California Ecology Notes

The Unique & Diverse Ecology of California

• California's biodiversity is remarkable, holding significant percentages of US species richness:
  • Vascular Plants: 5,047 species (6,272 varieties), making up 32% of US species.
  • Amphibians: 51 species, 22% of US species.
  • Reptiles: 84 species, 30% of US species.
  • Birds: 433 species, 56% of US species.
  • Mammals: 197 species, 47% of US species.
  • Freshwater Fish: 67 species, 8% of US species.
• California's biodiversity ranks highly among US states in:
  • Richness: 1st
  • Endemism: 1st
  • Rarity (percentage at risk): 2nd
• Endemic species numbers and rankings:
  • Vascular Plants: 2,153 (Rank 1)
  • Amphibians: 17 (Rank 1)
  • Reptiles: 5 (Rank 1)
  • Birds: 2 (Rank 2)
  • Mammals: 17 (Rank 1)
  • Freshwater Fish: 20 (Rank 1)

Topography

• California features a long coastline and a series of mountains and valleys in close proximity.
• There are rapid transitions in elevation, soil type, rain harvest/shadow, and solar exposure.
• This leads to isolated populations and communities.
• Snowpack provides year-long water supply.
• The highest and lowest points in the continental US are within 80 miles of each other, and 200 miles of the coast.
• Factors such as aspect (angle of sun exposure), elevation, slope, temperature, wind exposure, precipitation, soil depth, runoff & groundwater, and air pressure & gas partial pressures all contribute to the unique ecology.

Geology

• Igneous rock forms volcanic mountains.
• Metamorphic rock is found at plate boundaries.
• Sedimentary rock originates from old seabed.

California Ecology

• California is a long, narrow region bordered by mountains on the east and a long coastline on the west.
• Its climate is greatly affected by ocean conditions, leading to "Seasons of the Sea".
• Climate fluctuations are reduced by proximity to bodies of water.

Great Ocean Current Gyres

• Gyres rotate clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere.

Eastern Boundary Currents

• Draw cold, nutrient-rich water from sub-polar regions toward the tropics.
• The North Pacific Eastern Boundary Current is the "California Current".

North Pacific Gyre

• Waters from the California Current flow to the North Pacific Equatorial Current.
• They warm and lose nutrients as they flow westward across the tropics.
• Warm, oligotrophic (nutrient-poor) water flows north with a western boundary current.
• Water cools and picks up nutrients.
• Some North Pacific Equatorial Current flow reflects back as a countercurrent.
• Water crosses the tropics twice.

California Current

• Regional variations: Eddy currents produce local cells.
• Seasonal variations: Intensity, depth, and distance from shore vary.

California Seasons of the Sea

• Determined and defined by dominant nearshore ocean conditions:
  • Upwelling season
  • Oceanic season
  • Davidson season

Upwelling Season: mid-spring to summer

• High atmospheric pressure system develops offshore.
• Air is pushed away from high pressure.
• The Coriolis effect deflects wind clockwise.
• Prevailing wind along CA is north to south.
• Maximum nutrients and maximum sunshine lead to high primary productivity, amplifying all trophic levels from the bottom up.
• Typical daily pattern:
  • Hot, summer sunshine
  • Offshore surface water warms
  • Cold, upwelled water rises
  • Warm, moist air mass
  • Land heats up
  • Air warms and rises
  • Cold air mass
  • Cool, onshore seabreeze
  • Air cools; moisture condenses, leading to cool, windy, foggy summers in coastal areas.

Oceanic Season: late summer to autumn

• High pressure system weakens and moves onshore.
• Low pressure system develops offshore.
• Air is pulled toward low pressure.
• The Coriolis effect deflects wind counter-clockwise around the low.
• Prevailing wind along CA is south to north.
• Southerly winds cause nearshore downwelling.
• Warm, oligotrophic oceanic waters move nearshore.
• The weather is mild with low ocean productivity.

Davidson Season: winter to early spring

• Low pressure system intensifies, marking the storm season.
• Strong southerly winds intensify the very warm, very oligotrophic Davidson countercurrent.
• Extreme subarctic cold generates storms.
• Storm weather is pulled counterclockwise around the low.
• Storms travel south, warming and absorbing more moisture.
• They continue counterclockwise and approach California from the south as the "Pineapple Express", resulting in warm, wet winters.

El Niño Effect

• Occurs during the Davidson Season
• Warm, oligotrophic currents flow to the Americas.
• This leads to decreased nutrients, productivity, and fish populations.
• Westward equatorial current weakens and Eastward equatorial counter current intensifies.
• This phenomenon is part of the El Niño Southern Oscillation (ENSO).

Climate

• Major climate types in California:
  1. Mediterranean
  2. Steppe
  3. Cool interior
  4. Highland
  5. Desert

Vegetation

• California Floristic Province (CA-FP) is located west of the Sierra Nevadas.
• Much of the Mediterranean climate lands have been converted to urban and agricultural areas.

Geographical Information Systems (GIS)

• Used to map diversity, specifically species (taxon) richness.
• Also used for Rarity-weighted Richness Index (RWRI), an "index of irreplaceability" for "species of special status" which have, very limited distribution, low population levels, and/or are under immediate threat, especially from habitat loss.
  1. The state is divided into equal hexagonal grid cells (250.4 $mi^2$ each).
  2. The number of cells a species occupies determines its rarity rank.
  3. The RWRI for each cell is the sum of (special species x its rarity rank).

Diversity Maps

• Maps are shown for plant, mammal, amphibian, and reptile diversity.
• Maps are shown for Bird Diversity for both Summer and Winter Distribution, as well as Human Population Density.
• Example numbers from the Coastal Atlas of Bird Richness:
  • 22,325 Number of Native Bird Species.
  • 2,405 Average Number of People Per Square Mile.