Overview: Discovering Ecology Ecology is the scientific study
of the interactions between organisms and the environment These
interactions determine the distribution of organisms and their
abundance Modern ecology includes observation and
experimentation
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Global ecology is concerned with the biosphere, or global
ecosystem, which is the sum of all the planets ecosystems Global
ecology examines the influence of energy and materials on organisms
across the biosphere
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Figure 40.2a Global ecology
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Landscape ecology focuses on the exchanges of energy,
materials, and organisms across multiple ecosystems A landscape (or
seascape) is a mosaic of connected ecosystems
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Figure 40.2b Landscape ecology
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Ecosystem ecology emphasizes energy flow and chemical cycling
among the various biotic and abiotic components An ecosystem is the
community of organisms in an area and the physical factors with
which they interact
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Figure 40.2c Ecosystem ecology
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Community ecology deals with the whole array of interacting
species in a community A community is a group of populations of
different species in an area
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Figure 40.2d Community ecology
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Population ecology focuses on factors affecting population size
over time A population is a group of individuals of the same
species living in an area
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Figure 40.2e Population ecology
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Organismal ecology studies how an organisms structure,
physiology, and (for animals) behavior meet environmental
challenges Organismal ecology includes physiological, evolutionary,
and behavioral ecology
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Figure 40.2f Organismal ecology
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Concept 40.1: Earths climate influences the structure and
distribution of terrestrial biomes The long-term prevailing weather
conditions in an area constitute its climate Four major abiotic
components of climate are temperature, precipitation, sunlight, and
wind
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Abiotic factors are the nonliving chemical and physical
attributes of the environment Biotic factors are the other
organisms that make up the living component of the environment
Macroclimate consists of patterns on the global, regional, and
landscape level
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Biomes are major life zones characterized by vegetation type
(terrestrial biomes) or physical environment (aquatic biomes)
Climate is very important in determining why terrestrial biomes are
found in certain areas Climate affects the latitudinal patterns of
terrestrial biomes Climate and Terrestrial Biomes
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Figure 40.8 Temperate broadleaf forest Northern coniferous
forest Annual mean precipitation (cm) 15 Tropical forest Desert
Temperate grassland Arctic and alpine tundra Annual mean
temperature ( C) 15 0 0 30 100 200 300 400
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Natural and human-caused disturbances alter the distribution of
biomes A disturbance is an event that changes a community by
removing organisms and altering resource availability For example,
frequent fires kill woody plants preventing woodlands from
establishing
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General Features of Terrestrial Biomes Terrestrial biomes are
often named for major physical or climatic factors and for
vegetation Terrestrial biomes usually grade into each other,
without sharp boundaries The area of intergradation, called an
ecotone, may be wide or narrow
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Terrestrial biomes can be characterized by distribution,
precipitation, temperature, plants, and animals
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Tropical forest occurs in equatorial and subequatorial regions
Temperature is high year-round (2529 C) with little seasonal
variation In tropical rain forests, rainfall is relatively
constant, while in tropical dry forests precipitation is highly
seasonal
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Figure 40.9a A tropical rain forest in Costa Rica
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Tropical forests are vertically layered, and competition for
light is intense Tropical forests are home to millions of animal
species, including an estimated 530 million still undescribed
species of insects, spiders, and other arthropods Rapid human
population growth is now destroying many tropical forests
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Savanna occurs in equatorial and subequatorial regions
Precipitation is seasonal Temperature averages 2429 C but is more
seasonally variable than in the tropics
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Figure 40.9b A savanna in Kenya
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Grasses and forbs make up most of the ground cover The dominant
plant species are fire-adapted and tolerant of seasonal drought
Common inhabitants include insects and mammals such as wildebeests,
zebras, lions, and hyenas Fires set by humans may help maintain
this biome
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Deserts occur in bands near 30 north and south of the equator
and in the interior of continents Precipitation is low and highly
variable, generally less than 30 cm per year Deserts may be hot (
50 C) or cold (30 C) with seasonal and daily temperature
variation
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Figure 40.9c Organ Pipe Cactus National Monument, Arizona
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Desert plants are adapted for heat and desiccation tolerance,
water storage, and reduced leaf surface area Common desert animals
include scorpions, ants, beetles, snakes, lizards, migratory and
resident birds, and seed-eating rodents; many are nocturnal
Urbanization and conversion to irrigated agriculture have reduced
the natural biodiversity of some deserts
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Chaparral occurs in midlatitude coastal regions on several
continents Precipitation is highly seasonal with rainy winters and
dry summers Summer is hot (30 C); fall, winter, and spring are cool
(1012 C)
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Figure 40.9d An area of chaparral in California
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The chaparral is dominated by shrubs and small trees; many
plants are adapted to fire and drought Animals include browsing
mammals, insects, amphibians, small mammals, and birds Humans have
reduced chaparral areas through agriculture and urbanization
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Temperate grasslands occur at midlatitudes, often in the
interior of continents Precipitation is highly seasonal Winters are
cold (often below 10 C) and dry; summers are hot (often near 30 C)
and wet
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Figure 40.9e A grassland in Mongolia
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The dominant plants, grasses and forbs, are adapted to droughts
and fire Native mammals include large grazers such as bison and
wild horses and small burrowers such as prairie dogs Most
grasslands have been converted to farmland
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Northern coniferous forest, or taiga, spans northern North
America and Eurasia and is the largest terrestrial biome on Earth
Precipitation ranges from 3070 cm Winters are cold; summers may be
hot (e.g., Siberia ranges from 50 C to 20 C)
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Figure 40.9f A coniferous forest in Norway
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Conifers such as pine, spruce, fir, and hemlock dominate The
conical shape of conifers prevents too much snow from accumulating
and breaking their branches Animals include migratory and resident
birds and large mammals such as moose, brown bears, and Siberian
tigers Periodic insect outbreaks kill vast tracts of trees Some
forests are being logged at an alarming rate
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Temperate broadleaf forest is found at midlatitudes in the
Northern Hemisphere, with smaller areas in Chile, South Africa,
Australia, and New Zealand Significant amounts of precipitation
fall during all seasons as rain or snow Winters average 0 C;
summers are hot and humid (near 35 C)
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Figure 40.9g A temperate broadleaf forest in New Jersey
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Dominant plants include deciduous trees in the Northern
Hemisphere and evergreen eucalyptus in Australia In the Northern
Hemisphere, many mammals hibernate in the winter; birds migrate to
warmer areas These forests have been heavily settled on all
continents but are recovering in places
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Tundra covers expansive areas of the Arctic; alpine tundra
exists on high mountaintops at all latitudes Precipitation is low
in arctic tundra and higher in alpine tundra Winters are cold
(below 30 C); summers are relatively cool (less than 10 C)
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Figure 40.9h Dovrefjell National Park, Norway
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Vegetation is herbaceous (mosses, grasses, forbs, dwarf shrubs,
trees, and lichen) Permafrost, a permanently frozen layer of soil,
restricts growth of plant roots Mammals include musk oxen, caribou,
reindeer, bears, wolves, and foxes; many migratory bird species
nest in the summer Settlement is sparse, but tundra has become the
focus of oil and mineral extraction
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Concept 40.2: Aquatic biomes are diverse and dynamic systems
that cover most of Earth Aquatic biomes account for the largest
part of the biosphere in terms of area They show less latitudinal
variation than terrestrial biomes Marine biomes have salt
concentrations of about 3% The largest marine biome is made of
oceans, which cover about 75% of Earths surface and have an
enormous impact on the biosphere
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Freshwater biomes have salt concentrations of less than 0.1%
Freshwater biomes are closely linked to soils and the biotic
components of the surrounding terrestrial biome
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Video: Clownfish Anemone Video: Coral Reef Video: Hydrothermal
Vent Video: Shark Eating a Seal Video: Swans Taking Flight Video:
Tubeworms
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Aquatic biomes can be characterized by their physical and
chemical environment, geological features, photosynthetic
organisms, and heterotrophs
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Wetlands and estuaries are among the most productive habitats
on Earth Wetlands are inundated by water at least sometimes and
support plants adapted to water-saturated soil An estuary is a
transition area between river and sea; salinity varies with the
rise and fall of the tides High organic production and
decomposition in these biomes result in low levels of dissolved
oxygen
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Figure 40.10a A basin wetland in the United Kingdom
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Wetlands can develop in shallow basins, along flooded river
banks, or on the coasts of large lakes Estuaries include a complex
network of tidal channels, islands, and mudflats Plants are adapted
to growing in periodically anaerobic, water-saturated soils Wetland
plants include cattails and sedges; estuaries are characterized by
saltmarsh grasses
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Wetlands are home to diverse invertebrates and birds, as well
as frogs and alligators Estuaries support an abundance of marine
invertebrates, fish, waterfowl, and marine mammals Humans
activities have destroyed up to 90% of wetlands and disrupted
estuaries worldwide
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Lakes vary in size from small ponds to very large lakes
Temperate lakes may have a seasonal thermocline; tropical lowland
lakes have a year-round thermocline Oligotrophic lakes are
nutrient-poor and generally oxygen-rich Eutrophic lakes are
nutrient-rich and often depleted of oxygen if ice covered in
winter
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Figure 40.10b An oligotrophic lake in Alberta, Canada
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Eutrophic lakes have more surface area relative to depth than
oligotrophic lakes Rooted and floating aquatic plants live in the
shallow and well-lighted littoral zone close to shore Water is too
deep in the limnetic zone to support rooted aquatic plants; the
primary producers are phytoplankton
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Zooplankton are drifting heterotrophs that graze on the
phytoplankton Invertebrates live in the benthic zone Fishes live in
all zones with sufficient oxygen Human-induced nutrient enrichment
can lead to algal blooms, oxygen depletion, and fish kills
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Streams and rivers have varying environmental conditions from
headwater to mouth Headwater streams are generally cold, clear,
turbulent, swift, and oxygen-rich; they are often narrow and rocky
Downstream waters form rivers and are generally warmer and more
turbid; they are often wide and meandering and have silty bottoms
Salt and nutrients increase from headwaters to mouth; oxygen
content decreases from headwaters to mouth
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Figure 40.10c A headwater stream in Washington
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Coral reefs are formed from the calcium carbonate skeletons of
corals (cnidarians) Shallow reef-building corals live in the photic
zone in warm (about 2030 C), clear water; deep-sea corals live at
depths of 2001,500 m Corals require high oxygen concentrations and
a solid substrate for attachment A coral reef progresses from a
fringing reef to a barrier reef to a coral atoll
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Figure 40.10e A coral reef in the Red Sea
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Corals are the predominant animals on the reef They form
mutualisms with symbiotic algae that provide them organic molecules
A high diversity of fish and invertebrates inhabit coral reefs
Coral collection, overfishing, global warming, and pollution all
contribute to reduction in coral populations
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The oceanic pelagic zone is constantly mixed by wind-driven
oceanic currents Oxygen levels are high Turnover in temperate
oceans renews nutrients in the photic zones This biome covers
approximately 70% of Earths surface
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The marine benthic zone consists of the seafloor Organisms in
the very deep benthic (abyssal) zone are adapted to continuous cold
and high water pressure Substrate is mainly soft sediments; some
areas are rocky
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Figure 40.11 Zonation in a lake Littoral zone Limnetic zone
Pelagic zone Photic zone Aphotic zone Benthic zone
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Concept 40.3: Interactions between organisms and the
environment limit the distribution of species Species distributions
are the result of ecological and evolutionary interactions through
time Ecological time is the minute-to-minute time frame of
interactions between organisms and the environment Evolutionary
time spans many generations and captures adaptation through natural
selection
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Events in ecological time can lead to evolution For example,
Galpagos finches with larger beaks were more likely to survive a
drought, as they could eat the available larger seeds As a result,
the average beak size was larger in the next generation This
resulted in an evolutionary change
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Dispersal and Distribution Dispersal is the movement of
individuals away from centers of high population density or from
their area of origin Dispersal contributes to the global
distribution of organisms
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Biotic Factors Biotic factors that affect the distribution of
organisms may include Predation Herbivory For example, sea urchins
can limit the distribution of seaweeds Mutualism Parasitism
Competition
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Abiotic Factors Abiotic factors affecting the distribution of
organisms include Temperature Water and oxygen Salinity Sunlight
Rocks and soil
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Temperature is an important environmental factor in the
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 Most organisms function best within a
specific temperature range
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Availability of water and oxygen is an important factor in
species distribution Desert organisms exhibit adaptations for water
conservation Water affects oxygen availability, as oxygen diffuses
slowly in water Oxygen concentrations can be low in deep oceans and
deep lakes
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Salinity, salt concentration, affects the water balance of
organisms through osmosis Most aquatic organisms are restricted to
either freshwater or saltwater habitats Few terrestrial organisms
are adapted to high- salinity habitats
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Sunlight is the energy source for photosynthetic organisms and,
as such, can limit their distribution In aquatic environments most
photosynthesis occurs near the surface where sunlight is available
Shading by the canopy drives intense competition for light in
forests
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Rocks and soil have many characteristics that limit the
distribution of plants and thus the animals that feed on them
Physical structure pH Mineral composition
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Concept 40.4: Dynamic biological processes influence population
density, dispersion, and demographics Population ecology explores
how biotic and abiotic factors influence density, distribution, and
size of populations A population is a group of individuals of a
single species living in the same general area Populations are
described by their boundaries and size
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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
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Density is the result of an interplay between processes that
add individuals to a population and those that remove individuals
Additions occur through birth and immigration, the influx of new
individuals from other areas Removal of individuals occurs through
death and emigration, the movement of individuals out of a
population
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Patterns of Dispersion Environmental and social factors
influence the spacing of individuals in a population The most
common pattern of dispersion is clumped, in which individuals
aggregate in patches A clumped dispersion may be influenced by
resource availability and behavior
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Figure 40.15 (a) Clumped (c) Random(b) Uniform
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Figure 40.15d (a) Clumped (c) Random (b) Uniform
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Demographics 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
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Life Tables A life table is an age-specific summary of the
survival pattern of a population It is best made by following the
fate of a cohort, a group of individuals of the same age, from
birth to death
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Survivorship Curves A survivorship curve is a graphic way of
representing the data in a life table Survivorship curves plot the
proportion or numbers of a cohort still alive at each age
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Survivorship curves can be classified into three general types
Type I: low death rates during early and middle life and an
increase in death rates among older age groups Type II: a constant
death rate over the organisms life span Type III: high death rates
for the young and a lower death rate for survivors Many species are
intermediate to these curves
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Figure 40.16 1,000 Percentage of maximum life span III Number
of survivors (log scale) 100 10 0 1 10050 II I
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Concept 40.5: The exponential and logistic models describe the
growth of populations Unlimited growth occurs under ideal
conditions; in nature, growth is limited by various factors
Ecologists study growth in both idealized and realistic
conditions
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Per Capita Rate of Increase Change in population size can be
defined by the equation If immigration and emigration are ignored,
a populations growth rate (per capita increase) equals birth rate
minus death rate Change in population size Births Immigrants
entering population Deaths Emigrants leaving population
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The population growth rate can be expressed mathematically as
where N is the change in population size, t is the time interval, B
is the number of births, and D is the number of deaths NtNt B
D
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Births and deaths can be expressed as the average number of
births and deaths per individual during the specified time interval
where b is the annual per capita birth rate, m (for mortality) is
the per capita death rate, and N is population size B bN D mN
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The population growth equation can be revised NtNt bN mN
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The per capita rate of increase (r) is given by r b m Zero
population growth (ZPG) occurs when the birth rate equals the death
rate (r 0)
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Change in population size can now be written as NtNt rN
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Exponential Growth Exponential population growth is population
increase under idealized conditions Under these conditions, the
rate of increase is at its maximum, denoted as r max The equation
of exponential population growth is dN dt r max N
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Exponential population growth results in a J-shaped curve
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Figure 40.17 1,000 Number of generations Population size (N)
1.0N 10 0 0155 2,000 1,500 500 0.5N dtdt dNdN dtdt dNdN
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Figure 40.18 6,000 Year Elephant population 0 2,000 8,000 4,000
19001930194019501960197019101920
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Carrying Capacity 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 maximum population size the environment can support Carrying
capacity varies with the abundance of limiting resources
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The Logistic Growth Model In the logistic population growth
model, the per capita rate of increase declines as carrying
capacity is reached The logistic model starts with the exponential
model and adds an expression that reduces per capita rate of
increase as N approaches K dN dt r max N (K N) K
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The logistic model of population growth produces a sigmoid
(S-shaped) curve
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Figure 40.19 1,000 Number of generations Population size (N)
1.0N 10 0 0 155 2,000 1,500 500 1.0N dtdt dNdN Exponential growth
Population growth begins slowing here. K 1,500 dtdt dNdN (1,500 N)
1,500 Logistic growth
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The Logistic Model and Real Populations The growth of many
laboratory populations, including paramecia, fits an S-shaped curve
when resources are limited These organisms are grown in a constant
environment lacking predators and competitors Animation: Population
Ecology
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Figure 40.20 1,000 Time (days) Number of Paramecium/mL 10 0 0
15 5 (a) A Paramecium population in the lab 800 200 400 600 Time
(days) 140 0 0 160 30 (b) A Daphnia (water flea) population in the
lab 40 60 20 100 120 80 Number of Daphnia/50 mL 180 60 150 120
90
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The logistic model fits few real populations but is useful for
estimating possible growth Conservation biologists can use the
model to estimate the critical size below which populations may
become extinct
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Concept 40.6: Population dynamics are influenced strongly by
life history traits and population density An organisms life
history comprises the traits that affect its schedule of
reproduction and survival The age at which reproduction begins How
often the organism reproduces How many offspring are produced
during each reproductive cycle
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Trade-offs and Life Histories Organisms have finite resources,
which may lead to trade-offs between survival and reproduction
Selective pressures influence the trade-off between the number and
size of offspring Some plants produce a large number of small
seeds, ensuring that at least some of them will grow and eventually
reproduce
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Figure 40.21 Dandelions grow quickly and release a large number
of tiny fruits. The Brazil nut tree (above), produces a moderate
number of large seeds in pods (left).
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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
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Population Change and Population Density In density-independent
populations, birth rate and death rate do not change with
population density In density-dependent populations, birth rates
fall and death rates rise with population density
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Mechanisms of Density-Dependent Population Regulation
Density-dependent birth and death rates are an example of negative
feedback that regulates population growth Density-dependent birth
and death rates are affected by many factors, such as competition
for resources, territoriality, disease, predation, toxic wastes,
and intrinsic factors
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Competition for resources occurs in crowded populations;
increasing population density intensifies competition for resources
and results in a lower birth rate
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Figure 40.23a Competition for resources
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Toxic wastes produced by a population can accumulate in the
environment, contributing to density-dependent regulation of
population size
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Figure 40.23d Toxic wastes 5 m
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Predation may increase with increasing population size due to
predator preference for abundant prey species
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Figure 40.23b Predation
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Territoriality can limit population density when space becomes
a limited resource
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Figure 40.23e Territoriality
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Disease transmission rates may increase with increasing
population density
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Figure 40.23c Disease
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Intrinsic factors (for example, physiological factors like
hormonal changes) appear to regulate population size