxygen cycle is a mirror image (mostly)

of the carbon cycle. Since both are tied in to cellular respiration and photosynthesis, they mirror each other

Nitrogen Cycle Nitrogen cycling is connected to the

atmosphere, the soil and organisms. Essential for the formation of amino acids

(proteins) Composes 78.08% of atmosphere but cannot

be used in its atmospheric form (N2(g)) except for a few cases of nitrifying bacteria

In order to have usable nitrogen, we must convert it first to nitrates. This is done through lightning or nitrogen fixation (by bacteria)

Nitrogen Cycle

Disturbances to the Cycles Humans are really good at disturbing the

natural cycling of water, carbon, oxygen and nitrogen.Each time one of these cycles is messed with, it

affects the ecosystems connected to the cycles.In most cases, the effects of “messing” with the

cycles are negative, but in some cases, we can have positive effects.

OBJECTIVES:

Biodiversity

● describe the potential impact of habitat destruction on an ecosystem

● describe the effects of introducing a new species into, or largely removing an established species from, an environment; e.g., zebra mussel, carp and the Eurasian milfoil in Canada’s lakes, purple loosestrife in Alberta, the horse or the buffalo in the plains region of Alberta.

Biodiversity The International Union for the Conservation of Nature

(IUCN) defines biodiversity as:Biological diversity - or biodiversity - is a term we use to describe

the variety of life on Earth. It refers to the wide variety of ecosystems and living organisms: animals, plants, their habitats and their genes.

Biodiversity is everywhere. It occurs both on land and in water, from high altitudes to deep ocean trenches and it includes all organisms, from microscopic bacteria to more complex plants. Although many tools and data sources have been developed, biodiversity remains difficult to measure precisely. According to the Millenium Ecosystem Assessment, the total number of species on Earth ranges from five to 30 million and only 1.7–2 million species have been formally identified. IUCN – 2010 – www.iucn.org

Biodiversity But we do not need precise figures and answers to

devise an effective understanding of where biodiversity is, how it is changing over space and time, what are the drivers responsible for this change, its consequences for ecosystem services and human well-being, and the available response options.

There are many measures of biodiversity. Species richness (the number of species in a given area) represents a single but important metric that is valuable as the common currency of the diversity of life—but to fully capture biodiversity, it must be integrated with other metrics.

IUCN – 2010 – www.iucn.org

Biodiversity Our food and energy security strongly

depend on biodiversity and so does our vulnerability to natural hazards such as fires and flooding. Biodiversity loss has negative effects on our health, material wealth and it largely limits our freedom of choice. As all cultures gain inspiration from or attach spiritual and religious values to ecosystems or their components – e.g. landscapes, trees, hills, rivers or particular species - biodiversity loss also strongly influences our social relations.  IUCN – 2010 – www.iucn.org

Biodiversity Biodiversity is essential to global food

security and nutrition and also serves as a safety-net to poor households during times of crisis.

More than 70,000 plant species are used in traditional and modern medicine.

The value of global ecosystem services is estimated at $16-$64 trillion.

IUCN – 2010 – www.iucn.org

Habitat Fragmentation Habitat fragmentation is the conversion of

formerly continuous habitat into patches separated by non-habitat areas.

Some causes of habitat fragmentation common to Alberta are:Roads – usually oil and gas (seismic exploration

or access) or forestry accessWell sites

Habitat Fragmentation

Habitat Destruction Habitat destruction is the permanent alteration of

vital characteristics in an organism’s habitat.In other words, the habitat is no longer viable – it will no

revert to what it was before.Organisms are no longer able to use that habitat.

Habitat fragmentation will cause problems that can usually be avoided by organisms (e.g. they move to another location nearby).

Habitat destruction can be more devastating for organisms. Because the habitat is destroyed (lost), it is not something that can be used anymore, they must relocate.

Invasive Species An invasive species is a species that does not

normally occur in an area, is introduced by human action, and then expands to become a breeding population that threatens the area’s biodiversity.Zebra mussels, seven-spot ladybugs, purple loosestrife

and even house sparrows can be considered invasive species.

Quite often invasive species are better suited to adapting to their environment than the native species are. This means they are better able to compete for resources.

This competition can stress the native organisms, causing them major problems. In extreme cases, invasive species have forced native species to go extinct.

Invasive Species

Invasive Species What role do humans have to play with

respect to invasive species?Take a few minutes to think about how humans

might be making invasive species more of a problem.○ Share your thoughts with a partner.

Species at Risk When an organism’s population (usually on a

provincial-scale) is significantly reduced, often they are deemed a species at risk.What this designation means is that there is

concern that their population has fallen for many consecutive years and it is not looking like the population will recover unless we step in.

In nearly all cases of species at risk, humans are the central factor for the population’s decline.

Species at RiskCategory Description Examples

Extinct Species no longer exists anywhere (in the world).

Banff longnose dace (fish), passenger pigeon, dodo bird

Extirpated Species no longer exists in Alberta (or any region), but lives elsewhere.

Black-footed ferret, prairie dog

Endangered Species threatened with imminent extinction or extirpation through their range.

Woodland caribou, swift fox, burrowing owl

Threatened Species likely to become endangered if the factors that cause its vulnerability are not reversed.

Peregrine falcon

Vulnerable Species likely to become threatened or endangered

Wolverine

Species at Risk What role do humans have to play when it

comes to species at risk?Take a few moments to think about how humans

contribute to species becoming at risk.○ Share your thoughts with a partner.

BiodiversityHow is biodiversity being impacted? Name and

describe 2 sources that are causing biodiversity to be impacted. Explain what could be done to minimize the impact of these sources.

Introduce one species at risk in your ecosystem. What is it? Where does it live? Why is it at risk?

OBJECTIVES:

Primary Succession

● describe the key stages of primary succession in a specific ecosystem and the nature of its climax community; e.g., spruce bog, sand dune, pond, prairie

● differentiate between primary and secondary succession in a specific aquatic and a specific terrestrial ecosystem, e.g., pond, river, lake, forest, parkland, and compare natural and artificial means to initiate secondary succession in an ecosystem, e.g., reforestation or regrowth after a forest fire, flood or other natural disaster, strip mining, clearcutting, controlled burns by some Aboriginal groups promoting grassland biome regeneration

Ecosystems Change Every ecosystem undergoes change over time… trees

die and are decomposed, wind damages large parts of forest; fire, flooding and drought will all affect an ecosystem.

Even if an ecosystem were not to undergo a drastic, rapid change like those mentioned above, they still change gradually over time.The gradual change in ecosystems over time is succession.

It is NATURAL for ecosystems to change over their lifetimes.Most ecosystems change so slowly that it’s difficult for us to

see the changes within our lifetimes. Some might evolve over hundreds of years.

The next two lessons will be devoted to discussing two types of succession: primary and secondary.

Primary Succession Primary succession is the process of

changing – in successive, gradual stages – an ecosystem from an area of bare rock and few or no species to a complex community.Primary succession begins in places where soil

has been removed or has never existed.○ For example, bare land such as cooled lava, sand

dunes and mountain slopes.Primary succession is a SLOW process because

life must spring forth from “nothing” (bare rock).Let’s examine the stages of primary succession.

Primary Succession1. Primary succession begins with a clean slate (bare rock,

sand, lava, etc.)

2. A soil must then be developed (by wearing down rock and collecting some organic matter) before plants will grow.

3. Pioneer species (lichen and hardy plants) then populate the newly-formed, very sparse soil. When these organisms die, they add humus (organic matter) to the soil.

4. Once enough humus-rich soil is produced, larger plants can begin to grow. This will also start to attract more animals – starting with the smaller ones and moving on up.

5. Eventually forest will grow (if the climate allows) and this brings even more diverse plants and animals.

6. Ultimately a stable community results – forming what we call a climax community.

Primary Succession

Primary Succession Climax communities are different depending on

where you go in Alberta or the world. The type of community you find depends on the climate and accessibility to abiotic resources like water and sunlight.

For example:○ Due to the large amounts of rainfall, mild climate and

many days of sunlight, large cedar and fir dominated rainforest are climax communities on the west coast of BC.

○ In the Arctic, a climax community might be a vast area of shrubs and grasslands, limited by short growing seasons and a harsh climate.

Aquatic Succession In aquatic systems, we can encounter succession as

well. For example when water collects in a basin (likely

rocky), it is poor in nutrients. Runoff and other organisms that die in that basin begin to add to a “soil” created at its bottom

Eventually, enough soil collects to provide habitat for aquatic plants and aquatic invertebrates.

This will attract frogs, salamanders and other insects and eventually fish may even find their way into the ecosystem.

Once a vibrant community of organisms is thriving in this body of water, we have created a climax community yet again.

OBJECTIVES:

Secondary Succession● describe the key stages of primary succession in a specific

ecosystem and the nature of its climax community; e.g., spruce bog, sand dune, pond, prairie

● differentiate between primary and secondary succession in a specific aquatic and a specific terrestrial ecosystem, e.g., pond, river, lake, forest, parkland, and compare natural and artificial means to initiate secondary succession in an ecosystem, e.g., reforestation or regrowth after a forest fire, flood or other natural disaster, strip mining, clearcutting, controlled burns by some Aboriginal groups promoting grassland biome regeneration

Secondary Succession Secondary succession follows many of the

same general steps as in primary succession, but with one very important difference: secondary succession does not start from bare rock.It is the return to a stable climax community from an

area that has had its vegetation – but not its soil – removed.

This means that secondary succession proceeds much faster than primary succession because a soil is already developed.

Secondary Succession1. Secondary succession begins a major event that

eliminates all of the vegetation in an ecosystem, but not its soil. Major events could include fires, clear cuts, floods, etc.

2. Pioneer species (quite often grasses or fireweed) then populate the barren ground.

3. This attracts new, larger plants and of course more animals.

4. Eventually forest will grow (if the climate allows) and this brings even more diverse plants and animals.

5. Ultimately a stable community results – forming what we call a climax community.

Secondary Succession

Causes of Disturbances Secondary succession starts with a

disturbance that wipes out the vegetation in an ecosystem.This disturbance can originate naturally or can be

manmade. Here are some examples:○ Forest fire (most are natural, but some can be

manmade).○ Flooding○ Clear-cutting○ Reclamation of developed land.

Forest Fires Quite often, society associates forest fires with

being terrible catastrophes. This is only true, usually, when property or even lives are lost.

Forest fires are part of the natural cycle of forests (this could include grass fires on the prairies).A forest fire helps to regenerate the forest, returning

many nutrients that were locked up in the trees, back to the soil.

It opens the canopy allowing more light to the forest floor.

Many species of coniferous trees (namely pines) require fire to open their cones and release the seeds stored in side.

Forest Fires In many of our national parks (and even

some of our provincial parks), forest fires are set on purpose to burn areas of forest.These are called prescribed burns.Their goal is to mimic what nature does naturally

(i.e. setting fires by lightning).It is natural for a forest, when it reaches climax

community status, to burn sometime afterwards. It renews and regenerates the forest, forcing secondary succession to begin again.

OBJECTIVES:

Populations

● describe how factors including space, accumulation of wastes (e.g., salinization of soil), competition, technological innovations, irrigation practices (e.g., Hohokam farmers) and the availability of food impact the size of populations

● compare the growth pattern of the human population to that of other species.

A Population Recall that a population is the total number

of individuals of a certain species living in an area at a particular time.Human populations are determined based on

geographic area and so are other organisms’.Understanding populations of other organisms

has helped us understand human populations and vice versa.

Bacteria One of the best populations to study are

bacterial populations.Bacteria reproduce by dividing into two cells after

they have reached a certain size.Their populations experience exponential growth:

the rapid growth in population caused by a constant increase. This constant increase is achieved through the population doubling very quickly.

Bacterial populations, when graphed, create an exponential curve.

Bacteria

Factors Affecting Population Size The number of individuals in a population is

affected by four major factors:Number of births (natality): how many organisms

are born compared to the population size as a whole.

Number of deaths (mortality): how many organisms die compared to the population size as a whole.

Immigration: how many organisms move into (or join) the population’s area.

Emigration: how many organisms leave the population’s area.

Factors Affecting Population Size Open and closed populations have their

numbers change differently because different factors are at play:Open population is a group of organisms that

exists in a natural setting where births, deaths, immigration and emigration affect population size (most common in natural settings).

Closed population is a group of organisms that exist in a natural or artificial setting where immigration and emigration do not occur, and population size is only affected by births and deaths (think about a zoo, for example).

Limiting Factors Births, deaths, immigration and emigration

are simple, broad factors used to determine a population’s size.

Limiting factors are specific parts of an organism’s habitat that affect population size In other words, these are the factors that will

causes increases or decreases in births, deaths, immigration and emigration.

Limiting Factors Space

The amount of space available to a population will affect how it grows. Generally, the more space the better, so long as the space available includes suitable habitat.

Accumulation of wastesIf too many wastes accumulate in an ecosystem

(without being broken down or removed), a population’s size will decrease.○ For example if the soil is to saline (salty) plant

populations will struggle to grow, affecting other populations that rely on them.

Limiting Factors Competition

Competition between individuals of a species can significantly affect population size. Too much competition means resources are limited (food, water, shelter), therefore population size will decrease.

Availability of FoodAs food supplies become more scarce, population

size will decrease and vice versa.○ Scarcity of food can be cause by a population being too

large (not enough food to feed all the hungry mouths) or it could be caused by an external factor (for example a change in the climate of their ecosystem).

Carrying Capacity Each ecosystem has a specific carrying capacity for

each organism that inhabits the ecosystem.Carrying capacity is the maximum number of individuals

that can be sustained for an indefinite period of time in a given ecosystem.

If carrying capacity is exceeded, a population will likely experience a crash (especially if its growth was exponential). This crash will be due to a lack of resources.

For example an ecosystem is only able to support 3 grizzly bears because there are only enough resources within it to keep 3 grizzly bears alive. One more grizzly bear entering that ecosystem would put it over its carrying capacity. Something would have to give… a bear would need to die or leave.

Human Populations Like bacteria, human population has been

increasing exponentially.Human population has been able to grow

exponentially because of technological innovations:○ As we have developed better ways to stay alive in

our ecosystems, our life expectancy has increased, so has our natality. This has kept more of us alive longer, allowing us to reproduce.

○ Some innovations that have aided in this include: central heating, refrigerators, medicine, guns, and the list goes on…

Human Populations Many scientists and anthropologists believe

that Earth is nearing its carrying capacity for humans.In other words, we are getting close to not being

able to support any more humans.When we reach our carrying capacity for humans,

like in the example with grizzly bears, something is going to have to give…

OBJECTIVES:

Adaptations

● describe mutation as the principal cause for variation of genes in species and populations, identify the role of sexual reproduction in generating variability among individuals and describe the forces that drive evolution

● describe the adaptation of species over time due to variation in a population, population size and environmental change; e.g., bacterial resistance to antibiotics, giraffe neck length, gazelle speed

● describe evidence for evolution by natural selection; e.g., fossils, biogeography, embryology, homologous and vestigial structures, biochemical research

Changes in Populations Populations are changing all the time, not only

in size, but also in behaviour and appearance.What we mean by this is that what the species

looks like and how it behaves changes over time. There are two types of changes in populations:

Gradualism: changes to the organisms in a populations occur slowly and steadily over the Earth’s history.

Punctuated equilibrium: changes to the organisms in a population occur in rapid spurts, followed by long periods of little change.

Changes in Populations These changes bring about changes in

appearance and behaviour of the species that makes up the population.The rapid changes can be caused by major

events in the population’s ecosystem.Gradual changes are usually caused by minor,

slow changes to the population’s ecosystem. How do these changes cause a change in

the whole population?

Inheritance All living things have DNA

(deoxyribonucleic acid).DNA contains all the information necessary to make a

particular kind of organism.DNA is passed from one generation (parents) to the next

(offspring/kids).○ Another way to say this is that you inherit DNA from your

parents.

The DNA contains information that gives you some of the traits of your parents (e.g. eye colour, hair colour, facial features, etc.).Segments of DNA that “code” for particular traits are called

genes.

Inheritance In order to keep the genetic material

changing in a species (which keeps a population healthy), there is a mix of genes.This “mix” occurs during sexual reproduction.When organisms sexually reproduce, the male

donates half of the DNA needed, while the female donates the other half. This creates genetically diverse offspring.

So, we can say that we inherit our genetics from our parents – half from our mom and half from our dad.

Variation in Populations Every individual in a population is different

(usually only slightly) – think about hair colour, eye colour, etc.

Where does this variation come from?Sexual reproduction – the mixing of DNA from

your parents creates variation.Mutation – a change in the DNA sequence which

results (sometimes) in a change in the traits expressed by your genes.

Mutations Not all mutations are bad…

Mutations that help an organism to better survive in its environment are good mutations.○ These will make it more likely for the organism to

be healthy enough to reproduce and pass on their DNA.

Mutations that make it more difficult for an organism to survive are bad mutations.○ These will make it less likely for the organism to be

healthy enough to reproduce and pass on their DNA.

Adaptations An adaptation is a structural (part of the body) or

behavioural (what it does) trait that improves an organism’s success at surviving and reproducing in a particular environment.Structural: sharp claws, long neck, etc.Behavioural: migration, stalking, etc.

Adaptations are brought about by good mutations and are passed down to the next generation through DNA.Quite often these mutations are driven by changes in the

organisms environment.Sometimes these mutations occur at random – bringing on

a beneficial change.

A thought about inheritance and population change… In order for a population to change, a

mutation MUST be passed on to the next generation.If the change in DNA (mutation) is not passed on

in the genetic information from the parents to the offspring, the population will not change.

OBJECTIVES:

Evolutionary Theory

● describe evidence for evolution by natural selection; e.g., fossils, biogeography, embryology, homologous and vestigial structures, biochemical research

● compare gradual evolution with punctuated equilibrium

What is Evolution? Evolution is the progressive change in

organisms over time.

The Age of Earth based on the

rates of decay of radioactive isotopes the earth is over 4.5 billion years old

Evidence for Evolution Comparative Anatomy

Homologous – structures that are similar origin but have different functions (dolphin fin, dog leg)

Analogous- structures that are similar in use but have different origins (bird wing and butterfly wing)

Evidence for Evolution Fossil Evidence

When we begin to compare fossils of organisms of different times, we can see the progression of evolution.

Evolution of birds from dinosaurs is a great example.

Evidence for Evolution Biochemistry (Genetics)

The more closely related two organisms are, the more similar their genetic structures are

DNA similarities – when we begin to compare the genomes (genetic material) in organisms, we can see that organisms who are closely related share much of the DNA sequence, while distant relatives have few similarities.

Evolutionary Theories Evolution has not always been widely

accepted as the way to explain how organisms have changed over time.

It wasn’t until Charles Darwin published his book “On the Origin of Species” in November of 1859 that the scientific community started to come together on this matter.

Darwin’s theory was contested by another theory – that of Lamarck.

Jean Baptiste Lamarck Argued for the idea of spontaneous

generation: species are continually being created spontaneously from non-living matter.

We now refer to this as inheritance of acquired characteristics: environmental changes bring about changes in individuals, and these changes are passed on to their offspring. We know this to not be true.

Lamarck: an Example Lamarck would suggest that a giraffe used to be

a short-necked animal, but due to the need to reach higher food sources, their necks stretched. This stretching would be passed on to their offspring.

Charles Darwin In 1831, at the age of twenty-

two, Charles Darwin set off from England on a voyage around the world. He was serving as the ship's naturalist aboard the H.M.S. Beagle.

The observations that he made on this voyage were the first step toward his formulation of the theory of evolution by natural selection.

•WHY DID SOME SPECIES SURVIVE WHILE OTHERS BECAME EXTINCT?

•NATURAL SELECTION

Charles Darwin Following his voyage on the Beagle, Darwin

came up with 3 inferences:1. Individuals of the same species are in a

constant struggle for survival.With each other and with the environment.

2. Individuals with more favourable variations are more likely to survive and pass these variations on. Survival is not random. THIS is natural selection.Think about a tiger that can move faster or a mouse with

better camouflage.

Charles Darwin3. Since individuals with more favourable

variations contribute proportionately more offspring to succeeding generations, their favourable inherited variations (genetic information) will become more common. THIS IS EVOLUTION.A mouse that is better able to evade prey will survive longer

and thus pass its inherited superior speed/camouflage/instincts on to its offspring. We are evolving a better mouse.

Charles Darwin Initially, Darwin’s inferences were met with

much resistance. Over time, though his theory of natural selection was accepted and has become the way we explain evolution.