Download Ch. 18-20 Ecology Unit

Ecology of Organisms and
Populations
Ch. 18
Ecology
 Study of interactions between
organisms and their environment
 Ecology can be divided into four
increasingly comprehensive levels:
 Organismal
ecology
 Population ecology
 Community ecology
 Ecosystem ecology
Ecology
 Organismal ecology
 Is concerned with
evolutionary
adaptations that
enable individual
organisms to meet
the challenges posed
by their abiotic
environments.
http://www.seabird.org/assets/killer%20whales%20internet%202.jpg
Ecology
 Population ecology
 Is concerned with
populations, groups
of individuals of the
same species living
in the same area.
 Concentrates mainly
on factors that affect
population density
and growth.
http://newsimg.bbc.co.uk/media/images/44609000/jpg/_44609350_puffins512.jpg
Ecology
 Community ecology
 Is concerned with
communities,
assemblages of
populations of
different species.
 Focuses on how
interactions between
species affect
community structure
and organization.
http://www.mass.gov/envir/forest/images/multiLayerForest.jpg
Ecology
 Ecosystem ecology
 Is concerned with ecosystems, which include all the abiotic
factors in addition to the community of species in a certain
area.
 Focuses on energy flow and the cycling of chemicals among
the various abiotic and biotic factors.
http://www.african-books.com/images/Animals/montage.jpg
Components of the
Environment
 The abiotic component
 Consists
of nonliving chemical and
physical factors.
 The biotic component
 Includes
the living factors.
Abiotic Factors of the
Biosphere
 On a global scale, ecologists have recognized
striking regional patterns in the distribution of
terrestrial and aquatic life.
 Global distribution patterns

Reflect regional differences in climate and other abiotic
factors.
Sunlight
 Solar energy powers nearly all ecosystems.
 Availability of sunlight affects aquatic and
terrestrial environments.
http://artfiles.art.com/images/-/Aflo/Sun-Shining-in-BlueSky-Over-Tree-in-Winter-Snow-Biei-Hokkaido-JapanPhotographic-Print-C13062664.jpeg
Water
 Aquatic organisms may face problems
with water balance.
 For terrestrial organisms, the main
water problem is drying out.
Temperature
 Environmental
temperature

http://www.wildherps.com/images/herps/standard/desert_iguana.jpg
http://www.sciam.com/media/inline/A186A7F7-D8EADDDF-0F715313A7DA2A91_1.jpg
Is an important
abiotic factor
because of its effect
on metabolism.
Wind
 Some
organisms depend on nutrients
blown to them by wind.
 Organisms such as plants depend on wind
to disperse pollen and seeds.
 Can also affect the pattern of a plant’s
growth.
http://www.asdk12.org/staff/vanarsdale_mark/pages/Ecology_Images/wind_tree.jpg
Rocks and Soil
 Soil
variation contributes to the patchiness
we see in terrestrial landscapes.
 In streams and rivers, the composition of
the soil can affect water chemistry.
Periodic Disturbances
 Catastrophic disturbances
 Can devastate biological communities.
 After a disturbance,
 An area is recolonized by organisms, or repopulated by
survivors.
 The structure of the community undergoes a succession of
changes during the rebound.
Ecosystems
 What biotic and abiotic factors do you
see in this picture of the rain forest?
Ecosystems
 What biotic and abiotic factors do you
see in this picture of a tundra?
Populations
•
A population is…
Members of the same species…
 Who live in the same place
 At the same time.

Populations
•
The environment where a population
lives: habitat.
Populations
 Population ecologists study many
things about populations in their
habitats:
 Population size
 Population density
 Population growth
Population Density
 Population density
 Is the number of individuals of a species per unit of area or
volume.


In most cases, it is impractical or impossible to count all
individuals in a population.
In some cases, population densities are estimated by indirect
indicators, such as number of bird nests or rodent burrows.
Populations
 Populations are densest where there
are resources available.
Populations
Patterns of Dispersion
 The
dispersion pattern of a population is
the way individuals are spaced within the
population’s geographic range.
Clumped Pattern of Dispersion

Individuals aggregate in patches.
Uniform Pattern of Dispersion

Results from interactions among the individuals of
a population.
Random Pattern of Dispersion

Individuals are spaced in a patternless,
unpredictable way.
Population Growth Models
 Two
models, the exponential growth model
and the logistic growth model, will help us
understand population growth.
 The growth rate

Is the change in population size per time
interval.
The Exponential Growth Model: The
Ideal of an Unlimited Environment
 The exponential growth model
 Describes the rate of expansion of a population
under ideal, unregulated conditions.
The Exponential Growth Model: The
Ideal of an Unlimited Environment
• A key feature of the exponential growth model
is that the rate at which a population grows
depends on the number of individuals already
in the population.
The Logistic Growth Model: The
Reality of a Limited Environment
 In
nature, a population may grow
exponentially for a while, but eventually
one or more environmental factors will limit
its growth.
 Population-limiting factors restrict
population growth.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
The Logistic Growth Model: The
Reality of a Limited Environment
 The logistic growth model
 Describes growth of an idealized population that is
slowed by limiting factors.
 A comparison of the logistic growth model
and the exponential growth model
Carrying Capacity
 Is the number of
individuals in a
population that the
environment can
just maintain with no
net increase or
decrease.
http://www.abc.net.au/reslib/200710/r189329_709751.jpg
Regulation of Population
Growth
 Density-Dependent Factors
 Are population-limiting factors whose effects
intensify as the population increases in size.
 Increase a population’s death rate and decrease
the birth rate.
Regulation of Population
Growth
 Density-independent factors
 Are population-limiting factors whose intensity is
unrelated to population density.
 Include events such as seasonal freezing.
 In many natural populations, density-independent
factors limit population size before densitydependent factors become important.
Growth Rate
 Four influences:




Birth rate 
Death rate 
Immigration 
Emigration 
 Birth + Immigration – Death – Emigration
Population Cycles

Some populations


Have regular boomand-bust cycles.
Boom-and-bust
cycles of the
snowshoe hare and
one of its predators,
the lynx
Communities and Ecosystems
Ch. 19
Key Properties of
Communities
 Diversity—variety of different kinds of
organisms that make it up
 Prevalent form of vegetation—
determines kinds of organisms that
will survive in the area
 Stability—ability to resist change and
return to its original species
composition after being disturbed
 Trophic level—feeding relationships
among the various species
Diversity
Which community is more diverse?
 The diversity of a
community

Is the variety of different
kinds of organisms that
make up the community.


Species richness, the
total number of different
species in the
community
Relative abundance of
the different species
Interactions Between
Populations of Different
Species
 Interspecific interactions—occur b/w
populations of different species
 Coevolution—a change in one species
acts as a selective force on another
species
Interspecific Competition
 Competition occurs when 2 or more
populations overlap in their niches
 Limiting
resources
Food
 Space
 Mates

 Generally, one will out-compete the
other
Competition in Nature


Two possible Outcomes
1. Weaker competitor becomes extinct
2. One or both species may evolve
enough to use a different set of
resources (resource partitioning)
Competition cannot operate for long
periods of time
Competitive Exclusion
Principle
 Two species cannot
coexist in a community
if their niches are
identical
Joseph H. Connell Study
Interactions Between Populations of
Different Species
 Predation—consumption of
one organism by another
 Parasitism—specialized
predator (parasite) lives
on/in its host, not killed
immediately
 Endoparasitism—live
inside host
(tapeworms/viruses)
 Ectoparasitism—live
on surface
of host
(mosquitoes/aphids)
 Herbivory—herbivores
consume plants
http://www.dldigital.com/images/z_oldimages/2002-10-d28aphid2-fr18.jpg
Predator Adaptations
 Most predators have acute senses.
 Many predators


Have adaptations such as claws, teeth, fangs, stingers, or
poison to help catch and subdue prey.
Are fast and agile.
http://upload.wikimedia.org/wikipedia/commons/thumb/7/7c/H
awk_eating_prey.jpg/300px-Hawk_eating_prey.jpg
http://images.encarta.msn.com/xrefmedia/sharemed/targets/images/pho/00123/
00123ed3.jpg
Plant Defenses Against
Hebivores
www.treklens.com/.../Sweden/phot
o198584.htm
 Physical defenses
 thorns, hooks/spines
on leaves


http://en.wikipedia.org/wiki/Image:Toxic
odendron_radicans.jpg
 Chemical defenses
 Make plant
distasteful or
poisonous
Morphine from opium
poppy
Nicotine from tobacco
Poison Ivy
http://images.wildmadagascar.org/pictu
res/isalo/walking_stick0071.jpg
Animal Defenses Against
Predators
 Behavioral defenses

Alarm cries
 Distraction displays
 Cryptic coloration/shape
(camouflage)
Blend in with environment
 Asposematic coloration
 Red/black; yellow/black
Stick Insect
www.laspilitas.com/.../Monarch_butte
rfly.htm

 Mechanical/chemical
defenses

Quills, spines, and other
similar structures
 Toxins—distasteful or
poisonous
Monarch butterfly on Milkweed
Animal Defenses Against
Predators
 Mimicry—prey resembles
species that cannot be eaten
 Batesian mimicry: Imitate
color patterns or
appearance of more
dangerous/unpalatable
organisms
 Müllerian mimicry: 2
unpalatable species that
inhabit the same
community mimic each
other
Animal Defenses Against
Predators
Mimicry can be used to lure

prey
 Snapping turtle wriggles
tongue like a worm to
attract and capture small
fish
http://www.lancashiremcs.org.uk/g
allery/pics/lophius.jpg

Angler Fish attract prey
close enough to their
mouths to be easily
grabbed
Symbiotic Relationships
 Non-Beneficial
 Parasitism—host harmed
 Beneficial
 Mutualism—both partners benefit
Lichens-association b/w fungus and algae
 Nitrogen-fixing bacteria and legumes

Community Structure
 Predators can
moderate
competition among
its prey species
 Keystone species
can alter the whole
community
Community Structure
Lake Davis, CA
 Introduction of a
http://www.dfg.ca.gov/lakedavis/
Northern Pike
http://aquanauts_dc.homestead.com/files/northern_pike1.jpg
species (exotic
species) into a
community can have
drastic affects on the
existing community
members
Disturbances in a Community
 Storms, fire, floods, droughts,
overgrazing, or detrimental human
activities:
 Remove
organisms
 Alter resource availability
 Create opportunities for new species
that have not previously occupied the
habitat
 Humans are the biggest disturbance
 Logging,
agriculture, overgrazing
Ecological Succession
 Primary succession
 Begins in a virtually lifeless area where soil has
not formed
 Lichens and mosses colonize first
 Soil gradually forms and small plants and shrubs
take root
 Secondary succession
 Occurs where an existing community has been
cleared by some disturbance that leaves soil in
tact
 Earliest plants to recolonize are often those that
grow from wind-blown or animal-borne seeds
Ecological Succession
 Tolerance to abiotic conditions
determines early species
 Competition among early species shape
the succession of an area
Mt. St. Helen 1980 Eruption
MSH80_st_helens_spirit_lake_before_may_18_1980.jpg
http://www.jqjacobs.net/photos/volcano/st_helens.html
http://denali.gsfc.nasa.gov/research/volc2/MSHreflection.gif
Mt. St. Helen
Secondary Succession

http://www.kgw.com/newslocal/stories/L_IMAGE.101688cd0b5.93.88.fa.7c.2791
3b573.jpg
Red alder disperses easily and is
capable of rapid growth on the nutrientpoor, volcanic deposits.
 A red-legged frog –one of the creatures
living in one of the dozens of ponds
created after the eruption.
 70 species of birds, including
hummingbirds, western meadowlarks
and Savannah sparrows
www.kgw.com/news-local/stories/kgw_051505_env...
www.kgw.com/news-local/stories/kgw_051505_env...
An Overview of Ecosystem
Dynamics
 An

ecosystem
Is a biological community and the abiotic
factors with which the community interacts.
– Energy flow
• Is the passage of energy through the
components of the ecosystem.
– Chemical cycling
• Is the use and reuse of chemical elements within
the ecosystem.
Energy
 Flows through an
ecosystem when
consumers feed on
producers.
 Cannot be recycled
within an
ecosystem, but must
flow through
continuously.
Ecosystem Dynamics
 Energy

Depend on the transfer of substances in the
feeding relationships, or trophic structure, of an
ecosystem.
 Trophic

relationships
Determine an ecosystem’s routes of energy
flow and chemical cycling.
 Trophic

flow and chemical cycling
levels
Divide the species of an ecosystem based on
their main sources of nutrition.
Trophic Relationships
 Ecosystems divided into trophic levels
(feeding levels)
 Producers—autotrophs
(mostly
photosynthetic)
 Primary consumers—herbivores
 Secondary consumers—carnivores that eat
herbivores
 Tertiary consumers—carnivores that eat
other carnivores
 Detrivores—consumers that eat dead or
decaying matter
Food Chain/Food Web
Energy Flow in Ecosystems
 Each level in a food
web contains a different
quantity of stored
chemical energy
 When consumers eat
producers or 2
consumers eat 1
consumers, some
energy is lost in each
transfer from one level
to the next
Energy pyramid
 A diagram that represents the cumulative loss
of energy from a food chain.
Chemical Cycling in
Ecosystems
 Ecosystems
 Depend
on a recycling of chemical
elements.
 Biogeochemical cycles
 Are
chemical cycles in an ecosystem that
involve both biotic and abiotic components.
Biogeochemical Cycles
 Three key points :
 Each circuit has an
abiotic reservoir.
 A portion of chemical
cycling can rely
completely on geological
processes.
 Some chemicals require
processing before they
are available as inorganic
nutrients.
Examples of Biogeochemical
Cycles
 Carbon
 Nitrogen
 Phosphorus
 Water
Carbon Cycle
Human Impacts:
 Greenhouse Effect


Increase of
atmospheric CO2
 Combustion of
fossil fuels
 Burning of wood
from deforestation
Increase in global
temperature
Nitrogen Cycle
Human Impact:
 Cultivation—turns up soil and ↑
decomposition of organic
matter; Releases more nitrogen
 Harvesting ↓ nitrogen from
ecosystem
 Adding industrially
synthesized fertilizers to soil
has resulted in doubling
globe’s supply
 Excess nitrogen leeches
into soil and into rivers,
streams, and lakes and
ground water—
– ↑ levels are toxic to
aquatic organisms
and humans
– Algal blooms in
lakes ↑
eutrophication
Phosphorus Cycle
Human Impact:
 Sewage treatment
facilities and
fertilizers

↑ amounts of
phosphates to
aquatic systems,
causing
eutrophication of
lakes.
Water Cycle
Human Impact:
 Destruction of tropical
rain forest


Will change the amount
of water vapor in the air.
May alter local and global
weather patterns.
 To irrigate crops,
humans pump large
amounts of ground
water to the surface.