Ecosystems: Organisms, Populations, and Communities

• Ecosystem: System formed by the interaction of living organisms with the nonliving physical environment.
• Organisms: Individual living things.
• Species: A group of organisms whose members can produce offspring together, whose offspring are also able to reproduce.
• Similar-looking animals are not always the same species.
• Approximately 1.5 million species have been identified; this is considered a small fraction of the total number of species.

Populations and Communities

• Population: A group of individuals of the same species living together in the same area at the same time.
• Community: A group of organisms living together in the same region that interact with one another.

Interaction in Ecosystem

• Interaction in Ecosystem: Long lasting and complex.
• Examples of interaction: shelter, pollination, decomposition, and predation.
• Food web: Diagram using food chains to show the feeding relationships among organisms.
• Abiotic: Nonliving; Climate is a primary abiotic factor
• Biotic: Living
• Biome: A large geographic region with consistent weather, plants, and other organisms.
• Examples of biomes: tundra, desert, and coral reefs.
• Climate: The weather conditions, including temperature, rain, and wind, that are typical of a particular place.
• Habitat: The place where a particular plant or animal lives, and the natural processes that maintain that area.

Abiotic Condition and Productivity

• Rain forest: Daily precipitation and warm temperature make it highly productive.
• Subtropical desert: Very hot with very little precipitation, making it unproductive.
• Temperate grasslands: Variable temperature with seasons, dry, making it not very productive.
• Temperature forest: Freezing temperature in the winter, moderately high precipitation makes it moderately productive.
• Taiga and tundra: Below freezing most of the year, making it unproductive.

Aquatic Ecosystem

• Primary abiotic factors: light penetration, water movement, temperature, pH, and nutrients.
• Light penetration: Water absorbs and scatters the light.
• Photic zone: Area of water that receives enough light for photosynthesis.
• Aphotic zone: Area of water that doesn't receive enough light for photosynthesis.
• Productivity in fresh water depends on water movement.

Bogs

• Bogs: Very low water flow, unproductive, with poor oxygen, low pH, and unavailable nitrogen.

Swamps and Marshes

• Swamps and marshes have natural flow and are highly productive, with many grasses growing in shallow water.

Streams

• Streams: Water moves in one direction and are low in productivity due to nutrients being constantly swept downstream.
• Abiotic Condition of marine: salinity, temperature, and nutrient variability.
• Productivity in marine: Highly productive near shore and upwelling zones but unproductive in aphotic zones and the open ocean.
• Estuaries: Areas where fresh water mixes with salt water.
• Abiotic challenge for Estuaries: changing salinity.
• Productivity for Estuaries: extremely productive.

Stability and Change in an Ecosystem

• Ecosystems can be stable for hundreds or thousands of years.
• Introduced species: Organism brought into an ecosystem, also called a nonnative species.
• Nonnative species: Organism introduced to an ecosystem rather than naturally occurring there.
• Niche: All of the resources a species uses within its ecosystem.
• Two species with the same niche cannot coexist because one will eventually outcompete the other.
• Effect of climate: Determines abiotic factors but doesn't affect much.
• Ecosystem Stability: Competition and predation are two stabilizing factors.
• Keystone Species: Has a greater effect on its environment than other organisms and is not necessarily abundant in a community.
• Effect on stability: Help maintain stability in an ecosystem.
• The structure of a community will change if a predator or herbivore is removed from or added to the community.

Starfish Experiment

• In a series of tide pools, when sea stars were removed, the mussel population exploded, crowding out other life.
• The number of species and diversity in the tide pool were reduced by more than half.
• Competition: Two different species compete for the same limited resources.
• Effect on stability: Maintains balanced and constant populations.
• How predators keep prey species stable: They keep the population of prey species in balance by hunting them.
• How prey species keep predators species stable: Prey have defensive characteristics that prevent capture and keep the population of predators in balance.

Disturbances

• Disturbances: Events that remove organisms from a community. Examples: fires.
• Small disturbance: Removes organisms without affecting the entire ecosystem.
• Extreme disturbance: Removes all or most of the organisms from an area.
• Primary disturbance: Removes most organisms from an area while damaging or removing the soil. Example: A volcanic eruption.
• Secondary disturbance: Removes organisms above ground but leaves the soil and the organisms within it. Example: Logging.
• Cyclical disturbance: Repeating event that removes organisms from a community without making it unstable. Example: Migration.
• Effect of disturbance on organisms: Organisms have characteristics that allow them to survive these changes.
• Succession: A progressive series of changes in a community that results in its complete replacement by another community.
• Climax community: The final, stable community that results from succession.
• Pioneer plants: Plants that can disperse their seeds over long distances, withstand extreme abiotic conditions, have high reproductive rates, and change the abiotic conditions in the area.
• Biodiversity: The number and variety of living organisms in an ecosystem or geographic area.
• Human impact: Humans reduce the populations of many species by hunting and fishing and by destroying habitats, which reduces biodiversity.

Importance to Humans

• Essential natural resource; different organisms provide food, fibers for clothing, and medicine.
• Biological hot spots: Over half of Earth's species are found in seventeen regions, known as hot spots.
• found in the tropics and cover only about 2 % of Earth's land area. Diversity decreases closer to the poles.
• Humans decrease stability and biodiversity through habitat destruction, excessive hunting and fishing, and introduced species (invasive species).
• Invasive species: Non-native species that outcompete native species.
• Effect on the ecosystem: Destabilizes ecosystems, reduces food for native species, and increases predation.
• Extinction: Patterns of Extinction rates 100 to 1000 times greater than the average rate recorded over the last 550 million years.
• Endangered: Living things in danger of extinction throughout most or all of the area it lives in.
• Threatened: Snowmelt flooding, migration of animals through an ecosystem, seasons, and monsoons.
• Ecosystems are made up of many different populations of organisms.
• Temperate forest: A forest has four seasons.
• A change in the environment affects a population of organisms.

Keystone Species

• Keystone species greatly affect a community but are not necessarily abundant.
• Removing wolves destabilized the Yellowstone ecosystem.
• Population Size: Depends on birth, death, and movement.
• Birthrate: The number of births per 1,000 individuals in a population each year.
• Death rate: The number of deaths per 1,000 individuals in a population each year.
• If the birth rate exceeds the death rate for a period of time, the population will increase.
• If the death rate exceeds the birth rate, the population will decrease.
• The third major reason populations change is due to movement
• Competition: Interaction between groups of organisms that all requiring a particular resource.
• Competition Effect: When resources are limited, the population can only grow until the resources run out.
• Density-dependent factor: Has more of an effect when there are more members of a population
• Examples of Density-dependent factor : food availability and nesting sites.
• Density-independent factor: Is not affected by increasing population numbers.
• Examples of Density-independent factor: Natural disasters and fires.
• Increasing population size increases competition, making life more difficult for the entire population.

Relationships Between Species

• Relationships Between Species are, such as, squirrels & acorns or Lynx & hare.
• The study of how populations' genes are passed down from generation to generation is population genetics..
• Population in genetics: By the number and frequency of alleles.
• Gene Pools: All of the gametes produced in a generation represent the gene pool.
• Alleles: Versions of genes.

Allele frequency

• Allele frequency: Number of copies of a specific version of a gene divided by the number of copies of all versions of that gene.
• Allele: Determined by the number of specific alleles divided by the total number of alleles in the gene pool.
• Hardy-Weinberg Equation: Equation that shows how allele frequencies are transmitted from one generation to the next.
• P: Represents the dominant allele; equation: P = number of dominant alleles divided by total alleles in the gene pool.
• q: Represents the recessive trait; equation: q = number of recessive alleles divided by total alleles in the gene pool.
• The Hardy–Weinberg equation tries to answer what happens to the frequencies of alleles in a population over time.
• Developed a mathematical model to answer the question.
• What did Hardy & Weinberg discover about the frequencies of alleles from one generation to another, Allele frequencies do not change from generation to generation.

Hardy & Weinberg Discoveries

• Discovered the idea that alleles would eventually get to 50/50.
• Disproved the idea that dominant alleles eventually increase in frequency.

The Importance of Hardy – Weinberg equation

• Serves as a comparison for experimentation.
• Gives scientists a way to determine how much allele frequencies change over time.

Hardy – Weinberg Equilibrium

• Condition for Hardy – Weinberg Equilibrium for example. Each allele must ensure equal survival but in Real Life Situation ,Some traits give organisms advantage over the other.

Mechanism for Evolution

• Evolution: The process of the traits of a population of organisms changing over many generations.
• Natural selection: Organisms better suited to their environment thrive and pass their genetic characteristics to the next generation.
• Sexual selection: The method animals use to attract mates to reproduce.
• Adaptations of traits, The ability to attract mates determines reproductive success based on the traits of the individual animal.
• The selective pressure on males & females in a population are different & have different results,what drives sexual selection?
• Genetic drift: Changes from generation to generation in allele frequencies (the percentages of a specific version of a gene) that result from random processes.
• Bottleneck effect: Result after a random occurrence causes a population to shrink rapidly and change its allele frequencies. Example:Natural disaster.
• Founder effect: Result after a small group of a population separates and forms a new population with allele frequencies different from those of the original population.
• Gene flow: The exchange of genes between different populations of one species, due to the movement of individuals, or their gametes.
• Mutation: A permanent change, corruption, or structural alteration in DNA or RNA caused by radiation, mutagenic chemicals, or random chance events.

Genetic diversity

• Genetic diversity: The variety of alleles and genotypes in a population.
• Genetic drift results from random processes.
• Genetic mutations: Natural selection would favor a population because mutation increases genetic variety in population.
• Evolution: Without diversity between individuals there would be no differences for natural selection to act on.
• Polygenic trait: A trait controlled by two or more genes.
• Fitness: An organism's ability to survive and reproduce in its environment.
• Female's fitness depends more on her ability to get the resources needed to carry and raise young than on her ability to find a mate.
• Male's fitness: Number of offspring that live to reproduce themselves.
• Factors that affect the ability of males and females to reproduce are called selective pressures.
• Males: Are generally willing to mate with any female, so they must compete with each other for mates.
• Females: Choose mates carefully.

Reproductive strategies

• When females choose their mates, males that have characteristics that attract female attention are more likely to pass on their genes.
• These traits tell the female that the male has adaptations that enhance the survival of their offspring.
• When males compete to mate with females, large body size is an advantage.
• Selective pressures: Factors that give some organisms in a population the opportunity to reproduce and deny that opportunity to others.
• In some species, females choose mates that have attractive characteristics.
• In other species, the females don't choose; in these species, the males compete against each other for the right to mate with all of the females in a certain territory.
• Selective pressures lead to patterns of natural selection.
• Stabilizing selection: Which stabilizes the traits by selecting for characteristics in the middle of a range.
• Directional selection: Which selects for characteristics in just one direction of the range of traits.
• Disruptive selection: Disrupts the range of traits by selecting against characteristics in the middle of the range and selecting traits that are on the high and low ends of the range.
• All three types of selection tend to decrease the genetic variation of the population over time.
• Allele frequencies: The number of copies of a specific version of a gene divided by the number of copies of all versions of that gene.
• Artificial selection: The process in which humans select organisms with desirable traits and cause them to reproduce.
• Antibiotics: Chemical substances that inhibit the growth of bacteria and other microorganisms.
• Mass Extinction: An event in which at least 60 percent of the species living on Earth becomes extinct at a particular time.

Human effect on evolution

• Introduction of chemicals into human food production affects plants & animals.
• Humans are thought to be involved in mass extinction.
• Weed species quickly evolve herbicide resistance.
• Fossil Formation: Age of the fossil can be determined using radioactive decay.
• Its important to know how old the fossils are to used to trace evolutionary development.
• Relative Dating: Estimating the age of a rock or fossil by comparing it to something else to determine whether one fossil is older than the other.
• Fossil Record: The deeper fossils are generally older, while the higher up came later are younger. This time sequenced order of fossils is called the fossil record.
• Fossils are found in sedimentary rock, which forms in layers, with the oldest layer at the bottom.
• Homologous structure: A physically similar structure that performs different functions in different species.
• Provide evidence for evolution:The structures are variations of a common ancestor.
• Vestigial structures are body parts that are no longer needed in an organism.
• Provides evidence for evolution, its a genetic leftover, at one point an ancestor used this structure, but the modern day species do not.
• Comparative Embryology: A fertilized egg goes through several developmental stages as an embryo. The beginning stage of different species are very similar.
• DNA & protein sequence similarity:Sequences are more similar for organisms thought to be more closely related, indicating these organisms are more closely related.