Download Evolution and Populations

2/16/2015
Evolution, Biodiversity and Population Ecology
• Chapter 3
After this lecture, you will be able to:
• Explain the process of natural selection and cite evidence for
this process
• Describe the ways in which evolution influences biodiversity
• Discuss reasons for species extinction and mass extinction
events
• List the levels of ecological organization
• Outline the characteristics of populations that help predict
population growth
• Assess logistic growth, carrying capacity, limiting factors, and
other fundamental concepts in population ecology
Evolution is the wellspring of biodiversity
• Evolution simply means change over time
– Biological evolution is genetic change in populations over time
– These genetic changes lead to changes in appearance, functioning, or
behavior over generations
Evolution by natural selection
Natural selection
• Evolution may be random or can be driven by natural
selection
• Natural selection is the process whereby inherited
characteristics that enhance survival and reproduction are
passed on more frequently to future generations than those
that do not
Evidence of natural selection is everywhere
• Artificial selection is the process of selection conducted under
human direction
•
It is one of the best-supported and most illuminating concepts in science and is the
foundation of modern biology
•
Evolutionary processes influence agriculture, pesticide resistance, medicine, health,
etc.
•
In 1858, both Darwin and Wallace proposed natural selection as the mechanism of
evolution
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Natural selection shapes organisms
• Premises of natural selection:
– Organisms struggle to survive and reproduce
– They produce more offspring than can survive
– Individuals of a species vary in their characteristics
because of genes and the environment
– Some individuals are better suited to their environment
and reproduce more effectively
• Natural selection acts on genetic variation
Populations (NOT individuals) adapt to the
environment
• A parent that produces more offspring passes on more genes
to future generations
• Over time, characteristics (traits) that lead to better
reproductive success become more prevalent
• Adaptive trait (adaptation): a trait that promotes reproductive
success
• Sexual reproduction also leads to genetic variation
– Producing new combinations of genes
• Environmental conditions determine the pressures of natural
selection
– Organisms need time to adapt to changing conditions
Resolving religion and evolution
• Literal biblical account is not
compatible with evolution
• What we know is not
compatible with biblical
account
– E.g., species are
unchanging
Many religions accept evolution
Speciation
• Given enough geographical isolation or selective pressure
(from natural selection), members of a population become so
different from their ancestors that they may be considered an
entirely new species
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Speciation produces new types of organisms
• The process of generating new species from a single species
• Allopatric speciation occurs when species form as a result of
physical separation of populations
– Main mode of speciation
– Populations can be separated by glaciers, rivers, mountains
– Each population, with its own set of mutations, diverges
Convergent evolution
• Phylogenetic trees are branching diagrams that
show relationships among species, groups, genes,
etc.
– Represent life’s history
Divergent evolution
• Similar conditions lead to
similar adaptations
• Species look alike even if
they are not related
• Species evolve into
different types to
take advantage of
opportunities in
environment and
reduce competition
Producers rely on ____________ to capture chemical energy
and consumers rely on ____________ to release chemical
energy.
Respiration produces energy from
1.
2.
3.
4.
5.
Speciation results in diverse life forms
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water, carbon dioxide, and sugar.
Sugar and oxygen.
oxygen, carbon dioxide, and sugar.
carbon dioxide, enzymes, and sugar.
oxygen, water, and sugar.
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2.
3.
4.
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cellular respiration; photosynthesis
cellular respiration; cellular respiration
photosynthesis; cellular respiration
photosynthesis; photosynthesis
the sun; the sun
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_______ drives the hydrologic cycle by producing rain and
snow from evaporated surface water.
1.
2.
3.
4.
5.
Fossil fuels and living trees are known as “carbon
sinks” because
1.
2.
3.
4.
5.
Lunar tides
The Coriolis Effect
Hurricanes
Solar energy
none of the above
they have no carbon.
they create carbon.
they destroy carbon.
they store carbon.
due to gravity, carbon is found closer to the ground.
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1. the discovery of a desirable characteristic in a population.
2. better survival or reproduction rates by individuals with a
particular genetic characteristic.
3. an individual’s physiological modification.
4. environmental change that forces modification in a resident
species.
5. a population’s physiological modification
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Fossils show life’s history
Evolution occurs as a result of
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Extinction
• Most species that once lived
are now gone
• Extinction is the disappearance
of a species from Earth
– Species last 1–10 million
years
• Biological diversity is now being
lost at an astounding rate
– This loss of species is
irreversible
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• A fossil is an imprint in
stone of a dead organism
• Phylogenetic trees and the
fossil record show:
– Life has existed on Earth for 3.5
billion years
– Life evolved complex structures
from simple ones
– Life evolved large sizes from
small ones
– But natural selection can also
favor simplicity and small size
Some species are vulnerable to extinction
• Extinction occurs when the environment changes rapidly
• Many factors cause extinction:
– Climate change, changing sea levels, severe weather
– Arrival of new species, small populations
– Specialized species
• Endemic species exist only in a certain, specialized area
– Very susceptible to extinction
– These species usually have small populations
• Island species
Number of species = speciation – extinction
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Earth has had several mass extinctions
• Background extinction rate: extinction usually occurs slowly,
one species at a time
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•
Mass extinction events killed off massive numbers of species at once
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Occurred five times in Earth’s history
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50–95% of all species went extinct at one time
Cretaceous-Tertiary (K-T) event: 65 million years ago
•
A gigantic asteroid caused dinosaur extinction
• End-Permian event: 250 million years ago
•
75–95% of species went extinct
The sixth mass extinction is upon us
• Humans are causing the sixth mass extinction event
– Population growth, development, resource depletion
– Destruction of natural habitats
– Hunting and harvesting of species
– Introduction of non-native species
• This loss affects humans
– We need organisms for food, fiber, medicine, services
• Amphibians are disappearing faster than any other group
– 170 species have already vanished
We study ecology at several levels
• Ecology
studies
interactions
among
organisms abd
their
enviroment
• Ecology and
evolution are
tightly
intertwined
Species to ecosystems
• A species is a “type” of organism
• A population is all members of a species living in a given
area at the same time
• A community consists of all of the populations of
organisms living and interacting in a particular area
• An ecosystem is the biological community and its
physical environment
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Levels of ecological studies
• Organismal ecology examines relationships between
individuals and their environment
• Population ecology investigates population changes
– The distribution and abundance of individuals
– Why some populations increase and others decrease
• Community ecology focuses on patterns of species diversity
and interactions
• Ecosystem ecology studies living and nonliving components of
systems to reveal patterns
– Nutrient and energy flows
Each organism has habitat needs
• A habitat is the environment where an organism lives
– It includes living and nonliving elements
• Species use different criteria to select habitat
– Soil, topography, vegetation, other species
• Species have different habitat needs
– Depending on body size, season, etc.
• Species survival depends on having suitable habitats
The niche
• A niche is an organism’s use of resources
– Along with its functional role in a
community
– Habitat use, food selection, role in
energy and matter flow, interactions
with other individuals
• Specialists have narrow niches and specific
needs
– Extremely good at what they do
– But vulnerable when conditions change
• Generalists are species with broad niches
– They use a wide array of habitats and
resources
– Survive in many different places
Population size
• Number of individuals that contribute to a population’s gene
pool
• Immigration & Births add individuals
• Emigration & Deaths subtract individuals
Population
• Populations can be described by vital statistics or
demographics
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–
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Size
Age structure
Sex ratio
Density
Distribution
Population density
• Population density is the number of individuals in a
population per unit area
• Large organisms usually have low densities
– They need many resources and a large area to survive
• High densities make it easier to find mates
– But increase competition and vulnerability to predation
– Also increase transmission of diseases
• Low densities make it harder to find mates
– But individuals enjoy more space and resources
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Population distribution
Sex ratios and age structure
• Sex ratio is the proportion of males to females
• Population distribution (dispersion) is
the spatial arrangement of organisms
• Random - haphazardly located
individuals, with no pattern
– Resources are widespread
• Uniformn - evenly spaced individuals
– Territoriality, competition
– In monogamous species, a 1:1 sex ratio maximizes population growth
• Age structure (distribution) is the relative numbers of
organisms of each age in a population
– Helps predict population growth or decline
• In species that continue growing as they age
– Older individuals reproduce more (e.g., a tree)
– Experience makes older individuals better breeders
• Clumped - most common in nature
– Arranged according to resources
Population age structure
• Divide population into age categories
Four factors of population growth or decline
• Natality - the births within the population
• Mortality - deaths within the population
• Immigration - arrival of individuals from outside the
population
– Births and immigration add individuals to a population
• Emigration - departure of individuals from the population
– Deaths and emigration remove individuals
Population growth rate
• Growth rate is the rate of change in a population’s size per
unit time
– Equals (birth rate + immigration rate) – (death rate + emigration rate)
– Tells us the net changes in a population’s size per 1000 individuals per year
• Growth rate is expressed as a percent
Exponential population growth
• In exponential growth, a
population increases by a fixed
percent
– Graphed as a J-shaped curve
• It occurs in nature with:
– Small populations
– Low competition
– Ideal conditions
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Limiting factors restrain population growth
• Exponential growth rarely lasts
• Limiting factors: physical, chemical, and biological attributes
of the environment limiting population growth
• Environmental resistance is all limiting factors together
– Stabilizes the population size at its carrying capacity
– Terrestrial animals -space, food, water, mates, shelter, breeding sites,
temperature, disease, predators
– Plants- sunlight, moisture, soil chemistry
– Aquatic systems - salinity, sunlight, temperature, etc.
Population density affects limiting factors
• Density-dependent factors are limiting factors whose
influence is affected by population density
– Increased density increases the risk of predation, competition for mates, and
disease
– Results in the logistic growth curve
– Environmental resistance has a stronger effect on larger populations
• Density-independent factors are limiting factors whose
influence is not affected by population density
– Temperature extremes, floods, fires, and landslides
Carrying capacity
• Carrying capacity is the
maximum population
size the environment can
sustain
– Determined by limiting
factors
• Limiting factors slow and
stop exponential growth
– Forms an S-shaped logistic
growth curve
Carrying capacities can change
• Environments are complex and ever-changing
– The carrying capacity can change
• Humans lower environmental resistance for ourselves
– Increasing our carrying capacity
– Technologies have overcome limiting factors
– We have appropriated immense amounts of resources
• But by increasing the carrying capacity for humans
– We have reduced the carrying capacity for countless other organisms
– Calling into question our own long-term survival
Conserving biodiversity
• Human development, resource use, and population pressure
are changing populations and communities
• Factors threatening biodiversity have complex social,
economic, and political roots
– We must understand these factors to solve problems
• Millions of people are working to protect biodiversity and to
safeguard ecological and evolutionary processes
Costa Rica’s protection is paying off
• Costa Rica was losing forests at the world’s fastest rate
– Now, 25% of its area is under protection
• Ecotourism is when tourists visit protected areas
– Ecotourism provides thousands of jobs and billions of
dollars to Costa Rica’s economy
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