ECOLOGY

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ECOLOGY

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Title: ECOLOGY

1
ECOLOGY

A study of the interactions of living organisms
and the environment in which they live

2
A. Introduction

Ecology is the scientific study of the
interactions between organisms and their
environment.

The environment of any organism includes the
following components
Abiotic factors non-living chemical and physical
factors such as temperature, light, water, and
nutrients
Biotic factors the living components

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B. Abiotic factors affect the distribution of
organisms

Temperature some organisms can only tolerate
specific ranges of temperature.
Water some organisms can only tolerate either
fresh or salt water.
Sunlight provides energy that drives nearly all
ecosystems.
The intensity and quality of light, and
photoperiod can be important to the development
and behavior of many organisms.

Wind amplifies the effects of temperature by
increasing heat and water loss (wind-chill
factor).
Rocks and soil the physical structure and
mineral composition of soils and rocks limit
distribution of plants and the animals that feed
upon them.

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C. Approaches to studying ecology

Organismal ecology is concerned with the
behavioral, physiological, and morphologicalways
individualsinteract with theenvironment.

Fig. 50.2a
7

Population ecology a population is a group of
individuals of the same species living in a
particular geographic area.
An example of a population could be gray
squirrels living in Sea Cliff.
Population ecology examines factors that affect
population size and composition.

Community ecologya community consists of all
the organisms ofall the species thatinhabit a
particulararea. (all biotic)
An example of a community could be gray
squirrels, raccoons, cardinals, chipmunks, and
black crows living in Glen Head.

Fig. 50.2c
9

Ecosystem ecology an ecosystem consists of all
the abiotic factors in addition to the entire
community of species that exist in a certain
area.
Example? All bullfrogs, minnows, snails,
snapping turtles, algae in a pond and how ph,
temperature, sunlight impact this life

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D.Biomes can be aquatic or terrestrial

Marine biomes have a salt concentration of
approximately 3 and cover approximately 75 of
the earths surface.
Freshwater biomes are usually characterized by
salt concentration of less than 1 and are
closely linked to the soils and biotic components
of the terrestrial biomes through which they pass.

Freshwater biomes (ponds and lakes, small and
large freshwater).
The littoral zone is shallow and close to shore.
The limnetic zone is the open surface water.
The profundalzone consistsof the deep,aphotic
regions.

Lakes
Oligotrophic lakes are deep, nutrient-poor and do
not contain much life.

Eutrophic lakes are shallower and have increased
nutrients.

Mesotrophic have a moderate amount of nutrients
and phytoplankton productivity.
Over long periods of time, oligotrophic lakes may
become mesotrophic as runoff brings in nutrients.
Pollution from fertilizers can cause explosions
in algae population and cause a decrease in
oxygen content.

Streams and rivers are bodies of water moving
continuously in one direction.

Wetlands are areas covered with water that
supports many types of plants.
They can be saturated or flooded and include
areas known as marshes, bogs, and swamps.
They are home tomany differenttypes of
organisms,from herbivoresto crustaceans.
Unfortunately,humans havedestroyed them,but
many are nowprotected inmany places.

Fig. 50.21a
17

Estuaries are areas where freshwater and salt
water meet.
The salinity of these areas can vary greatly.
They are crucial feeding areas for many types of
water fowl.

Zonation in Marine communities.
The intertidal zone is where the land meets the
water.
The neritic zone includes the shallow regions
over the continental shelves.
The oceanic zone extends past the continental
shelves, and can be very deep.
The pelagic zone is the open water.
The benthic zone is the seafloor.

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Coral reefs exist in the neritic zone.
They constitute aconspicuous anddistinctive
biome.
They are dominatedby coral and includea very
diverseassortment ofvertebrates
andinvertebrates.

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E.The geographic distribution of terrestrial
biomes is based mainly on regional variations in
climate
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Vertical stratification is also important in
these biomes.
The canopy of the tropical rain forest is the top
layer, covering the layers below.
The permafrost in the tundra is a permanently
frozen stratum that lies under ground.
Human activity has radically altered the natural
patterns of many biomes.

Tropical forests are close to the equator,
receive high amounts of rainfall (although this
can vary from region to region), and contain a
great variety of plants and animals.
The vegetation is layered, with the canopy
being one of the top layers.

Savannas are grasslands with scattered trees,
that show distinct seasons, particularly wet and
dry.
Fire is an important abiotic factor.

Deserts have low rainfall, and are generally hot.
Vegetation is usually sparse, and includes cacti
and succulents.
Many animalsare nocturnal,so they canavoid the
heat.

Fig. 50.25c
26

Chaparrals have mild wet winters and dry hot
summers.
They containdense spiny,evergreenshrubs
andhave periodicfires.
Some plantsproduce seedsthat will
onlygerminateafter a fire.

Fig. 50.25d
27

Temperate grasslands exhibit seasonal drought,
occasional fires, and are usually used for
grazing and agriculture.

Temperate deciduous forests contain dense stands
of trees and have very cold winters and hot
summers.
The trees loseleaves and godormant in winter.
This biomeincludes a largevariety of plantsand
animals.
Humans havelogged many ofthese forestsaround
the world.

Fig. 50.25f
29

Coniferous forests (taigas) are the largest
terrestrial biome on earth.
They exhibit long cold winters and short wet
summers.

Tundra contains low growing plants.
The climate is windy and cold which
causes a short growing season.
A layer of permafrost is found below 1 meter and
does not thaw, which prevents root growth not
many animals live in tundra biomes.
There are two types, arctic, which is found in
areas of Alaska and the Arctic circle, and
alpine, which is found on very high mountaintops.

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F. Population ecology

Populations have size and geographical
boundaries.
The density of a population is measured as the
number of individuals per unit area.
The dispersion of a population is the pattern of
spacing among individuals within the geographic
boundaries.

Measuring density of populations is a difficult
task.
We can count individuals we can estimate
population numbers.

One sampling technique that researchers use is
known as the mark-recapture method.
Individuals are trapped in an area and captured,
marked with a tag, recorded, and then released.
After a period of time has elapsed, traps are set
again, and individuals are captured and
identified.
This information allows estimates of population
changes to be made.

Patterns of dispersion vary
Clumped xxx
xxx
This dispersion pattern is mostly due to
resource distribution.
Uniform x x x
x x x
This dispersion pattern is due to direct
interactions between individuals such as
competition for resources.
Random xx x xxx
x xxxx
This pattern is due to the absence of
interactions within a population.

Clumped dispersion is when individuals aggregate
in patches.

By contrast, uniform dispersion is when
individuals are evenly spaced.

In random dispersion, the position of each
individual is independent of the others.

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Click here- how to study biodiversity
40
G. Demography is the study of factors that affect
the growth and decline of populations

Additions occur through birth, and subtractions
occur through death.
Demography studies the vital statistics that
affect population size.
Life tables and survivorship curves.
A life table is an age-specific summary of the
survival pattern of a population.

A graphic way of representing the data is a
survivorship curve.
This is a plot of the number of individuals in a
cohort still alive at each age.
A Type I curve shows a low death rate early in
life (humans).
The Type II curve shows constant mortality
(squirrels).
Type III curve shows a high death rate early in
life (oysters).

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Reproductive rates.
Demographers that study populations usually
ignore males, and focus on females because only
females give birth to offspring.
A reproductive table is an age-specific summary
of the reproductive rates in a population.
For sexual species, the table tallies the number
of female offspring produced by each age group.

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H. Population Growth

To understand how much a populations growth may
be changing, birth and death rates must be
considered.

Using mathematical notation we can express this
relationship as follows
If N represents population size, and t represents
time, then ?N is the change is population size
and ?t represents the change in time, then
?N/?t B-D
Where B is the number of births and D is the
number of deaths

If B D then there is zero population growth
Under ideal conditions, a population grows
rapidly.
Exponential population growth is said to be
happening
Under these conditions, we may assume the maximum
growth rate for the population (rmax) to give us
the following exponential growth
dN/dt rmaxN

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I. The logistic model of population growth
incorporates the concept of carrying capacity

Typically, unlimited resources are rare.
Population growth is therefore regulated by
carrying capacity (K), which is the maximum
stable population size a particular environment
can support.

The logistic growth equation
We can modify our model of population growth to
incorporate changes in growth rate as population
size reaches a carrying capacity.
The logistic population growth model incorporates
the effect of population density on the rate of
increase.

The graph of this equation shows an S-shaped
curve.

How well does the logistic model fit the growth
of real populations?
The growth of laboratory populations of some
animals fits the S-shaped curves fairly well.

Different types of populations may show different
life history strategies relative to their
population growth.
In K-selection, organisms live and reproduce
around K, and are sensitive to population
density- they follow the logistic growth curve.
In r-selection, organisms exhibit high rates of
reproduction and occur in variable environments
in which population densities fluctuate- they
follow an exponential growth curve for a period
of time.

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Who are r-selected and k-selected populations?

An example of an r-selected population is a group
of mosquitoes in the spring.
An example of a k-selected population is a group
of giraffes living on a savanna.

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r-selected K-selected
Homeostatic capability Limited Extensive
Maturation time Short Long
Lifespan Short Long
Mortality rate High Low
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r-selected K-selected
offspring and size/ reproductive episode Many, small Few, large
reproductions/lifetime 1 Several
Age at 1st reproduction Early (young) Late (older)
Parental care None Often extensive
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J. How does density impact population growth?

Why do all populations eventually stop growing?
What environmental factors stop a population from
growing?
The first step to answering these questions is to
examine the effects of increased population
density.

Density-dependent factors increase their effect
on apopulation as populationdensity increases.
This is a type of negativefeedback.
Density-independent factorsare unrelated to
populationdensity, and there is nofeedback to
slow populationgrowth.

Examples of density dependent factors include
disease, available food or territory, health,
predation, pollution Examples of density
independent factors include hurricanes, tsunami,
fires, earthquakes
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Some populations have regular boom-and-bust
cycles.
The populations of predators and their prey can
fluctuate greatly.

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K. The human population has been growing almost
exponentially for three centuries but cannot do
so indefinitely

The human population increased relatively slowly
until about 1650 when the Plague took an untold
number of lives.
Ever since, human population numbers have doubled
twice
How might this population growth ever stop?

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Age structure.
Age structure is the relative number of
individuals of each age.
Age structure diagrams can reveal a populations
growth trends, and can point to future social
conditions.

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What can we learn from these graphs?

Kenyas population ? Bulge in the young
population means that most of these individual
can reproduce in the future, although there is a
high mortality rate at old age.
US population ?shows a bulge in the baby
boomers and more of the population survives into
old age.

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L. Estimating Earths carrying capacity for
humans is a complex problem

Predictions of the human population vary from 7.3
to 10.7 billion people by the year 2050.
Will the earth be overpopulated by this time?

Wide range of estimates for carrying capacity.
What is the carrying capacity of Earth for
humans?
This question is difficult to answer.
Estimates are usually based on food, but human
agriculture limits assumptions on available
amounts.

We may never know Earths carrying capacity for
humans, but we have the unique responsibility to
decide our fate and the fate of the rest of the
biosphere.

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M. Community Ecology

Possible interspecific interactions exist in a
community and can have positive or negative
effects.

Competition.
Interspecific competition for resources can occur
when resources are in short supply.
There is potential for competition between any
two species that need the same limited resource.
The competitive exclusion principle two species
with similar needs for same limiting resources
cannot coexist in the same place.

The ecological niche is the role an organism
plays in an environment.
For example, a squirrels niche would include
where it lives, the territory it covers, the
other squirrels or other species it encounters,
its mate, etc..
The competitive exclusion principle can be
restated to say that two species cannot coexist
in a community if their niches are identical.

Classic experiments confirm this.

Predation.
A predator eats prey.
Predator adaptations many important feeding
adaptations of predators are both obvious and
familiar.
Claws, teeth, fangs, poison, heat-sensing organs,
speed, and agility.

Plant defenses against herbivores include
chemical compounds that are toxic.
Animal defenses against predators.
Behavioral defenses include fleeing, hiding,
self-defense, noises, and mobbing.
Camouflage includes cryptic coloration, deceptive
markings.

Chemical defenses include odors and toxins
Aposematic coloration is indicated by warning
colors, and is sometimes associated with other
defenses (toxins).

Mimicry is when organisms resemble other species.
Batesian mimicry is where a harmless species
mimics a harmful one.

Fig. 53.7
76

Müllerian mimicry is where two or more
unpalatable or harmful species resemble each
other.

Fig. 53.8
77

Mutualism is where two species benefit from their
interaction. (ie ants and the Acacia tree)
Commensalism iswhere one speciesbenefits from
theinteraction, but otheris not affected.
An example wouldbe barnacles thatattach to a
whale.

In parasitism, predators
live on/in a host and depend
on the host for nutrition.
Example a tick is a parasite to
a dog or human

Coevolution refers to reciprocal evolutionary
adaptations of two interacting species.
When one species evolves, it exerts selective
pressure on the other to evolve to continue the
interaction.
Example many flowers have coevolved with the
pollinators that are attracted to them.

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N. Trophic structure is a key factor in community
dynamics

The trophic structure of a community is
determined by the feeding relationships between
organisms.
The transfer of food energy from its source in
photosynthetic organisms through herbivores and
carnivores is called the food chain.

Click animation
81

Charles Elton firstpointed out that the length
of a food chain is usually four or five links,
called trophic levels.
He also recognizedthat food chains are not
isolated units butare hooked togetherinto food
webs.

Food webs.
Who eats whom in a community?
A given species may weave into the web at more
than one trophic level.

Fig. 53.11
83

The autotrophs are the
primary producers, and are usually
photosynthetic (plants or algae).
They use light energy to synthesize sugars and
other organic compounds.

Heterotrophs areat trophic levelsabove the
primaryproducers anddepend on
theirphotosyntheticoutput.

Herbivores that eat primary producers are called
primary consumers.
Carnivores that eat herbivores are called
secondary consumers.
Carnivores that eat secondary consumers are
called tertiary consumers.
Another important group of heterotrophs is the
detritivores, or decomposers.
They get energy from detritus, nonliving organic
material and play an important role in material
cycling.

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Food chains can be represented as food pyramids

The pyramid of energy
Energy is transferred from the sun to producers
to primary, secondary and then tertiary
consumers.
There is a 10 transfer of energy from on level
to the next.
Most energy is used for metabolism or lost as
heat at each level.

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Fig. 54.11
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The dynamics of energy through ecosystems have
important implications for the human population.

Pyramid of biomass Producers are greatest in
biomass at the bottom of the pyramid.As you go
up the food chain, biomass decreases
Most biomass pyramids narrow sharply from primary
producers to top-level carnivores because energy
transfers are inefficient.

Pyramids of numbers show how the number of
individuals present in each trophic level
decreases from producer to each level of consumer.

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O. Decomposition connects all trophic levels

The organisms that feed as detritivores often
form a major link between the primary producers
and the consumers in an ecosystem.
The organic material that makes up the living
organisms in an ecosystem gets recycled.

An ecosystems main decomposers are fungi and
prokaryotes (bacteria), which secrete enzymes
that digest organic material and then absorb the
breakdown products.

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P. Ecological succession is the sequence of
community changes until a stable climax community
is formed.

Ecological succession is the transition in
species composition over ecological time.
Primary succession begins in a lifeless area
where soil has not yet formed.
Example?
lichen ?moss? grass?shrubs?trees

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Mosses and lichens colonize first and cause the
development of soil.
They are called the pioneer species
The climax community is the last stable stage to
appear.
In NY state, the climax community consists of
oak, maple and beach trees.

Secondary succession occurs where an existing
community has been cleared by some event (ie
fire,earthquake, volcanic eruption, hurricane),
but the soil is left intact.
Grasses grow first, then trees and other
organisms.

animation
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Q. Ecosystems rely on cycles

Cycles include
The water cycle
The carbon cycle
The nitrogen cycle
The phosphorus cycle

The water cycle

The carbon cycle also includes hydrogen and
oxygen.

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animation
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The nitrogen cycle.
Nitrogen enters ecosystems through two natural
pathways.
Nitrogen from the atmosphere can enter the soil
by rain and dust.
Nitrogen fixation, where certain bacteria convert
N2 to compounds in the soil that can be used to
synthesize nitrogenous organic compounds like
amino acids.
These archeabacteria are found on the root
nodules of legumes like clover and represent a
mutualism.

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The direct product of nitrogen fixation is
ammonia, which picks up H and becomes ammonium
in the soil (ammonification), which plants can
use.
Certain aerobic bacteria oxidize ammonium into
nitrate, a process called nitrification.
Nitrate can also be used by plants.
Some bacteria get oxygen from the nitrate and
release N2 back into the atmosphere
(denitrification).

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The phosphorous cycle.
Organisms require phosphorous for many things.
This cycle is simpler than the others because
phosphorous does not come from the atmosphere.

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R. The human population is disrupting chemical
cycles throughout the biosphere

The growing human population size coupled with
technology that is not environmentally friendly
leads to great disruptions in our ecosystems.

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In agricultural ecosystems, a large amount of
nutrients are removed from the area in the crop
biomass.
After awhile, the natural store of nutrients can
become exhausted.

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Recent studies indicate that human activities
have approximately doubled the worldwide supply
of fixed nitrogen, due to the use of fertilizers,
cultivation of legumes, and burning.
This may increase the amount of nitrogen oxides
in the atmosphere and contribute to atmospheric
warming, depletion of ozone and possibly acid
rain.

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Excess nitrogen can runoff into water systems,
which leads to algae blooms, which ultimately
leads to oxygen depletion after aerobic bacteria
consume the dead algae.
This process is calledeutrophication

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Controlling pollution may help control
eutrophication.

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S. Combustion of fossil fuels is the main cause
of acid precipitation

The burning offossil fuelsreleases
sulfuroxides and nitrogen thatreact with
waterin the atmosphereto produce sulfuric and
nitric acids.

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These acids fall back to earth as acid
precipitation, and can damage ecosystems greatly.
The acids can kill plants, and can kill aquatic
organisms by changing the pH of the soil and
water.

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T. Toxins can become concentrated in successive
trophic levels of food webs

Humans produce many toxic chemicals that are
dumped into ecosystems.
These substances are ingested and metabolized by
the organisms in the ecosystems and can
accumulate in the fatty tissues of animals.
These toxins become more concentrated in
successive trophic levels of a food web, a
process called biological magnification.

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The pesticide DDT, before it was banned, showed
this affect.

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U. Human activities may be causing climate change
by increasing carbon dioxide concentration in the
atmosphere

Rising atmospheric CO2.
Since the Industrial Revolution, the
concentration of CO2 in the atmosphere has
increased greatly as a result of burning fossil
fuels.

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Measurements in 1958 read 316 ppm and increased
to 370 ppm today

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The greenhouse effect.
Rising levels of atmospheric CO2 may have an
impact on Earths heat budget.
When light energy hits the Earth, much of it is
reflected off the surface.
CO2 causes the Earth to retain some of the energy
that would ordinarily escape the atmosphere.
This phenomenon is called the greenhouse effect.

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Global warming.
Several studies predict a doubling of CO2 in the
atmosphere will cause a 2º C increase in the
average temperature of Earth.
Rising temperatures could cause polar ice cap
melting, which could flood coastal areas.
It is important that humans attempt to stabilize
their use of fossil fuels.

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V. Human activities are depleting the atmospheric
ozone

Life on earth is protected from the damaging
affects of ultraviolet radiation (UV) by a layer
of O3,or ozone.
Studies suggest thatthe ozone layer hasbeen
graduallythinning since 1975.

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The destruction of ozone probably results from
the accumulation of chlorofluorocarbons,
chemicals used in refrigeration and aerosol cans,
and in certain manufacturing processes.
The result of a reduction in the ozone layer may
be increased levels of UV radiation that reach
the surface of the Earth.
This radiation has been linked to skin cancer and
cataracts.

122
W. Biodiversity is vital to human welfare

Why should we care about biodiversity?
How does it benefit us to maintain species
diversity and genetic diversity?

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Biodiversity is acrucial naturalresource,
andspecies that arethreatened couldprovide
crops, fibers, and medicines forhuman use.
The loss of species also means the loss of genes.
Biodiversity represents the sum of all the
genomes on Earth.

Fig. 55.3
124
X. The four major threats to biodiversity are
habitat destruction, introduced species,
overexploitation and food chain disruption

Habitat destruction
Human alteration of habitat is the single
greatest cause of habitat destruction.
Destruction of physical habitat is responsible
for the 73 of species designated extinct,
endangered, vulnerable, or rare.
About 93 of the worlds coral reefs have been
damaged by humans.

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Introduced species
Introduced species are those that humans move
from native locations to new geographic regions.
The Nile perch wasintroduced into LakeVictoria
as a food fish,but led to the extinctionof
several native species.

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There are manyexamples of howexotic
specieshave disruptedecosystems.

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Overexploitation
This refers to the human harvesting of wild
plants and animals at rates that exceed the
ability of those populations to rebound.
The great auk was overhunted and became extinct.

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The African elephant has been overhunted and the
populations have declined dramatically.
The bluefin tuna is another example of an
over-harvested species.

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