Ecosystems to Biomes Study Notes

Chapter 5: From Ecosystems to Biomes

Overview

• Instructor: Dr. Laura M. Basirico
• Term: Spring 2026

Ecosystems

• Definition: Ecosystems consist of communities of interacting species and their abiotic (non-living) factors.
• Processes: Participate in key processes such as:   - Photosynthesis   - Respiration   - Energy flow   - Nutrient cycling
• Human Interaction: Humans rely on ecosystems and assign value to ecosystem goods and services.
• Distribution Patterns: The distribution of ecosystems follows predictable patterns around the world.
• Biomes: Large-scale ecosystems characterized by similar vegetation and climatic conditions.

Trophic Levels

• Definition: Trophic levels are defined by the primary source of energy (E), representing feeding levels in an ecosystem.
• Photosynthesis Process: In photosynthesis, plants utilize light energy, carbon dioxide (CO2), and water (H2O) to produce organic molecules (e.g., sugars).
• Energy Movement: Energy and nutrients move up through trophic levels to higher organisms.

Food Chains and Food Webs

• Food Chain: A linear sequence illustrating how energy and nutrients flow from one organism to another.
• E moves upward through the food chain, with not all energy and nutrients transferred to higher trophic levels.
• Food Web: A complex network of interconnected food chains, often observed in aquatic systems.

Aquatic Food Webs

• Illustrates the interconnections between various organisms in aquatic environments:   - Includes Arctic ecological examples: Arctic fox, polar bear, seal pup, Arctic cod, ringed seal, zooplankton, phytoplankton, etc.

Types of Organisms

Autotrophs

• Producers: Organisms that produce organic matter from inorganic matter using an external energy source.   - Examples: Green plants, photosynthetic bacteria, and chemosynthetic bacteria.
• Primary production: The production of organic matter through photosynthesis and growth of organisms.
• Chemosynthesis: A process where bacteria utilize energy from inorganic chemicals to synthesize organic matter.

Heterotrophs

• Definition: Organisms that must feed on organic matter to obtain energy.
• Categories:   - Primary Consumers: Herbivores that eat producers.   - Secondary Consumers: Carnivores that feed on primary consumers.   - Tertiary and Quaternary Consumers: Higher-order carnivores.   - Omnivores: Feed on both plants and animals.   - Decomposers: Organisms that feed on dead organic material, categorized as:     - Scavengers (eat larger dead organisms)     - Detritus feeders (consume partly decomposed matter)     - Chemical decomposers (fungi and bacteria that break down molecules).

Biomass and Trophic Levels

• Biomass: The total combined (net dry) weight of organisms at each trophic level.
• Typically, each higher trophic level has approximately 90% less biomass.   - Example: In a grassland with 2,000 lbs of biomass:     - Herbivores: 200 lbs     - Primary Carnivores: 20 lbs.
• Biomass Pyramid: A graphical representation of biomass across trophic levels.

Energy Flow in Ecosystems

• Standing-Crop Biomass: Refers to the biomass of primary producers at any given time.
• Factors influencing biomass and primary production include ecosystem type and climate:   - Forests have larger biomass, while grasslands show high primary production.   - On average, primary production captures only 2% of available solar energy, resulting in about 120 gigatons of organic matter each year.

Efficiency of Energy Flow

• Only a small percentage of energy moves from one trophic level to the next.
• Energy Use:   - 60-90% of consumed energy is oxidized, while 10-40% is converted to body tissues.   - Undigested food is excreted as waste, along with carbon dioxide, nitrogen, phosphorus, and water.
• Secondary Production: The growth of consumers over time, reflecting energy and matter incorporated from lower trophic levels.

Trophic Inefficiency

• Organisms at higher trophic levels require more energy from the sun for the same amount of body tissue than those at lower levels.
• Certain materials, such as heavy metals and pesticides, bioaccumulate and biomagnify through food chains, posing environmental risks.

Aquatic vs. Terrestrial Systems

• Aquatic systems can be more efficient, with greater available energy at each level and longer food chains.
• They often have a reversed biomass pyramid, where smaller biomass of algae supports larger fish populations.
• Life spans and growth rates vary between trophic levels in aquatic ecosystems.

Transition from Ecosystems to Biomes

• Ecosystem patterns lead to predictable populations of organisms under specific conditions.
• Biome: A large geographical terrestrial biotic community, shaped by climate and often named after its dominant vegetation, without set boundaries.

Climate Factors

• Definition: Climate refers to the average weather conditions of a region, including temperature and precipitation.
• Variations:   - Equatorial areas experience warm temperatures and high rainfall.   - Temperature becomes seasonal above and below the equator, with longer and colder winters occurring toward the poles.   - Climate variations influenced by latitude (distance from equator) and altitude (distance from sea level).

Effects of Latitude and Altitude

• Biomes and vegetation types (e.g., tropical rainforest, temperate deciduous forest, tundra) are mapped across latitudinal and altitudinal gradients.
• Microclimate: Localized environmental conditions differing from the broader regional climate, leading to biodiversity variations within ecosystems.

Precipitation

• Precipitation levels can range from nearly 0 to over 100 inches/year, influencing plant and animal species distributions.
• Optimal conditions occurring at the intersection of temperature and precipitation maximize biodiversity, while extremes can exclude species exceeding their limits of tolerance.

Temperature and Biomes

• Different biomes characterized by temperature tolerance:   - Tropical Rain Forests: Broadleaf evergreens that cannot tolerate freezing.   - Deciduous Forests: Trees that seasonally shed leaves.   - Coniferous Forests: Trees that endure harsh winters.   - Tundra: Characterized by permafrost, preventing tree root growth.

Aquatic Systems

• Categories:   - Freshwater (lakes, marshes, streams)   - Marine (oceans, coastal regions)   - Mixed ecosystems (estuaries, bays)
• The primary productivity of these systems varies and can support organisms from other biomes, as seen in tropical rain forests and open oceans.

Productivity in Different Ecosystems

• Biome primary productivity varies extensively   - E.g., tropical rainforests are highly productive due to optimal temperatures and rainfall.   - Open oceans, while expansive, have low rates of productivity, limited by nutrient availability.

Ecosystem Disturbance

• Definition: A disturbance can be natural or human-induced, disrupting ecological succession and creating new ecological conditions.
• Different ecosystems exhibit distinct capacities to respond to disturbances, showcasing resilience.

Resilience and Recovery

• Resilience: The ecosystem's ability to prepare for and recover from disturbances while maintaining function and biodiversity.
• Mechanisms include:   - Resistance: Ability to endure disturbance without significant change.   - Recovery: The speed and extent of return to the pre-disturbance state.

Ecological Succession

• Definition: The process of transition from one biotic community to another following a disturbance.
• Pioneer Species: The first organisms to colonize new or disturbed areas.
• Climax Ecosystem: The final stage of ecological succession that achieves a stable state, although it can still change due to species introduction or removal.
• Primary Succession: Initiates in environments without prior soil, while secondary succession occurs in areas with existing soil cleared by disturbances.

Aquatic Succession

• Similar to terrestrial environments, aquatic systems experience succession, with soil erosion filling water bodies, leading to the gradual disappearance of lakes or ponds.

Natural Disturbances

• Natural disturbances create gaps in ecosystems, fostering biodiversity and impacting succession.

Fire and Succession

• Fire serves as a crucial disturbance with various species displaying differing tolerances.
• Fire can rejuvenate ecosystems, releasing nutrients and facilitating certain plants' germination.

Ecosystem Capital

• Ecosystems provide essential services, including:   - Flood control   - Soil maintenance   - CO2 absorption   - Nutrient cycling
• These services contribute substantially to human welfare, estimated at $44 trillion annual contribution to the economy, which surpasses half of the global GDP.

Loss of Ecosystem Services

• Ignoring ecosystem services leads to environmental degradation. For instance, converting tropical rainforests to agriculture results in significant ecosystem service loss, outweighing economic gains from land conversion.

Ecosystem Restoration

• Restoration efforts are crucial due to increasing demands for goods and services from Earth. Some areas may require intensive restoration strategies.

Managing Ecosystems

• Effective ecosystem management depends on an understanding of:   - Ecosystem functions   - Responses to disturbances   - Delivered goods and services
• U.S. agencies involved in ecosystem management include:   - Forest Service   - Department of Wildlife and Fisheries   - National Park Service   - Environmental Protection Agency (EPA)   - NOAA (National Oceanic and Atmospheric Administration)