ecosystems and material cycles
Levels of Organisation
Individuals: A single organism capable of interbreeding within its species to produce fertile offspring.
Population: A group of individuals of the same species living together in a specific habitat at a given time (e.g., oak trees in a forest).
Community: All the different populations (plants, animals, microorganisms) interacting within a particular habitat (e.g., fish, frogs, insects in a pond).
Habitat: The natural environment where a particular species resides.
Ecosystem: A dynamic system of interacting biotic (community) and abiotic (non-living) components, characterized by food chains, nutrient cycling, and energy flow.
Abiotic and Biotic Factors Affecting Communities
Abiotic Factors: Non-living physical and chemical influences:
Light intensity: Essential for photosynthesis; high intensity increases plant growth and affects food webs.
Temperature: Affects metabolic rates and enzyme activity; influences species distribution due to adaptations.
Moisture levels: Crucial for all life; water availability limits growth and survival.
Soil pH and minerals: Influence availability of vital mineral ions for plants, affecting soil fertility and vegetation types.
Wind: Increases transpiration, causes physical damage, aids dispersal/pollination, and can limit tree growth.
\text{CO}_2 levels: Key for photosynthesis; higher levels can increase primary productivity.
Oxygen levels: Critical in aquatic and soil environments; low oxygen affects survival of aquatic life and microorganisms.
Biotic Factors: Living influences:
Food availability: Directly impacts carrying capacity; scarcity leads to competition and population decline.
New predators: Can drastically reduce prey populations with cascaded effects on food webs.
New pathogens: Cause widespread illness and mortality, impacting population size and health.
Competition: For limited resources (food, water, light, mates, space) between individuals of the same species (intraspecific) or different species (interspecific).
Interdependence
Organisms within an ecosystem are interconnected, relying on each other for food, shelter, and reproductive success.
Food Chains and Webs: Illustrate energy and nutrient flow; changes in one species significantly impact others and overall community structure.
Community stability: A balanced state where species populations fluctuate within a narrow range, indicating ecosystem resilience to disturbances.
Types of Relationships
Parasitism: One organism (parasite) benefits by living on or in another (host), causing harm but usually not immediate death (e.g., tapeworms).
Mutualism: A symbiotic relationship where both species directly benefit (e.g., bees pollinating flowers).
Commensalism: One species benefits, while the other is neither significantly harmed nor helped (e.g., barnacles on whales).
Fieldwork and Counting Organisms
Purpose: Ecologists study organism distribution, abundance, and interactions, including population estimation.
Quadrats: Square frames (e.g., 0.25 \text{m}^2 or 1 \text{m}^2 ) used for random sampling of non-motile organisms, recording individual counts or percentage cover.
Transects: Lines or belts used to observe changes in organism distribution across environmental gradients.
Random sampling: Ensures unbiased data collection by giving every area an equal chance of being sampled, allowing population estimates to be extrapolated.
Estimating population size: Calculated by scaling up average counts from sampled quadrats to the total area (e.g., 4 \text{ dandelions/m}^2 \times 100 \text{m}^2 = 400 \text{ dandelions} ).
Trophic Levels and Pyramids of Biomass
Trophic levels: Positions in a food chain:
Producers: Photosynthetic organisms (plants, algae).
Primary Consumers (Herbivores): Feed on producers.
Secondary Consumers (Carnivores/Omnivores): Feed on primary consumers.
Tertiary Consumers (Top Carnivores): Feed on secondary consumers.
Pyramids of Biomass: Graphical representation showing a significant decrease in the total mass of living organisms at each successively higher trophic level.
Energy Transfer: Only 10-20\% of biomass/energy is transferred between trophic levels; the rest is lost as heat (respiration), undigested food, or used for life processes.
Efficiency formula: Quantifies energy transfer: Efficiency = \frac{ \text{Biomass transferred to the next trophic level}}{ \text{Biomass available at the previous trophic level}} \times 100 .
Human Interactions with Ecosystems
Positive Impacts:
Habitat preservation: Establishing national parks and reserves to conserve environments.
Increasing awareness: Education on biodiversity and sustainable practices.
Reducing pollution: Stricter regulations, cleaner technologies, renewable energy, and effective waste management.
Negative Impacts:
Deforestation: Habitat loss, soil erosion, reduced \text{CO}_2 absorption, and biodiversity loss.
Pollution: Contamination by harmful substances (air pollution from emissions, water pollution from waste/pesticides, land pollution from landfills).
Introducing non-indigenous (alien) species: Can become invasive, outcompeting natives, disrupting food webs, and causing extinctions.
Maintaining Biodiversity
Biodiversity: The variety of life (genetic, species, ecosystem diversity), crucial for ecosystem stability.
Strategies:
Breeding programs: For endangered species to increase populations and preserve genetic diversity.
Protecting and regenerating habitats: Restoring degraded ecosystems and preventing destruction.
Reducing deforestation: Sustainable forestry and conservation efforts.
Recycling and reducing waste: Minimizes raw material need, energy consumption, and pollution.
Factors Affecting Levels of Food Security
Food Security: Reliable access to sufficient, affordable, nutritious food.
Influenced by:
Population growth: Increases demand on agricultural systems.
Changing diets: Shifts to meat/dairy products require more resources.
Pests and pathogens: Devastate harvests, leading to shortages.
Climate change: Causes extreme weather events, impacting agricultural productivity.
Conflicts: Disrupt food production, infrastructure, and distribution.
Cycling of Materials
Essential elements (carbon, water, nitrogen) are continuously recycled between biotic and abiotic components.
Carbon Cycle:
Photosynthesis: Removes \text{CO}_2 from the atmosphere.
Respiration: Releases \text{CO}_2 by living organisms.
Combustion: Burning fossil fuels and biomass releases large amounts of \text{CO}_2 .
Decomposition: Decomposers break down organic matter, releasing \text{CO}_2 and returning carbon to soil.
Water Cycle (Hydrological Cycle):
Evaporation: Water changes from liquid to vapor.
Transpiration: Evaporation from plant leaves.
Condensation: Water vapor cools to form clouds.
Precipitation: Water returns to Earth (rain, snow).
Runoff and Infiltration: Water flows over or into the ground.
Nitrogen Cycle (and Nitrates)
Nitrogen is vital for proteins and DNA; atmospheric \text{N}_2 is unreactive.
Nitrogen fixation: Conversion of \text{N}_2 to ammonia/ammonium by nitrogen-fixing bacteria (free or in legume root nodules) or lightning.
Nitrification: Ammonia/ammonium converted to nitrites and then nitrates ( \text{NO}_3^- ) by nitrifying bacteria.
Assimilation: Plants absorb nitrates to synthesize organic nitrogen compounds.
Decomposition/Ammonification: Decomposers release ammonia/ammonium from dead organisms and waste.
Denitrification: Denitrifying bacteria convert nitrates back to \text{N}_2 gas in anaerobic conditions.
Indicator Species and Assessing Pollution
Indicator species: Organisms reflecting environmental conditions or pollution levels due to their sensitivity.
Water pollution:
Clean water (high oxygen): Presence of stonefly larvae, mayfly nymphs, freshwater shrimps.
Polluted water (low oxygen): High numbers of bloodworms and rat-tailed maggots.
Air pollution ( \text{SO}_2 ):
Clean air: Variety of bushy and leafy lichens.
Polluted air: Only tolerant crusty lichens survive, or no lichens at all.
Factors Affecting Rate of Decomposition
Decomposition: Breakdown of dead organic matter by decomposers, recycling nutrients.
Influenced by:
Temperature: Optimal rates at 20^\circ \text{C} to 30^\circ \text{C} ; extremes inhibit activity.
Moisture: Required for metabolic processes of decomposers.
Oxygen availability: Most decomposers are aerobic; anaerobic conditions slow decomposition and produce different by-products (e.g., methane).
Decomposition: The process by which dead organic matter (dead plants, animals, waste products) is broken down by decomposers (bacteria, fungi, detritivores like worms) into simpler inorganic substances, recycling nutrients back into the ecosystem.
Influenced by:
Temperature: Decomposition rates are highest at optimal temperatures (warm but not too hot, typically between 20^ ext{o} ext{C} and 30^ ext{o} ext{C}) because decomposer enzymes work most efficiently within this range. Too cold, and microbial activity slows down; too hot, and enzymes denature.
Moisture: Decomposers require water for their metabolic processes. Moist conditions generally promote faster decomposition as water is needed for chemical reactions and to allow decomposers to move and excrete enzymes. Very dry conditions inhibit decomposition.
Oxygen availability: Most common decomposers (aerobic bacteria and fungi) require oxygen for respiration to break down organic matter efficiently. In anaerobic (oxygen-lacking) conditions (e.g., waterlogged soil, landfills), decomposition is much slower and produces different by-products (e.g., methane gas by anaerobic bacteria).