Transcript Population density

Chapter 5
Evolution, Biodiversity, Population Ecology
Evolution
• Biological evolution consists of
genetic change in organisms
across generations.
• May proceed randomly or be
directed by natural selection.
Natural Selection
• Process by which traits that enhance
survival and reproduction are passed
on more frequently to future
generations, altering the genetic
makeup of populations through time.
Natural Selection
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Charles Darwin
Alfred Russell Wallace
Both naturalists – studied plants/animals
Proposed natural selection as a
mechanism for evolution and as a way to
explain the great variety of living things.
Logic of Natural Selection
• a. Individuals of the same species
vary in their characteristics.
• b. Organisms produce more
offspring than can possibly
survive.
• c. Some offspring may be more
likely to survive and reproduce.
Logic (continued)
• d. Characteristics that give individuals an
advantage in surviving and reproducing
might be inherited by their offspring.
• e. These characteristics would tend to
become more prevalent in the
population in future generations.
*A trait that promotes success is called an
adaptation.
Natural Selection
• Acts on genetic variation:
1. Accidental changes in DNA are called
mutations
2. Most mutations have little effect;
some are deadly; a few are beneficial.
3. Sexual reproduction generates
variation – genes from both parents
Natural Selection
• 3 ways that genetic variation alters
organisms’ characteristics:
1. Directional selection
2. Stabilizing selection
3. Disruptive selection
*draw each graph (a, b, c) from page 115 in
your notes at this time
Artificial Selection
• Process of selection conducted
under human direction
*With a partner, come up with at least
2 examples of artificial selection –
you have 3 minutes
Book Work
• With a partner you have not worked with:
– Page 137
• Testing Your Comprehension – 1 &2
• Seeking Solutions – 1
• Keep this paper, you will be adding to it
daily during this chapter (answers will be
checked periodically)
Evolution generates biodiversity
• Biological diversity, or biodiversity,
is the sum total of all organisms in an
area, taking into account the
diversity of species, the diversity of
populations within a community, and
the diversity of communities within
an ecosystem.
What is a species?
• A species is a population whose
members share certain
characteristics and can freely
breed with one another and
produce fertile offspring.
What is a population?
• A group of individuals of a
particular species that live in the
same area.
Speciation
• Speciation produces new types of
organisms.
• 1. When populations of the same
species are kept separate, their
individuals no longer come in
contact, so their genes no longer
mix.
• Called allopatric speciation
Speciation
2. If there is no contact, the
mutations that occur in one
population cannot spread to the
other.
• Called sympatric speciation
Read through the section “Populations
can be separated in many ways” and
list the mechanisms that can cause
allopatric speciation
Vocab Study Time
• With a partner, use your flash cards
to study your vocabulary words.
• We will have a vocab competition at
the end of class today!
“Mapping” the History of Diversity
• Phylogenetic trees
–Show relationships among groups
of organisms
–Used to study how traits have
evolved over time
–Page 119 – arrows used to indicate
when traits orginated
Speciation and Extinction
Contribute to Biodiversity
• Extinction – the disappearance of a
species from Earth
• Number of species in existence =
Number added through speciation –
Number removed by extinction
• Extinction brought on by humans is
biggest environmental problem we are
facing
Some Species more
Vulnerable than Others
• Generally, extinction occurs when
environmental conditions change
rapidly or severely enough that a
species cannot genetically adapt to
the change.
• Some species are vulnerable because
they are endemic, occurring in only a
single place on the planet.
Episodes of Mass Extinction
• There have been five mass
extinction events at widely spaced
intervals in Earth’s history that have
wiped out anywhere from 50 to 95%
of Earth’s species each time.
• Best known – 65 million years ago –
end to dinosaurs (“Science Behind
the Story 122-123)
6th Mass Extinction – Is it near?
• Biologist conclude that Earth is entering its 6
mass extinction
• Caused by
– Population growth
– Development
– Resource depletion
– Destruction of natural habitats
– Harvesting/Hunting
– Non-native species introductions
Book Work
• Add this to your previous assignment
and turn in when finished – due
Wednesday morning!
• Page 137
–Testing Your Comprehension
#s 3, 4, and 5
Levels of Ecological Organization
• Organisms Population 
Community Ecosystem 
Biosphere
• Biosphere is the cumulative total
of living things on Earth and the
areas they inhabit
Levels of Organization
• A group of organisms of the same species that
live in the same area is a population
• Species are often composed of multiple
populations
• Communities are made up of multiple
interacting species that live in the same area.
• Ecosystems encompass communities and the
abiotic (nonliving) material and forces with
which their members interact.
Population Ecology
• Investigates how individuals
within a species interact with one
another.
• Why do some populations
increase?
• Who do some populations
decrease?
Community Ecology
• Focuses on interactions among
species
• From one-to-one interactions to
complex relationships involving
entire communities
• Roane County Park
Ecosystem Ecology
• Studies living and nonliving components of
systems
• Reveals patterns, such as energy and nutrient
flow
Ecology at the Organism Level
• Habitat, niche, and degree of
specialization are important in
organismal ecology
• The specific environment in which an
organism lives is its habitat.
• Each organism has patterns of
habitat use. (p.124)
Organism Level (continued)
• A species’ niche reflects its use of
resources and its functional role in a
community.
• Species with very specific requirements
are said to be specialists.
• Those with broad tolerances, able to use
a wide array of habitats or resources, are
generalists.
• Pros/Cons page 125
Population Ecology:
Population Characteristics
• Populations exhibit characteristics
that help predict their dynamics.
• 1. Population size is the number of
individual organisms present at a
given time.
• 2. Population density is the number
of individuals in a population per unit
area.
Characteristics (contd.)
• 3. Population distribution is the spatial
arrangement of organisms within an area.
• 4. Sex ratio -proportion of males to females.
• 5. Age structure, describes the relative
numbers of organisms of each age within a
population.
• 6. Birth and death rates measure the number
of births and deaths per 1,000 individuals for a
given time period.
Population Distribution
• 3 Types:
–Random – individuals are not located
in any particular pattern; resources are
found throughout an area
–Uniform – individuals are evenly
spaced; desert need equal space for
their roots to gather water
–Clumped – (most common) individuals
are arranged around resources
Age Structure
• Population of mostly individuals past
reproductive age will decline
• Population of mostly individuals preproductive age will increase
• Population with even age
distribution will remain stable
• Page 128, figure 5.13
Survivorship Curves
• Based on birth and death rates
• Page 128, figure 5.14
• Type I – survival rates for young are high
and decrease at an old age (humans)
• Type II – survival rates equal among age
(birds)
• Type III – highest death rate at young
ages (amphibians – tadpoles)
Populations may grow, shrink,
stablilize
• Population growth or decline is
determined by births, deaths,
immigration, and emigration.
• Immigration – into
• Emigration – away *E for Exit
Unregulated Populations
• No external limits
• Mold growing on bread, bacteria on dead
animal, trees in a new area
• When a population increases by a fixed
percentage each year, it is said to
undergo exponential growth.
• Relate this type to a savings account,
page 129, Table 5.3
Book Work
• Page 137, Testing Your
Comprehension
• #s 6-8
Limiting Factors Restrain
Population Growth
• Populations are contained by limiting
factors - physical, chemical, and
biological characteristics of the
environment
• The interaction of the limiting factors
determines the carrying capacity.
• Carrying capacity – max population size
of a species that an environment can
sustain
Logistic Growth Curve
• Populations increase sharply at first
and then level off due to limiting
factors
• Known as environmental resistance
• Page 130, Fig. 5.16 L.G.C.
• Look at page 131, Fig. 5.17 for other
types of growth models
What are examples of limiting
factors?
– Water
– Space
– Food
– Predators
– Disease
– Breeding sites
– Temperature
– pH
– Salinity (salt content)
– Pollutants
Carrying Capacities Can Change
• Some organisms can alter their
environment to reduce environmental
resistance and increase carrying capacity.
• Humans have used immense proportions
of the planet’s resources to increase our
carrying capacity, but have reduced the
carrying capacities for many other
organisms
Affects on Limiting Factors
• Density-dependent factors -based on
population density
- Increased pop., increased chance for mating
- Increased pop., increased competition and disease
• Density-independent factors -not affected by
population density
– Temperature extremes
– Catastrophic events (floods, fires, landslides, etc.)
– Can eliminate large #s no matter the density
Biotic Potential
• Ability to produce offspring
• Fish – high biotic potential, lay 1000s of
eggs in a short time
• Whale – low biotic potential, birth to one
calf after a long gestation (pregnancy)
period
• Low biotic potential organisms protect
their offspring
K-Selected Species
• Low biotic potential
• Populations stabilize over time at or
near carrying capacity
• K stands for carrying capacity
• Competition is high between
organisms
R-Selected Species
• High biotic potential
• Devote energy to produce large amounts
of offspring
• R stands for rate
• Rate at which species increase/decline
varies and number at or near carrying
capacity can be very high or very low