Transcript Document
Ecosystems
Part 2
Edge effects
How the local environment changes
along the boundary or edge in a habitat
Caused by:
natural events (tree fall)
humans (deforestation)
Results:
Changes in species composition and
diversity
Vocabulary
Interior species: can only live in the
undisturbed core of a habitat
Edge species: can live in edge habitats
Open community: edge is gradual or
has indistinct boundaries which many
species cross over
Closed community: community is
sharply devided from its neighbors
U.S. Roads
3.9 million miles of public roads in the
United States.
Wildlife and highways
Road kill – animals
that are killed by
being run over by
cars each year
Millions of animals
die each year
Have a significant
impact on
populations
Costs $8 billion per
year
Wildlife crossings:
bridges and tunnels
Ecosystem diversity
Involves:
Biodiversity
Natural selection
Evolution
Ecosystem services
Biodiversity
Attempts to describe diversity of life
at three levels:
Genetic – range of all genetic traits in a
population
Species – number of different species
that inhabit a different area
Estimated between 10 and 30 million
species on Earth
Named around 1.5 million
Ecosystem – the range of habitats that
can be found in a defined area
Biodiversity
Increases
Diverse habitats
Moderate disturbance
in the habitat
Environmental
conditions with low
variation
Trophic levels with
high diversity
Middle states of
succession
Evolution
Decreases
Extreme stress
Extreme environments
Extreme limitations in
the supply of a
fundamental resource
Extreme amounts of
disturbance
Introduction of
species from other
areas
Geographic isolation
Natural Selection
The mechanism of how organisms
evolve
Works on the individual level by
determining which organisms
survive and reproduce
The range of genetic variation in a
population determines if the species
Natural Selection
“Survival of the fittest”
Fittest = how many babies you have
who go on to have babies
New genes enter the population
through mutation
Natural selection
Types of selection
Stabilizing
Directional
Disruptive
Stabilizing Selection
Selects against the
extremes of a
population
Most common
form of natural
selection
Results:
Decreased diversity
Maintenance of a
stable gene pool
No evolution
Directional Selection
Affects one
extreme of a
population
Gives an
advantage to other
extreme
Results
Change in
population
characteristics
Can lead to
evolution of a new
species
Disruptive Selection
Acts against the
individuals in the
middle
Favors both
extremes
Results:
Splitting of
population into two
smaller populations
Results in evolution
of two new species
Evolution
Change in the genetic composition
of a population over successive
generations
Supported by evidence from:
Fossil record
Genetics
Homologous traits
Embryological similarities
Computer models
Speciation
Results when segments of a
population becomes isolated so
gene flow stops
The isolated populations eventually
become new species
Maintaining gene flow
Some species of spiders balloon to
disperse through the environment
They let out a long strand of silk which is
caught by air currents and transports
them over long distances
Patterns in Evolution
(A) Divergent (adaptive radiation) – similar species
become less similar
(B) Convergent – Unlike species evolve similar
(analogous) traits while evolving in separate
ecosystems
(C) Parallel – Two independent species evolve at the
same time, in the same ecosystem, and acquire similar
traits
Convergent Evolution
Adaptive Radiation
Parallel Evolution
Gradualism vs. Punctuated Equilibrium
Gradualism
Views evolution as
slow, stepwise
development of
species over a
long period of time
Punctuated Equilibrium
Proposes some
species arose
suddenly in a short
period of time after
long periods of
stability
Ecosystem services
Things the environment does for us
for free.
Includes but not limited to:
Moderate weather extremes and their
impacts
Disperse seeds
Mitigate droughts and floods
Cycle and move nutrients
Detoxify and decompose waste
Purify air and water