Free Unit Notes

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I. Introduction to Biodiversity (Topic 2.1)

  A. Levels of biodiversity

1. Biodiversity is the variety of life within populations, among species, and across habitats.

2. Genetic diversity is the variety of inherited traits within a population or species. Different versions of a gene are called alleles.

3. Species diversity considers the number of species and how evenly individuals are distributed among them.
   a. Species richness is the number of different species present.
   b. Species evenness describes how evenly individuals are distributed among those species. Sites with equal richness can have different evenness.

4. Habitat diversity is the variety of habitats in an area, such as forests, wetlands, and streams. Different habitats support different communities.

  B. Biodiversity and stability

1. Greater genetic diversity increases the chance that some individuals can survive a stressor and reproduce. It does not guarantee survival.

2. A population bottleneck is a sharp reduction in population size that can remove alleles by chance. Population recovery does not automatically restore lost genetic diversity.

3. Ecosystems with more species are often better able to recover from disturbances because species respond differently and can maintain similar functions.

4. Resistance is the ability to remain relatively unchanged during a disturbance. Resilience is the ability to recover afterward.

  C. Habitat loss and species requirements

1. A species’ ecological niche includes its resource use, environmental requirements, and interactions with other organisms.

2. Specialists have narrow resource requirements or tolerances. Generalists use a wider range of resources or conditions.

3. Habitat loss often eliminates specialists before generalists because specialists have fewer alternatives. Continued loss can eliminate both.

4. Species that need large territories also decline when remaining habitat cannot meet their needs.

  D. Measuring biodiversity

1. Compare sites using similar sampling areas, methods, seasons, and effort. Larger samples often detect more species.

2. Quadrats are sampling plots used to count organisms or estimate cover. Transects are lines along which observations reveal changes across a habitat.

3. Relative abundance = (individuals of one species ÷ total individuals counted) × 100%. If 8 of 40 plants belong to one species, its relative abundance is 20%.

II. Ecosystem Services (Topic 2.2)

  A. Four categories of services

1. Ecosystem services are benefits people receive from functioning ecosystems.

2. Provisioning services supply products such as food, freshwater, timber, fibers, and medicinal compounds.

3. Regulating services moderate environmental conditions. Examples include pollination, water purification, flood control, erosion control, and climate regulation.

4. Cultural services provide nonmaterial benefits, such as recreation, education, spiritual meaning, and enjoyment of nature.

5. Supporting services are underlying processes that make other services possible, including nutrient cycling, soil formation, and primary production.

  B. Human disruption and consequences

1. Anthropogenic means caused by human activities. One activity can disrupt several ecosystem services.

2. Draining wetlands removes habitat and floodwater storage. Increased downstream flooding can damage homes and raise flood-control costs.

3. Removing streamside vegetation increases erosion and sediment runoff. This can damage aquatic habitat and increase water-treatment costs.

4. Removing pollinator habitat can reduce crop pollination and yields. Clearing forests reduces carbon storage and can remove food and timber resources.

5. Services have value even when people do not pay for them directly. Replacing a lost service can be expensive or impossible.

6. Protecting wetlands and native vegetation helps preserve services. Restoration can improve services, but recovery takes time and may be incomplete.

III. Island Biogeography (Topic 2.3)

  A. Island size and isolation

1. Island biogeography studies the distribution of organisms and their ecological relationships on islands.

2. Colonization occurs when organisms arrive and establish populations. Organisms may reach islands by flying, swimming, drifting, or being carried.

3. Other conditions being similar, nearby islands receive more immigrants than distant islands because they are easier to reach.

4. Larger islands generally contain more habitats and support larger populations, lowering local extinction risk.

5. Large, nearby islands generally support the most species; small, distant islands support the fewest. A large, distant island and a small, nearby island cannot always be ranked without more information.

  B. Immigration, extinction, and equilibrium

1. Immigration brings organisms into an area. An arriving species increases richness only if it is not already present.

2. Local extinction, or extirpation, removes a species from one area. Global extinction removes the species everywhere.

3. As island richness rises, the immigration rate of new species generally falls because fewer species remain available to arrive. The local extinction rate generally rises.

4. At equilibrium species richness, new-species immigration and local extinction rates balance. Species identities can still change through species turnover.

5. Richness tends to rise when immigration exceeds extinction and fall when extinction exceeds immigration.

  C. Island evolution and introduced species

1. Isolation allows populations to evolve separately. An endemic species occurs naturally only in a particular geographic region.

2. Limited food and territory have favored specialization in many island species. Narrow requirements can make them vulnerable to environmental change.

3. A nonnative species is introduced by people beyond its natural range. An invasive species spreads and causes harm; not every nonnative species is invasive.

4. Invasive generalists may outcompete native specialists. Introduced predators can also threaten prey that evolved without similar predators, such as rats eating island birds’ eggs.

  D. Habitat islands and conservation

1. Habitat fragmentation divides continuous habitat into smaller, isolated patches. A forest surrounded by roads or farms can function as an island.

2. Small, isolated patches often have fewer immigrants and greater local extinction risk.

3. Edge effects are changes near habitat boundaries, such as increased wind, light, drying, or predator access. They can reduce suitable interior habitat.

4. Protecting large habitats and adding wildlife corridors can support movement and gene flow, the movement of alleles between populations.

5. Corridors can also spread disease or invasive organisms. Their benefits depend on the species and landscape.

IV. Ecological Tolerance (Topic 2.4)

  A. Tolerance ranges

1. Ecological tolerance is the range of conditions an organism can endure before injury or death. Limiting factors include temperature, salinity, water flow, sunlight, and dissolved oxygen.

2. The optimal range supports the greatest success in growth, survival, or reproduction.

3. In zones of physiological stress, organisms may survive but grow slowly or reproduce less.

4. Beyond the limits of tolerance, organisms cannot persist under those conditions.

5. Several factors act together. Suitable temperature does not ensure survival if dissolved oxygen is too low.

  B. Individual differences and evidence

1. Tolerance applies to individuals and species. Inherited traits, age, health, and prior conditions can produce different limits; eggs and larvae may be more sensitive than adults.

2. Brief survival does not prove that conditions allow a population to reproduce and persist.

3. On a tolerance graph, identify the environmental condition on the horizontal axis and the response on the vertical axis. The optimum lies where the measured response is greatest.

4. To test one factor, vary it while keeping other conditions similar and use repeated trials. A field association alone does not establish the cause.

V. Natural Disruptions to Ecosystems (Topic 2.5)

  A. Disturbance patterns and effects

1. A disturbance changes ecosystem structure, resources, or physical conditions. Fires, floods, droughts, storms, and volcanic eruptions can alter habitats and kill organisms.

2. A natural event can cause damage as great as, or greater than, many human disruptions. Some ecosystems also depend on recurring disturbance.

3. Periodic processes recur in cycles, such as seasonal flooding. Episodic events occur in separate episodes, such as volcanic eruptions.

4. Random events have timing or locations that are unpredictable at the scale considered, such as the exact location of a lightning strike. These descriptions can overlap.

5. Effects depend on frequency, intensity, duration, and area affected. Frequent or severe disturbance can prevent recovery.

6. Fire can release nutrients and open growing space. Floods can erode or deposit sediment. Hurricanes can open forest canopies and increase light below.

  B. Long-term climate and sea-level change

1. Earth’s climate has changed over geological time because of factors such as orbital changes, volcanic activity, continental movement, and changes in greenhouse gases.

2. More water stored in land-based glaciers and ice sheets lowers sea level. Melting land ice raises sea level; warming seawater also expands.

3. Melting floating sea ice has little direct effect on sea level because it already displaces water.

4. Sea-level and climate changes can transform large areas of habitat. Past natural climate change does not explain all current warming, which is primarily driven by human greenhouse gas emissions.

  C. Movement in response to change

1. Wildlife may move to escape disturbance, find food, or reach breeding habitat. Migration can occur over short or long periods.

2. A range shift changes where a species lives over the long term. Warming can move suitable conditions toward higher latitudes or elevations.

3. Roads, cities, isolation, and slow movement can prevent organisms from reaching suitable habitat. Species moving at different rates may lose important interactions.

VI. Adaptations (Topic 2.6)

  A. Natural selection across generations

1. An adaptation is an inherited trait that improves survival or reproductive success in a particular environment. Adaptations can involve structure, physiology, or behavior.

2. Individuals already differ in inherited traits. Mutation introduces new genetic variation, and sexual reproduction reshuffles existing variation.

3. Natural selection occurs when individuals with certain heritable traits leave more surviving offspring than others.

4. Those traits and their alleles can become more common over generations. Populations evolve; individuals do not develop inherited adaptations simply because they need them.

5. During repeated droughts, plants with inherited traits that conserve water may leave more offspring. These traits can become more common in later generations.

6. Fitness means reproductive success in a particular environment. A trait that helps under one condition may be harmful under another.

  B. Responses within a lifetime

1. Individuals may change behavior, move, or die when conditions change. Seeking shade or leaving a burned area can provide immediate protection.

2. Acclimation is an individual’s physiological adjustment to changed conditions. It differs from inherited population change across generations.

3. Adaptation depends on available genetic variation and enough generations for selection to act. Sudden or rapid change can outpace a population’s response.

4. When interpreting changes in trait frequency, consider heritability and reproductive success. Migration and sampling differences can also change observed frequencies.

VII. Ecological Succession (Topic 2.7)

  A. Primary succession

1. Ecological succession is change in a community’s species composition over time. Organisms alter conditions, affecting which species can establish later.

2. Primary succession begins where little or no developed soil exists, such as new lava or rock exposed by a retreating glacier.

3. Pioneer species are early colonizers. Microbes, lichens, and mosses can colonize suitable bare surfaces and help begin soil formation.

4. Weathering breaks rock into particles. Dead organisms add organic matter, and decomposers release nutrients. Developing soil allows rooted plants to establish.

  B. Secondary succession

1. Secondary succession follows disturbance where soil remains, such as abandoned farmland or a forest after a fire that leaves soil intact.

2. Surviving seeds, roots, and soil organisms often make recovery faster than primary succession.

3. Grasses and herbs may be followed by shrubs and trees where climate and soil support them. The path depends on local conditions and later disturbances.

4. The presence of soil determines the type of succession. A fire does not automatically mean secondary succession if it removes the soil.

5. A climax community is a traditional term for a relatively persistent later community. It can still change; succession does not always end in a forest.

  C. Biomass, richness, and productivity

1. Biomass is the mass of living material present, often measured as dry mass per unit area. It generally increases as vegetation establishes.

2. Species richness often rises as habitats develop, but competition, shading, or disturbance can cause it to level off or decline.

3. Gross primary productivity (GPP) is the rate at which producers capture energy in organic matter. Net primary productivity (NPP) is the rate remaining after producer respiration.

4. NPP = GPP − R, where R is producer respiration. If GPP is 1,800 g C/m²/year and R is 1,100 g C/m²/year, NPP is 700 g C/m²/year.

5. Productivity is often low on bare sites and rises as plants establish. Later, resource limits and respiration can reduce net accumulation even while stored biomass stays high.

6. Biomass is an amount; productivity is a rate. High biomass does not prove high productivity or high species richness, and succession patterns are not identical everywhere.

7. Colonizing populations may adapt and eventually form new species through speciation. Succession changes communities; speciation is not required for succession.

  D. Keystone and indicator species

1. A keystone species strongly affects community structure relative to its abundance. It need not be the largest or most common species.

2. Sea otters eat sea urchins, reducing grazing on kelp. Losing otters can increase urchins and reduce kelp habitat, an example of a trophic cascade across feeding levels.

3. An indicator species reveals environmental conditions through its presence, abundance, scarcity, or chemical composition.

4. Many mayfly larvae require well-oxygenated water. Changes in their abundance can signal changing stream conditions, but other factors must be checked before identifying a cause.

5. A keystone species shapes a community; an indicator species provides evidence about its conditions. One species can serve both roles.

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