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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
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 random
Or directed by natural selection
• Natural Selection = traits that enhance survival and reproduction
Are passed on more frequently to future generations
Than those that do not
Evolution by natural selection• It is one of the bestsupported and most illuminating concepts in all science
It is the standpoint of modern biology
• We must understand it to appreciate environmental science
Knowing ecology and learning the history of life
• Evolutionary processes influence pesticide resistance, agriculture, medicine, health, etc.
• In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution
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 (adaptation) = a trait that promotes reproductive success
• Mutations = accidental changes in DNA that may be passed on to the next generation
Nonlethal mutations provide the genetic variation on which natural selection acts
• Sexual reproduction also leads to variation
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
Populations
Communities
• Scientists have described 1.8 million species
Up to 100 million species may exist
Tropical rainforests are rich in biodiversity
Speciation produces new types of organisms• The process of generating new species from a single species
• 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
Tamiasciurus douglasii
Orcas Island Photos
Richard Lovison
Tamiasciurus hudsonicus
Cyanocitta stelleri
audubon.org
Cyanocitta cristata
allaboutbirds.org
Another type of speciation• Sympatric speciation = species form from populations that become reproductively isolated within the same area
Feed in different areas
Mate in different seasons
Hybridization between two species
Mutations
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 110 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
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
• Endemic species = a species only exists in a certain, specialized area
Very susceptible to extinction
These species usually have small populations
The Olympic Torrent Salamander
Endemic species
Earth has had several mass extinctions• Background extinction rate = extinction usually occurs one species at a time
• Mass extinction events = killed off massive numbers of species at once
Occurred five times in Earth’s history
5095% of all species went extinct at one time
• CretaceousTertiary (KT) event: 65 million years ago
Dinosaurs went extinct
• EndPermian event: 250 million years ago
7595% of all species went extinct
The sixth mass extinction is upon us• Humans are causing the sixth mass extinction event
Resource depletion, population growth, development
Destruction of natural habitats
Hunting and harvesting of species
Introduction of nonnative species
• It is 1001,000 times higher than the background rate and rising
• Amphibians are disappearing the fastest
• 170 species have already vanished
• It will take millions of years for life to recover
Ecology is studied at several levels• Ecology and evolution are tightly intertwined
• Biosphere = the total living things on Earth
And the areas they inhabit
• Community = interacting species living in the same area
• Ecosystem = communities and the nonliving material and forces they interact with
Levels of ecological studies• Population ecology = investigates the dynamics of population change
The factors affecting the distribution and abundance of members of a population
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• Habitat = the environment where an organism lives
It includes living and nonliving elements
• Habitat use = each organism thrives in certain habitats, but not in others
Results in nonrandom patterns of use
• Habitat selection = the process by which organisms actively select habitats in which to live
Availability and quality of habitat are crucial to an organism’s wellbeing
• Human developments conflict with this process
Habitats vary• Habitats vary with the body size and needs of species
A soil mite vs. an elephant
• Species have different habitat needs at different times
Migratory birds use different habitats during migration, summer and winter
• Species use different criteria to select habitat
Soil, topography, vegetation, other species
Water temperature, salinity, prey
• Species survival depends on having suitable habitat
Organismal ecology: niche• Niche = an organism’s use of resources
Along with its functional role in a community
Habitat use, food selection, role in energy and nutrient flow, interactions with other individuals
• Specialists = have narrow niches and specific needs
Extremely good at what they do
But vulnerable when conditions change
• Generalists = species with broad niches
They use a wide array of habitats and resources
They can live in many different places
A specialized frog• Epiphytes grow on trees for support
Obtaining water from the air
They collect pools of rainwater and pockets of leaf litter
Frogs lay their eggs in these rainwater pools
https://www.youtube.com/watch?v=4SispCYjUTE
Population characteristics• All populations show characteristics that help scientists predict their future dynamics
• Population size = the number of individual organisms present at a given time
Numbers can increase, decrease, cycle or remain the same
Population characteristics• Population density = 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
Increased transmission of diseases
• Low densities make it harder to find mates
But individuals enjoy plentiful resources and space
Population characteristics• Population distribution (dispersion) = spatial arrangement of organisms
• Random = haphazardly located individuals, with no pattern
• Uniform = individuals are evenly spaced
Territoriality, competition
• Clumped = arranged according to availability of resources
Most common in nature
• Sex ratio = proportion of males to females
In monogamous species, a 1:1 sex ratio maximizes population growth
• Age distribution (structure) = the relative numbers of organisms of each age in a population
Age structure diagrams (pyramids) = show the age structure of populations
• In species that continue growing as they age
Older individuals reproduce more (i.e. a tree)
Experience makes older individuals better breeders
Population characteristics
Birth and death rates
• Type I: more deaths at older ages
• Type II: equal number of deaths at all ages
• Type III: more deaths at young ages
Survivorship curves = the likelihood of death varies with age
Reproductive strategies vary among species• Biotic potential = an organism’s capacity to produce offspring
• Kselected species = species with long gestation periods and few offspring
Have a low biotic potential
Stabilize at or near carrying capacity
Good competitors
• rselected species = species which reproduce quickly
Have a high biotic potential
Often little parental care, populations fluctuate greatly
Four factors of population change• Natality = births within the population
• Mortality = deaths within the population
• Immigration = arrival of individuals from outside the population
• Emigration = departure of individuals from the population
So....Births and immigration add individuals
Deaths and emigration remove individuals
Population growth rate• Natural rate of population growth =
(Crude birth rate) – (crude death rate)
Population change due to internal factors
• Population growth rate =
(Crude birth rate + immigration rate) – (Crude death rate + emigration rate)
Net changes in a population’s size/1000/year
• Growth rate as a percent =
Population growth rate X 100%
Populations of different sizes can be compared
Exponential population growth• Exponential growth
A population increases by a fixed percent
Graphed as a Jshaped curve
• Exponential growth cannot
be sustained indefinitely
• It occurs in nature with a:
Small population
Low competition
Ideal conditions
Limiting factors restrain population growth• Limiting factors = physical, chemical and biological attributes of the environment
They restrain population growth
Environmental resistance = all limiting factors taken together
Stabilizes the population size
Space, food, water, mates, shelter, suitable breeding sites, temperature, disease, predators
Aquatic systems: salinity, sunlight, temperature, etc.
Carrying capacity• Carrying capacity = the maximum population size of a species that its environment can sustain
• Limiting factors slow and stop exponential growth
An Sshaped logistic growth curve
Many factors contribute to environmental resistance and influence a population’s growth rate and carrying capacity
Perfect logistic curves aren’t often found
Population density impacts limiting factors• Densitydependent factors = limiting factors whose influence is affected by population density
Increased density increases the risk of predation and competition for mates
Results in the logistic growth curve
Larger populations have stronger environmental resistance
• Densityindependent factors = limiting factors whose influence is not affected by population density
Events such as floods, fires, and landslides
Carrying capacities can change• Environments are complex and everchanging
Changing carrying capacities
• Humans lower environmental resistance for themselves
Increasing our carrying capacity
Technologies overcome limiting factors
• By increasing carrying capacity for humans
We have reduced the carrying capacity for countless other organisms
Calling into question our own longterm survival
Population changes affect communities• As the population of one species declines, other species may appear
• Human development displaces other species and threatens biodiversity
• As Monteverde dried out, species disappeared
Golden toads, harlequin frogs and more had been pushed from their cloudforest habitat into extinction
20 of 50 frog species, 2 lizard species went extinct
• Species from lower, drier habitats appeared
15 species tolerant of drier conditions had moved in
Conserving biodiversity• Human development, resource extraction and population pressure are speeding changes
In populations and communities
• Impacts threatening biodiversity have complex social, economic and political roots
We must understand these factors to solve problems
Costa Rica and its environment• Past economic and social forces still threaten Costa Rica’s species and ecological communities
Lush forests are seen as obstacles to agriculture and for timber
The country’s population grew to 3.34 million
Pasture land increased from 12% to 33%
Forests decreased from 80% to 25%
Species were declining and becoming endangered
Costa Rica’s species were in danger• Few people saw the need to conserve biological resources
Until it became clear they were being rapidly lost
Costa Rica is protecting its environment• The privately managed 10,500 ha (26,000 acre) Monteverde Cloud Forest Reserve was founded in 1972
To protect the forest, its plants and animals
• Costa Rica created the country’s first national parks and protected areas in 1970
Centered on areas of spectacular scenery
Protecting valuable tropical dry forests, turtle nesting beaches, coral reef systems
Government support remains strong
Over 25% of its land is under some type of protection
Costa Rico’s protection is paying off• Ecotourism: tourists visit protected areas
Providing thousands of jobs and billions of dollars to local economies
• But parks are still underprotected and underfunded
Restoration is a step beyond preservation
Conclusion• The fundamentals of evolution and population ecology are integral to environmental science
• Natural selection, speciation and extinction help determine earth’s biodiversity
• Understanding how ecological processes function at the population level is crucial to protecting biodiversity
