Chapter 29: Energy Flow and Nutrient Cycling in Ecosystems

Introduction

• Overview of nutrients and energy in ecosystems.
• Focus on biotic (living) and abiotic (non-living) components of environments.
  • Biotic: Living organisms.
  • Abiotic: Climate, light, temperature, water, minerals.

Nutrient Cycling vs. Energy Flow

• Nutrient Cycling:
  • Nutrients cycle within and between ecosystems.
  • Illustrated by purple arrows in diagrams.
• Energy Flow:
  • Flows in one direction through ecosystems, starting from the Sun.
  • Main source of energy is sunlight, used primarily for photosynthesis by plants.

Trophic Levels and Energy Transfer

• Trophic Levels:
  • Producers (autotrophs) like green plants are at the base.
  • Consumers (heterotrophs) rely on others for energy.
  • Primary consumers eat producers; secondary and tertiary consumers follow.
• Net Primary Production:
  • Amount of energy captured by producers; varies by ecosystem (e.g., grassland vs. rainforest).
  • Biomass as a measure of stored energy.
• Energy Pyramid:
  • Visualizes decreasing energy as it moves up trophic levels.
  • 10% Law: Only 10% of energy is transferred to the next trophic level.

Food Chains and Food Webs

• Food Chains:
  • Describe feeding relationships; e.g., plants > caterpillars > birds in terrestrial ecosystems.
  • Phytoplankton > zooplankton > higher consumers in aquatic ecosystems.
• Food Webs:
  • Show interconnected food chains within a community.

Special Organisms

• Omnivores:
  • Eat both plants and animals, acting as primary, secondary, or tertiary consumers.
• Detritivores and Decomposers:
  • Detritivores like dung beetles recycle materials.
  • Decomposers (fungi, bacteria) break down organic material.

Inefficiency of Energy Transfer

• Energy transfer between levels is inefficient.
• Biological Magnification:
  • Concentration of substances as they move up the food chain (e.g., mercury in marine ecosystems).

Nutrient Cycles

• Water Cycle:
  • Movement from oceans to atmosphere to lakes/rivers/groundwater and back.
• Carbon Cycle:
  • Carbon moves from atmosphere/oceans through plants and animals, then back.
  • Basis for all organic molecules.
• Nitrogen Cycle:
  • Main reservoir in atmosphere; crucial for proteins and nucleic acids.
• Phosphorus Cycle:
  • Reservoir in rock; important for biological molecules and skeletal structure.

Human Impact on Nutrient Cycles

• Historical Impact:
  • Limited by small populations and technology.
• Modern Impact:
  • Fossil fuels and fertilizers disrupt nitrogen, phosphorus, sulfur, and carbon cycles.
  • Dead zones from fertilizer runoff (e.g., Gulf of Mexico).
  • Seaweed blooms from nutrient runoff.
• Acid Rain:
  • Results from sulfur/nitrogen cycles; impacts forests and materials.
• Greenhouse Effect:
  • Energy balance maintained by equal incoming and outgoing energy.
  • Greenhouse gases trap heat, contributing to global warming.

Climate Change

• Consequences of warming atmosphere:
  • Severe storms, changing precipitation patterns, droughts.
  • Ocean acidification, melting ice, affecting species like polar bears.

This summary captures the key topics and insights from the preview video of Chapter 29, providing a comprehensive overview of how energy flows and nutrients cycle within ecosystems, and the impact of human activities on these processes.