The 3 EEEs • Environmental Science – the study of how
humans interact with the environment • Ecology – the study of how living things
interact with each other and with the nonliving environment
• Ecosystem – All the organisms living in an area together with their physical environment.
Biotic vs. Abiotic • The parts of an ecosystem are either
– Biotic: living or once living
– Abiotic: Nonliving
Levels of Ecological Organization
Levels of organization 1. Individual = 1 living thing 2. Population: all members of the same species
that live in the same place at the same time
– Species = a group of closely related organisms that can mate and produce fertile offspring
3. Community: all the various species that live in the same place at the same time
4. Ecosytem: All the communities and their physical environment
5. Biosphere: All of the ecosystems
Habitat • Habitat: The place an organism lives. Its “address” – It has everything an organism needs to survive • Example: a corral reef contains seawater,
coral sunlight and a wide variety of other organisms
Population Size
Lesson 4.2 Describing Populations
• The number of individuals in a population at a given time
• Sudden and dramatic decreases in population size can indicate
an unhealthy population headed toward extinction.
• Ecologists often use sampling techniques to
estimate population size.
Did You Know? The passenger pigeon was
once North America’s most abundant bird.
Hunting drove them to extinction in less than
100 years.
Counting Laysan Albatross Nests
Population Density
Lesson 4.2 Describing Populations
• Measure of how crowded a population is
• Larger organisms
generally have lower
population densities.
• Low population density:
More space, resources;
finding mates can be difficult
• High population density:
Finding mates is easier; tends to be more competition;
more infectious disease; more vulnerability to predators
Northern pintail ducks
Population Distribution
Lesson 4.2 Describing Populations
• How organisms are arranged within an area:
• Random distribution:
Organisms arranged in
no particular pattern
• Uniform distribution:
Organisms evenly spaced
• Clumped distribution:
Organisms grouped near resources;
most common distribution in nature
Age Structure
Lesson 4.2 Describing Populations
• Relative number
of organisms of each
age group within
population
• Can be used to
predict future
population growth of
a population
Sex Ratios
Lesson 4.2 Describing Populations
• Proportion of males to females
• Age structure diagrams give information about sex ratios.
• For a monogamous species, the ideal sex ratio is 50:50.
Calculating Population Growth
Lesson 4.3 Population Growth
• Determined by the following equation:
(birthrate + immigration rate) – (death rate + emigration rate)
• Growing populations have a positive growth rate; shrinking
populations have a negative growth rate.
• Usually expressed in terms of individuals per 1000
Did You Know?Immigration contributes more than 1 million people to the U.S. population per year.
Biotic Potential
Lesson 4.3 Population Growth
• An organism’s maximum ability
to produce offspring in ideal
conditions
• Many factors influence biotic
potential, including gestation
time and generation time.
• Organisms with high biotic potential
can recover more
quickly from population declines than
organisms with low biotic potential.
How fast can a population grow?
• Populations usually stay about the same size • Biotic potential – fastest rate at which populations
can grow. This is limited by: • Reproductive potential – maximum number of
offspring each member of a population can produce. Reproductive potential increases when individuals: – produce more offspring at a time – like rabbits or dogs – reproduce more often – Reproduce early in life – most important factor because it
decreases generation time (the average age at which the species first reproduces).
• Small organisms like bacteria and insects have short generation times and high reproductive potential.
• Large animals like elephants and humans have long generation times and low reproductive potential
What limits population growth?
• Carrying capacity – maximum population an ecosystem can support. A population may increase over this but it wont stay at the increased size.
• Limiting Resource: A species reaches its carrying capacity when it consumes a particular resource as quickly as the resource is produced. – Plant growth is limited by supplies of sunlight, water and
nutrients
• carrying capacity is predicted by graphing populations over time and observing average population or by observing a population crash.
• Ex: originally there were no rabbits in Australia, so when they were introduced, they experienced exponential growth as there was plenty of food, no predators and no competition. But then the population crashed due to disease and starvation. Overtime, population recovered but never to highest level
Carrying Capacity
Types of Population Regulation
Population growth is limited by deaths. The cause of death may be:
• Density dependent – death occurs more quickly in crowded populations due to due to disease, limited resources, predation
• Density independent – regardless of density, some individuals of a population will die; weather, natural disasters
Birth and Death Rates
Lesson 4.3 Population Growth
• A population’s relative
birth and death rates
(mortality and natality)
affect how it grows.
• Survivorship curves show
how the likelihood of
death varies with age.
Survivorship Curves
• Survivorship – percentage of members of a group that are likely to survive to any given age
• Type I – wealthy developed countries, most people live to old age
• Type II – Transitional. similar death rate at all ages
• Type III – Developing. many children die
Fertility Rates and Migration
• Fertility rate - # of babies born each year per 1000 women
• Migration – movement of individuals between areas
• Immigration – movement in (keeping population of developed nations from decreasing)
• Emigration - movement out
Exponential Growth
Lesson 4.3 Population Growth
• Population increases by
a fixed percentage
every year.
• Normally occurs only when
small populations are
introduced to an
area with ideal
environmental conditions
• Rarely lasts long
Logistic Growth and Limiting Factors
Lesson 4.3 Population Growth
• Growth almost always slows and
stops due to limiting factors.
• Limiting factors: Environmental
characteristics slow population
growth
and determine carrying
capacity.
• Density-dependent:
Influence changes with
population density.
• Density-independent:
Influence does not change with
population density.
Evolution and Natural Selection
• Gene: A sequence of DNA that codes for a particular trait
• Gene pool: All the genes present in a population
• Biological evolution: The change in a population’s gene pool over time
A starting population of fish. Genes control the color
and pattern of the fish’s scales.
4.2 Evolution Natural Selection – reproduction due to the
presence or absence of particular traits
Evolution – a change in the genetic characteristics of a population from one generation to the next
Adaptation – inherited trait that increases chances of survival and reproduction
Nature Selects for certain traits such as sharper claws or lighter feathers because traits increase an organisms chance to survive.
Artificial Selection
Lesson 5.1 Evolution
• Selection under human direction
• Throughout history, humans have chosen and bred
animals and plants with beneficial traits.
Mechanisms of Biological Evolution: Mutation and Migration
Mutation
Accidental change in DNA
that can give rise to variation
among individuals
Migration (gene flow)
Movement of individuals into
(immigration) or out of (emigration) a
population
Mechanisms of Biological Evolution: Genetic Drift and Natural Selection
Genetic Drift
Natural Selection
Evolution that occurs by chance
Process by which traits useful for survival and reproduction are passed on more frequently than those that are not
Conditions of Natural Selection
(1) Organisms produce
more offspring than
can survive.
(2) Individuals vary in
characteristics, some of
which are heritable.
(3) Individuals vary in
fitness, or reproductive
success.
Did You Know? Darwin privately researched natural selection for two decades before publishing On the Origin of Species.
Extinction
Lesson 5.1 Evolution
• The disappearance of species
from Earth
• Generally occurs gradually,
one species at a time, when
environmental conditions
change more rapidly than the
species can adapt
• There are five known mass
extinction events, each of
which wiped out a large
proportion of Earth’s species.
Did You Know? During the Permo-Triassic
extinction 250 million years ago, 70% of all
land species and 90% of all marine species
went extinct.
Trilobites
Marine arthropods that went extinct at the
end of the Permian period.
Speciation
Lesson 5.1 Evolution
• Process by which new
species are generated
• Can occur in a number
of different ways; the
most important way is
called allopatric
speciation
• Has resulted in every
form of life on Earth—
today and in the past Allopatric Speciation
The Niche
Lesson 5.2 Species Interactions
• Describes an organism’s use of resources and functional role in a
community
• Affected by an organism’s tolerance—its ability to survive and
reproduce under changing environmental conditions
• Often restricted by competition
Lesson 5.2 Species Interactions
The zebra mussel has completely
displaced 20 native mussel species in
Lake St. Clair.
Competition •Organisms compete when they seek the same limited resource.
•In rare cases, one species can entirely exclude another from using resources.
•To reduce competition, species often partition resources, which can lead to character displacement.
Lesson 5.2 Species Interactions
Resource Partitioning
Predation (+/–) • The process by which a predator
hunts, kills, and consumes prey
• Causes cycles in predatory and prey population sizes
• Defensive traits such as camouflage, mimicry, and warning coloration have evolved in response to predator-prey interactions.
• Some predator-prey relationships are examples of coevolution, the process by which two species evolve in response to changes in each other.
Lesson 5.2 Species Interactions
Did You Know? A single rough-skinned newt contains enough poison to kill 100 people. Unfortunately for the newt, its predator, the common garter snake, has coevolved resistance to the toxin.
Rough-Skinned Newt
Parasitism and Herbivory (+/–)
Lesson 5.2 Species Interactions
Did You Know? One study of Pacific estuaries suggests that parasites play an important role in keeping these ecosystems healthy by controlling host populations.
Hookworm (a parasite)
• Parasitism: One
organism (the parasite)
relies on another (the
host) for nourishment or
for some other benefit
• Herbivory: An animal
feeding on a plant
Mutualism (+/+) and Commensalism (+/0)
Lesson 5.2 Species Interactions
Did You Know?Symbiosis describes a long-lasting and physically close relationship between species in which at least one species benefits.
• Mutualism: a
relationship in which two
or more species benefit
• Commensalism: a
relationship in which one
species benefits while
the other is unaffected Lichen: a symbiotic relationship
between a fungus and a photosynthetic
partner, such as an alga
Life Depends on the Sun Energy from the sun enters an ecosystem
through photosynthesis
Photosynthesis – plants use sunlight to make sugar molecules – During photosynthesis, plants, algae, and some
bacteria capture solar energy that drives a series of chemical reactions that use carbon dioxide and water to make carbohydrates
Energy Transfer When an animal (like a mouse) eats a plant, some
energy is transferred from the plant to an animal Energy is transferred again, when another animal
(like a hawk) eats the 1st animal. Food chains show this transfer of energy. Energy
transfers every time one organism eats another – Algae krill cod leopard seal killer whale
• Food web : shows many feeding relationships in an ecosystem (Figure 8, p. 122)
Equations for Photosynthesis and Respiration
Chapter 5
• Photosynthesis
• Respiration
Movement of energy • Producer (autotroph) - an organism that makes its
own food. Plants and algae get energy directly from the sun
• Consumer (heterotroph) – organisms that get their energy indirectly by eating other organisms – Primary consumer eats producers – Secondary consumer eats primary consumers – Tertiary consumer eats secondary consumers
What Eats What
Organism Energy Source Examples
Herbivore Eat Plants Cows, sheep, deer, grasshoppers
Carnivore Eat Meat Lions, hawks, snakes, spiders, whales,
sharks
Omnivore Eat plants and
meat
Bears, pigs, gorillas,
rats, raccoons, some
insects, humans
Detrivores
and
Decomposer
Breaks down
dead organisms
Fungi and
bacteria
Burning the Fuel • Your body gets the energy out of the
food you eat through cellular respiration. • Cellular respiration – uses the oxygen you
breath to break down food to yield energy • All organisms (plants and animals) use
cellular respiration to get the energy they need to do anything (play, grow, stay healthy)
Trophic Levels • Trophic level – a step in a food chain
or food web – Each time energy is transferred, some
energy is lost as heat.
– Only about 10% of the energy an organism has consumed gets passed along to the next organism that eats it.
Chapter 5 Section 1 Energy Flow in
Ecosystems
Food Chain
Chapter 5 Section 1 Energy Flow in
Ecosystems
Food Web
Energy Pyramids • You can visualize how energy is lost from
one trophic level to the next with an energy pyramid. (figure 9, p. 123)
• Each layer of the pyramid represents one energy level. The producers are at the bottom of the pyramid. As you go up, each level is smaller (has fewer organisms) because energy is lost.
Chapter 5 Section 1 Energy Flow in
Ecosystems
Energy Pyramid
Energy Loss Less energy at each level of pyramid • Decreases by 90 % at each level
– L1 – 1000 producers (plants and algae) – L2 – 100 primary consumers (sheep, mice, deer) – L3 – 10 secondary consumers(lions, spiders, snakes) – L4 – 1 tertiary (hawks, killer whales)
• Species that have strong and/or wide-reaching effects on a community
• Removal of a keystone species can significantly alter the structure of a community.
Keystone Species
Lesson 5.3 Ecological Communities
Lesson 5.4 Community Stability
A 2010 report on invasive species suggests that they cost the U.S. $120 billion a year in environmental losses and damages.
Invasive kudzu
Ecological Disturbances
• Disturbances or changes in the environment can throw a community into disequilibrium.
• Severe disturbances can cause permanent changes to a community and initiate a predictable series of changes called succession.
• A community in equilibrium is generally stable and balanced, with most populations at or around carrying capacity.
Forest fire
Primary Succession
Lesson 5.4 Community Stability
• Occurs when there are no traces of the original community remaining, including vegetation and soil
• Pioneer species, such as lichens, are the first to colonize.
• The environment changes as new species move in, adding nutrients and generating habitat.
Ecological Succession • A gradual process of change and
replacement of the types of species in a community.
• May take hundreds or thousands of years.
Two types of succession • Primary – occurs on a surface where no ecosystem existed
previously such as rocks, cliffs or sand dunes. Moss and lichens are usually the pioneer species because they grow on rocks. Examples of Primary Succession: – Volcanic islands formed from eruptions – Weeds/grass in sidewalk cracks – Land caused by glacier retreats
• Secondary – occurs on a surface where an ecosystem has previously existed. Examples: – Disturbed/ disrupted by humans, animals – Natural disturbances such as storms, fires, floods, volcanoes
(on existing land)
Steps of Secondary Succession
1. A disruption occurs and destroys the plants 2. 1st year: Pioneer Species such as annuals, are
the first organisms to colonize a newly cleared area
3. 2nd year: perennial plants and grasses start to grow.
4. 3-10 years: larger species such as shrubs and small trees crowd out the smaller plants
5. 20 years: fast growing evergreen trees take over
6. 150 years: achieve a Climax community – final and stable community of slower growing deciduous trees such as oak, hickories, beech and maple stay until next disturbance
Secondary SuccessionHow Ecosystems Change
Chapter 5
Old Field Succession
• Old field succession is a type of secondary succession that occurs on abandoned farmland. It follows the steps of secondary succession.
Climax Communities
Lesson 5.4 Community Stability
• Ecologists once thought succession leads to stable “climax” communities.
• Today, ecologists see communities as temporary, ever-changing associations of species.
• Communities are influenced by many factors and constant disturbances.
Beech-maple forest, a classic “climax community”
Invasive Species
Lesson 5.4 Community Stability
• Nonnative organisms that spread widely in a community
• A lack of limiting factors such as predators,
parasites, or competitors enables their
population to grow unchecked.
• Not all invasive species are harmful.
Did You Know? Although the European honeybee is
invasive to North America, it is beneficial because it
pollinates our agricultural crops.
