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Evolution Ch 3, pgs 50-61 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 – Key to 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 common 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 Micro vs. Macroevolution • Micro: describes small genetic changes that occur in a population • Macro: describe long-term, largescale evolutionary changes in which… 1. A new species is formed from ancestral species 2. Other species are lost through extinction 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 • 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 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 Misconceptions about evolution • Two common misconceptions - Survival of the fittest does not mean survival of the strongest. Fittest means the measure of reproductive success. - Evolution does not involve some grand plan of nature in which species become more perfectly adapted. Final Thoughts • Genetic engineering can’t stop the loss of biodiversity because there are no new genes created through genetic engineering. - Genetic engineers merely transfer existing genes from one organism to another. We rely on biodiversity for raw material. Populations Ch 3, pgs 61-72 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 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 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 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 - Different from habitat, which is the physical location where it lives • Specialists = have narrow niches and specific needs - Extremely good at what they do, but vulnerable when conditions change - Ex: giant panda (only eats bamboo) • Generalists = species with broad niches - They use a wide array of habitats and resources - They can live in many different places - Ex: cockroaches, mice, humans 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 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 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 - Examples: elephants, gorillas, humans • r-selected species = species which reproduce quickly - Have a high biotic potential - Little parental care, populations fluctuate greatly - Insects, rodents, grass 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 curves • K selected species are usually associated with s-curves • R selected species are generally associated with j-curves (which then crash) 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 Shannon-Weiner Diversity Index The Shannon-Weiner Index is a common way of showing that diversity involves not only numbers of different species but also how well each of these species is represented in different habitats. It can range from no diversity at 0.0 to a maximum diversity of 4.0 ○ A large H value means if you randomly pick two organisms in your test area, the odds are the second individual will be different from the first The values have no real meaning by themselves, but can be used to compare different habitats Shannon-Weiner Diversity Index H= - sum( pi ln pi ) Where pi=the ratio of the number of organisms of a species to the total number of organisms H= Shannon-Weiner Diversity Index Example You must first calculate pi for each species. Next, calculate ln pi. Species # of individuals pi ln pi Beach 32 32/62= 0.52 -0.65 Oak 18 18/62= 0.29 -1.24 Maple 12 12/62= 0.19 -1.66 Total 62 We can now calculate diversity H = - [(0.52 X -0.65) + (0.29 X -1.24) + (0.19 X -1.66)] H = -[(-0.338) + (-0.360) + (-0.315)] H = -[(-1.01)] = 1.01 Biomes Ch 4, pgs 96-103 Widely separated regions share similarities • Biome = major regional complex of similar communities Multiple factors determine a biome • The type of biome depends on abiotic factors - Temperature, precipitation, soil type, atmospheric circulation - Similar biomes occupy similar latitudes Altitudes create “latitudinal patterns” • Vegetative communities rapidly change along mountain slopes • The climate varies with altitude • A mountain climber in the Andes - Begins in the tropics and ends on a glacier • Rainshadow effect = air going over a mountain releases moisture - Creating an arid region on the other side Hiking up a mountain in the southwest U.S. is like walking from Mexico to Canada Biomes • Biome type is determined by precipitation, temperature and soil type Biomes and biodiversity • Biomes are not uniform, but patches of communities - Climate and vegetation vary with latitude (distance from equator) and altitude (elevation above sea level) - Each biome contains many ecosystems whose communities have adapted to differences in climate, soil, and other environmental factors. Vegetation Changes • Parallel changes occur in vegetation type when we travel from the equator to the poles or from lowlands to mountaintops. Plant Survival Strategies • Desert – succulent plants, no leaves (no water loss), store water in fleshy tissue, open stomata for CO2 only at night • Tropical rainforest – broadleaf evergreens allow for collection of sunlight and radiation of heat • Cold/dry winters – broadleaf deciduous survive drought and cold by shedding leaves and becoming dormant • Cool/short summer – coniferous evergreens – waxy coating and shape of needles slow heat loss/evap during cold winter Aquatic systems have biome-like patterns • Various aquatic systems make up distinct communities - Coastlines, continental shelves - Open ocean, deep sea - Coral reefs, kelp forests • Some coastal systems (estuaries, marshes, etc.) have both aquatic and terrestrial components • Aquatic systems are shaped by - Water temperature, salinity, and dissolved nutrients - Wave action, currents, depth, light levels - Substrate type, and animal and plant life Biomes on Earth • Major biomes on Earth include forests, grasslands, deserts, wetlands, and estuaries - There’s more than that, but these are the ones most likely to show up on the AP test! Forests • Characterized by the growth of mature trees and a closed canopy. Rainfall must be high enough to support the growth of large trees - Forest types largely determined by the seasonal temperature range and the length of the growing season - Tropical forests: warm year-round with large amounts of rain - Temperate forests: deciduous with four equal seasons, moderate rainfall - Boreal forests (Taiga): evergreen forests with short growing seasons, moderate to high precipitation Grasslands • Characterized by a lack of trees and lots of grasses and other non-woody plants. Rainfall generally not high enough to support large woody plants - Grassland types determine largely on seasonal temperature range - Tropical grasslands: warm yearround, growing season is largely determined by seasonal droughts - Temperature grasslands: tend to have cold winters and short growing seasons. Soils tend to be rich due to decomposing of dead plant material Deserts • Driest of all biomes, usually with so little rainfall there’s little diversity of life - Generally characterized as either hot or cold - Hot deserts: hot and dry with sandy soils - Cold deserts: very cold with low precipitation and permafrost or ice cover for most of the year Wetlands • Characterized as an area where the soils are flooded with water during part of its natural cycle. Water plays and important role in determining the plant and animal life of the ecosystem - Swamps and marshes have standing or flowing water year round - Bogs and fens have saturated soil and occasional standing water, but generally have less water and seasonal dryness Estuaries • An area where freshwater and saltwater mixes. Known for having high biodiversity - Often found at the mouth of a river where it flows into the ocean - The brackish (slightly salty) water makes this a valuable habitat for shellfish, birds, fish and other types of wildlife to reproduce Food Webs Ch 4, pgs 83-90 Ecological communities • Community = a collection of populations of organisms living in the same place at the same time - Members interact with each other - Interactions determine the structure, function, and species composition of the community • Community ecologists are people interested in how: - Species coexist and relate to one another - Communities change, and why patterns exist Energy passes through trophic levels • One of the most important species interactions - Who eats whom? • Matter and energy move through the community • Trophic levels = rank in the feeding hierarchy - Producers (autotrophs) - Consumers - Detritivores and decomposers Producers: the first trophic level • Producers, or autotrophs (“selffeeders”) = organisms capture solar energy for photosynthesis to produce sugars - Green plants - Cyanobacteria - Algae • Chemosynthetic bacteria use the geothermal energy in hot springs or deep-sea vents to produce their food Consumers: consume producers • Primary consumers = second trophic level - Organisms that consume producers - Herbivores consume plants - Deer, grasshoppers • Secondary consumers = third trophic level - Organisms that prey on primary consumers - Carnivores consume meat - Wolves, rodents Consumers occur at higher trophic levels • Tertiary Consumers = fourth trophic level - Predators at the highest trophic level - Consume secondary consumers - Are also carnivores - Hawks, owls • Omnivores = consumers that eat both plants and animals Detritivores and decomposers • Organisms that consume nonliving organic matter - Enrich soils and/or recycle nutrients found in dead organisms • Detritivores = scavenge waste products or dead bodies - Millipedes, soil insects • Decomposers = break down leaf litter and other non-living material - Fungi, bacteria - Enhance topsoil and recycle nutrients Energy, biomass, and numbers decrease • Most energy organisms use is lost as waste heat through cellular respiration - Less and less energy is available in each successive trophic level - Each level contains only 10% of the energy of the trophic level below it • There are also far fewer organisms and less biomass (mass of living matter) at the higher trophic levels A human vegetarian’s ecological footprint is smaller than a meat-eater’s footprint QUESTION: Weighing the Issues Would you be willing to decrease the amount of meat you consume (e.g., eat lower on the food chain) to decrease your ecological footprint? a) Yes, if the extra food was sent to countries with starving people. b) Yes, because it would decrease environmental degradation. c) I don’t eat meat now. d) No, I don’t see the need to eat lower on the food chain. Pyramids of energy, biomass, and numbers Food webs show relationships and energy flow • Food chain = a series of feeding relationships • Food web = a visual map of feeding relationships and energy flow - Includes many different organisms at all various levels - Greatly simplified; leaves out most species Some organisms play big roles • Community dynamics are complex - Species interactions differ in strength and over time • Keystone species = has a strong or wide-reaching impact - Far out of proportion to its abundance - Example: sea otters, elephants, bees, prairie dogs • Removal of a keystone species has substantial ripple effects - Alters the food chain Species can change communities • Trophic Cascade = predators at high trophic levels indirectly affect populations at low trophic levels - By keeping species at intermediate trophic levels in check - Extermination of wolves led to increased deer populations, which overgrazed vegetation and changed forest structure • Ecosystem engineers = physically modify the environment - Beaver dams, prairie dogs, ants, zebra mussels Species Interactions Ch 4 pgs 77-83 Species interactions • Species interactions are the backbone of communities • Natural species interactions: - Competition = both species are harmed - Exploitative = one species benefits and the other is harmed - Predation, parasitism, and herbivory - Mutualism = both species benefit Competition • Competition = multiple organisms seek the same limited resources - Food, space, water, shelter, mates, sunlight • Intraspecific competition = between members of the same species - High population density = increased competition • Interspecific competition = between members of 2 or more species - Strongly affects community composition - Leads to competitive exclusion or species coexistence Results of interspecific competition • Competitive exclusion = one species completely excludes another species from using the resource - Zebra mussels displaced native mussels in the Great Lakes • Species coexistence = neither species fully excludes the other from resources, so both live side by side - This produces a stable point of equilibrium, with stable population sizes - Species minimize competition by using only a part of the available resource (niche) Niche: an individual’s ecological role • Fundamental niche = the full niche of a species • Realized niche = the portion of the fundamental niche that is actually filled - Due to competition or other species’ interactions Resource partitioning • Resource partitioning = species use different resources - Or they use shared resources in different ways - Ex: one species is active at night, another in the day - Ex: one species eats small seeds, another eats large seeds Character displacement • Character displacement = competing species diverge in their physical characteristics - Due to the evolution of traits best suited to the resources they use - Results from resource partitioning • Birds that eat larger seeds evolve larger bills - Birds that eat smaller seeds evolve smaller bills Competition is reduced when two species become more different Exploitation: predation • Exploitation = one member exploits another for its own gain (+/- interactions) - Predation, parasitism, herbivory • Predation = process by which individuals of one species (predators) capture, kill, and consume individuals of another species (prey) - Structures food webs - The number of predators and prey influences community composition Case Study: black and white and spread all over • In 1988, Zebra mussels were accidentally introduced to Lake St. Clair - In discharged ballast water • By 2010, they had invaded 30 states - No natural predators, competitors, or parasites • They cause millions of dollars of damage to property each year Zebra mussel predation on phytoplankton • Zebra mussels eat phytoplankton and zooplankton - Both populations decrease in lakes with zebra mussels • Zebra mussels don’t eat cyanobacteria - Population increases in lakes with zebra mussels • Zebra mussels are becoming prey for some North American predators: - Diving ducks, muskrats, crayfish, flounder, sturgeon, eels, carp, and freshwater drum Effects of predation on populations • Increased prey populations increase predators - Predators survive and reproduce • Increased predator populations decrease prey - Predators starve • Decreased predator populations increase prey populations Predation has evolutionary ramifications • Natural selection leads to evolution of adaptations that make predators better hunters • Individuals who are better at catching prey: - Live longer, healthier lives - Take better care of offspring • Prey face strong selection pressures: they are at risk of immediate death - Prey develop elaborate defenses against being eaten Defenses against being eaten Exploitation: parasitism • Parasitism = a relationship in which one organism (parasite) depends on another (host) - For nourishment or some other benefit - The parasite harms, but doesn’t kill, the host • Some are free-living - Infrequent contact with their hosts - Ticks, sea lampreys • Some live within the host - Disease, tapeworms Parasites evolve in response to each other • Parasitoids = insects that parasitize other insects - Killing the host • Coevolution = hosts and parasites become locked in a duel of escalating adaptations - Has been called an evolutionary arms race - Each evolves new responses to the other - It may not be beneficial to the parasite to kill its host Exploitation: herbivory • Herbivory = animals feed on the tissues of plants - Widely seen in insects • May not kill the plant - But affects its growth and survival • Defenses against herbivory include: - Chemicals: toxic or distasteful - Thorns, spines, or irritating hairs - Other animals: protect the plant Mutualism • Two or more species benefit from their interactions • Symbiosis = mutualism in which the organisms live in close physical contact - Each partner provides a service the other needs (food, protection, housing, etc.) - Microbes within digestive tracts - Mycorrhizae: plant roots and fungi - Coral and algae (zooxanthellae) • Pollination = bees, bats, birds and others transfer pollen from one flower to another, fertilizing its eggs Pollination In exchange for the plant nectar, the animals pollinate plants, which allows them to reproduce Relationships with no effect on one member • Amensalism = a relationship in which one organism is harmed while the other is unaffected - Difficult to confirm, because usually one organism benefits from harming another - Allelopathy = certain plants release harmful chemicals - Or, is this a way to outcompete another for space? • Commensalism = a relationship in which one organism benefits, while the other remains unaffected Succession Ch 4, pgs 90-95 Communities respond to disturbances • Communities experience many types of disturbance - Removal of keystone species, spread of invasive species, natural disturbances - Human impacts cause major community changes • Resistance = community of organisms resists change and remains stable despite the disturbance • Resilience = a community changes in response to a disturbance, but later returns to its original state • A disturbed community may never return to its original state Succession • Succession = the predictable series of changes in a community following a disturbance that removes all vegetation and/or soil life Primary succession • Primary succession: Gradual establishment on nearly lifeless ground - Glaciers, drying lakes, volcanic lava **No soil in terrestrial or no bottom sediment in aquatic • Before life can colonize, there must be soil - Takes several hundred to several thousands • Pioneer species = the first species to arrive in a primary succession area (i.e. lichens) Secondary succession • Secondary succession = a disturbance dramatically alters, but does not destroy, all local organisms - The remaining organisms form “building blocks” which help shape the process of succession - Fires, hurricanes, farming, logging • Climax community = remains in place with few changes - Until another disturbance restarts succession Ex: Piedmont region of NC • Central region of NC, European settlers cleared mature native oak and hickory forests to replant the land with crops - Later, abandoned land because of erosion and loss of soil nutrients - Area underwent secondary succession Primary Succession Secondary Succession How do disturbance affect succession and species diversity? • Changes in environmental conditions that disrupt a community can set back succession. - Ex: Fire, drought, mining, plowing climate change can move succession back to an earlier stage. Can be natural or man-made • Not all disturbances are detrimental – some can create unfilled niches or release nutrients. • Communities that experience fairly frequent but moderate disturbances have the greatest species diversity. Communities may undergo shifts • The dynamics of community change are more variable and less predictable than thought - Conditions at one stage may promote another stage - Competition may inhibit progression to another stage - Chance factors also affect changes • Phase (regime) shift = the overall character of the community fundamentally changes - Some crucial threshold is passed, a keystone species is lost, or an exotic species invades - i.e. overfishing and depletion of fish and turtles has allowed algae to dominate corals Invasive species threaten stability • Invasive species = non-native (exotic) organisms that spread widely and become dominant in a community - Introduced deliberately or accidentally from elsewhere - Growth-limiting factors (predators, disease, competitors, etc.) are removed or absent - They have major ecological effects - Chestnut blight from Asia wiped out American chestnut trees • Some species help people (i.e., European honeybees) Top invasive species • • • • • • • • • • Asian Carp Rabbits (Australia, South Africa) Cane Toads (Australia) Kudzu Gray Squirrel (Great Britain) Killer Bees Starlings Northern Snakehead Zebra Mussels Burmese Python Two invasive mussels Controlling invasive species • Techniques to control invasive species - Removing them manually - Applying toxic chemicals - Drying them out - Depriving them of oxygen - Stressing them with heat, sound, electricity, carbon dioxide, or ultraviolet light • Control and eradication are hard and expensive Prevention, rather than control, is the best policy Altered communities can be restored • Humans have dramatically changed ecological systems - Severely degraded systems cease to function • Ecological restoration = efforts to restore communities • Restoration is informed by restoration ecology = the science of restoring an area to an earlier condition - To restore the system’s functionality (i.e. filtering of water by a wetland) - It is difficult, time-consuming, and expensive • It is best to protect natural systems from degradation in the first place Restoration efforts • Prairie restoration = replanting native species, controlling invasive species • The world’s largest project = Florida Everglades - Flood control and irrigation removed water - Populations of wading birds dropped 90-95% - It will take 30 years and billions of dollars to restore natural water flow QUESTION: Weighing the Issues Although mustangs are not native to the United States, they exist in several western states on federally owned land. As an introduced species, what should be done with them? a) As an exotic species, they should immediately be removed and adopted or killed. b) Although they are an exotic species, they are part of our heritage, and should be allowed to stay. c) They have been here so long, we should just leave them alone. d) Many countries eat horse flesh, so we should round them up and export them to horse-eating countries.