Ecology and
Humans
Chapters 3, 4 (up to
biomes), 5, 8
Levels of Organization in Ecology

Ecology is the study of interactions among organisms and
between organisms and their environment

Species/Organisms
Populations: in population ecology, scientists study the
dynamics of population change and the factors that
affect distribution/abundance of organisms (Chapter 3)
Communities: in community ecology, scientists study
patterns in species diversity and all interactions (Chapter
4)
Ecosystems: in ecosystem ecology, scientists study the
flow of energy and nutrients, both the living and non-living
components of a system (Chapter 5)
Biomes
Biosphere
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Population Ecology
in population ecology, scientists study the dynamics
of population change (natural selection and
evolution) and the factors that affect
distribution/abundance of organisms (Chapter 3)
Evolution and Natural Selection



How are these two terms different?
Darwin versus Wallace
Evolution (mutation) leads to adaptation and
adaptive traits in a population


Changes can result in no change, positive change, or
negative change
Natural selection acts on changes

Selection can be
Directional
 Stabilizing
 Disruptive


Take a minute to draw a sketch of these three trends
Evolution and Natural Selection
 The
environment can
influence selection


Convergent Evolution
Divergent Evolution
 Selection
can be seen
in our everyday lives

Ex: Breeding in dogs,
artificial selection in
plants
 Biological
diversity is a
result of evolution

100 million species in
world
Speciation
 Generation
of
new species can
occur in several
ways


Allopatric
Speciation (main
mode)
Sympatric
Speciation
(sym….same)
Fossils and Extinction
 Fossils





can show us many things
Existence of life on Earth for 3.5 B years
Evolution of organisms
Number of exiting species generally increases
Most species are now extinct
Several mass extinctions have occurred
 Background
extinction rate
 6th mass extinction is occurring now
 Phylogenetic
trees can be used to trace the
divergence of organisms
Resources needed by organisms
 Habitat


Habitat use
Habitat selection
 Niche


Specialists versus
Generalists
Fundamental
niche versus
realized niche
Characteristics of populations
 The
following characteristics can be used to
predict the future dynamics of a population


Population Size
Population Density
 What

are the advantages of high/low density?
Population Distribution
 Random,
Uniform, Clumped
 Take a minute, to sketch a diagram of these three
distributions and an example of each



Sex Ratio
Age Structure
Birth and Death Rates
 Can
be used to develop survivorship curves
Survivorship Curves
 Take
a minute to graph Type I, II, and III
survivorship curves and list an example of species
of each curve, note which are K-selected and
which are R-selected
 Growth is determined by




Births (natality)
Deaths (mortality)
Immigration
Emigration
 How
can you calculate the natural rate of
population growth?
 How can you calculate the population growth
rate?
Factors that influence population growth

Exponential growth is seen in populations that grow
by a fixed percent each year


In reality, limiting factors will prevent a population
from growing forever, this type of scenario is shown in
a logistic growth curve




Take a second to sketch a graph of this type of curve
and give an example of an organism
Populations rise sharply at first, but them begin to level
off as limiting factors become stronger, the force of
these factors is called the environmental resistance and
stabilizes the population at its carrying capacity
Take a second to sketch a graph of this type of curve
and give an example of an organism
Density-dependent factors versus densityindependent factors; both can be limiting factors
and create variations in a growth curve
Carrying capacity is not set in stone
Community Ecology
in community ecology, scientists study patterns in
species diversity and all interactions (Chapter 4);
changes in populations can influence the
composition of the community
How do species interact?

Competition (- -)
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Predation, Parasitism (*S), Herbivory (+ -)

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Predation can drive cyclical population dynamics, take a
second to graph this type of relationship and give an
example
Coevolution, evolutionary arms race
Mutualism (*S) (+ +)


Intraspecific versus Interspecific
Competitive exclusion or species coexistence
Resource partitioning and character displacement: role of
natural selection
Mycorrhizae
Digestion
Amensalism (- 0)
Commensalism (*S)(+ 0)
*S=Symbiosis: a close relationship between two organisms
Energy flows through ecosystems
 Types
of organisms: producers, consumers,
detrivores, decomposers
 Trophic level: literally means feeding level, traced
through food web or food chain
 Energy, biomass and number of organisms
decrease a higher trophic levels
10% Rule
1) The 10% rule states that only 10% of energy is transferred
between each trophic level. It is argued that this
percentage is an inappropriate measurement. Assume that
the producers in this diagram obtain 3,745 kcals of energy
through the processes of photosynthesis. How much energy
would the secondary consumers receive if 8.2% of energy is
transferred between tropic levels?
2)Using the ideas of energy
transfer through trophic
levels, number of organisms,
and biomass, explain why
vegetarians have a smaller
energy footprint than a
person who eats meat.
Role of organisms in communities
 Keystone


species
What is a keystone in architecture?
Trophic cascade
 High
level predators can keep levels of secondary
consumers in check, which promotes the success of
the producers
 Ecosystem

Physical changes in the ecosystem
 Ex:

engineers
dams, aeration of soil
Affecting the environment
 Ex:
moving seeds around, filtering the water
Disturbances in the ecosystem
 Resistance
versus resilience versus
permanent change
 Succession

Primary succession: think glaciers, volcanoes,
anything that exposés rock and sand
 Pioneer
species: most commonly liches that can
break down the stone and create new soil

Secondary succession: think fires, hurricanes,
logging, farming, anything that removes the
majority of living things
 Both
types of succession will lead to climax
communities
How stable are communities?
 Clements
(communities) versus Gleason
(populations)

Most people now agree with Gleason, populations
can come and go from communities
 Ecologists
will study how conditions in different
stages of succession can lead to other stages
 Phase shifts/Regime shifts can sometimes occur if
keystone species are lost, declining populations,
or major environmental changes

Invasive species can have a major role in changing
communities
 May

be missing limiting factors
Restoration ecology/Ecological restoration
Ecosystem Ecology
in ecosystem ecology, scientists study the flow of energy and
nutrients, both the living and non-living components of a
system (Chapter 5), this study focuses on systems including
the lithosphere (rocks), atmosphere (air), hydrosphere
(water), and biosphere (living things). It also focuses on
ecosystem services that we rely upon.
Environmental Systems



Systems are networks of relationships among parts that interact with and
influence each other through the exchange of energy, matter and
information
Feedback loops: a systems output can also create input for a system
 Negative feedback loop (you want negative test results in the
doctors office): output brings the system back to a starting point, and
is therefore stabilized, these are stable systems and the only ones that
can be sustained over a long period of time (dynamic equilibrium,
homeostasis)
 More prey increased the number of predators, which in turn
decrease the number of prey
 Positive feedback loops: drive the change to a further extreme
 Melting ice decreases the amount of sunlight reflected from the
planet, increasing the temperatures and melting more ice
It is hard to understand feedback without looking at the larger systems
because properties emerge at different levels
 If a property emerges at the ecosystem level, looking only at a single
population may not allow you to see the loop
Example of interactions in a system (hydrosphere)



There is a dead zone in the Gulf of Mexico due to
hypoxia, it is more easily understood if we look at entire
area of land that drains into the gulf, the river’s
watershed
As nutrients from farmers fertilizers and waste water
treatment facilities enter the watershed, the drive the
growth of phytoplankton, which in turn increases the
number of consumers, when these organisms die and
sink to the bottom of the water, bacteria populations
grow quickly, these bacteria use cellular respiration to
break down their food, consuming oxygen and
creating hypoxia for fish and other organisms living in
lower regions of the water
This process is called eutrophication and is considered
to be a negative feedback loop
Ecosystems
 Arthur
Tansley was the first to recognize that living
and nonliving entities interact


Energy flows in one direction, matter is cycled
Sketch an image that shows the flow of energy and
the cycling of matter through trophic levels
 Nutrients
systems

tend to be limiting factors in marine
Macronutrients are required in large amounts
(nitrogen, carbon, phosphorus)
 Phosphorus
is more limiting in freshwater while nitrogen
is more limiting in ocean waters

Micronutrients are necessary, but needed in small
amounts
Primary Productivity



Energy is converted to biomass
 Starting with producers, photosynthesis creates energy in the
chemical bonds of sugar, this energy is the gross primary
production
Energy that remains after producers complete cellular
respiration is the net primary production, this is what will
become biomass
 The gross productivity of the producers in an ecosystem is
5,327kcals of energy. Producers in this system will use
300kcals of energy for cellular respiration. What is the net
primary productivity of this system?
The overall rate at which energy is produced is productivity
Secondary Productivity

The biomass generated by consumers after eating
producers is known as secondary production
 In the previous system, 10% of energy is passed between
trophic levels. It takes 350kcals of energy to support every
100g of biomass in primary consumers. The average
consumer in the system has a mass of 400g, how many
primary consumers can be supported in this ecosystem?
 Human
currently use approximately ¼ of the Earth’s net
primary productivity, why could this lead to a problem
that could topple food chains/webs?
Studying Ecosystems



Geographic Information System (GIS) is used to create
a picture of the landscape being studied
Boundaries are not firm, areas where ecosystems
interact are called ecotones
Landscape ecology allows scientists to study how
structures in the landscape affected organisms




Patches are spread in a mosaic
Populations that stay within patches, but could move
and mate within the patches are called
metapopulations,
If organisms can not move between patches, extinction is
a greater possibility, so this research is important to
conservation biologists
Modeling is also used to represent complex
relationships seens in ecosystems
Ecosystem Services
(you will want to memorize and use these throughout the course, you
will need to know them for the AP test!)
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Forming soil, preventing soil erosion
Purifying water
Purifying air
Regulating oxygen and other atmospheric gasses
Storing water
Protect against floods
Pollinating plants we eat
Removing toxins from soil, water and air
Controlling pests
Provides habitats
Provides medications, pets, plants, genes
Breaking down waste products
Stabilize the climate
Recreation
Aesthetic enjoyment
Biogeochemical Cycles
 Unlike
energy, nutrients cycle through an
ecosystem
 Nutrients are said to move from one reservoir
(pool) to another, and spend a varying amount of
time in each (residence time)
 The rate at which nutrients move is called flux
 Reservoirs that release more than they accept are
called sources, those that accept more are called
a sink
 Human activities have changed fluxes which may
cause negative and/or positive feedback loops
Demography/Human
Populations
Demography is studying the statistical changes of
human populations through the application of
principles of population ecology
How did we get here?


7B+ humans (1 million x 1,000 = 1 billion)
Exponential growth: increasing in a quantity by a fixed
percentage per unit of time
 Global growth rate peaked in the 1960’s and has
declined since then
 Currently grows at 1.2% (this seems small)
Calculating Growth Rate
 We
can roughly estimate the doubling rate
of human populations with some
knowledge of how populations grow


Human growth is exponential (logrithmic)
100 x .7 = ln 2
 Therefore,

we can use 70 as a shortcut!
If you know the growth rate, you can figure
out how many years it will take for the
population to double
 China’s


population growth rate is 1.2
70/1.2=58.3
ln2/1.2=.578x100=57.8
Is this a problem?
 Malthus
and Ehrlich
 Food production has balanced rapid
growth in recent decades


What would cornucopians think of this?
What would environmental scientists say?
 Can
we maintain quality of life for all
people?
 How do the views of Asian governments
differ from those of European governments
on this topic?
Demographic transitions
Life Expectancy change due to
living conditions (healthcare,
sanitation, food supplies, need
for labor) that can be linked to
demographic transitions
 Pre-industrial stage
 High death and birth rates
 Relatively stable
population
 Industrialization
 Low death, high birth
rates
 Industrial Stage
 Low death, falling birth
rates
 Post-Industrial Stage
 Low birth and death rates
 Population may be
impacted by immigration
IPAT(S) Model
The IPAT model offers us a way to measure the impact
human population may have on the Earth.
I=PxAxTxS





I= impact on environment
P= population
A= affluence
T= technology
S?= sensitivity of environment
1)
Name one way that technology could increase the impact
on the environment and one way it could decrease the
impact on the environment.
2)
According to this equation, would an arid region of
southeastern China where plants grow slowly be more or less
impacted by increasing affluence than a moist region where
crops are plentiful?
Studying Human Populations
 Demography:
can be used to predict what will
happen to populations and potential
environmental impacts of populations

Population Size
 Doesn’t

really tell us the entire story, need other factors
Density/distribution of population
 Human
populations tend to be clumped (draw a quick
sketch of this), this means environmental impacts will be
greater in some areas than others



Age structure of population
Sex Ratio of population
Rates of birth, death, immigration, emigration
Interpreting age structure diagrams
 Draw
a sketch of an increasing, stable, and
decreasing population (assume that the ratio of
males to females is around 50:50)
 Interpret the following graphs:
Growth versus total population
 What
does this graph show us?
Demographics are linked to society

Fertility Rates

Total fertility rate: number of children an average woman
has in her lifetime, should not fall below 2.1



Fertility rates drop when woman have access to birth
control
Population policies


Natural rate of population change (only birth versus death
rates) is becoming a problem in Europe
Empowering woman


Replacement fertility: each couple only having 2 children
(2.1 actually)
Most countries do not have a firm policy at this point, but
encourage reproductive rates at or below 2.1
Poverty


99% of the next billion people will be born in developing
nations
More than 82% of people live in developing nations
Demographics are linked to society

Consumption/Affluence




HIV/AIDS


Humans are living with a 30% overshoot in our ecological
footprint
1 American = 4.5 Chinese = 10 Indians = 19 Afgans
Wealth Gap
Some regions still have increasing death rates
Economic repercussions

Demographic fatigue: overwhelming challenges faced by
countries including



Losing young and productive members of society to disease
Educating/finding jobs for young people
Population Goals/Sustainable Development


United Nations Millennium Declaration: sets forth 8 goals for
society
http://www.un.org/millenniumgoals/