Ecology Notes

Lecture 20: Intro to Ecology 2

LG: What explains the distribution and abundance of species?

• Distribution and abundance of species are influenced by various factors.

Major drivers of weather/climate

• Sunlight Angle and Intensity: The angle at which sunlight strikes the Earth affects the amount of sunlight per unit area. Sunlight is most direct at the equator and least direct at the poles.
  • Low angle at the North Pole: small amount of sunlight per unit area.
  • Moderate angle: moderate amount of sunlight per unit area.
  • Sunlight directly overhead: large amount of sunlight per unit area.

Atmospheric Circulation

• Hadley Cells: These are large-scale atmospheric convection cells in the tropics.

• Ferrel Cells: Mid-latitude circulation cells.

• Polar Cells: High-latitude circulation cells.

• Global Air Circulation Patterns

  • Polar High: Located at the poles; characterized by high pressure and descending cold, dry air.
  • Polar Easterlies: Cold, dry winds blowing from the east near the poles.
  • Polar Front: Boundary between the polar easterlies and the westerlies.
  • Subpolar Low: Area of low pressure where the polar front is located.
  • Westerlies: Winds blowing from the west in the mid-latitudes.
  • Horse Latitudes: Areas of calm or light winds around 30° latitude, associated with the subtropical high.
  • Subtropical High: Zone of high pressure and descending air around 30° latitude.
  • NE Trade Winds: Winds blowing from the northeast towards the equator.
  • Equatorial Low/Doldrums: Area of low pressure and calm winds near the equator.
  • SE Trade Winds: Winds blowing from the southeast towards the equator.

• Position of the Three Cells in June

  • The sun is overhead at the Tropic of Cancer (23°N of the Equator).
  • The cells shift northwards as the heat equator is in the northern hemisphere.

• Position of the Three Cells in December

  • The sun is overhead at the Tropic of Capricorn (23°S of the Equator).
  • The cells shift southwards as the heat equator is in the southern hemisphere.

Ocean Currents

• Gyres: Large circular ocean currents.

  • North Pacific Gyre
  • South Pacific Gyre
  • Atlantic Gyre
  • Indian Ocean Gyre

• Warm and Cold Currents

  • Warm Currents: N. Equatorial C., Kuroshio C., N. Atlantic Drift, etc.
  • Cold Currents: California C., Canary C., Benguela C., West Wind Drift, etc.

Regional Effects

• Rain Shadow: Air rises over mountains, cools, and releases precipitation. The leeward side of the mountain range becomes a dry area (desert). Example: Cascade Mountains.
  • West: Moisture-laden air blows onshore from the Pacific Ocean.
  • East: Dry air creates desert conditions.

Biomes

• Major groupings of plant and animal communities defined by a dominant vegetation type.
• Most important variables: Temperature and Water availability.

Climate and Biomes

• Relationship Between Temperature, Precipitation, and Biomes: Different biomes are correlated with specific ranges of temperature and precipitation.

  • Tropical rainforest: High precipitation and temperature.
  • Subtropical desert: Low precipitation.
  • Temperate grassland/desert
  • Boreal forest
  • Tundra: Low temperature and precipitation.

• As a rule of thumb, about 20 mm of monthly precipitation for each 10°C in temperature provides sufficient moisture for plant growth.

Specific Biomes and Climates

• Boreal Forest: Low temperatures, moderate precipitation.

  • Location: Whitehorse, Canada.
  • Climate: Boreal (VIII).
  • Elevation: 703 meters.
  • Annual precipitation: 267 mm.
  • Average temperature: -0.7 °C.

• Temperate Seasonal Forest: Moderate temperatures and precipitation.

  • Location: Omaha, Nebraska.
  • Climate: Nemoral (VI).
  • Elevation: 337 meters.
  • Annual precipitation: 700 mm.
  • Average temperature: 10.8 °C.

• Tundra: Very low temperatures, low precipitation.

  • Location: Baker Lake, Canada.
  • Climate: Polar (IX).
  • Elevation: 4 meters.
  • Annual precipitation: 208 mm.
  • Average temperature: -11.9 °C.

• Temperate Grassland/Desert: Moderate temperatures, low to moderate precipitation.

  • Location: Salt Lake City, Utah.
  • Climate: Continental (cold deserts) (VII).
  • Elevation: 1,329 meters.
  • Annual precipitation: 339 mm.
  • Average temperature: 11.0 °C.

• Subtropical Desert: High temperatures, very low precipitation.

  • Location: Chiclayo, Peru.
  • Climate: Subtropical (hot deserts) (III).
  • Elevation: 31 meters.
  • Annual precipitation: 31 mm.
  • Average temperature: 21.9 °C.

• Tropical Rain Forest: High temperatures, very high precipitation.

  • Location: Andagoya, Colombia.
  • Climate: Equatorial (I).
  • Elevation: 65 meters.
  • Annual precipitation: 6,905 mm.
  • Average temperature: 27.2 °C.

Anthropogenic Biomes

• Biomes significantly altered by human activities, including urban areas, villages, and agricultural lands.

Aquatic Biomes

• Fresh and saltwater environments.
• Key physical factors:
  1. Nutrient availability
  2. Water depth
  3. Water movement
• Light Wavelengths: Red wavelengths are not available underwater; blue wavelengths dominate.
  • Many organisms require wavelengths of about 680 nm for peak photosynthetic efficiency.

Lakes

• Zonation: Photic zone (light penetration) and aphotic zone (no light penetration).
• Stratification and Turnover: Seasonal changes in water temperature and density lead to stratification in summer and winter, and turnover in spring and fall, which mixes nutrients and oxygen.
  1. Winter: Dense 4°C water at the bottom, nutrient-rich. Surface becomes oxygenated.
  2. Spring Turnover: Surface water warms to 4°C and sinks, carrying O_2 down and driving nutrients up.
  3. Summer: Dense 4°C water at the bottom, nutrient-rich. Surface becomes oxygenated.
  4. Fall Turnover: Surface water cools to 4°C and sinks, carrying O_2 down and driving nutrients up.

Oceans

• Zonation: Photic zone and aphotic zone; continental shelf.
• Upwelling: Winds and Earth's rotation cause surface water to move offshore, replaced by nutrient-laden water from the bottom.
  1. Winds Blow: Along the coast of Peru, the prevailing winds blow north, moving water at the surface.
  2. Surface Water Moves: As the Earth rotates, the moving surface water is forced offshore.
  3. Upwelling: As surface water leaves, it is replaced by nutrient-laden water welling up from the bottom.

Population Ecology I

• Why it matters: Applications in conservation biology and invasive species management.

Global, Regional, and Local Ranges of Species: Example given of Lacerta vivipara.

Factors Determining Population Size

• Population size is determined by births, deaths, immigration, and emigration.
  • Births and immigration add individuals to a population.
  • Deaths and emigration remove individuals from a population.

Life Tables

• Life tables track survivorship and fecundity in a population.
  • Example: Life Table for Lacerta vivipara Females in the Netherlands.
  • x: Age Class
  • N_x: Number of Survivors
  • l_x: Survivorship
  • m_x: Age-Specific Fecundity
  • lx mx: Average Births/Year/Original Female
  • R0 = \$sum lx m_x: Net reproductive rate

Survivorship Curves

• Three basic types of survivorship curves.
  • Can be species- or stage-specific.
  • Example: Belding’s ground squirrels.

Population Growth Parameters

• R_0: Net reproductive rate.
• r_{max}: Intrinsic per capita rate of increase (or population growth) = b - d, estimated as r.
• K: Carrying capacity.

Life-History Continuum

• Trade-offs between fecundity and survivorship.
  • Low Fecundity, High Survivorship: Few offspring, large offspring, late maturity, large body size, high disease resistance, high predator resistance, long life span.
  • High Fecundity, Low Survivorship: Many offspring, small offspring, early maturity, small body size, low disease resistance, low predator resistance, short life span.

Population Growth Models

• Examples of r values for different organisms.
  • Bacterium E. coli: 59.
  • Ciliate P. caudatum: 1.6.
  • Flour beetle: 0.10.
  • Domestic cow: 0.001.
  • Beech tree: 0.000075.
• Density Dependence: Growth rate slows at high density.
• Logistic Growth Equation: Accounts for carrying capacity (
  • \frac{dN}{dt} = r_{max}N
  • \frac{dN}{dt} = r_{max}N \frac{K - N}{K}
  • \frac{dN}{dt} = r_{max}N (1 - \frac{N}{K})

Examples of Density Dependence

• Survival of gobies declines at high population density.
• Fecundity of sparrows declines at high population density.
• Reindeer introduced to St. Paul Island (Alaska).

Density-Dependent Factors That Limit Population Size

• Competition for Resources
  • Food, territory, water, light, nesting sites, nutrients, oxygen.
• Disease and Parasitism
  • Infectious disease, parasitism.
• Stress-Related Degradation of Health
• Predation
• Toxic Wastes
  • Ammonia, uric acid, alcohol, carbon dioxide.
• Social Behavior
  • Stress-mediated behavior, dominance behavior, mating behavior, parental-care behavior, predator-avoidance behavior.

The Hare-Lynx Cycle

• The hare-lynx populations cycle every 10 years, on average. Changes in lynx density lag behind changes in hare density.

• Hypotheses

  • Bottom-Up Hypothesis: Food availability for the hares controls the hare-lynx cycle.
  • Top-Down Hypothesis: Predation controls the hare-lynx cycle.
  • Interaction Hypothesis: The interaction of food availability and predation controls the hare-lynx cycle.
  • Null Hypothesis: The hare-lynx cycle isn't driven by predation, food availability, or a combination of those two factors.

• Conclusion: Hare populations are limited by both predation and food availability. When predation and food limitation occur together, they have a greater effect than either factor does independently.