Ecology & Environmental Science Lecture Review

Concepts and Energy Flow in Ecological Systems

• Ecosystem Definition: A community of living organisms interacting with their abiotic (non-living) environment.
• Habitat vs. Niche:     - Habitat: Referred to as the "address" or the specific location where an organism lives.     - Niche: Referred to as the "profession"; it encompasses the organism's role, trophic level, and specific interactions within the ecosystem.
• Competitive Exclusion Principle: This principle states that no two species can occupy the exact same niche indefinitely. Eventually, one species will outcompete the other.
• Questions & Discussion: Energy Flow:     - Question: Explain why biomass decreases at higher trophic levels.     - Response (Model Answer): Energy transfer between trophic levels is inefficient, operating at approximately $10\%$ efficiency. Energy is lost at each stage due to:         1. Respiration: Loss of energy as heat.         2. Movement and Metabolic Processes: Energy consumed for the organism's physical activity and internal functions.         3. Excretion and Inedible Parts: Energy lost through waste (excretion) and parts that cannot be consumed or digested, such as bones and fur.     - Conclusion: Consequently, fewer organisms (lower biomass) can be supported at the top of the food chain.

Biogeochemical Cycles

• General Principle: Unlike energy, which flows through an system, nutrients recycle within an ecosystem.
• The Carbon Cycle:     - Drivers: Powered by photosynthesis, which removes $CO_2$ from the atmosphere, and respiration/combustion, which adds $CO_2$ back to the atmosphere.     - Anthropogenic Impact: The burning of fossil fuels disrupts the natural balance of the carbon cycle.
• The Nitrogen Cycle:     - Nitrogen Fixation: The process where bacteria, specifically Rhizobium, convert atmospheric nitrogen ($N_2$) gas into Ammonia.     - Nitrification: The two-step process of converting Ammonia into Nitrites and then into Nitrates, which are the form usable by plants.     - Denitrification: The process where bacteria convert Nitrates back into $N_2$ gas.
• Questions & Discussion: Decomposers:     - Question: Describe the role of decomposers in the nitrogen cycle.     - Response (Model Answer): Decomposers, such as bacteria and fungi, perform a process called ammonification. They break down proteins and urea from dead organisms and waste products. This process converts organic nitrogen back into ammonium ions ($NH_4^+$), which makes the nitrogen available again for nitrifying bacteria to continue the cycle.

Biological Interactions and Symbiosis

• Mutualism ($+/+$): An interaction where both species benefit.     - Example 1: Lichens: A partnership between Algae (which provides food via photosynthesis) and Fungus (which provides structure and moisture).     - Example 2: Rhizobium: Bacteria receive sugar from the plant, while the Legumes receive fixed nitrogen.
• Parasitism ($+/-$): An interaction where one species (the parasite) benefits and the other (the host) is harmed.     - Ectoparasites: Organisms that live on the outside of the host, such as Ticks and Fleas.     - Endoparasites: Organisms that live inside the host's body, such as Tapeworms in the gut.
• Commensalism ($+/0$): An interaction where one species benefits while the other is unaffected.     - Example: Cattle Egrets and Livestock: As livestock (cows) walk, they stir up insects in the grass. The birds eat these insects. The cows are indifferent to the birds' presence.
• Ammensalism ($-/0$): An interaction where one species is harmed and the other is unaffected. This often involved chemical inhibition.     - Classic Example: Penicillium mold: This mold secretes penicillin, an antibiotic that kills nearby bacteria. While the bacteria are harmed, the mold gains no direct immediate benefit from their death, other than perhaps long-term space.     - Allelopathy: Black Walnut trees secrete a substance called juglone into the soil, which inhibits the growth of other plants in their vicinity.
• Synergism / Protocooperation ($+/+$): An interaction where both species benefit, but the association is not obligatory for survival.     - Example: Methanogenic ecosystems: One species of bacteria produces $H_2$, which a second species consumes to produce methane. They grow faster together than apart but can survive separately.     - Comparison: In obligate mutualism, the link is essential for survival; in synergism, the interaction is considered "helpful" or catalytic.

Habitats and Ecosystem Types

• Terrestrial Habitats (Land-based):     - Forests: Includes Tropical Rainforests (characterized by high biodiversity), Deciduous forests, and Coniferous forests (also known as Taiga).     - Grasslands: Includes Savanna (noted for scattered trees) and Temperate Grasslands.     - Deserts: Defined by low precipitation; examples include Hot deserts (Sahara) and Cold deserts (Gobi).     - Arboreal: Habitats located in tree canopies, utilized by organisms such as monkeys and epiphytes.
• Aquatic Habitats (Water-based):     - Freshwater:         - Lentic: Still water environments like ponds and lakes.         - Lotic: Flowing water environments like rivers and streams.     - Marine (Saltwater):         - Pelagic Zone: The open ocean.         - Benthic Zone: The ocean floor.         - Intertidal Zone: The shoreline, characterized by harsh, fluctuating conditions.     - Estuarine: Brackish water where rivers meet the sea; these areas often serve as nurseries for fish.

Ecological Field Equipment and Methodology

• Quadrat:     - Description: A square frame, commonly $1\,m^2$.     - Use: Defines a sample area to count density or percentage cover.     - Target Organisms: Plants and slow-moving animals like snails.
• Transect Line:     - Description: A tape measure laid across a habitat.     - Use: Used to study changes in species distribution across an environmental gradient (zonation).     - Target Organisms: Plants across a shoreline or a woodland edge.
• Sweep Net:     - Description: A net swept through vegetation.     - Use: Dislodges and catches insects in long grass.     - Target Organisms: Flying insects, beetles, and bugs.
• Pooter:     - Description: A suction device with two tubes.     - Use: Safely collects small insects into a jar without crushing them.     - Target Organisms: Small insects like ants and aphids.
• Secchi Disk:     - Description: A black and white disk.     - Use: Lowered into water to measure turbidity or water clarity.     - Target Organisms: Used in water quality studies to assess algae or silt levels.

Population Study: Capture-Mark-Recapture

• Application: Used for mobile animals such as fish or beetles.
• Methodological Steps:     1. Capture an initial sample ($n_1$).     2. Mark the organisms harmlessly (using paint or tags).     3. Release them and allow sufficient time for the marked individuals to mix with the population.     4. Capture a second sample ($n_2$).     5. Count how many individuals in the second sample are marked ($m_2$).
• The Lincoln Index Formula:     - $N = \frac{n_1 \times n_2}{m_2}$     - Where $N$ is the Total Population Estimate.
• Calculation Example:     - Scenario: 40 voles are caught, marked, and released. One week later, 50 voles are caught, and 10 of them have marks.     - Variables: $n_1 = 40$, $n_2 = 50$, $m_2 = 10$.     - Math: $N = \frac{40 \times 50}{10} = \frac{2000}{10} = 200$.     - Answer: The estimated population is $200$ voles.
• Assumptions: The study assumes there are no births, deaths, or migration during the period of the study.

Natural Selection and Climate change

• Ecological Drivers: Ecology provides the pressure for Natural Selection.
• Adaptation to Niche: Species evolve specific traits to fit their abiotic and biotic environments.
• Predator-Prey Co-evolution: Described as an "arms race." For example, as Gazelles evolve to be faster, Cheetahs evolve to be faster in response.
• Camouflage and Directional Selection: The Peppered Moth is the primary example. During the Industrial Revolution, soot darkened tree trunks. Dark-colored moths survived predation better than light-colored moths, leading to a population shift.
• Environmental Impacts:     - Coral Bleaching: Rising ocean temperatures stress coral polyps, causing them to expel their symbiotic algae (zooxanthellae). These algae provide the coral with food and color. Without them, the coral turns white and may die, leading to a significant reduction in biodiversity.     - Polar Habitats: Melting sea ice reduces hunting grounds for Polar Bears, who hunt seals from the ice. Bears must swim further, expending more energy, which leads to starvation and lower reproduction rates.     - Ocean Acidification: Oceans absorb excess atmospheric $CO_2$, forming carbonic acid ($H_2CO_3$) and causing the pH to drop. This prevents shell-forming organisms like oysters and plankton from forming calcium carbonate shells effectively, disrupting the base of the food web.

Exam Methodology Review

• "Describe how you would…" Questions: When answering, always list the specific equipment, the sampling method (random vs. systematic), the sample size/number of repeats, and any relevant safety considerations.
• "Explain the relationship…" Questions: Use technical terms such as "Interdependence" or "Symbiosis." Be specific about who benefits (using $+/+$ or $+/-$ notation).
• "Calculate…" Questions: Always show your working. For population studies, write the Lincoln Index formula first. For energy efficiency, use the following calculation:     - $\text{Efficiency} = (\frac{\text{Energy After}}{\text{Energy Before}}) \times 100$