Chapter 37 Communities and Ecosystems PPT

Introduction to Ecosystems

• Ecosystems provide essential services:

  • Purification of air and water

  • Decomposition of waste

  • Nutrient recycling

• Healthy ecosystems enhance human well-being:

  • Outdoor recreation

  • Understanding ecological relationships helps in resource management.

Community Structure and Dynamics

Definition of Community

• A community is an assemblage of populations of different species interacting in a particular area.

• Community ecology focuses on species composition and community dynamics.

Interspecific Interactions

Types of Interactions

• Interspecific interactions significantly impact community structure:

  • Competition: Limited resources lead to competition between different species.

  • Mutualism: Both species benefit from the interaction.

  • Predation: One species (predator) benefits at the expense of another (prey).

  • Herbivory: Animals consume plant parts (or algae).

  • Parasitism: One organism benefits while harming another.

Examples of Interspecific Interactions

• Squirrels and black bears competing for acorns.

• Mutualism example: Plants and mycorrhizae.

• Herbivory example: Caterpillars eating leaves.

• Parasitism example: Heartworms in dogs.

Competition and Ecological Niches

Ecological Niche

• Niche: The role an organism plays within its ecosystem, including biotic and abiotic resource use.

• Overlapping niches can lead to interspecific competition, reducing each population's carrying capacity.

Mutualism

Benefits and Relationships

• Example: Coral and dinoflagellates relationship:

  • Dinoflagellates provide energy through photosynthesis.

  • Corals offer shelter and nutrients in return.

• Coral bleaching occurs when stressed corals expel dinoflagellates, adversely affecting reefs.

Adaptations Due to Predation

Predator-Prey Dynamics

• Predation drives evolutionary adaptations in prey:

  • Camouflage: Hiding from predators.

  • Mechanical defenses: Thorns, spines.

  • Chemical defenses: Toxic substances.

Plant Adaptations Against Herbivory

• Plants evolve various defenses:

  • Structural defenses (thorns).

  • Chemical toxins that deter herbivores.

  • Coevolution between plants and herbivores illustrates adaptive strategies.

Parasites and Pathogens

• Parasites: Organisms living on or in a host, deriving nutrients from them.

  • Types include internal (e.g., nematodes) and external (e.g., ticks).

• Pathogens cause diseases, altering community composition (e.g., chestnut blight).

Trophic Structure and Dynamics

Definitions

• Trophic Structure: Feeding relationships in a community categorized into multiple levels:

  • Producers (autotrophs): Support all other levels.

  • Consumers (heterotrophs): Ranging from primary to quaternary consumers.

  • Detritivores and Decomposers: Break down dead material, recycling nutrients back into the ecosystem.

Food Chains and Food Webs

• Food Chains: Linear transfer of energy.

• Food Webs: More accurate representation of feeding relationships; interconnected food chains.

Species Diversity

Components of Diversity

• Species Richness: Total number of species in a community.

• Relative Abundance: Proportional representation of each species.

• Low species diversity is often seen in agricultural systems.

Keystone Species

• Keystone species prevent monopolization of resources, maintaining community diversity despite low biomass.

• Example: Sea stars in marine ecosystems.

Disturbance and Ecological Succession

Types of Disturbances

• Events like storms, floods, or human actions can reshape communities.

• Primary Succession: Occurs in lifeless areas (e.g., lava flows).

• Secondary Succession: Occurs in areas that retain soil post-disturbance (e.g., after a wildfire).

Invasive Species

• Invasive species: Introduced by human activities; can threaten native biodiversity.

Ecosystem Ecology

Key Concepts

• Ecosystems: Interaction of biotic and abiotic components.

• Energy Flow: Movement of energy through various levels.

• Chemical Cycling: Movement of matter within ecosystems versus food chain dynamics.

Primary Production

• Gross Primary Production: Total energy produced by photosynthesis.

• Net Primary Production: Energy available after producers' own respiration.

Biogeochemical Cycles

• Key cycles include carbon, phosphorus, and nitrogen cycles:

  • Carbon Cycle: Involves photosynthesis, respiration, and decomposition.

  • Phosphorus Cycle: Lacks a gaseous phase; depends on geological weathering.

  • Nitrogen Cycle: Involves nitrogen fixation via bacteria and is crucial for living organisms.

Human Impact on Ecosystems

• Overexploitation of agricultural resources threatens ecosystem health.

• Sustainability aims to balance current resource use with future generations' needs.