Transcript Ecological

Chapter 52
Population Ecology
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
LE 52-2
Births
Immigration
Population
size
Emigration
Deaths
LE 52-3a
Clumped. For many animals, such as these wolves, living in
groups increases the effectiveness of hunting, spreads the work
of protecting and caring for young, and helps exclude other
individuals from their territory.
LE 52-3b
Uniform. Birds nesting on small islands, such as these king penguins
on South Georgia Island in the South Atlantic Ocean, often exhibit
uniform spacing, maintained by aggressive interactions between
neighbors.
LE 52-3c
Random. Dandelions grow from windblown seeds that land at
random and later germinate.
Demography
• Demography is the study of the vital statistics of
a population and how they change over time
• Death rates and birth rates are of particular
interest to demographers
LE 52-4
Number of survivors (log scale)
1,000
100
Females
10
Males
1
0
2
4
6
Age (years)
8
10
Number of survivors (log scale)
LE 52-5
1,000
I
100
II
10
III
1
0
50
Percentage of maximum life span
100
Life History Diversity
• Life histories are very diverse
• Species that exhibit semelparity, or “big-bang”
reproduction, reproduce once and die
• Species that exhibit iteroparity, or repeated
reproduction, produce offspring repeatedly
“Trade-offs” and Life Histories
• Organisms have finite resources, which may lead to
trade-offs between survival and reproduction
LE 52-8a
Most weedy plants, such as this dandelion, grow quickly and produce a
large number of seeds, ensuring that at least some will grow into plants
and eventually produce seeds themselves.
LE 52-8b
Some plants, such as this coconut palm, produce a moderate number of
very large seeds. The large endosperm provides nutrients for the
embryo, an adaptation that helps ensure the success of a relatively
large fraction of offspring.
• In animals, parental care of smaller broods may
facilitate survival of offspring
• Carrying capacity (K) is the maximum
population size the environment can support
The Logistic Model and Life Histories
• Life history traits favored by natural selection
may vary with population density and
environmental conditions
• K-selection, or density-dependent selection,
selects for life history traits that are sensitive to
population density
• r-selection, or density-independent selection,
selects for life history traits that maximize
reproduction
Territoriality
• In many vertebrates and some invertebrates,
territoriality may limit density
Health
• Population density can influence the health and
survival of organisms
• In dense populations, pathogens can spread
more rapidly
Predation
• As a prey population builds up, predators may
feed preferentially on that species
Toxic Wastes
• Accumulation of toxic wastes can contribute to
density-dependent regulation of population size
LE 52-22
Human Population Growth
5
4
3
2
The Plague
1
8000
B.C.
4000
B.C.
3000
B.C.
2000
B.C.
1000
B.C.
0
1000
A.D.
0
2000
A.D.
Human population (billions)
6
Regional Patterns of Population Change
• To maintain population stability, a regional
human population can exist in one of two
configurations:
– Zero population growth =
High birth rate – High death rate
– Zero population growth =
Low birth rate – Low death rate
• The demographic transition is the move from
the first state toward the second state
LE 52-24
Birth or death rate per 1,000 people
50
40
30
20
10
Sweden
Birth rate
Mexico
Birth rate
Death rate
0
1750
1800
Death rate
1850
1900
Year
1950
2000
2050
Age Structure
• One important demographic factor in present and
future growth trends is a country’s age structure
• Age structure is the relative number of individuals
at each age
• It is commonly represented in pyramids
LE 52-25
Rapid growth
Afghanistan
Male
Female
Slow growth
United States
Male
Female
Age
Age
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
8
6
4
2
0
2
4
Percent of population
6
8
Decrease
Italy
Male
Female
85+
80–84
75–79
70–74
65–69
60–64
55–59
50–54
45–49
40–44
35–39
30–34
25–29
20–24
15–19
10–14
5–9
0–4
8
6
4
2
0
2
4
Percent of population
6
8
8
6
4
2
0
2
4
Percent of population
6
8
• Age structure diagrams can predict a
population’s growth trends
• They can illuminate social conditions and help
us plan for the future
Infant Mortality and Life Expectancy
• Infant mortality and life expectancy at birth vary
greatly among developed and developing
countries but do not capture the wide range of
the human condition
LE 52-26
80
50
Life expectancy (years)
Infant mortality (deaths per 1,000 births)
60
40
30
20
60
40
20
10
0
0
Developed
countries
Developing
countries
Developed
countries
Developing
countries
LE 52-27
Ecological footprint (ha per person)
16
14
12
New Zealand
10
USA
Germany
Netherlands
Japan
Norway
8
6
Australia
Canada
Sweden
UK
Spain
4
World
China
India
2
0
0
2
4
6
10
12
8
Available ecological capacity
(ha per person)
14
16
Competition
• Interspecific competition occurs when species
compete for a resource in short supply
• Strong competition can lead to competitive
exclusion, local elimination of a competing species
The Competitive Exclusion Principle
• The competitive exclusion principle states that
two species competing for the same limiting
resources cannot coexist in the same place
LE 53-2
Chthamalus
Balanus
High tide
High tide
Chthamalus
realized niche
Chthamalus
fundamental niche
Balanus
realized niche
Ocean
Low tide
Ocean
Low tide
Resource Partitioning
• Resource partitioning is differentiation of
ecological niches, enabling similar species to
coexist in a community
LE 53-3
A. insolitus
usually perches
on shady branches.
A. ricordii
A. distichus
perches on
fence posts
and other
sunny
surfaces.
A. insolitus
A. aliniger
A. distichus
A. christophei
A. cybotes
A. etheridgei
Predation
• Predation refers to interaction where one species,
the predator, kills and eats the other, the prey
• Some feeding adaptations of predators are claws,
teeth, fangs, stingers, and poison
• Prey display various defensive adaptations
• Behavioral defenses include hiding, fleeing, selfdefense, and alarm calls
• Animals also have morphological and
physiological defense adaptations
• Cryptic coloration, or camouflage, makes prey
difficult to spot
Video: Seahorse Camouflage
• Animals with effective chemical defense often
exhibit bright warning coloration, called
aposematic coloration
• Predators are particularly cautious in dealing
with prey that display such coloration
• In Batesian mimicry, a palatable or harmless
species mimics an unpalatable or harmful model
LE 53-7
Green parrot snake
Hawkmoth larva
• In Müllerian mimicry, two or more unpalatable
species resemble each other
LE 53-8
Cuckoo bee
Yellow jacket
Herbivory
• Herbivory refers to an interaction in which an
herbivore eats parts of a plant or alga
• It has led to evolution of plant mechanical and
chemical defenses and adaptations by herbivores
Parasitism
• In parasitism, one organism, the parasite,
derives nourishment from another organism, its
host, which is harmed in the process
• Parasitism exerts substantial influence on
populations and the structure of communities
Disease
• Effects of disease on populations and
communities are similar to those of parasites
• Pathogens, disease-causing agents, are typically
bacteria, viruses, or protists
Mutualism
• Mutualistic symbiosis, or mutualism, is an
interspecific interaction that benefits both species
Video: Clownfish and Anemone
Commensalism
• In commensalism, one species benefits and the
other is apparently unaffected
• Commensal interactions are hard to document
in nature because any close association of two
species likely affects both
LE 53-12
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Carnivore
Primary
consumers
Herbivore
Zooplankton
Primary
producers
Plant
A terrestrial food chain
Phytoplankton
A marine food chain
LE 53-13
Humans
Smaller
toothed
whales
Baleen
whales
Crab-eater
seals
Birds
Leopard
seals
Fishes
Sperm
whales
Elephant
seals
Squids
Carnivorous
plankton
Copepods
Euphausids
(krill)
Phytoplankton
LE 53-14
Sea nettle
Juvenile striped bass
Fish larvae
Fish eggs
Zooplankton
Keystone Species
• In contrast to dominant species, keystone species
are not necessarily abundant in a community
• They exert strong control on a community by their
ecological roles, or niches
Number of species
present
LE 53-16
20
With Pisaster (control)
15
10
Without Pisaster (experimental)
5
0
1963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73
LE 53-21
Before a controlled burn.
A prairie that has not burned for
several years has a high propor-tion of
detritus (dead grass).
During the burn. The detritus serves as
fuel for fires.
After the burn. Approximately one
month after the controlled burn,
virtually all of the biomass in this
prairie is living.
LE 53-22
Soon after fire. As this photo taken soon after the fire shows, the
burn left a patchy landscape. Note the unburned trees in the
distance.
One year after fire. This photo of the same general area taken the
following year indicates how rapidly the com-munity began to
recover. A variety of herbaceous plants, different from those in the
former forest, cover the ground.
Human Disturbance
• Humans are the most widespread agents of
disturbance
• Human disturbance to communities usually
reduces species diversity
• Humans also prevent some naturally occurring
disturbances, which can be important to
community structure
Ecological Succession
• Ecological succession is the sequence of
community and ecosystem changes after a
disturbance
• Primary succession occurs where no soil exists
when succession begins
• Secondary succession begins in an area where
soil remains after a disturbance
• Early-arriving species and later-arriving species
may be linked in one of three processes:
– Early arrivals may facilitate appearance of later
species by making the environment favorable
– They may inhibit establishment of later species
– They may tolerate later species but have no impact
on their establishment
LE 53-24
Pioneer stage, with fireweed dominant
Dryas stage
60
Soil nitrogen (g/m2)
50
40
30
20
10
0
Pioneer
Dryas
Alder
Successional stage
Spruce
Nitrogen fixation by Dryas and alder
increases the soil nitrogen content.
Spruce
stage
LE 54-2
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Decomposition
• Decomposition connects all trophic levels
• Detritivores, mainly bacteria and fungi, recycle
essential chemical elements by decomposing
organic material and returning elements to
inorganic reservoirs
Pyramids of Production
• A pyramid of net production represents the loss
of energy with each transfer in a food chain
LE 54-11
Tertiary
consumers
Secondary
consumers
Primary
consumers
Primary
producers
10 J
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
Pyramids of Biomass
• In a biomass pyramid, each tier represents the
dry weight of all organisms in one trophic level
• Most biomass pyramids show a sharp decrease
at successively higher trophic levels
LE 54-12a
Trophic level
Dry weight
(g/m2)
Tertiary consumers
1.5
Secondary consumers
11
Primary consumers
37
Primary producers
809
Most biomass pyramids show a sharp decrease in biomass at successively higher
trophic levels, as illustrated by data from a
bog at Silver Springs, Florida.
• Certain aquatic ecosystems have inverted
biomass pyramids: Primary consumers outweigh
the producers
LE 54-12b
Trophic level
Primary consumers (zooplankton)
Primary producers (phytoplankton)
Dry weight
(g/m2)
21
4
In some aquatic ecosystems, such as the English Channel, a small standing crop of
primary producers (phytoplankton) supports a larger standing crop of primary
consumers (zooplankton).
Pyramids of Numbers
• A pyramid of numbers represents the number of
individual organisms in each trophic level
LE 54-13
Trophic level
Tertiary consumers
Number of
individual organisms
3
Secondary consumers
354,904
Primary consumers
708,624
Primary producers
5,842,424
LE 54-17a
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
LE 54-17b
CO2 in atmosphere
Photosynthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Carbon compounds
in water
Higher-level
Primary consumers
consumers
Detritus
Decomposition
LE 54-17c
N2 in atmosphere
Assimilation
NO3–
Nitrogen-fixing
bacteria in root
nodules of legumes
Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
Nitrifying
bacteria
Nitrification
NH4+
NO2–
Nitrifying
bacteria
Denitrifying
bacteria
LE 54-17d
Rain
Geologic
uplift
Weathering
of rocks
Plants
Runoff
Consumption
Sedimentation
Soil
Plant uptake
of PO43–
Leaching
Decomposition
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
Toxins in the Environment
• Humans release many toxic chemicals, including
synthetics previously unknown to nature
• 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
LE 54-23
Concentration of PCBs
Herring
gull eggs
124 ppm
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
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
LE 54-26
350
Ozone layer thickness (Dobson units)
300
250
200
150
100
50
0
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Year (Average for the month of October)
• Destruction of atmospheric ozone probably
results from chlorine-releasing pollutants
produced by human activity
LE 54-27
Chlorine from CFCs interacts with ozone (O3),
forming chlorine monoxide (CIO) and oxygen (O2).
Chlorine atoms
O2
O3
Chlorine
CIO
O2
Sunlight causes Cl2O2
to break down into O2
and free chlorine
atoms. The chlorine
atoms can begin the
cycle again.
CIO
Cl2O2
Sunlight
Two CIO molecules react,
forming chlorine peroxide
(Cl2O2).
LE 54-28
October 1979
October 2000