Post on 10-Mar-2020
Scope of Ecology
• Ecology is the scientific study of the interactions between organisms and the environment.
• These interactions determine distribution of organisms and their abundance
• Ecologists work at levels ranging from individual organisms to the planet• Ecology has a long history as a descriptive science
• It also is a rigorous experimental science
Fig. 52-2Organismalecology
Populationecology
Communityecology
Ecosystemecology
Landscapeecology
Globalecology
Key Terms
• A population is a group of individuals of the same species living in an area.
• A community is a group of populations of different species in an area.
• An ecosystem is the community of organisms in an area and the physical factors with which they interact
• Biosphere is the global ecosystem, the sum of all the planet’s ecosystems
Interactions between organisms and the environment• Global and regional patterns of distribution of organisms within the
biosphere are recognized
• Ecologists recognize two kinds of factors that determine distribution: biotic – living, and abiotic – non-living.
Fig. 52-6
Why is species X absentfrom an area?
Does dispersallimit its
distribution?Does behavior
limit itsdistribution?
Area inaccessibleor insufficient time
Yes
No
No
No
Yes
YesHabitat selection
Do biotic factors(other species)
limit itsdistribution?
Predation, parasitism,competition, disease
Do abiotic factorslimit its
distribution?
Chemicalfactors
Physicalfactors
WaterOxygenSalinitypHSoil nutrients, etc.
TemperatureLightSoil structureFireMoisture, etc.
• Dispersal is the movement of individuals away from centres of high pop’n density or from their area of origin. This contributes to global distribution of organisms.
• Natural range expansions show the influence of dispersal on distribution
• Species transplants include organisms that are intentionally or accidentally relocated from their original distribution.
• Species transplants can disrupt ecosystems to which they have been introduced
• Some organisms do not occupy all of their potential range
• Species distribution may be limited by habitat selection behavior
• Biotic factors that affect distribution may include:• Interactions with other species
• Predation
• competition
Fig. 52-8
RESULTS
Sea urchin
100
80
60
40
20
0
Limpet
Seaw
ee
d c
ove
r (%
)
Both limpets and urchinsremoved
Only urchinsremoved
Only limpets removed
Control (both urchinsand limpets present)
August1982
August1983
February1983
February1984
• Abiotic factors affecting distribution of organisms include:• Tempurature
• Water
• Sunlight
• Wind
• Rocks and soil
• Most abiotic factors vary in space and time
Tempurature
• Enviro temperature is an important factor in distribution of organisms because of its effects on biological processes
• Cells may freeze and rupture below 0°C, while most proteins denature above 45°C
• Mammals and birds expend energy to regulate their internal temp
• Water availability• For example desert organisms exhibit adaptations for water conservation
• Salinity affects water balance of organisms through osmosis• For example few terrestrial organisms are adapted to high-salinity habitats
Sunlight
• Light intensity and quality affect photosynthesis
• Water absorbs light, meaning in aquatic enviros most photosynthesis occurs near surface
• In deserts, high light levels increase temp and can stress organims
Rocks and Soil
• Many characteristics of soil limit distribution of plants and thus the animals that feed upon them:• Physical structure
• pH
• Mineral composition
Climate
• 4 major abiotic components of climate are temp, water, sunlight, and wind
• Climate is the long-term prevailing weather conditions
• Macroclimate – patterns on the global, regional, and local level
• Microclimate – very fine patterns within a community such as organisms under a fallen log
Global Climate Patterns
• Global climate patterns are determined largely by solar energy and the planet’s movement in space• Sunlight intensity
• Tropics – more heat and light than higher latitudes
• Seasonal variations of light and temp increase steadily toward the poles
Fig. 52-10aLatitudinal Variation in Sunlight Intensity
Low angle of incoming sunlight
Sun directly overhead at equinoxes
Low angle of incoming sunlight
Atmosphere
90ºS (South Pole)60ºS
30ºS
23.5ºS (Tropic ofCapricorn)
0º (equator)
30ºN23.5ºN (Tropic ofCancer)
60ºN90ºN (North Pole)
Seasonal Variation in Sunlight Intensity
60ºN
30ºN
30ºS
0º (equator)
March equinox
June solstice
Constant tiltof 23.5º
September equinox
December solstice
• Global air circulation and precipitation patterns play major roles in determining climate patterns
• Warm wet air flows from the tropics toward the poles
Fig. 52-10dGlobal Air Circulation and Precipitation Patterns
60ºN
30ºN
0º (equator)
30ºS
60ºS
Global Wind Patterns
Descendingdry airabsorbsmoisture
Ascendingmoist airreleasesmoisture
Descendingdry airabsorbsmoisture
Aridzone
Tropics Aridzone
0º
66.5ºN(Arctic Circle)
60ºN
30ºN
0º(equator)
30ºS
60ºS66.5ºS(Antarctic Circle)
Westerlies
Northeast trades
Doldrums
Southeast trades
Westerlies
23.5º30º 23.5º 30º
• Air flowing close to Earth’s surface creates predictable global wind patterns
• Cooling trade winds blow from east to west in the tropics; prevailing westerlies blow from west to east in the temperate zones
Regional, Local and Seasonal Effects on Climate• Proximity to bodies of water and topographic features contribute to
local variations in climate
• Seasonal variation also influences climate
• Example: Gulf Stream carries warm water from the equator to the North Atlantic
• Ocean currents and large lakes moderate the climate of nearby terrestrial enviros.
• During the day, air rise over warm land and draws a cool breeze from the water across the land
• As the land cools at night, air rises over the warmer water and draws cooler air from land back over the water, which is replaced by warm air from offshore
Fig. 52-12
Warm airover land rises.1
23
4
Air cools athigh elevation.
Cool air over watermoves inland, replacingrising warm air over land.
Coolerair sinksover water.
Mountains
• Mountains have significant effect on• Amount of sunlight reaching an area
• Local temp
• Rainfall• Rising air releases moisture on the windward side of peak and creates a “rain shadow” as
it absorbs moisture on the leeward side
Seasonality
• The angle of the sun leads to many seasonal changes in local enviros
• Lakes are sensitive to seasonal temperature change and experience seasonal turnover
Microclimate
• Microclimate is determined by fine-scale differences in the enviro that affect light and wind patterns
Population Ecology
• The study of pop’ns in relation to environment, including environmental influences on density and distribution, age structure, and population size
• Density and Dispersion• Density is the number of individuals per unit are or volume
• Dispersion is the pattern of spacing among individuals within the boundaries of the pop’n
Estimating population sizes
• In most cases, it is impossible to count all individuals in a pop’n
• Sampling techniques can be used to estimate densities and total pop’n sizes
• Population size can be estimated by either extrapolation from small samples, and index or population size, or the mark-recapture method
Factors that add and remove individuals to a pop’n• Immigration – new individuals from other areas
• Emigration – movement of individuals out of a pop’n
• Births
• Deaths
Fig. 53-3
Births
Births and immigrationadd individuals toa population.
Immigration
Deaths and emigrationremove individualsfrom a population.
Deaths
Emigration
Pattern of Dispersion
• Spacing of individuals in a pop’n is influenced by environmental and social factors• In a clumped dispersion, individuals aggregate in patches – may be influenced
by resource availability and behavior
• Uniform dispersion – evenly distributed• Influenced by social interactions such as territoriality
• Random dispersion – position is independent of other individuals• Occurs in the absence of strong attractions or repulsions
Demography and Life Tables
• Study of vital statistics of a population and how they change over time
• Death and birth rates – interest demographers
• Life table – age specific summary of the survival pattern of a pop’n
• Follow a cohort (group of individuals of same age)
• Survivorship curve – represent data of a life table in a graphic way. There are three general types:• Type I: low death rates during early and middle life, then an increase among
older age groups
• Type II: the death rate is constant over the org’s life span
• Type III: high death rates for the young, then a slower death rate for survivors
Fig. 53-6
1,000
100
10
10 50 100
II
III
Percentage of maximum life span
Nu
mb
er
of
su
rviv
ors
(lo
g s
ca
le)
I
Reproductive Rates
• For species with sexual reproduction, females used
• A reproductive table, or fertility schedule is an age-specific summary of the reproductive rates in a population
• Describes reproductive patterns of a pop’n
• Life history of org comprises the traits that affect its schedule of reproduction and survival:• Age at which reproduction begins
• How often the organism reproduces
• How many offspring are produced during each reproductive cycle
• Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organism
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
• Highly variable or unpredictable environments likely favor big-bang reproduction, while dependable environments may favor repeated reproduction
“Trade-offs” and Life Histories
• Organisms have finite resources, which may lead to trade-offs between survival and reproduction• Some plants produce a large number of small seeds, ensuring that at least
some of them will grow and eventually reproduce
• Other types of plants produce a moderate number of large seeds that provide a large store of energy that will help seedlings become established
Fig. 53-8
MaleFemale
100
RESULTS
80
60
40
20
0Reduced
brood sizeNormal
brood sizeEnlarged
brood sizePare
nts
su
rviv
ing
th
e f
oll
ow
ing
win
ter
(%)
Population Growth Models
• It is useful to study pop’n growth in an idealized situation• Help us understand the capacity of a species to increase and the conditions
that may facilitate this growth
Per Capita Rate of Increase
• Ignoring immigration and emigration, a population’s growth rate (per capita increase) equals birth rate minus death rate
• Zero population growth – birth rate=death rate
• Growth rate at an instant in time:• Where N=pop’n size, t=time, r=per capita rate of increase = birth-death
Nt
= rN
Exponential population growth
• Increase under idealized conditions
• Rate of reproduction is at its max, called intrinsic rate of increase
• Eq’n of exponential pop’n growth:
• Growth results in a J-shaped curve
• J-shaped curve of exponential growth characterizes some rebounding pop’ns dN
dtrmaxN
Fig. 53-10
Number of generations
0 5 10 15
0
500
1,000
1,500
2,000
1.0N=dN
dt
0.5N=dN
dtP
op
ula
tio
n s
ize (
N)
Logistic Growth Model
• Exponential growth cannot be sustained for long in any population
• A more realistic population model limits growth by incorporating carrying capacity
• Carrying capacity(K) is the max pop’n size the enviro can support
• In the logistic pop’n growth model, the per capita rat of increase declines as carrying capacity is reached
• Produces a sigmoid (S-shaped) curve
• The growth of lab pop’ns of paramecia fits an S-curve
• These orgs are grown in a constant enviro lacking predators and competitors
dNdt
=(K - N)
Krmax N
Fig. 53-12
2,000
1,500
1,000
500
00 5 10 15
Number of generations
Po
pu
lati
on
siz
e (
N)
Exponentialgrowth
1.0N=dN
dt
1.0N=dN
dt
K = 1,500
Logistic growth
1,500 – N
1,500
Fig. 53-13
1,000
800
600
400
200
0
0 5 10 15
Time (days)
Nu
mb
er
of
Pa
ram
ec
ium
/mL
Nu
mb
er
of
Da
ph
nia
/50 m
L
0
30
60
90
180
150
120
0 20 40 60 80 100 120 140 160
Time (days)
(b) A Daphnia population in the lab(a) A Paramecium population in the lab
• Some pop’ns overshoot K before settling down to a relatively stable density
• Some pop’ns fluctuate greatly and make it difficult to define K
• Some pop’ns show an Allee effect, in which individuals have a more difficult time surviving or reproducing in the pop’n size is too small
Logistic Model and Life Histories
• Life history traits favoured by natural selection may vary with pop’ndensity and environmental conditons
• K-selection, or density dependent selection, selects for life history traits that are sensitive to pop’n density
• r-selection, or density-independent selection, selects for life history traits that maximize reproduction
Density dependent factors in population growth
• General questions about regulation of pop’n growth:
• What environmental factors stop a population from growing indefinitely
• Why do some populations show radical fluctuations in size over time, while others remain stable?
• In density-independent populations, birth rate and death rate do not change with pop’n density
• In density-dependent pop’ns, birth rates fall and death rates rise with pop’n density
• Density-dependent birth and death rates are an example of negative feedback that regulates pop’n growth
• They are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors
Fig. 53-15
(a) Both birth rate and death rate vary.
Population density
Density-dependentbirth rate
Equilibriumdensity
Density-dependentdeath rate
Bir
th o
r d
ea
th r
ate
per
cap
ita
(b) Birth rate varies; death rate is constant.
Population density
Density-dependentbirth rate
Equilibriumdensity
Density-independentdeath rate
(c) Death rate varies; birth rate is constant.
Population density
Density-dependentdeath rate
Equilibriumdensity
Density-independentbirth rate
Bir
th o
r d
ea
th r
ate
per
cap
ita
• In crowded populations, increasing pop’n density intensifies competition for resources and results in a lower birth rate
• In many vertebrates competition for territory may limit density
• Ex: cheetah are highly territorial, use chemical communication to warn other cheetahs of their boundaries
• Ex: oceanic birds exhibit territoriality in nesting behavior
Fig. 53-16
Population size
100
80
60
40
20
0200 400 500 600300P
erc
en
tag
e o
f ju
ven
iles
pro
du
cin
g l
am
bs
• Disease• Pop’n density can influence the health and survival or organisms
• In dense pop’ns, pathogens can spread more rapidly
• Predation• As a prey pop’n build up, predators may feed preferentially on that species
• Toxic wastes - accumulation of toxic wastes can contribute to density-dependent regulation of pop’n size
• Intrinsic factors – for some pop’ns, physiological factors appear to regulate pop’n size
Population Dynamics
• Focuses on the complex interactions between biotic and abiotic factors that cause variation in pop’n size
• Weather can affect pop’n size over time
• Changes in predation pressure can drive population fluctuations
Fig. 53-18
2,100
1,900
1,700
1,500
1,300
1,100
900
700
500
01955 1965 1975 1985 1995 2005
Year
Nu
mb
er
of
sh
eep
Fig. 53-19
Wolves Moose
2,500
2,000
1,500
1,000
500
Nu
mb
er
of
mo
ose
0
Nu
mb
er
of
wo
lve
s
50
40
30
20
10
01955 1965 1975 1985 1995 2005
Year
Population Cycles
• Some pop’ns undergo regular boom-and-bust cycles
• Lynx pop’ns follow the 10 year boom-and-bust cycle of hare populations
• Three hypotheses have been proposed to explain the hare’s 10-year interval
Fig. 53-20
Snowshoe hare
Lynx
Nu
mb
er
of
lyn
x
(th
ou
sa
nd
s)
Nu
mb
er
of
ha
res
(th
ou
sa
nd
s)
160
120
80
40
01850 1875 1900 1925
Year
9
6
3
0
Hypothesis: the hare’s pop’n cycle follows a cycle of winter food supply
• If this hypothesis is correct, then the cycles should stop if the food supply is increased
• Additional food was provided experimentally to a hare pop’n and the whole pop’n increased in size but continued to cycle
• No hares appeared to have died of starvation
Hypothesis: the hare’s pop’n cycle is driven by pressure from other predators
• In a field study conducted by field ecologists, 90% of the hares were killed by predatorys
• These data support this second hypothesis
Hypothesis: the hare’s pop’n cycle is linked to sunspot cycles
• Sunspot activity affects light quality, which in turn affects the quality of the hares’food
• There is good correlation between sunspot activity and hare pop’nsize
• The results of all these experiments suggest that both predation and sunspot activity regulate hare numbers and that food availability plays a less important role
Human Pop’n – exponential growth
• No pop’n can grow indefinitely, humans are no exception
• The human pop’n increased relatively slowly until about 1650 and then began to grow exponentially
• Though the global pop’n is still growing, the rate of growth began to slow during the 1960s
Fig. 53-23
2005
Projecteddata
An
nu
al
pe
rce
nt
inc
rea
se
Year
1950 1975 2000 2025 2050
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
• To maintain pop’n stability, a regional human pop’n can exist in one of two configurations:• Zero pop’n growth = high birth rate – high death rate
• Zero pop’n growth = low birth rate – low death rate
• The demographic transition is the move from the first state toward the second state
Fig. 53-24
1750 1800 1900 1950 2000 2050
Year
1850
Sweden Mexico
Birth rate Birth rateDeath rateDeath rate
0
10
20
30
40
50
Bir
th o
r d
ea
th r
ate
per
1,0
00 p
eo
ple
• The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women
• Most of the current global pop’n growth is concentrated in developing countries
Global Carrying Capacity
• How many humans can the biosphere support?
• The carrying capacity of Earth for humans is uncertain
• The average estimate is 10-15 billion
Limits on Human Population Size
• The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation
• It is one measure of how close we are to the carrying capacity of Earth
• Countries vary greatly in footprint size and available ecological capacity
• Our carrying capacity could potentially be limited by food, space, non-renewable resources, or buildup of wastes
• An ecosystem consists of all of the organisms living in a community, as well as the abiotic factors with which they interact
• Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest
• Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling
• Energy flows through ecosystems while matter cycles within them
• Laws of physics and chemistry apply to ecosystems, particularly energy flow
• The first law of thermodynamics states that energy cannot be created or destroyed, only transformed
• Energy enters an ecosystem as solar radiation, is conserved, and is lost from organisms as heat
• The second law of thermodynamics states that every exchange of energy increases the entropy of the universe
• In an ecosystem, energy conversion are not completely efficient, and some energy is always lost as heat
• The law of conservation of mass states that matter cannot be created or destroyed
• Chemical elements are continually recycled within ecosystems
• In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water
• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products
Energy, Mass and Trophic Levels
• Autotrophs build molecules themselves using photosynthesis as an energy source; heterotrophs depend on the output of other organisms
• Energy and nutrients pass from primary producers to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores)
• Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter
• Prokaryotes and fungi are important detritivores
• Decomposition connects all trophic levels
Fig. 55-4
Microorganismsand other
detritivores
Tertiary consumers
Secondaryconsumers
Primary consumers
Primary producers
Detritus
Heat
SunChemical cycling
Key
Energy flow
• Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period
• The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget
Energy transfer between trophic levels is typically only 10% efficient• Secondary production of an ecosystem is the amount of chemical
energy in food converted to new biomass during a given period of time
• When a caterpillar feeds on a leaf, only about 1/6 of the leaf’s energy is used for secondary production
• An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration
Fig. 55-9
Cellularrespiration100 J
Growth (new biomass)
Feces
200 J
33 J
67 J
Plant materialeaten by caterpillar
• Trophic efficiency is the percentage of production transferred from one trophic level to the next
• It usually ranges from 5% to 20%
• Trophic efficiency is multiplied over the length of food chain
• Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer
• A pyramid of net production represents the loss of energy with each transfer in a food chain
Fig. 55-10
Primaryproducers
100 J
1,000,000 J of sunlight
10 J
1,000 J
10,000 J
Primaryconsumers
Secondaryconsumers
Tertiaryconsumers
• Life depends on recycling chemical elements
• Nutrient circuits in ecosystems involve biotic and abiotic components
• Biogeochemical cycles include: carbon, oxygen, sulfur, nitrogen, and phosphorus
Fig. 55-14b
Higher-levelconsumersPrimary
consumers
Detritus
Burning offossil fuelsand wood
Phyto-plankton
Cellularrespiration
Photo-synthesis
Photosynthesis
Carbon compoundsin water
Decomposition
CO2 in atmosphere
Fig. 55-14c
Decomposers
N2 in atmosphere
Nitrification
Nitrifyingbacteria
Nitrifyingbacteria
Denitrifyingbacteria
Assimilation
NH3 NH4 NO2
NO3
+ –
–
Ammonification
Nitrogen-fixingsoil bacteria
Nitrogen-fixingbacteria