Ecology: Principles and Laws

INTRODUCTION TO ECOLOGY, PRINCIPLES, AND LAWS

Ecology: Definition and Scope

• Ecology is the study of how organisms interact with each other and their environment.
• The term "ecology" was coined by German Biologist Hackle in 1869.
• The word is derived from the Greek words "Oikos" (house or environment) and "Logos" (to study).
• Ecology examines the interdependence of life, where all living things on Earth are connected and affect each other.
• Changes in organisms (evolution, movement) influence their environment and other living beings.

Applications of Ecology

• Ecology has applications in various fields:
  • Environmental Science
  • Conservation
  • Natural History
  • Agriculture, Forestry, and Resource Management
  • Food Science
  • Human Demography
  • Epidemiology of Human Disease
  • Public Health Science

The Scientific Method in Ecology

• Ecologists use the scientific method:
  1. Make observations.
  2. Formulate hypotheses.
  3. Test hypotheses through experiments and statistical analysis.
  4. Use theory to test hypotheses and make predictions.

Ecological Modeling: HIV Dynamics Example

• Models are used to understand ecological phenomena.
• Example: Modeling HIV transmission
  • Goal: Understand the transmission rate of the virus.
  • Variables: Number of uninfected people, number of infected people with the virus, number of people with the virus and AIDS.
  • Simple models indicate that the virus would go extinct with fewer contacts between infected and uninfected individuals.
  • Rate of spread depends upon sexual contacts, intravenous drug use, blood transfusions, birth rate, etc.

Examples of Ecological Questions

• How do humans affect the atmosphere and contribute to global warming?
• How does the population of wolves affect the population of rabbits?
• Do clownfish and anemones benefit each other?

Levels of Environmental Organization

1. Organism/Species: A single organism (lowest level).
2. Population: A group of individuals of the same species living in the same area that can produce fertile offspring.
3. Community: A group of all the populations living in a defined area (e.g., fish, plants, animals, and microorganisms in a stream).
4. Ecosystem: All the organisms in a particular place together with their nonliving environment. Studies biotic and abiotic factors.
5. Biosphere: The combined parts of the planet where all life exists, including land, water, and air.

Types of Species within Communities

• Native species: Species that normally live and thrive in a particular community.
• Nonnative/Invasive species:
  • Also known as exotic species or aliens.
  • Not native to the area/habitat.
  • Can reduce biodiversity.
• Indicator species:
  • Species that respond quickly to environmental changes.
  • Examples: Birds indicate tropical forest destruction, trout indicate pollutants in water, amphibians are classic indicators.
• Keystone Species:
  • A species whose presence significantly influences the structure of a community.
  • Roles: pollination, seed dispersion, habitat modification, predation, efficient recycling of animal waste.
  • Examples: Purple sea star, gray wolves, elephants, mangrove trees, beavers, sharks, saguaro cactus, grizzly bears, sea otters.
  • Umbrella Species: Their influence is tied to geographic range (e.g., Siberian Tiger).
  • Foundation Species: Species that create or maintain a habitat (e.g., corals).
• Indicator Species: Species that indicate changes in the ecosystem (e.g, oyster, bees).

r & K Selected Species

$r$ and $K$ refer to parameters in the logistic growth equation.

• Examples:
  • Oysters: r-strategy, produce 500,000,000 eggs/year, no parental care.
  • Great apes: K-strategy, produce 1 infant every 5-6 years, extensive parental care.

Biotic vs. Abiotic Factors

• Biotic factors: All living things (e.g., bacteria, archea, animals, protists, plants, fungi).
• Abiotic factors: Nonliving things (e.g., water, light, air, minerals, soil, temperature).

Ecosystem Characteristics

1. Energy Flow: Constant flow of energy into the ecosystem; primary source is sunlight.
2. Cycling of Matter: Cycle of materials between living organisms and the environment.

Biomes

• Biome: A large area of Earth with the same climate and similar vegetation.
• Grasslands are predicted by rainfall and temperature.
• Boundaries grade into the next biome.
• Biomes describe terrestrial systems.
• Aquatic and wetland ecosystems are determined by depth, salinity, and permanence of water.
• Biosphere: One huge system formed by all living things.
• Examples of Biomes: Tropical Rainforest, Savanna, Desert, Marine, Taiga, Chaparral, Tundra, Temperate Rainforest, Freshwater.

Ecological Approach/Perspectives

• Organism Approach:
  • Focuses on adaptations that suit the organism for life in its environment.
  • Adaptations result from evolutionary change by natural selection.
• Population Approach:
  • Studies factors affecting the abundance of species (birth, death, immigration, emigration).
  • Influenced by evolutionary processes.
  • Studies factors that increase or decrease species population size.
  • Key areas: population growth factors and limitations.
• Community Approach:
  • How are communities structured from their component populations?
  • Population interactions, promoting and limiting coexistence.
  • Feeding relationships, fluxes of energy and materials.
• Ecosystem Approach:
  • Focus on energy flow and nutrient cycling with the physical environment and among biotics.
  • Studies physical processes (weather, climate changes).
• Biosphere Approach:
  • Studies global movements of air and water.
  • Formation and significance of ocean currents and winds.
  • Global climate patterns and changes and global productivity of ecosystems.

Ecosystem Components

• Niches
• Habitats
• Competitive Exclusion Principle

The Niches

• Niche: Organism’s occupation (role), where it lives, and how it uses the conditions they exist in.

• Function of an organism in its community: habitat requirements, energy cycling (consumer, decomposer, producer), water, space, structure.

• Fundamental Niche: Everything an organism could possibly do in a competitor-free environment.

• Realized Niche: Everything an organism does after competition limits them.

Niche Based on Kingdoms

• How organisms obtain food, mates, and protection from predators.
  • PLANTS: Producers or autotrophs.
  • ANIMALS: Heterotrophs; consumers.
  • FUNGUS: Decomposers; nutrient recyclers.
  • PROTISTS: Photosynthesizers, grazers, predators, decomposers.
  • BACTERIA: Decomposers; producers.
  • ARCHAEBACTERIA: Primarily autotrophs.

Niche Differences

• Generalists:
  • Organisms with a broad niche.
  • Eat many types of food.
  • Live in many types of environments (e.g., house mice).
• Specialists:
  • Organisms with a narrow niche.
  • Eat a narrow range of food items.
  • Live in few, specific types of habitats (e.g., panda bear).

The Habitat

• Physical environment to which an organism has become adapted and survives in.
• Habitat concept is useful in identifying/classifying habitats (e.g., aquatic vs. terrestrial, marine vs. freshwater, oceanic vs. estuarine, benthic vs. pelagic).

Laws & Principles of Ecology

1. Competitive Exclusion Principle

   • Two different species cannot occupy the same niche in the same geographic area.
     *Resource Partitioning is a way different species of warblers reduce the competition among themselves by feeding at different levels and on different parts of trees.
     *Character displacement

2. Law of Backlash

   • To every action, there is a reaction (e.g., global warming).

3. Law of Interrelatedness

   • Everything in the environment is connected or interrelated with some other factor.

4. Law of Chemical Non-Interference

   • No chemical produced or discharged should interfere with natural processes in the environment.

5. Law of Carrying Capacity

   • No population grows indefinitely; the ecosystem has limited space.

6. Law of Limits

   • Natural systems can take stress but only so much.