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 best supported 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 Non lethal 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
Tamiasciurus hudsonicus Richard Lovison
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 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
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 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
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 50 95% of all species went extinct at one time Cretaceous Tertiary (K T) event: 65 million years ago Dinosaurs went extinct End Permian event: 250 million years ago 75 95% 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 non native species It is 100 1,000 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 well being Human developments conflict with this process
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
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
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
Population characteristics 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
Birth and death rates Survivorship curves = the likelihood of death varies with age Type I: more deaths at older ages Type II: equal number of deaths at all ages Type III: more deaths at young ages
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 * 100% Populations of different sizes can be compared
Exponential population growth Exponential growth A population increases by a fixed percent Graphed as a J shaped 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 S shaped logistic growth curve Many factors contribute to environmental resistance and influence a population s growth rate and carrying capacity
Population density impacts limiting factors Density dependent 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 Density independent factors = limiting factors whose influence is not affected by population density Events such as floods, fires, and landslides
Perfect logistic curves aren t often found
Carrying capacities can change Environments are complex and ever changing 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 long term survival
Reproductive strategies vary among species Biotic potential = an organism s capacity to produce offspring K selected species = species with long gestation periods and few offspring Have a low biotic potential Stabilize at or near carrying capacity Good competitors r selected species = species which reproduce quickly Have a high biotic potential Little parental care, populations fluctuate greatly
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 cloud forest 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 under protected 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