Ecology Lecture Notes

Intro to Ecology 2

LG: Distribution and Abundance of Species

• What explains the distribution and abundance of species?

Major Drivers of Weather/Climate

• Sunlight Angle and Intensity:
  • North Pole: Low angle of incoming sunlight, small amount of sunlight per unit area.
  • Moderate Latitudes: Moderate angle of incoming sunlight.
  • Equator: Sunlight directly overhead, large amount of sunlight per unit area.

Global Air Circulation

• Hadley Cells:
  • Circulation between 30°N and 30°S latitude.
• Ferrel Cells:
  • Air circulation cells in mid-latitudes.
• Polar Cells:
  • Air circulation cells near the poles.
• Features:
  • Subpolar low
  • Polar high
  • Polar easterlies
  • Polar front
  • Subtropical high (Horse latitudes)
  • Westerlies
  • NE and SE trade winds
  • Equatorial low (Doldrums)

Global Wind Patterns

• General Patterns:
  • Polar Easterlies.
  • Westerlies.
  • Trade Winds (Northeast and Southeast).
• Ocean Currents:
  • North Pacific Gyre, South Pacific Gyre, Atlantic Gyre, Indian Ocean Gyre.
  • California Current, North Equatorial Current, South Equatorial Current, West Wind Drift, East Wind Drift, Kuroshio Current, Australian Current, Benguela Current, etc.
  • Warm and cold currents are indicated on the map.

Seasonal Shift of Cells

• June:
  • Sun overhead at the Tropic of Cancer (23°N).
  • The cells shift northwards as the heat equator is in the northern hemisphere.
• December:
  • Sun overhead at the Tropic of Capricorn (23°S).
  • The cells shift southwards as the heat equator is in the southern hemisphere.

Regional Effects

• Rain Shadows:
  • Air rises over mountains and cools, causing rain.
  • Example: Cascade Mountains.
    • West side: Moisture-laden air from the Pacific Ocean.
    • East side: Dry air creates desert conditions.

Biomes

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

Biome Distribution Factors

• Temperature and Precipitation:
  • Annual precipitation (cm) vs. Average temperature (°C) determine biome type.
  • Examples:
    • Tropical rain forest: High precipitation and temperature.
    • Temperate seasonal forest: Moderate precipitation and temperature.
    • Boreal forest: Low temperature, moderate precipitation.
    • Tundra: Very low temperature, low precipitation.
    • Subtropical desert: High temperature, very low precipitation.
• Rule of Thumb:
  • 20 mm of monthly precipitation for each 10°C in temperature provides sufficient moisture for plant growth.
  • When the precipitation line is above the temperature line on a graph, plant growth is supported.

Climate and Biome Examples

• Boreal Forest:
  • Location: Whitehorse, Canada.
  • Climate: Boreal (VIII).
  • Elevation: 703 meters.
  • Annual precipitation: 267 mm.
  • Average temperature: -0.7 °C.
• Temperate Seasonal Forest:
  • Location: Omaha, Nebraska.
  • Climate: Nemoral (VI).
  • Elevation: 337 meters.
  • Annual precipitation: 700 mm.
  • Average temperature: 10.8 °C.

Additional Biome Examples

• Tundra:
  • Location: Baker Lake, Canada.
  • Climate: Polar (IX).
  • Elevation: 4 meters.
  • Annual precipitation: 208 mm.
  • Average temperature: -11.9 °C.
• Temperate Grassland/Desert:
  • 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:
  • Location: Chiclayo, Peru.
  • Climate: Subtropical (hot deserts) (III).
  • Elevation: 31 meters.
  • Annual precipitation: 31 mm.
  • Average temperature: 21.9 °C.
• Tropical Rain Forest:
  • Location: Andagoya, Colombia.
  • Climate: Equatorial (I).
  • Elevation: 65 meters.
  • Annual precipitation: 6,905 mm.
  • Average temperature: 27.2 °C.

Terrestrial Biomes

• Ice sheet and polar desert
• Tundra
• Taiga (Boreal Forest)
• Temperate Broadleaf Forest
• Temperate Steppe
• Subtropical Rainforest
• Mediterranean Vegetation
• Monsoon Forest
• Desert
• Xeric Shrubland
• Dry Steppe
• Semiarid Desert
• Grass Savanna
• Tree Savanna
• Subtropical Dry Forest
• Tropical Rainforest
• Alpine Tundra
• Montane Forests

Anthropogenic Biomes

• Biomes significantly altered by human activities.
  • Examples: Dense Settlements, Urban, Cropped & Pastoral, Pastoral Villages, Rainfed Villages, Rainfed Mosaic Villages, Irrigated Cropland, etc.
• Wildlands: Natural, Semi-natural.
• Inhabited: Residential, Villages, Rangeland, Cropland, Forested.
  *Reference: Ellis, E. C., and N. Ramankutty (2008). Putting people in the map: anthropogenic biomes of the world. Frontiers in Ecology and the Environment, vol. 6. doi: 10.1890/070062.

Aquatic Biomes

• Fresh and salt water (salinity).
• Key Physical Factors:
  1. Nutrient availability.
  2. Water depth.
  3. Water movement.
• Light Penetration:
  • Red wavelengths are not available underwater.
  • Blue wavelengths dominate underwater.
  • Many organisms require wavelengths of about 680 nm for peak photosynthetic efficiency.

Lakes

• Zones:
  • Photic zone: light for photosynthesis
  • Aphotic zone: little or no light
• Stratification and Turnover:
  1. Winter: Dense 4°C water at the bottom becomes 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 becomes 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

• Zones:
  • Photic zone
  • Aphotic zone
  • Continental shelf
• Upwelling:
  1. Winds blow along the coast, moving surface water.
  2. Surface water is forced offshore due to Earth's rotation.
  3. Nutrient-laden water wells up from the bottom to replace the surface water.

Population Ecology I

• Why does it matter?
  • Conservation biology
  • Invasive species management
  • …

Range

• Global Range: entire distribution of a species.
• Regional Range: distribution within a specific area.
• Local Range: distribution within a small area.

Population Size

• Factors Determining Population Size:
  • Births: Add individuals to a population.
  • Deaths: Remove individuals from a population.
  • Immigration: Add individuals to a population.
  • Emigration: Remove individuals from a population.

Life Table for Lacerta vivipara (Females in the Netherlands)

• Variables:
  • x: Age Class
  • N_x: Number of Survivors
  • l_x: Survivorship
  • m_x: Age-Specific Fecundity
  • lxmx: Average Births/Year/Original Female
• Example Data Points:
  • Age 0: Nx = 1000, lx = 1.000, mx = 0.00, lxm_x = 0.00
  • Age 2: Nx = 308, lx = 0.308, mx = 1.47, lxm_x = 0.45
  • Age 5: Nx = 10, lx = 0.010, mx = 3.25, lxm_x = 0.04
• R0 = [Sigma] lxm_x = 1.00 (Net reproductive rate)

Survivorship Curves

• Sex-specific survival (e.g., Belding’s ground squirrels).
• Three basic survivorship curves.
• Can be species or stage-specific.

Population Growth Parameters

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

Life-History Continuum

• 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 Equations

• Exponential Growth:
  • \frac{dN}{dt} = r_{max}N
• Logistic Growth:
  • \frac{dN}{dt} = r_{max}N \frac{K - N}{K}
  • Alternatively: \frac{dN}{dt} = r_{max}N (1 - \frac{N}{K})
• Density Dependence: Growth rate slows at high density.

Density Dependence

• Survival of gobies declines at high population density.
• Fecundity of sparrows declines at high population density.

Density-Dependent Factors Limiting Population Size (Table 51.2)

• Competition for resources: food, territory, water, light, nesting sites, nutrients, oxygen.
• Disease and parasitism: infectious disease, parasitism.
• Stress-related degradation of health.
• Toxic wastes: ammonia, uric acid, alcohol, carbon dioxide.
• Social behavior: stress-mediated behavior, dominance behavior, mating behavior, parental-care behavior, predator-avoidance behavior.
• Predation: increased predation as prey density increases.

Hare-Lynx Population Cycle

• Cycles every 10 years on average; changes in lynx density lag behind changes in hare density.

Hypotheses

• Research Question: What factors control the hare-lynx population cycle?
• Bottom-Up Hypothesis: Food availability for the hares controls the cycle.
• Top-Down Hypothesis: Predation controls the cycle.
• Interaction Hypothesis: Interaction of food availability and predation controls the 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.