Ecology and Ecosystems: Study Notes (General Biology)

Chapter 3: What is Ecology?

Definition and Scope of Ecology

Ecology is the study of relationships between organisms and their physical environment. It examines how organisms interact with each other and with their surroundings, and investigates the distribution and abundance of organisms.

• Ecology: The scientific study of interactions among organisms and between organisms and their environment.

• Key Focus Areas:

  • Interactions among organisms (biotic factors)

  • Interactions with the physical environment (abiotic factors)

  • Distribution and abundance of organisms

Levels of Organization in Ecology

Hierarchical Structure

Ecological studies are organized into several levels, each representing increasing complexity.

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

• Community: All living organisms occupying a given area.

• Ecosystem: The community plus the physical environment.

• Biome: Large regions characterized by specific climate and communities.

• Biosphere: The global sum of all ecosystems.

Population Ecology

Definition of Population

A population is defined as the number of organisms of the same species within a given area.

• Population Size: The total number of individuals.

• Population Density: Number of individuals per unit area.

Factors Limiting Population Growth

• Density-independent factors (Abiotic):

  • Oxygen

  • Nutrient quality

  • Weather

  • Climate

• Density-dependent factors (Biotic):

  • Competition

  • Predation

  • Parasitism

  • Disease

Carrying Capacity

Carrying capacity (K) is the maximum number of individuals of a particular population that an ecosystem can support sustainably.

• Population growth often follows a logistic curve, leveling off at carrying capacity.

Equation:

$\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right)$

Where: $N$ = population size $r$ = intrinsic rate of increase $K$ = carrying capacity

Community Ecology

Definition of Community

A community consists of all living organisms occupying a given area.

• Community Structure is shaped by:

  • Competition

  • Predation

  • Symbiosis

  • Phenology

  • Climate

Symbiosis

Symbiosis is a close association between two or more species. Types include:

• Mutualism: Both species benefit (e.g., pollination, mycorrhizae).

• Commensalism: One benefits, the other is unaffected.

• Parasitism: One benefits, the other is harmed.

Mutualism Examples

• Plants and microbes (e.g., rhizobium in root nodules)

• Protists and fungi (e.g., lichen)

• Terrestrial plants and insects (e.g., pollination)

• Animals and protists/bacteria (e.g., ruminants, corals)

• Animals and other animals (e.g., crocodile and plover bird)

Mycorrhizae

• Most terrestrial plants have symbiotic mycorrhizal fungi.

• Fungi assist with decomposition in the rhizosphere and can decompose lignin.

• Mycelial growth enables fungi to spread rapidly and aids in physical breakdown of organic matter.

Microorganisms in Ecosystems

• Produce plant growth hormones

• Stimulate plant growth

• Compete with disease organisms

Phenology

Phenology studies the relationships between periodic biological events—usually the life cycles of plants and animals—and environmental changes.

• Examples: Migration, flowering, breeding seasons

• Environmental changes (e.g., climate change) can shift phenological events

Ecosystems

Energy Flow and Trophic Levels

Energy moves through ecosystems via trophic levels:

• Primary producers (autotrophs): Convert light energy to chemical energy (photosynthesis)

• Primary consumers: Herbivores that eat producers

• Secondary consumers: Carnivores that eat herbivores

• Tertiary consumers: Carnivores that eat other carnivores

• Decomposers: Break down dead organic matter

Energy Transfer Efficiency

• Only about 10% of energy is transferred to the next trophic level; the rest is lost as heat.

Example: If a plant stores 20,000 kcal/m2/yr, only 2,000 kcal/m2/yr is available to primary consumers.

Primary Production

• Gross Primary Production (GPP): Total energy captured by producers.

• Net Primary Production (NPP): Energy available to consumers after producers' respiration.

Equation:

$\text{NPP} = \text{GPP} - \text{Respiration}$

Ecological Succession and Disturbance

Most ecosystems are not static; disturbance and succession are common.

• Ecological succession: The process of change in species structure over time.

• Disturbance: Events (natural or anthropogenic) that disrupt ecosystem structure.

• Intermediate Disturbance Hypothesis: Species diversity is highest at intermediate levels of disturbance.

Biodiversity

Definition and Importance

Biodiversity is the variety of life on Earth at all its levels, from genes to ecosystems, and can encompass evolutionary, ecological, and cultural processes that sustain life.

• Biocultural diversity: Includes humans and human cultural diversity as a part of biodiversity.

• Importance:

  • Enhances stability and resilience of ecosystems

  • Promotes soil formation, nutrient cycling, and pollination

  • Maintains food chains and ecosystem services

Feeding Strategies and Resource Partitioning

• Feeding strategies: Predators, omnivores, parasites, herbivores

• Resource partitioning: Multiple species utilize similar resources but avoid competition by using them differently (e.g., different feeding times, locations, or methods)

Guilds and Niches

• Guild: Group of species from different taxonomic groups sharing ecological functions.

• Niche: The unique role an organism plays in its environment, including interactions and resource use.

Competitive Exclusion Principle (Gause's Principle)

Two species with identical niches cannot coexist indefinitely. Resource partitioning allows coexistence.

Example Table: Resource Partitioning in Birds

Species	Resource Use
Black-throated Green Warbler	Upper canopy
Cape May Warbler	Outer branches
Bay-breasted Warbler	Middle canopy
Additional info: Other warblers	Lower canopy

Coexistence Example: Burying Beetles

• Burying beetles avoid competition by using different sized hosts for reproduction.

• Resource partitioning in reproduction allows multiple species to coexist.

Synergy in Ecosystems

Synergy occurs when the effect of interacting forces is stronger than the sum of the forces acting independently.

• Example: Ladybugs and ground beetles together eat more aphids than either alone.

Earth's Biomes

Major Biomes

Biomes are large ecological areas on the Earth's surface, with fauna and flora adapting to their environment.

• Tropical rainforest

• Desert

• Temperate forest

• Taiga

• Grassland

• Tundra

• Marine

• Savanna

Additional info: Ecosystem Services

• Provisioning: Providing food, water, and resources

• Supporting: Nutrient cycles, soil formation

• Regulating: Climate regulation, disease control

• Cultural: Recreational, spiritual, and educational benefits

• All categories are likely to be impacted by climate change