Transcript Ecological Pyramids Definition

Ecosystems – Species Diversity &
Environmental Interactions
After this unit you should be able to:
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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
Identify efforts and challenges involved in the conservation of
biodiversity
Learning Targets:
• Natural selection
• How evolution influences
biodiversity
• Reasons for species
extinction
• Ecological organization
• Population characteristics
• Population ecology
• Conserving biodiversity
Organisms and Species
• Organisms, the different forms of life on earth,
can be classified into different species based on
certain characteristics.
Figure 3-3
Evolution generates biodiversity
• Species = a population or group of populations
– Whose members share characteristics
– They can breed with one another and produce fertile
offspring
• Population = a group of individuals of a species
that live in the same area
• Evolution = means change over time
– Biological evolution: genetic change in populations
over time
– Genetic changes lead to changes in appearance,
functioning or behavior over generations
Natural selection
• Evolution may be seen as random
– directed by natural selection
• Natural Selection = traits that enhance survival
and reproduction
– Are passed on more frequently to future generations
– those that do not lead to survival, disappear in the
gene pool.
Evolution by natural selection
Micro-evolution: The concept of change over time.
 change is through populations of species, not individuals.
 Occurs over many generations, through environmental influence and
genetic variation.
 Micro-evolution can lead to Macro-Evolution (geologically speaking).
• It is one of the best-supported and most informative concepts in all science
– It is the main standpoint of modern biology and the basis for
Biodiversity.
– Both, Darwin and Wallace proposed natural selection as the mechanism
of evolution
– Knowing ecology and learning the history of life helps us to understand
and appreciate environmental science
• Evolutionary processes influence pesticide resistance, agriculture, medicine,
health, etc.
Natural selection shapes organisms
• Premises of natural selection:
- Organisms struggle to survive and reproduce
- Organisms produce more offspring than can
survive
- Individuals of a species vary in their
characteristics due to genes and the
environment
- Some individuals are better suited to their
environment and reproduce more effectively
• Natural selection acts on genetic variation
Genetic variation
• Adaptation = the process where, over time,
characteristics (traits) that lead to better
reproductive success
– Become more prevalent in the population
• Adaptive trait (leads to adaptation) = a trait that
promotes reproductive success
• Mutations = accidental changes in DNA that may be
passed on to the next generation
– Non-lethal mutations provide the genetic variation on
which natural selection acts
• Sexual reproduction = also leads to variation through
mating preferences.
Natural selection acts on genetic
variation
• Natural selection changes
characteristics through:
• Directional selection =
drives a feature in one
direction
• Stabilizing selection =
favors intermediate traits
– Preserving the status quo
• Disruptive selection =
traits diverge in two or
more directions
Environmental conditions affect
selection
• Environmental conditions determine the
pressures natural selection exerts
– These pressures affect who survives and reproduces
– Traits evolve that allow success in that environment
• But traits that promote success at one time or
place may not do so at another
• Natural selection weeds out unfit individuals
– It also elaborates and diversifies traits that may
produce new species
Selective pressures influence adaptation
• Divergent evolution =
Related species in
different environments
– Experience different
pressures
– Evolve different traits
• Convergent evolution =
unrelated species may
evolve similar traits
– Because they live in
similar environments
Evidence of natural selection is everywhere
• It is evident in every adaptation of every
organism
• Artificial Selection = the process of selection
conducted under human direction
– Producing the great variety of dog breeds and food
crops
Evolution generates biological diversity
• Biological diversity (biodiversity) = the variety of
life across all levels of biological organization
– Species
– Genes
– Environmental
• Scientists have described 1.8 million species
– Up to 100 million species may exist
– Tropical rainforests are rich in biodiversity
Speciation
Speciation produces new types of organisms
• The process of generating new species
from a single species
Geographic Isolation
Where changes and isolations within
the environment and habitat cause new
species to form.
• Allopatric speciation: species formation
due to physical separation of populations
– The main mode of speciation
– Populations can be separated by glaciers,
rivers, mountains
– Each population gets its own set of
mutations
Another type of speciation
• Sympatric speciation = species form from
populations that become reproductively isolated
within the same area
– Feed in different areas or eat different foods.
– Mate in different seasons or because of mating rituals.
– Hybridization between two species
– Mutations
Bird dances: rifle bird ; moonwalk.
Speciation results in diverse life forms
• How do major groups diverge over time?
• Phylogenetic trees (cladograms) = show
relationships among species, groups, genes, etc.
– Scientists can trace how certain traits evolved
The fossil record
• Fossil: an imprint in stone of a dead organism
• Fossil record: the cumulative body of fossils
worldwide
• The fossil record shows:
– Life has existed on Earth for at least 3.5 billion years
– Earlier types of organisms evolved into later ones
– The number of species has increased over time
– Most species have gone extinct
– There have been several mass extinctions in the past
Extinction
• Extinction = 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
Number of species = speciation - extinction
Extinction is a natural process, but …
• Humans profoundly affect rates of extinction
• Biodiversity loss affects people directly
– Food, fiber, medicine, ecosystem services
Some species are more vulnerable to
extinction
• Extinction occurs when the environment changes
rapidly
– Natural selection can not keep up
• Many factors cause extinction:
– Severe weather, climate change, changing sea levels
– New species, small populations
– Specialized species
• Endemic species = a species only exists in a
certain, specialized area
– Very susceptible to extinction
– These species usually have small populations
Many U.S. amphibian species are vulnerable
• Many U.S. amphibians have very small ranges
– They are vulnerable to extinction
– The Yosemite toad, Houston toad, Florida bog frog
• 40 salamander species are restricted to areas
the size of a typical county
Some U.S. salamander species live on top of single mountains
Striking gold in Costa Rica
• In 1964, Golden toads
were discovered in
Monteverde, Costa Rica
• The mountainous cloud
forest has a perfect
climate for amphibians
• They became extinct
within 25 years
– Climate change’s drying
effect on the forest
– A lethal fungus