Biodiversity and Ecological Tolerance Notes

2.1 Intro to Biodiversity

• Biodiversity is the diversity of life forms within an ecosystem.
• It's measured on three different levels: genetic diversity, species diversity, and ecosystem diversity.
• Higher biodiversity generally indicates a healthier ecosystem and population.

Biodiversity Basics

• Genetic Diversity:
  • How different the genes are of individuals within a population (group of the same species).
  • Random mutations in DNA copying and chromosome recombination in sex cells lead to new gene combinations and traits.
  • More genetic diversity in a population improves its ability to respond to environmental stressors like drought, disease, or famine.
  • This increases the likelihood that some individuals will possess traits enabling them to survive the stressor.
• Species Diversity:
  • The number of different species in an ecosystem, considering the balance and evenness of population sizes of all species.
  • Species Richness: the total number of different species found in an ecosystem.
  • Evenness: a measure of how the individual organisms in an ecosystem are balanced between species.
  • High species richness generally indicates good ecosystem health because more species mean more quality resources like water and soil.
  • Evenness indicates whether there are one or two dominant species or if population sizes are well-balanced.
• Ecosystem Diversity:
  • The number of different habitats available in a given area.

Genetic Drift

• Genetic drift is the random shifting of the genetic makeup between generations, entirely due to chance.
• Some generations may exhibit more of a particular feature, whereas others may show less of it.
• Population size significantly affects genetic drift.
• Large populations tend to stabilize allele frequencies.

Bottleneck Event

• A bottleneck event is an environmental disturbance (natural disaster or human habitat destruction) that drastically reduces population size and kills organisms regardless of their genome, thus reducing genetic diversity.
• Surviving population doesn't accurately represent the genetic diversity of the original population.
• Smaller and less genetically diverse populations are more vulnerable to future environmental disturbances.

Genetic Bottlenecks

• A bottleneck is a dramatic reduction in population size, usually resulting in significant genetic drift due to a catastrophe.
• Example: A population of 10,000 dropping to 50 will experience a significant genetic bottleneck.

How Bottleneck Events Happen

• Population reduction can occur in various ways:
  • Overhunting
  • Habitat loss
  • Natural disaster

As the Population Recovers

• If the population recovers, it will be limited to the few traits remaining after the bottleneck.
• Bottleneck results:
  • Reduces the size of the gene pool and genetic variety
  • Increases vulnerability to disease
  • Leads to low reproductive success
  • Increases infant mortality

The Founder Effect

• This effect occurs when a small number of individuals separate from their original population and establish a new population, leading to a smaller gene pool.
• Expect less variation within the new population.

Bottleneck vs. Founder Effect

Inbreeding Depression

• Inbreeding occurs when organisms mate with closely related "family" members.
• Smaller populations are more likely to experience inbreeding due to difficulty in finding non-related mates.
• This leads to a higher chance of offspring having harmful genetic mutations because they're getting similar genotypes from both parents.
• Example: Florida panther population decreased to 30 in the 1900s, leading to kinked tails, heart defects, low sperm count, and undescended testicles.

Simpson Diversity Index

• D = 1 - \frac{\sum n(n-1)}{N(N-1)}
  • Where:
    • D = Simpson Diversity Index
    • n = the number of individuals of each species
    • N = the total number of individuals of all species

Ecosystem Resilience

• Resilience is the ability of an ecosystem to return to its original conditions after a major disturbance like a windstorm, fire, flood, or clear-cutting.
• Higher species diversity equals higher ecosystem resilience.
• High species diversity means more plant species to repopulate disturbed ground, anchor soil, and provide food and habitat for animal species.

Environmental Stressors

• Physical Stress (natural disasters)
• Wildfires
• Pollution
• Thermal stress
• Radiation
• Climatic (light, temperature)
• Biological (predation, competition, parasitism, lack of mates)

Resistance

• Ability to remain unchanged when being subjected to disturbance.

Resistant VS Resilient

• Resistant ecosystems remain unchanged by disturbances.
• Resilient ecosystems recover quickly from disturbances.

Intermediate Disturbance Hypothesis

• Ecosystems that experience moderate amounts of disturbance are the most diverse and healthiest.
• Too much disturbance limits biodiversity, wiping out more sensitive species.
• Too little disturbance encourages only a handful of species to dominate.
• Frequent, low-intensity disturbances encourage diversification of species.

Ecosystem Services

• Ecosystem services are the benefits that humans obtain from ecosystems.
• There are four categories:
  • Provisioning
  • Regulating
  • Cultural
  • Supporting

Types of Ecosystem Services

• Provisioning Services: Products obtained from ecosystems, such as energy, seafood, biomedical resources, transportation routes, and resources for national defense.
• Regulating Services: Benefits obtained from the regulation of ecosystem processes. These includes flood prevention, climate regulation, erosion control, and control of pests and pathogens.
• Cultural Services: Nonmaterial benefits obtained from ecosystems. These include educational, recreational, heritage, and spiritual benefits.
• Supporting Services: Services necessary for the production of all other ecosystem services like biological diversity maintenance, nutrient recycling, and primary productivity.

Ecosystem Services = $

• These are goods that come from natural resources or services/functions that ecosystems carry out that have measurable economic/financial value to humans.
• Regulating: Natural ecosystems regulate climate/air quality, reducing storm damage and healthcare costs.
• Provisioning: Goods taken directly from ecosystems or made from natural resources (wood, paper, food).
• Supporting: Natural ecosystems support processes we do ourselves, making them cheaper & easier (bees pollinate crops).
• Cultural: Money is generated by recreation (parks, camping, tours) or scientific knowledge.

Humans Disrupt Ecosystem Services

• Human activities disrupt the ability of ecosystems to function, decreasing the value of ecosystem services provided.
• This has ecological (natural) and economic (money-based) consequences.
• Examples:
  • Clearing land for agriculture/cities removes trees that store CO2 (more CO2 in atmosphere = more climate change = more storm damage & crop failure).
  • Overfishing leads to fish population collapse, resulting in lost fishing jobs and lower fish sales in the future.

Provisioning Services

• Goods/products directly provided to humans for sale/use by ecosystems.
• Examples: Fish, hunting animals, lumber (wood for furniture/buildings), naturally grown foods like berries, seeds, wild grains, and honey.
• Things made from natural resources: paper, medicine, rubber.
• Disrupted by overharvesting, water pollution, clearing land for agriculture/urbanization.

Regulating Services

• Benefits provided by ecosystem processes that moderate natural conditions like climate and air quality.
• Examples:
  • Trees in a forest sequester (store) CO_2 through photosynthesis, which reduces the rate of climate change, lessens damage caused by rising sea levels, and reduces crop failure from drought.
  • Trees filter air by absorbing air pollutants, which reduces healthcare costs for treating diseases like asthma and bronchitis.
• Disrupted by deforestation.

Supporting Services

• Natural ecosystems support processes we do ourselves, making them less costly and easier for us.
• Examples:
  • Wetland plant roots filter pollutants, leading to cleaner groundwater, so we don’t have to pay as much to purify with expensive water treatment plants.
  • Bees & other insects pollinate our agricultural crops, leading to more crop production & higher profits.
• Disrupted by pollinator habitat loss & filling in wetlands for development.

Cultural Services

• Revenue from recreational activities (hunting/fishing licenses, park fees, tourism-related spending) & profits from scientific discoveries made in ecosystems (health/agriculture/educational knowledge).
• Examples:
  • Beautiful landscapes draw tourists who pay to enter parks, spend money at local stores/restaurants, or pay camping fees.
  • Fishermen pay for fishing licenses to catch fish in clean rivers.
  • Scientists learn about plant compounds that can lead to the creation of new medicines, which are sold for profit.
• Disrupted by deforestation, pollution, and urbanization.

2.3 Theory of Island Biogeography

• Island biogeography studies ecological relationships & community structure on islands.
• Islands can be actual islands in a body of water or figurative habitat islands such as Central Park in New York City or National Parks (natural habitats surrounded by human-developed land).
• Two rules:
  • The larger the island, the greater the ecosystem diversity
  • The closer the island to the mainland, the greater the number of species

Island Biogeography Basics

• Islands have been colonized by new species arriving from elsewhere.
• Many island species have evolved to be specialists rather than generalists because of limited resources, such as food and territory, on most islands.
• The long-term survival of specialists may be jeopardized when invasive species, typically generalists, are introduced and outcompete the specialists.
• Islands closer to the “mainland” support more species. Easier for colonizing organisms to get to the island from the mainland = more genetic diversity in new population.

Larger Islands Support More Species

• Larger islands = higher ecosystem diversity.
• More available “niches” or roles.
• Larger population sizes (more genetically diverse and more resistant to environmental disturbance).
• Lower extinction rate (species less likely to die off).
• Positive correlation between island size & species richness.

Distance to Mainland

• Closer to mainland = higher species richness.
• Easier for more species to migrate to the island from the mainland (swim/fly).
• More continual migration of individuals to the island habitat results in frequent migration bringing more genetic diversity & larger population size.
• Inverse relationship between island distance from mainland & species richness. The further away from the mainland, the fewer species.

Evolution on Islands

• Islands have limited space & resources, creating unique conditions for evolution.
• There’s more pressure for species to adapt to narrower niches (more specific food/habitat).
• Adaptive radiation = single species rapidly evolving into several new species to use different resources & reduce competition.
• Example: Galapagos Finches – different beaks quickly evolve to fit a variety of different food sources on islands, single colonizing species from the mainland quickly evolves to many slightly different species to adapt to new island conditions.

2.4 Ecological Tolerance

• Ecological tolerance refers to the range of conditions, such as temperature, salinity, flow rate, and sunlight, that an organism can endure before injury or death results.
• Ecological tolerance can apply to individuals and to species.

Ecological Range of Tolerance - Zones

• Optimal range: range where organisms survive, grow, and reproduce.
• Zone of physiological stress: range where organisms survive, but experience some stress such as infertility, lack of growth, or decreased activity.
• Zone of intolerance: range where the organism will die from thermal shock, suffocation, or lack of food/water/oxygen.

FRQ Writing Tips

• On FRQs about human activities or natural events that cause environmental disturbance, connect the answer to the ecological range of tolerance.
• If possible, connect human activity to climate change: electricity generation, transportation, and agriculture all release CO_2$$ which causes climate change and global warming.
• Global warming shifts temperature outside the range of tolerance for many tree species, causing their populations to decline.
• Global warming warms the ocean, shifting the temperature outside the range of tolerance for many fish species, causing die-offs.

FRQ Writing Tips

• Try to connect a shift in range of tolerance to a specific kind of physiological stress, such as suffocation, thermal shock, or lack of water/food/nutrients/oxygen.
• Global warming warms the ocean, shifting the temperature outside the range of tolerance for many fish species; since global warming increases ocean temperature and warm water holds less oxygen, fish may suffocate due to lack of oxygen.
• Global warming can increase droughts; with increased droughts, rainfall patterns may shift outside the range of tolerance for many plant species; without enough rainfall, these species may suffer population decline as their roots are unable to absorb enough water from the soil.

2.5 Natural Disruptions to Ecosystems

• A natural event disrupts the structure and/or function of an ecosystem, such as tornadoes, hurricanes, asteroids, or forest fires.
• Natural disturbances can be even greater than human disruptions.
• These can occur on periodic, episodic, or random time frames:
  • Periodic: occurs with regular frequency (ex: dry-wet seasons).
  • Episodic: occasional events with irregular frequency (ex: hurricanes, droughts, fires).
  • Random: no regular frequency (volcanoes, earthquakes, asteroids).

Natural Climate Change

• Earth’s climate has varied over geologic time for numerous reasons.
• Example: Slight changes in Earth’s orbit & tilt cause mini ice ages & warmer periods as Earth shifts slightly closer to & further from the sun.
• Major environmental disturbances result in widespread habitat changes and/or loss; for example, rising sea level floods coastal & estuary habitats.
• Wildlife may migrate to a new habitat as a result of natural disruptions.
• Examples:
  • Wildebeests migrating to follow rain patterns of the African savanna
  • Ocean species moving further north as water temperature warms
  • Bird migration & breeding shifting earlier as insect hatching shifts earlier with warming climate

2.6 Adaptation

• Organisms adapt to their environment over time, both in short- and long-term scales, via incremental changes at the genetic level.
• Environmental changes, either sudden or gradual, may threaten a species' survival, requiring individuals to alter behaviors, move, or perish.

Fitness & Adaptation

• All populations have some genetic diversity, or variability in genomes of individuals, because random mutations while DNA is being copied create new traits and crossing over in parent chromosomes creates new combinations of genes (and therefore traits).
• Adaptation is a new trait that increases an organism’s fitness (ability to survive and reproduce).

Adaptation & Natural Selection

• Natural selection: organisms better adapted to their environment survive and reproduce more offspring.
• Individuals with adaptations pass them on to offspring & individuals without adaptations die off, leading to the entire population having the adaptation over time (evolution).
• Selective pressure/force: the environmental condition that kills individuals without the adaptation (predation by a hawk).

Environmental Change & Evolution

• The environment an organism lives in determines which traits are adaptations.
• As environments change, different traits may become adaptations & old traits may become disadvantages.
• Example: A drought can kill off finches with smaller beaks, making larger beaks for cracking harder seeds an adaptation.

Pace of Evolution

• The more rapidly an environment changes, the less likely a species in the environment will be to adapt to those changes.
• If the pace of environmental change is too rapid, many species may migrate out of the environment or die off completely.
• Example: If the ocean warms too quickly, many species of fish may not be able to migrate before they run out of oxygen and suffocate.
• The more genetic diversity in a population, the better they’re able to adapt to environmental change (higher chance that some individuals have good mutations).
• The longer the lifespan of the organism, the slower the rate of evolution.
• Examples: Bacteria & viruses can adapt and evolve in days, human evolution takes thousands to millions of years.

2.7 Ecological Succession

• Ecological succession is a series of predictable stages of growth that a forest goes through.
• There are two types of succession:
  • Primary Succession: starts from bare rock in an area with no previous soil formation; occurs in an area that hasn’t previously been colonized by plants (bare rock).
  • Secondary Succession: starts from already established soil, in an area where a disturbance (fire/tornado/human land clearing) cleared out the majority of plant life; occurs in an area that already has established soil, but has had most plant life removed by a disturbance.

Stages of Succession

• Pioneer or early succession species appear first, when the ground is simply bare rock or bare soil after a disturbance;
• Mid-successional species appear after pioneer species have helped develop deeper soil with more nutrients by their cycles of growth/death.
• Examples:
  • Moss, lichen (bare rock)
  • Wildflowers, raspberries, grasses/sedges
• Stages are characterized by which types of plant species dominate the ecosystem; different species are adapted to the conditions of the different stages.
• Pioneer Species: Seeds spread by wind or animals, fast-growing, tolerant of shallow soil and full sunlight
• Mid-Successional Species: Relatively fast-growing, larger plants that need deeper soils with more nutrients than pioneers, sun-tolerant

Late Successional Species

• Late successional or climax community species appear last, after the soil is deepened and enriched with nutrients by cycles of growth and death by early & mid-successional species.
• Examples: maples, oaks, and other large trees.
• Characteristics: Large, slow-growing trees that are tolerant of shade and require deep soils for large root networks

Primary Succession Explained

• Moss and lichen (spores dispersed by wind) are able to grow directly on rock by secreting acids that break down rock & release minerals containing nutrients they need (N/P/K).
• Chemical weathering of rocks by moss & lichen, combined with organic matter from moss & lichen dying, forms the initial shallow soil.
• Occurs in an area that hasn’t previously been colonized by plants (bare rock).
• Examples: volcanic rock, rock exposed after glacial retreat.

Secondary Succession Explained

• Pioneer species are still wind-dispersed seeds of plants that are fast-growing and sun-tolerant, but grasses/wildflowers/weeds instead of moss/lichen.
• Soil is already established & sometimes even enriched by nutrient-rich ash from fire; overall more rapid process than primary succession.
• Occurs in an area that already has established soil but has had most plant life removed by a disturbance.