Ecology: Succession and Climax Communities

Succession

• Organisms in a community change over time in a predictable way
• Climax community: A stable, long-lasting community resulting from succession
• Disturbances such as fire and floods start the succession process again

Primary Succession

• Begins with bare rock
• Very slow process because there is initially no soil
• Example: volcanic islands

Secondary Succession

• Begins after the disturbance of an existing ecosystem
• Occurs more rapidly than primary succession because soil and some organisms already exist
• Examples: hurricanes, fires, floods
• Wildlife habitat management often mimics secondary succession

Climax Community Characteristics

• Maintains a mix of species over time
• At equilibrium with the environment
• Has increased biodiversity
• Human settlement has altered climax communities by introducing exotic species, disease, and changing land use

Biomes

• Large-scale terrestrial climax communities

Factors Affecting Biomes

• Precipitation: Amount and form (rain or snow)
• Temperature: Tropical vs. temperate regions
• Other factors: Fire, wind, soil type, flora, and fauna

Elevation

• Affects vegetation in a similar way to latitude
• Higher elevations have similar vegetation to higher latitudes

Tropical Rainforest

• Receives 80-128 inches of rain per year
• Contains the highest biodiversity of any biome
• Threatened by logging, cattle grazing, urban sprawl, and biofuels production
• Difficult to restore, so preservation is critical

Temperate Deciduous Forest

• Has distinct seasons with both hot and cold periods
• Deciduous trees lose their leaves in the fall
• Receives 30-60 inches of rain per year
• Less tree diversity than tropical rainforests, but more individuals of dominant species (oak, beech)
• Management includes selective logging, thinning, and prescribed burning in some cases

Taiga (Boreal Forest)

• Located at northern latitudes
• Evergreen coniferous forests
• Short summers, long winters, and heavy snowfall
• Conservation involves selective logging

Tundra

• "Arctic prairie" that lacks trees
• Has a layer of permanently frozen soil called permafrost
• Shallow water supports nesting birds
• Alpine tundra occurs at high elevations
• Preservation is critical because tundra plants grow very slowly

Aquatic Ecosystems

• Factors affecting aquatic ecosystems:
  • Light penetration: Affects depth of the euphotic zone
  • Water temperature: Affects species distribution and metabolism
  • Nature of the bottom substrate: Provides habitat for benthic organisms
  • Amount of dissolved minerals: Influences nutrient availability

Plankton

• Small, drifting organisms
• Phytoplankton: Photosynthetic plankton (algae and bacteria) found in the euphotic zone
• Zooplankton: Animals that feed on phytoplankton

Benthic Organisms

• Live on the ocean bottom
• Examples: Kelp, coral reefs, mangroves
• Abyssal ecosystem: Deep ocean system that receives detritus from the euphotic zone

Estuaries

• Marine ecosystems with a mix of freshwater and saltwater
• Shallow, partially enclosed areas with an inflow of freshwater
• Serve as nurseries for young fish and shrimp

Freshwater Ecosystems

• Lakes and Ponds:

  • Emergent plants: Rooted on the bottom but extend above the water surface (e.g., cattails, water lilies)
  • Submerged plants: Rooted on the bottom but stay below the surface (e.g., coontail)
  • Littoral zone: Shallow area with emergent vegetation near the shore
  • Limnetic zone: Open water area without rooted vegetation
  • Oligotrophic: Cold, deep, nutrient-poor lakes
  • Eutrophic: Shallow, warm, nutrient-rich lakes

• Streams and Rivers:

  • Periphyton: Attached algae and other organisms found on submerged surfaces
  • Slow-moving rivers accumulate material and fill in over time

Wetlands

• Transition areas between aquatic and terrestrial systems
• Swamps: Wetlands with trees that tolerate flooding
• Marshes: Wetlands dominated by grasses and reeds
• Wetlands tend to shift towards terrestrial systems over time