Unit B: Ecosystems and Population Change
Themes: Energy, Matter and Systems
Overview: In this unit, students become familiar with a range of ecosystems by studying their distinctive biotic and abiotic characteristics. Students are introduced to the concept of populations as a basic component of ecosystem structure and complete the unit by examining population change through the process of natural selection.
The content in Unit B prepares students for the study of populations and community dynamics in Biology 30.
This unit builds on:
• Grade 7 Science, Unit A: Interactions and Ecosystems
• Grade 8 Science, Unit E: Freshwater and Saltwater Systems
• Grade 9 Science, Unit A: Biological Diversity Focusing Questions:
What are the major biotic and abiotic characteristics that distinguish aquatic and terrestrial ecosystems?
What data would one need to collect in a field study to illustrate the major abiotic characteristics and diversity of organisms?
What mechanisms are involved in the change of populations over time?
In what ways do humans apply their knowledge of ecosystems to assess and limit the impact of human activities?
General Outcomes: There are two major outcomes in this unit.
Students will:
1. explain that the biosphere is composed of ecosystems, each with distinctive biotic and abiotic characteristics
2. explain the mechanisms involved in the change of populations over time.
Key Concepts:
The following concepts are developed in this unit and may also be addressed in other units or in other courses. The intended level and scope of treatment is defined by the outcomes.
ecosystem
adaptation and variation
niche
population
biotic/abiotic characteristics
natural selection
limiting factors
species
binomial nomenclature
evidence for evolution
General Outcome 1
Students will explain that the biosphere is composed of ecosystems, each with distinctive biotic and abiotic characteristics.
Specific Outcomes for Knowledge Students will:
define species, population, community and ecosystem and explain the interrelationships among them
Explain the interrelationship of energy, matter and ecosystem productivity (biomass production); e.g.,
Antarctic Ocean versus tropical seas
tropical rain forest versus desert
taiga versus tundra
intertidal zone versus deep-sea benthos
Arctic versus Antarctic
explain how terrestrial and aquatic ecosystems support a diversity of organisms through a variety of habitats and niches; e.g.,
o terrestrial: canopy, sub-canopy, forest floor, soil o aquatic: littoral, limnetic, profundal and benthic zones
identify biotic and abiotic characteristics and explain their influence in an aquatic and a terrestrial ecosystem in the local region; e.g., stream, lake, prairie, boreal forest, vacant lot, sports field
explain how limiting factors influence organism distribution and range; e.g., o abiotic factors: soil, relative humidity, moisture, ambient temperature,
sunlight, nutrients, oxygen
o biotic factors: competitors, predators and parasites Interactions within Ecosystems:
Define ecosystem:
Type of Ecosystem Examples
Prairie, grassland, forest
Pond, lake, stream
• Ecosystems rarely have sharp boundaries,
– Organisms can move back and forth from one ecosystem to another.
• This area between ecosystems is where organisms from both ecosystems interact with each other.
Ecotones contain species from both bordering ecosystems
o so they often contain greater _______________________than either ecosystem.
Describe why ecotones tend to be less fragile. How do ecotones guard against extinction?
Roles in Ecosystems Define ecological niche:
In ecosystems, having a different niche is important to _______________
_____________ between species.
Owls and hawks feed on many of the same organisms, but occupy distinctly different niches.
Example One: The table below summarizes adaptations that allow Owls and Hawks to occupy different niches
Owl Hawk
Huntin g
Activit y
Nesting
Example Two: Figure Two on the left shows different niches of warbler in one tree.
Competition for Niches
When a new species enter an ecosystem, it causes a disturbance because it comes into competition for a niche with one or more of the species already in the ecosystem.
Define Exotic species –
• The introduction of new species happens naturally. Animals are mobile and can move from one ecosystem to another.
• The introduction of new species by humans to an ecosystem is one of the main causes of species depletion and extinction, second only to habitat loss.
• Problems with introducing Exotic Species:
•
•
• Define a biome:
Canada has four major Biomes:
1. Tundra 2. Taiga
3. Temperate deciduous forest 4. Grassland
Using page 97 of your textbook, identify the Abiotic and Biotic factors that contribute to the creation of Albertan Ecosystems.
Name Abiotic Factors Biotic community
Taiga
Muskeg
Grassland
Factors Affecting Terrestrial Ecosystems
Each ecosystem is defined not only by the organisms that live in it but also by the abiotic factors that affect them.
1. Soil
Soil can be viewed as a series of layers
i. _____________________ - partially decomposed leaves/grasses
ii. _____________________ - small particles of rock mixed with decaying plant
& animal matter called humus
iii. _____________________ - more rock particles with only small amounts of organic matter.
iv. _____________________ - composed of rocks
Quantity of each layer will affect ecosystem productivity
Quality of soil can also affect productivity o E.g. pH, human impact
2. Available Water
All organisms depend on water to live. Availability is determined by:
o o o 3. Temperature
Organisms are able to adapt to temperature fluctuations
Why do trees in Alberta can keep their leaves during winter?
What are two other ways organisms escape undesired temperatures –
– 4. Sunlight
Sunlight vary between different ________________
– Less sunlight during winter in Canada vs in Jamaica
Sunlight can also vary within the ________________
– Less sunlight during winter in Canada vs during summer in Canada
Factors Affecting Aquatic Ecosystems 1. Chemical Environment
2. Temperature and Sunlight
3. Water Pressure
4. Seasonal Variation
Ice/snow covers lakes and acts as insulators
Therefore, environment underneath the ice is very stable, even if it gets colder above the ice.
Oxygen can now pass from air into water Upper level of lake (epilimnion) warms up
Lower level of lake (hypolimnion) remains at low temperature Middle level of lake (thermocline) drops in temperature from warm to cold
Water goes from warm to cool and sinks to bottom. This rotates oxygen levels to the bottom of the lake
Limits on Populations and Communities in Ecosystems Define Biotic Potential:
Biotic potential is regulated by four important factors:
Factor Description and Example
Limiting Factors
Factors in the environment can prevent pollutions from attaining their biotic potential.
Any resource that is in short supply is a limiting factor on a population.
Factors that limit populations are seen in Table 1 on page 108 of your text.
•
•
•
• Carrying Capacity
Populations commonly fluctuate because of an interaction of the many biotic and abiotic limiting factors. Ecosystem is stable when none of the populations exceeds the carrying capacity.
Explain what is meant by the carrying capacity of an ecosystem-
Limits of Tolerance
Carrying capacity for any species is determined by the availability of resources (food, water). Populations can exceed the carrying capacity of the ecosystem, but not for long.
Organism’s can survive within a certain range of an abiotic factor, above and below the range it cannot survive.
Law of Tolerance:
Law of the minimum:
The number of organisms in an ecosystem is important when considering the effects of some abiotic and biotic factors. Population is said to be dense when there is a large number of organisms in a small area.
Factors that cause Change in Populations:
Factor Definition
Density-independent factors
Density-dependent factors
General Outcome 2
Students will explain the mechanisms involved in the change of populations over time.
Specific Outcomes for Knowledge Students will:
1. Explain the fundamental principles of taxonomy and binomial nomenclature, using modes of nutrition at the kingdom level and morphological characteristics at the genus species level.
2. Summarize and describe lines of evidence to support the evolution of modern species from ancestral forms; i.e., the fossil record, Earth’s history, biogeography,
homologous and analogous structures, embryology, biochemistry
3. Compare Lamarckian and Darwinian explanations of evolutionary change
4. Explain that variability in a species results from heritable mutations and that some mutations may have a selective advantage
5. Discuss the significance of sexual reproduction to individual variation in populations and to the process of evolution
6. Explain speciation and the conditions required for this process Evolution
Evolution means a slow, gradual development or change. If the fossils of the wooly mammoth of the ice age are compared with the elephants of today, the basic changes that have occurred can be seen. According to the theory of evolution, the hereditary traits, or characteristics, of a population of organism gradually change over a period of time. The process of evolution occurs in a population of organisms as generations pass through time. During evolution, the gene pool of an entire population of organisms changes. The gene pool contains all the genes of a population. When the genes change, the traits expressed by those genes also change.
Classification of Organisms Students will:
Explain the fundamental principles of taxonomy and binomial nomenclature, using modes of nutrition at the kingdom level and morphological characteristics at the genus species level.
The value of classifying organisms includes:
1. To understand the complex variety of living things
3. Enables prediction of characteristics shared by members of a group
4. Shows evolutionary links; the evolutionary history of a species or a group of related species (phylogeny)
Define taxonomy:
The binomial system of nomenclature is a system of naming organisms developed by Carolus Linnaeus.
– “Binomial” – Two part Latin scientific name.
•
•
– Each genus can include many species of related organisms
• Felis sylvestris is the domestic cat
• Felis lynx is the lynx – Rules or nomenclature:
•
•
The two-name system provides an added advantage by indicating similarities in anatomy, embryology and evolutionary ancestry.
Level s of Classification
Classification recognizes seven levels in the hierarchy of taxa:
– – – – – –
The filing system groups species into a hierarchy of increasingly ____________________.
– Similar species are grouped in the same genus – Similar genera are grouped in to the same family – Families are grouped into orders
– Orders are grouped into phyla – Phyla are grouped into kingdoms
Each taxonomic level is more inclusive than the one below.
– The more closely related two species are, the more levels they share.
Today most scientists believe that organisms have changed over time.
Define phylogeny:
Relationships are shown in a diagram called a __________________.
– Starts from oldest (most ancestral) form and branches off to descendants.
Students will explain the mechanisms involved in the change of population over time.
Define Evolution:
Evolution does not refer to individual change or development
Evolution occurs within a population of organisms
Evidence of a Changing Earth
Summarize and describe lines of evidence to support evolution of modern species from ancestral forms eg fossil record, earth’s history, biogeography
Direct Evidence for Evolution –
There is much evidence to suggest the organisms have changed or evolved over time.
Some of this is direct evidence such as the fossilized remains of plants and animals Fossils are:
Fossils are formed in three ways:
1.
2.
3.
Radioactivity was discovered in 1903. Radioactive decay provides a form of geological clock helping scientists determine the absolute age of the Earth and items on it with great precision.
Using decay rates in units called half lives physicists can determine the age of a specimen
Define Biogeography
Earth’s landmasses have undergone great change over time. Fossils of the same species have been found in different continents suggesting the continents were once joined.
Fossils younger than 150 million years old are not found on different continents suggesting they evolved after the breakup.
What does evidence from Biogeography suggest?
HOMOLOGOUS STRUCTURES: Forelimbs of each of these creatures are adapted to carryout very different functions yet have very similar bone structure
Evidence of Evolution from Biology
Summarize and describe lines of evidence to support evolution of modern species from ancestral forms e.g. homologous and analogous structures, embryology and biochemistry
Direct evidence provided through fossils is not the only evidence that supports the theory of evolution. Some of the evidence for evolution is indirect, gained only by comparing the structure, function and embryology of present day organisms. Like fossils, observations from living organisms, show the links between existing forms and their ancestors.
Evidence from Anatomy Define Embryology:
• offers valuable insight into the process of evolution.
Homologous structures
Formed from DIVERGENT EVOLUTION
Define Vestigial Features and give an example:
What does the presence of a vestigial feature suggest?
Analogous structures:
Examples: wing of an insect and a bird
Biochemical Evidence:
Similar proteins in species diversify as evolution takes place
DNA and cytochrome enzyme C (respiration) are similar in all organisms
DNA analysis-used determine how closely related organisms are o suggest a common ancestor
The Making of a Theory – Accounting for Evidence
Students will compare Lamarckian and Darwinian explanations of evolutionary change
Lamarck – 1801 Key Factor-Environment
Theory Description
Organisms change because they need to change.
e.g. snake needed to crawl through small space so legs were scrapped off
Use-remains strong. Disuse-weakens and disappears.
Eg. Snake’s legs.
Traits acquired in life time could be passed on to offspring.
E.g. masters of the piano pass on skills to offspring Nice try Lamarck but acquired traits can't be inherited. Too bad!
Darwin's Theory of Natural Selection
Scholars of the ancient world generally believed that living species had been created according to some special design for the universe and did not change through time.
However in the last two hundred years time, scholars began to question the concept of unchanging species. They began to believe that organisms have changed over time through the process of evolution. Direct evidence (fossils) and indirect evidence (e.g.
from living organisms) was used to support the theory of evolution. Many scientists proposed theories as to how evolution occurs but the theory of natural selection is generally thought to be the modern view of how evolution occurs.
The theory of natural selection was proposed by Charles Darwin in 1838. It was based on the observations he made during a five year voyage to South America and the South Sea Islands, in particular the Galapagos Islands. Darwin proposed that competition for food, space, and mates “selects” only the most fit individuals within a species to survive and reproduce. He argued that if the characteristic was favored by natural selection, it could be passed on to the young of the selected individuals. As the traits were passed on, the evolution of the species would result.
– Overproduction – Struggle for
existence
– Variation – Survival of the
fittest
– Origin of new species
Darwin’s Theory on Evolution:
Darwin’s Ideas Description of Idea
Overproduction
Struggle for Existence (competition)
Variation
Survival of the fittest (natural selection)
Origin of New Species (speciation)
Evolution causes speciation
Occurs by the accumulation of inherited variations, over numerous generations and is complete when reproductive isolation occurs.
– “Reproductive isolation” has occurred when two organisms can no longer reproduce fertile offspring.
Comparison of Lamarck and Darwin
Darwin Lamarck
Sources of Inherited Variation
Students will discuss the significance of sexual reproduction to individual variation in populations and to the process of evolution
Without understanding genetics, Darwin was unable to explain 2 important factors
What is the source of variation?
How inheritable traits are passed from one generation to the next?
Define Variation:
• Variation can be beneficial, neutral or harmful depending on the type.
• Variation contributes to evolution because of a concept called selective advantage
Define Selective Advantage:
The two main sources of genetic variation are mutations and the genetic shuffling that results from sexual reproduction
Mutations:
Gene Shuffling:
Students will explain that variability in species results from heritable mutations and that some mutations may have a selective advantage.
Natural selection on certain traits can lead to changes in trait frequencies and thus to evolution.
Beneficial mutations may increase the fitness and reproductive success of an individual and therefore will become more common in a population. These traits are selected for.
In your OWN WORDS fill out the chart below using Table
Darwinian Evolution Genetic Mechanism
Inherited Characteristics
Population Variability
Source of new variation Natural selection
Evolutionary change
Speciation and Evolution
Students will explain speciation and the conditions required for this process Define Speciation:
Behavioral isolation:
Geographic isolation:
When natural selection works on the separated groups independently the populations evolve independently.
The Rate of Evolution:
Using your textbook on page 158, describe the modern evolutionary theories:
Punctuated Equilibrium Gradualism
