Ecology

The ecological pyramid illustrates energy transfer, trophic levels, and decreasing numbers within an ecosystem.

Ecological Pyramid

• Represents the flow of energy through trophic levels.

• Energy is lost as heat at each transfer (typically around 90% loss), following the 10% rule.

Trophic Levels

1. Producers (Autotrophs)

   • Base of the pyramid.

   • Examples: Plants, algae, phytoplankton.

   • Convert sunlight into energy through photosynthesis.

2. Primary Consumers (Herbivores)

   • Consume producers.

   • Examples: Grasshoppers, rabbits, zooplankton.

3. Secondary Consumers (Carnivores)

   • Consume primary consumers.

   • Examples: Snakes, frogs, small fish.

4. Tertiary Consumers (Top Carnivores)

   • Consume secondary consumers.

   • Examples: Hawks, lions, large fish.

Example of an Ecological Pyramid

• Imagine a grassland ecosystem:

  • Producers: Grasses $(\approx 10,000 \text{ kg})$

  • Primary Consumers: Grasshoppers $(\approx 1,000 \text{ kg})$

  • Secondary Consumers: Frogs $(\approx 100 \text{ kg})$

  • Tertiary Consumers: Snakes $(\approx 10 \text{ kg})$

• Notice the decreasing biomass at each level.

Biomass

Definitions

• Total mass of living organisms in a given area or volume.

• Usually decreases as you move up the trophic levels because energy is lost as heat, and organisms use energy for life processes.

• Measured in units like grams per square meter $\text{g/m}^2$ or kilograms per hectare $\text{kg/ha}$.

Density-Dependent and Density-Independent Factors

Density-Dependent Factors

• Factors that affect population growth based on the population's density.

1. Competition: Increased competition for resources (food, water, shelter) as population density rises.

2. Predation: Predators may focus on more abundant prey, increasing mortality in dense populations.

3. Disease: Spreads more easily in dense populations due to increased contact.

4. Parasitism: Parasites can transmit more efficiently in dense populations.

Density-Independent Factors

• Factors that affect population growth regardless of the population's density.

1. Natural Disasters: Floods, fires, hurricanes, and volcanic eruptions can reduce populations regardless of density.

2. Weather Conditions: Extreme temperatures, droughts, or severe storms can impact populations.

3. Human Activities: Habitat destruction, pollution, and pesticide use affect populations irrespective of their density.

• Population: A group of individuals of the same species living in the same area and interacting.

• Community: An assemblage of different populations of different species living and interacting in the same area.

Trophic Level

• The position an organism occupies in a food chain or ecological pyramid (e.g., producer, primary consumer, etc.).

Biomass Pyramid

Definitions

• A graphical representation of the biomass present in each trophic level of an ecosystem.

Example

• In a forest:

  • Producers (Trees): Have the highest biomass.

  • Primary Consumers (Insects): Have less biomass than the trees.

  • Secondary Consumers (Birds): Have even less biomass.

  • Tertiary Consumers (Hawks): Have the least biomass.

Niche

Definitions

• The role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. Includes all its interactions with the biotic and abiotic factors of its environment.

Biodiversity

Definitions

• The variety of life in a particular habitat or ecosystem.

Benefits of Biodiversity

• Ecosystem Stability: More diverse ecosystems are more resilient to disturbances.

• Resource Provision: Provides a variety of resources like food, medicine, and raw materials.

• Ecosystem Services: Pollination, water purification, climate regulation.

Intraspecific vs. Interspecific Interactions

• Intraspecific: Interactions between individuals of the same species.

  • Example: Competition for mates among male deer.

• Interspecific: Interactions between individuals of different species.

  • Example: Predation of rabbits by foxes.

Types of Symbiosis

1. Mutualism: Both species benefit. $(+,+)$

   • Example: Bees pollinating flowers.

2. Commensalism: One species benefits, and the other is neither harmed nor helped. $(+,0)$

   • Example: Barnacles attaching to whales.

3. Parasitism: One species benefits, and the other is harmed. $(+,-)$

   • Example: Ticks feeding on a dog.

Primary vs. Secondary Succession

• Primary Succession: Occurs in an environment where new substrate devoid of vegetation and other organisms usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited. Pioneer species need to create soil here from bare rock.

  • Pioneer Species: Lichens and mosses that break down rock to form soil.

• Secondary Succession: Occurs in an area that already has soil but has been disturbed (e.g., by fire, flood, or human activity). Soil is already present here so the pioneer species can be grass and small flowering plant.

  • Pioneer Species: Grasses and weeds.

Biogeochemical Cycling

Definitions

• The process in which elements and chemical compounds are transferred through biotic and abiotic components of an ecosystem.

Carbon Cycle

Definitions

• The process by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.

Key Processes in the Carbon Cycle

• Photosynthesis: Plants absorb carbon dioxide from the atmosphere.

• Respiration: Organisms release carbon dioxide into the atmosphere.

• Decomposition: Decomposers break down organic matter, releasing carbon into the soil and atmosphere.

• Combustion: Burning fossil fuels releases carbon dioxide into the atmosphere.

Factors Affecting Biogeochemical Cycles

• Water Cycle: Affected by deforestation, urbanization, and climate change (altering precipitation patterns).

• Carbon Cycle: Affected by burning fossil fuels, deforestation (reducing carbon sinks), and changes in land use.

• Nitrogen Cycle: Affected by synthetic fertilizers (leading to excess nitrogen runoff), industrial emissions, and agricultural practices.

• Phosphorus Cycle: Affected by mining for phosphate rocks (used in fertilizers) and runoff from agricultural fields and urban areas.

Carbon Cycle
Definitions

• The process by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth.

Key Processes in the Carbon Cycle

• Photosynthesis: Plants absorb carbon dioxide from the atmosphere.

• Assimilation: The incorporation of carbon into organic molecules by living organisms.

  • Example: Plants use carbon dioxide during photosynthesis to build sugars, which are then used to create more complex carbohydrates, proteins, and lipids.

• Respiration: Organisms release carbon dioxide into the atmosphere.

• Decomposition: Decomposers break down organic matter, releasing carbon into the soil and atmosphere.

• Combustion: Burning fossil fuels releases carbon dioxide into the atmosphere.

Two Ways Carbon Is Removed and Released into the Atmosphere:

• Removed: Photosynthesis removes carbon dioxide from the atmosphere as plants use it to grow. Additionally, carbon can be stored long-term in forests, oceans, and soil.

• Released: Carbon is released back into the atmosphere through natural processes such as respiration, decomposition, and volcanic eruptions, as well as through human activities like burning fossil fuels and deforestation.

Example of the Carbon Cycle

• Consider a forest ecosystem:

  • Photosynthesis: Trees absorb carbon dioxide from the atmosphere to produce glucose.

  • Consumption: Herbivores eat the plants, incorporating the carbon into their bodies.

  • Respiration: Both plants and animals release carbon dioxide back into the atmosphere through respiration.

  • Decomposition: When plants and animals die, decomposers break down their organic matter, releasing carbon back into the soil and atmosphere.

  • Combustion: Forest fires can rapidly release large amounts of stored carbon into the atmosphere.

Nitrogen is crucial for plant growth and is a key component of amino acids and nucleic acids.

Nitrogen Cycle

• The nitrogen cycle is a biogeochemical process that transforms nitrogen and its compounds.

Key Processes

1. Nitrogen Fixation:

   • Conversion of atmospheric nitrogen $(N<em>2)$ into ammonia $(NH</em>3)$. This process is essential because plants cannot use atmospheric nitrogen directly.

   • Biological Fixation: Carried out by certain bacteria (e.g., Rhizobium in legumes) and cyanobacteria. These bacteria have enzymes called nitrogenases that catalyze the conversion.

     • Equation: $N<em>2 + 8H^+ + 8e^- + 16ATP \rightarrow 2NH</em>3 + H_2 + 16ADP + 16Pi$

   • Abiotic Fixation: Occurs through lightning or industrial processes (Haber-Bosch process) to produce ammonia or nitrogen oxides.

2. Ammonification:

   • Decomposition of organic matter (e.g., dead plants and animals, waste) by decomposers (bacteria and fungi) into ammonia $(NH<em>3)$ or ammonium $(NH</em>4^+)$.

   • Ammonia is released into the environment, making the nitrogen available to other organisms.

3. Nitrification:

   • A two-step process where ammonia $(NH<em>3)$ is converted into nitrite $(NO</em>2^-)$, and then nitrite is further converted into nitrate $(NO_3^-)$.

   • Step 1: Ammonia is oxidized to nitrite by bacteria such as Nitrosomonas.

     • Equation: $2NH<em>3 + 3O</em>2 \rightarrow 2NO<em>2^- + 2H^+ + 2H</em>2O$

   • Step 2: Nitrite is oxidized to nitrate by bacteria such as Nitrobacter.

     • Equation: $2NO<em>2^- + O</em>2 \rightarrow 2NO_3^-$

   • Nitrate is the primary form of nitrogen absorbed by plants.

4. Denitrification:

   • Conversion of nitrate $(NO<em>3^-)$ back into atmospheric nitrogen gas $(N</em>2)$ or nitrous oxide $(N_2O)$. This process is carried out by denitrifying bacteria under anaerobic conditions (e.g., in waterlogged soils).

   • These bacteria use nitrate as an alternative electron acceptor instead of oxygen.

   • Equation: $2NO<em>3^- \rightarrow N</em>2 + O_2$

   • Denitrification reduces the availability of nitrogen in the soil but is a necessary step in the nitrogen cycle to balance nitrogen levels.

Key Nitrogen Compounds

• Ammonia $(NH_3)$: A toxic gas produced by nitrogen fixation and ammonification.

• Ammonium $(NH_4^+)$: The ionized form of ammonia, which can be used by plants.

• Nitrite $(NO_2^-)$: An intermediate product in nitrification, toxic at high concentrations.

• Nitrate $(NO_3^-)$: The primary form of nitrogen absorbed by plants, produced during nitrification.

• Nitrous Oxide $(N_2O)$: A greenhouse gas produced during denitrification.

• Atmospheric Nitrogen $(N_2)$: The most abundant form of nitrogen in the atmosphere, but unusable by most organisms until it is fixed.