Ecology: The Biosphere, Populations, and Communities

Chapter 34: The Biosphere and Biomes

What is the Biosphere?

• Biosphere: The sum of all Earth's ecosystems; the global ecosystem where all life exists, including land, water, and the atmosphere to a certain depth.

• It encompasses all living organisms and their physical environments, interacting as a system.

Key Components Linking the Biosphere

• Energy flow (primarily from the sun) and nutrient cycling (such as carbon, nitrogen, and water cycles) connect all parts of the biosphere.

• Physical factors like climate, soil, and water also link ecosystems within the biosphere.

Ecological Levels and Their Characteristics

• Habitat: The specific environment where an organism lives, including biotic and abiotic factors.

• Biome: Large ecological regions defined by climate, vegetation, and animal life (e.g., tropical forest, desert).

• Biosphere: The global sum of all ecosystems.

• Ecosystem: A community of organisms and their physical environment interacting as a system.

Levels of Organization in the Biosphere

• Species (Individual): A single organism of a particular species.

• Population: A group of individuals of the same species living in a specific area.

• Community: All populations of different species living and interacting in an area.

• Ecosystem: The community plus the abiotic environment.

Major Terrestrial Biomes and Their Defining Characteristics

• Tropical Forests: High rainfall, warm temperatures year-round, high biodiversity.

• Savannas: Grasslands with scattered trees, seasonal rainfall, frequent fires.

• Deserts: Low precipitation, extreme temperature fluctuations, drought-adapted plants and animals.

• Temperate Grasslands: Seasonal drought, occasional fires, dominated by grasses.

• Temperate Broadleaf Forests: Moderate climate, deciduous trees, rich soil.

• Coniferous Forests: Cold, long winters, dominated by cone-bearing trees (taiga).

• Tundra: Cold, permafrost, low-growing vegetation, short growing season.

• Chaparral: Mild, wet winters and hot, dry summers; shrubs and small trees.

• Polar Ice: Extremely cold, ice-covered, minimal vegetation.

Aquatic Biomes and Their Zones

• Pelagic Zone: Open water area of oceans or lakes.

• Intertidal Zone: Area between high and low tide, subject to periodic submersion and exposure.

• Benthic Zone: Bottom of aquatic environments; includes sediment surface and sub-surface layers.

• Estuarine Zone: Where freshwater meets saltwater; highly productive and variable.

• Aphotic Zone: Deep water where sunlight does not penetrate; little to no photosynthesis.

Rain Shadow Effect

• Rain Shadow: A dry area on the leeward side of a mountain range, caused when moist air rises, cools, and loses moisture on the windward side, leaving dry air to descend on the other side.

Chapter 36: Population Ecology

Characteristics of Species, Subspecies, Population, and Community

• Species: A group of organisms capable of interbreeding and producing fertile offspring.

• Subspecies: Populations of a species that are distinct in some characteristics but can interbreed with other subspecies.

• Population: All individuals of a species in a given area.

• Community: All populations of different species in a shared environment.

Population Density

• Population Density: The number of individuals per unit area or volume.

• Calculated as: $\text{Population Density} = \frac{\text{Number of Individuals}}{\text{Area or Volume}}$

Dispersion Patterns

• Uniform: Individuals are evenly spaced (e.g., territorial animals).

• Clumped: Individuals aggregate in patches (e.g., schools of fish, herds).

• Random: Unpredictable spacing, not influenced by strong attractions or repulsions.

Factors Influencing Population Growth

• Availability of resources (food, water, shelter)

• Predation and disease

• Competition

• Abiotic factors (climate, disasters)

Life Tables and Survivorship Curves

• Life Table: A chart showing the probability of survival and reproduction at each age.

• Survivorship Curves:

  • Type I: High survivorship until old age (e.g., humans).

  • Type II: Constant survivorship throughout life (e.g., some birds).

  • Type III: Low survivorship early in life (e.g., oysters, many plants).

Chapter 37: Communities and Ecosystems

What is a Community?

• Community: An assemblage of populations of different species living close enough for potential interactions.

Importance of Studying Community Ecology

• Helps understand species interactions, biodiversity, and ecosystem stability.

• Informs conservation and management of natural resources.

Types of Community Interactions

• Mutualism: Both species benefit (e.g., bees and flowers).

• Parasitism: One species benefits, the other is harmed (e.g., tapeworms in mammals).

• Competition: Both species are harmed by shared resource limitation.

• Predation: One species (predator) kills and eats another (prey).

• Herbivory: An animal consumes plant parts.

Predatory Avoidance Mechanisms

• Camouflage, mimicry, warning coloration, chemical defenses, behavioral adaptations.

• These evolve primarily due to predation pressure.

Coevolution

• Coevolution: Reciprocal evolutionary adaptations between interacting species (e.g., predator-prey, plant-herbivore).

Positive and Negative Interspecific Interactions

• Positive: Mutualism, commensalism (one benefits, other unaffected).

• Negative: Parasitism, predation, competition.

Food Chains and Trophic Levels

• Producer: Organisms that make their own food (e.g., plants, algae).

• Primary Consumer: Herbivores that eat producers.

• Secondary Consumer: Carnivores that eat primary consumers.

• Tertiary Consumer: Carnivores that eat secondary consumers.

• Detritivore: Organisms that feed on dead organic matter (e.g., earthworms, fungi).

Species Richness

• Species Richness: The number of different species in a community.

Keystone Species

• Keystone Species: A species with a disproportionately large effect on its ecosystem relative to its abundance.

• Example: Sea otters maintain kelp forest ecosystems by controlling sea urchin populations.

Invasive Species

• Invasive Species: Non-native species that spread widely and cause harm to native species and ecosystems.

Flow of Energy vs. Flow of Chemicals in Ecosystems

• Energy flows one-way through ecosystems (from sun to producers to consumers to heat).

• Chemicals (e.g., carbon, nitrogen) are recycled within ecosystems.

Atmospheric CO2 Balance (Excluding Human Impact)

• CO2 remains relatively constant due to the balance between photosynthesis (removes CO2) and respiration/decomposition (releases CO2).

Importance of Healthy Ecosystems to Humans

• Provide ecosystem services: clean air and water, pollination, climate regulation, nutrient cycling, and resources (food, medicine).

• Support biodiversity and human well-being.