An Introduction to Ecology and the Biosphere

An Introduction to Ecology and the Biosphere

Key Concepts

• 52.1 Earth's climate varies by latitude and season and is changing rapidly.
• 52.2 The distribution of terrestrial biomes is controlled by climate and disturbance.
• 52.3 Aquatic biomes are diverse and dynamic systems that cover most of Earth.
• 52.4 Interactions between organisms and the environment limit the distribution of species.
• 52.5 Ecological change and evolution affect one another over long and short periods of time.

Study Tip

• Make a table: As you read the chapter, build a table listing factors that influence species distribution in terrestrial and aquatic environments. Add figure numbers or page numbers that give examples of these factors in each type of environment.

Environment Factors

• Amount of light: Strongly affects where organisms live (both terrestrial and aquatic).
• Temperature: Impacts the distribution of species and their ecosystems.
• Precipitation: Variability can lead to different species adapting to the same climate (Illustrated in Figure 52.11).
• Nutrients: Availability is critical for life, impacting growth and reproduction in organisms.

Ecology as a Scientific Field

• Definition: Ecology is the scientific study of interactions between organisms and their environment, including both biotic factors (other organisms) and abiotic factors (physical surroundings).

Levels of Ecological Study

1. Organismal Ecology

   • Focuses on individual organism's adaptation mechanisms (structure, physiology, behavior) to challenges in their environment.
   • Example question: "How do flamingos select a mate?"

2. Population Ecology

   • Investigates factors influencing population size and dynamics over time.
   • Example question: "What environmental factors affect the reproductive rate of flamingos?"

3. Community Ecology

   • Examines interactions among species and their impact on community structure.
   • Example question: "What factors influence species diversity at this African lake?"

4. Ecosystem Ecology

   • Studies energy flow and nutrient cycling between organisms and their environment, considering both biotic communities and their physical context.
   • Example question: "What factors control photosynthetic productivity in this aquatic ecosystem?"

5. Landscape Ecology

   • Looks at exchanges between ecosystems within a landscape and how they interact.
   • Example question: "To what extent do nutrients from terrestrial ecosystems affect organisms in the lake?"

6. Global Ecology

   • Addresses the relationship between energy and material exchange on a global scale, affecting organism distribution in the biosphere.
   • Example question: "How do global patterns of air circulation affect organism distribution?"

Distribution of Terrestrial Biomes

Climate and Terrestrial Biomes

• Biomes: Major life zones characterized by vegetation in terrestrial areas (or by physical environment in aquatic biomes).
• Crucial Factors: Climate influences plant species distribution, thus impacting biome locations.

Climographs

• Climographs plot annual mean temperature against precipitation; they help visualize biome characteristics, revealing distinct climates.
• Example: Climographs demonstrate differences between temperate and coniferous forests (Figure 52.11).
• Notable Observation: Areas may have similar annual averages but differ based on seasonal patterns, affecting biodiversity.

General Features of Terrestrial Biomes

• Terrestrial biomes are typically named after climatic characteristics and predominant vegetation types.
• Each biome supports specific microorganisms, fungi, and animals adapted to that ecosystem.
• Disturbances like storms or human activities reshape biome compositions over time and can lead to unique community dynamics.
• Vertical Layering: Vegetation in biomes often stratifies into layers, creating diverse habitats.

Disturbance in Terrestrial Biomes

• Disturbance Definition: An event altering community structure (e.g., storms, fire, human activity), leading to resource changes.
• Example: Post-Hurricane Katrina, cypress trees became more dominant in affected areas due to their resilience.
• Ecotones: Transitional areas between biomes often exhibit mixed community structures and diverse characteristics.

Specific Terrestrial Biomes

1. Tropical Forest:

   • Distribution: Equatorial and subequatorial regions.
   • Precipitation: Constant (200-400 cm annually for rainforests, seasonal 150-200 cm for dry forests).
   • Temperature: High year-round (25-29°C).
   • Species Richness: Home to millions of species, many still undescribed.
   • Human Impact: Deforestation for agriculture/urbanization.

2. Desert:

   • Distribution: Bands near 30° N/S latitude.
   • Precipitation: Low & variable (< 30 cm annually).
   • Adaptations: Heat and drought resistance in plants (e.g., cacti).
   • Human Impact: Urbanization and agriculture altering natural biodiversity.

3. Savanna:

   • Distribution: Equatorial and subequatorial regions.
   • Precipitation: Averages 30-50 cm; dry season lasts 8-9 months.
   • Adaptations: Fire-tolerant plants, with grasses dominating the ground cover.
   • Wildlife: Large herbivores and predators common; migratory patterns during dry seasons.

4. Chaparral:

   • Distribution: Midlatitude coastal regions.
   • Precipitation: Highly seasonal (30-50 cm).
   • Adaptations: Tough evergreen leaves and fire-resistant seeds.
   • Human Impact: Settled areas facing reductions due to agriculture/urbanization.

5. Temperate Grassland:

   • Distribution: Found on multiple continents (e.g., North America's prairies).
   • Precipitation: Seasonal 30-100 cm; periodic droughts common.
   • Adaptations: Fire and grazing-tolerant grasses.
   • Human Impact: Conversion to agriculture has simplified original ecosystems.

6. Northern Coniferous Forest:

   • Distribution: Broad region across North America; largest terrestrial biome.
   • Precipitation: Ranges from 30-70 cm; coastal areas receive >300 cm.
   • Adaptations: Coniferous trees adapted to cold, with structures preventing snow accumulation.
   • Human Impact: Heavy logging threatening remaining stands.

7. Temperate Broadleaf Forest:

   • Distribution: Mainly in midlatitudes; significant areas in other continents.
   • Precipitation: Averaging 70-200 cm annually; rainfall through all seasons.
   • Adaptations: Trees adapted to seasonal temperature variations—deciduous in northern regions.
   • Human Impact: Heavily impacted by land clearing and urban development, with recovery seen in some areas.

8. Tundra:

   • Distribution: Covers 20% of Earth's land surface; includes alpine tundra at high altitudes.
   • Precipitation: 20-60 cm on average; low and sometimes permafrost-affected.
   • Adaptations: Herbaceous vegetation; adapted to cold and short growing seasons.
   • Human Impact: Environmental exploitation for minerals and oil extraction.

Aquatic Biomes

Diversity and Classification

• Aquatic biomes cover 75% of Earth's surface and exhibit less latitude variation than terrestrial biomes.
• Marine Biomes: Salt concentration ~3%.
• Freshwater Biomes: Salt concentration <0.1%.

Zonation in Aquatic Biomes

• Aquatic systems display vertical and horizontal stratification.
• Photic Zone: Sufficient light for photosynthesis; supports a variety of life forms.
• Aphotic Zone: Limited light penetration; reduced biodiversity.
• Benthic Zone: Bottom area filled with sediments, sustaining benthos communities feeding on detritus.
• Thermocline: A layer of abrupt temperature change, impacting biological processes in lakes and oceans.

Seasonal Turnover in Lakes

• Lakes undergo seasonal turnovers that result in oxygenated water molecules reaching the cold depths during spring and autumn, affecting nutrient cycling.

Species Distribution

• Species in aquatic biomes are distributed based on water depth, light penetration, distance from the shore, and whether they are in open water or on the bottom.

Interactions and Species Distribution

• Species distribution results from both ecological factors and evolutionary history:
  • Example: Kangaroos are isolated to Australia due to continental drift and specific ecological adaptation factors.
  • Factor interplay: Not only geographical isolation but interactions with biotic factors such as food availability and habitat suitability determine where species thrive.
• Saguaro Cactus: Specific habitat (Sonoran Desert) rather illustrating biotic and abiotic factor influences on species distribution.

Continued Relevance

• The study of ecology incorporates various factors impacting species and interactions over short and extended timelines, influencing biodiversity and ecosystem stability.