Ecology The Biosphere Population Ecology Community Ecology Ecosystems.
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Transcript of Ecology The Biosphere Population Ecology Community Ecology Ecosystems.
Ecology
The BiospherePopulation EcologyCommunity Ecology
Ecosystems
Introduction to Ecology and the Biosphere
Chapter 50
Abiotic Factors of the Biosphere
Climate– Water/Rainfall –Light– Temperature –Wind
Rocks and Soil– Particle size –Mineral composition– pH
Periodic Disturbances– Catastrophic events: fire, flood, earthquake, etc.
Global Climate Patterns
Determined by:– input of solar energy
• Shape of earth—latitudinal variation• 23.5° tilt of earth’s axis—seasonal variation
– earth’s movement in space
Global Air Circulation, Precipitation, and
Winds
Local and Seasonal Effects on Climate
Proximity to bodies of water– Oceanic currents along continental coasts– Large inland bodies of water—lakes
Topographic features– Mountain ranges
Rain Shadows
Seasonal Turnover of Lakes/Ponds
Lake stratification and biannual mixing– Temperature water densest at 4°C,– Density it sinks below water that is
warmer or colder
Chapter 52
Population Ecology
Overview: Earth’s Fluctuating Populations
To understand human population growth, we must consider general principles of population ecology
Population ecology = study of populations relative to environment, including environmental influences on density and distribution, age structure, and population size
Population = group of individuals of a single species living in the same general area
Density and Dispersion
Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals
within the boundaries of the population– Environmental and social factors influence spacing of individuals
in a population
Clumped distribution may be influenced by resource availability (living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young)
Uniform distribution may be influenced by social interactions such as territoriality
Random distribution—the position of each individual is independent of other individuals
Demography
Study of theory and statistics behind population growth and decline
N = size of the population
Demographic Statistics
Birth rate = number of offspring produced per time period
Death rate = number of deaths per time period
Sex ratio = proportion of males and females in a population
Generation time = time needed for individuals to reach reproductive maturity
Demographic Statistics
Age structure = statistic that compares the relative number of individuals in the population from each age group
Immigration rate = rate at which individuals relocate into a given population
Emigration rate = rate which individuals relocate out of a give population
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Demographic Statistics
These statistics together determine the size and growth rate of a given population
Population Growth = (Births + immigration) - (deaths + emigration)
If birth rates are greater than death rates:
Population Growth Fictional "Tribbles" from
Star Trek: Defining characteristic of the
Tribbles is their extreme reproductive rate. Over half of a Tribbles metabolism is devoted to reproduction, allowing them to bear a litter of young every twelve hours.
With an average litter of ten, a single Tribble can therefore create a population of 1,771,561 within three days, and an amazing 304,481,639,541,400,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 in thirty days!
Short generation time = faster rate of population growth
Population Growth and Size
Biotic potential = maximum growth rate of a population given unlimited resources, unlimited space, and lack of competition or predators– Rate varies from species to species
Carrying capacity = maximum number of individuals that a population can sustain in a given environment without destroying the habitat
Density-dependent factors come into play when population approaches and/or passes the carrying capacity– Food supplies, waste products, population-
crowding diseases Density-independent factors have nothing
to do with the population size– Floods, droughts, earthquakes, other natural
disasters and weather conditions
Limiting Factors Control Population Sizes
Population Growth Exponential Growth =
population grows as if there are no limitations as to how large it can get (biotic potential)
A population increases slowly at first (the "lag phase") and then grows increasingly rapidly as time passes (the "log phase"). When numbers are low, a doubling does not produce much addition to the population, but as numbers increase, each successive doubling adds larger and larger increments.
Population Growth
Logistic Growth = population growth slows to zero and population size tends to stabilize because of environmental resistance (limiting factors)
Exponential growth can be represented by the following equation:
dN/dt = rNwhere:
– dN/dt is the instantaneous rate of change in population size– r is the intrinsic rate of increase of the population– N is population size at any given point in time
The S-shaped (sigmoid) curve that shows the effect of environmental resistance upon population growth can be represented by the following equation, often referred to as the logistic equation:
dN/dt = rN (K-N) / K where K is the carrying capacity (maximum value of
N for a given set of environmental conditions)
Point of Maximum growth (K/2)
Number of generations
Po
pu
lati
on
siz
e (N
)
K = 1,5001,500
2,000
1,000
500
1510500
Logistic growth
Exponentialgrowth
= 1.0NdNdt
= 1.0NdNdt
1,500 – N1,500
Carrying Capacity
Life History Strategies
K-selected populations are of a roughly constant size whose members have low reproductive rates.– Offspring require extensive postnatal care until
sufficiently matured (humans) R-selected populations experience rapid
growth– Offspring are numerous, mature rapidly, and
require little postnatal care (bacteria)
Predator-Prey Cycling
Many populations undergo boom-and-bust cycles
Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors
Community EcologyChapter 53
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
Interactions Between Populations of Different Species
Predation (+/–)—consumption of one organism by another– Predator eats prey– 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
Plant Defenses Against Hebivores
Physical defenses– thorns, hooks/spines on
leaves Chemical defenses
– Make plant distasteful or poisonous
• Morphine from opium poppy
• Nicotine from tobacco
Animal Defenses Against Predators Behavioral defenses
– Alarm cries– Distraction displays
Cryptic coloration/shape (camouflage)
– Blend in with environment– Asposematic coloration
• Red/black; yellow/black
Mechanical/chemical defenses– Quills, spines, and other similar structures– Toxins—distasteful or poisonous
• Monarch butterfly stores toxin of milkweed as larvae• Poisonous toads secrete toxin
Animal Defenses Against Predators Mimicry—prey resembles species that cannot
be eaten– Batesian mimicry: Imitate color patterns or
appearance of more dangerous organisms Mimicry can be used to lure prey
– Snapping turtle wriggles tongue like a worm to attract and capture small fish
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
Competitive Exclusion Principle Two species cannot coexist in a community if
their niches are identical
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
Competition cannot operate for long periods of time
Evolution Drives Reduced Niche Overlap
0
2
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10
12
2 4 6 8 10 12 14 16 18 20
Height of nesting site in apple trees
Num
ber
of in
divi
dual
s
Population 1Population 2
0
2
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10
12
2 4 6 8 10 12 14 16 18 20
Resource Partitioning
Character Displacement
Joseph H. Connell Study
Symbiotic Relationships
Non-Beneficial– Parasitism (+/–)—host harmed
Beneficial– Commensalism (+/0)—one partner benefits
while not harming the other• Cattle egrets—egrets eat ectoparasites/cattle are
groomed
– 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
Effects of a Keystone Predator:Sea Star (Pisaster)
0
5
10
15
20
25
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
Year
Num
ber
of S
peci
es
Pre
sent With Pisaster
Without Pisaster
Community Structure Introduction of a species (exotic species)
into a community can have drastic affects on the existing community members
Habitats that are more varied can support a more diverse community – provides more ecological niches
Nonequilibrium and 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
Competition among early species shape the succession of an area
Tolerance to abiotic conditions determines early species
EcosystemsChapter 54
Trophic Relationships Ecosystems divided into trophic levels
(feeding levels)– Primary 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 Webs Feeding
relationships woven into elaborate interconnections between species
Energy Flow in Ecosystems Each level in a food web contains a
different quantity of stored chemical energy When consumers eats producers or 2
consumers eat 1 producers, some energy is lost in the each transfer from one level to the next– Gross primary productivity= [total chemical
energy generated by producers]– Net primary productivity= [total chemical
energy – respiration by plants]
Pyramid of Net Productivity:
10% of energy at each level converted
to new biomass
Pyramids of Standing Crop
Biomass
Sharp decrease in biomass at
successively higher levels
Small crop of 1 producers
support larger crop of 1 consumers
Pyramid of Numbers:In higher trophic levels, the
small amount of biomass contained in a few organisms
Biogeochemical Cycles Chemical elements available only in limited
amounts Movement of essential elements between
the biotic and abiotic environment
Carbon Cycle Nitrogen Cycle Phosphorus Cycle Water Cycle
Carbon Cycle
*
Human Impacts
Greenhouse Effect– Increase of atmospheric CO2
• Combustion of fossil fuels• Burning of wood from deforestation
– Increase in numbers of C3 plants in areas previously inhabited by C4 plants
– Increase in global temperature
Nitrogen Cycle
*
Human Impacts
Agricultural effects– Cultivation—turns up soil and increases rate of
decomposition of organic matter; Releases more nitrogen
– Harvesting removes 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—
– high amounts are toxic to aquatic organisms and humans
– Algal blooms in lakes speed up eutrophication
Phosphorus Cycle
*
Water Cycle
The human population is disrupting chemical cycles throughout the biosphere
As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems
Nutrient Enrichment
In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems
Agriculture and Nitrogen Cycling
Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil
Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle
Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful
Contamination of Aquatic Ecosystems
Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem
When excess nutrients are added to an ecosystem, the critical load is exceeded
Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems
Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems
Acid Precipitation Combustion of fossil
fuels is the main cause of acid precipitation
North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid
North America
Europe
4.3 4.6
4.14.34.6
4.34.6
4.6
Field pH
5.35.2–5.35.1–5.25.0–5.14.9–5.04.8–4.94.7–4.84.6–4.74.5–4.64.4–4.54.3–4.4<4.3
5.3
5.3
5.35.3
5.3 5.3
5.3
5.2
5.3
5.6
5.9
5.4
5.2
5.2
5.2
5.2
5.4
5.56.0
5.0
5.4
6.3
5.3
5.3
6.1
5.5
5.4
5.4
5.4
5.4
5.6
5.5
5.5
5.6
5.65.2
5.1
5.15.74.9
5.7
5.0
5.0
5.0
5.04.9
4.9
4.9
4.9
4.14.3
4.3
4.34.4
4.44.4
4.4
4.4
4.5
4.54.5
4.54.5
4.54.5
4.5
4.5
4.54.5
4.5
4.5
4.5
4.54.5
4.5
4.54.5
4.5
4.5
4.64.6
4.64.6
4.6
4.6
4.64.6
4.64.64.6
4.64.6
4.6
4.7
4.7
4.74.74.7
4.7
4.7
4.74.7
4.7
4.74.7
4.7
4.7
4.7
4.84.8
4.8
4.8
4.8
4.8
4.8
4.8
4.8
5.0
5.0
5.3
5.2
5.1
5.1
5.1
5.1
5.2
5.25.2
5.3
5.4
5.4
5.5
5.5
4.74.7
4.7
4.7
4.7
4.7
4.7
4.9
4.8
4.8
4.64.7
4.7
4.7
4.84.8
4.8
4.8
4.9
4.9
4.9
5.0
5.0
5.0
5.1
5.1
5.0
5.0 5.05.1
5.2
5.3
5.45.4
5.7
By the year 2000, acid precipitation affected the entire contiguous United States
Environmental regulations and new technologies have allowed many developed countries to reduce sulfur dioxide emissions
Toxins in the Environment
In some cases, harmful substances persist for long periods in an ecosystem
One reason toxins are harmful is that they become more concentrated in successive trophic levels
In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower
Zooplankton0.123 ppm
Phytoplankton0.025 ppm
Lake trout4.83 ppm
Smelt1.04 ppm
Herringgull eggs124 ppm
Co
nc
en
tra
tio
n o
f P
CB
s
Atmospheric Carbon Dioxide
One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide
Rising Atmospheric CO2
Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing
The Greenhouse Effect and Global Warming
The greenhouse effect caused by atmospheric CO2 keeps Earth’s surface at a habitable temperature
Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change
Depletion of Atmospheric Ozone
Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere
Satellite studies suggest that the ozone layer has been gradually thinning since 1975 O
zon
e l
ay
er
thic
kn
es
s (
Do
bs
on
un
its
) 350
300
250
200
150
100
50
0196019651970197519801985 199019952000 2005
Year (Average for the month of October)1955
Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity
Chlorine atoms
O3Chlorine
Cl2O2
CIO
O2
O2
CIO
Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (CIO) and oxygen (O2).
Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.
Two CIO molecules react, forming chlorine peroxide (Cl2O2).
Sunlight
Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased
October 1979 October 2000