Ecology notes IB Bio

Science Literacy, Critical Thinking, and Societal Trends

• Definition and Role of Science:

  • Science represents far more than a simple body of static knowledge; it is fundamentally a systematic way of critical thinking.

  • Sustained progress and democratic governance depend heavily on public scientific literacy and critical evaluation of evidence.

• Carl Sagan's 1996 Warning on Societal Decline:

  • Foretold a future United States transitioning into a service and information economy where major manufacturing industries have migrated abroad.

  • Warned of concentration of immense technological power in the hands of a very few, while public representatives lack the technical capacity to grasp the underlying issues.

  • Highlighted the risk of citizens losing the ability to set their own societal agendas or knowledgeably question authority.

  • Described a societal slide back into superstition and darkness characterized by clutching crystals, nervously consulting horoscopes, and declining critical faculties that can no longer distinguish between what feels good and what is true.

  • Identified the "dumbing down of America" through the decay of substantive content in influential media, exemplified by 30-second sound bites shortening to 10 seconds or less, lowest-common-denominator programming, and credulous presentations of pseudoscience.

  • Noted that contemporary media trends celebrate ignorance, conveying the lesson that study and learning—in science or any domain—are avoidable or undesirable.

  • Specific cultural indicators referenced from 1996 include the film Dumb and Dumber being the number one videocassette rental in America and the widespread popularity of Beavis and Butt-Head among young viewers.

• Viral RNA Mutation Cases:

  • Specific point mutations in the original coronavirus RNA genome led directly to major variants:

    • Alpha Variant: Mutation converted the original amino acid Proline to Histidine.

    • Delta Variant: Mutation converted the original amino acid Proline to Arginine.

• Organismal World Record Quantitative Fact:

  • The world record pumpkin weight is recorded at $2,624.6\,\text{lbs}$ (documented by N.E.G.P.S. / E.G.).

Ecological Principles, Modes of Nutrition, and Nutrient Cycling

• Fundamental Definitions in Ecology:

  • Ecology: The scientific study of the interactions between organisms and their abiotic and biotic environments.

  • Community: A group formed by populations of different species living together and interacting with each other in a shared location.

  • Ecosystem: A dynamic system formed by the interactions of a biological community with its surrounding abiotic environment.

• Nutritional Modes of Organisms:

  • Autotrophs: Primary producers that synthesize organic molecules from inorganic substances obtained from the abiotic environment.

    • Photoautotrophs: Convert solar radiation into chemical energy in carbon compounds via photosynthesis (e.g., plants, algae, cyanobacteria).

    • Chemoautotrophs: Convert chemical energy from inorganic molecules into organic compounds (strictly prokaryotic organisms, such as those found in deep-sea hydrothermal vents).

  • Heterotrophs: Organisms that obtain organic molecules from other organisms.

  • Mixotrophs: Rare species that combine both autotrophic and heterotrophic modes of nutrition.

  • Consumers: Heterotrophs that ingest living or recently killed organisms to obtain organic nutrients.

  • Detritivores: Heterotrophs that obtain organic nutrients from detritus (dead organic debris) via internal digestion (e.g., earthworms).

  • Saprotrophs: Heterotrophs that obtain organic nutrients from dead organisms via external digestion by secreting digestive enzymes into the environment and absorbing the soluble breakdown products (e.g., fungi and decomposer prokaryotes).

• Energy Flow vs. Inorganic Nutrient Cycling:

  • Energy Flow: Ecosystems require a continuous, infinite incoming supply of energy (predominantly sunlight). Energy enters, flows through trophic levels, is converted to heat via cellular respiration, and eventually dissipates out of the ecosystem. Organisms cannot recycle heat energy back into chemical energy.

  • Nutrient Cycling: The supply of inorganic nutrients (e.g., carbon, nitrogen, phosphorus) within ecosystems is finite and limited. Nutrients must be endlessly cycled between living organisms and the abiotic environment.

  • Sustainability: Ecosystems possess the potential to remain sustainable over extremely long periods provided nutrient cycling pathways remain unbroken and solar energy inputs continue.

Abiotic and Biotic Drivers of Species Distribution

• Overview of Distribution Determinants:

  • The geographic distribution and local abundance of organisms are dictated by interaction limits set by both biotic and abiotic environmental factors.

• Biotic Factors:

  • Includes living components such as competitors, prey availability, predators, parasites, and pathogens.

  • Predation: Limits prey distribution and population density. Predator removal experiments explicitly show how top predators restrict prey populations and alter community structure. Time lags occur naturally between prey population changes and corresponding predator population responses.

• Abiotic Factors:

  • Includes non-living physical and chemical variables: temperature, water salinity/availability, sunlight, wind, soil pH, and mineral nutrient availability.

  • Water: Organisms exhibit strict physiological limits for freshwater versus saltwater environments, as well as total moisture availability.

  • Sunlight: Serves as the primary energy input for primary productivity. Sunlight intensity, wavelength quality, and photoperiod (day length) govern organismal development, behavior, and seasonal cycles.

• Thermal Physiology and the $Q_{10}$ Effect:

  • Most biochemical and physiological metabolic processes are extremely sensitive to thermal changes.

  • $Q_{10}$ Temperature Coefficient: The factor by which a chemical or enzymatic reaction rate increases for every $10\,^\circ\text{C}$ increase in body temperature, provided temperatures do not exceed structural stability limits.

    • Formula/Relationship: The reaction rate typically increases by a factor of $2\text{ to }3$ per $10\,^\circ\text{C}$ rise until heat denatures the proteins.

    • Calculation Example: If the rate of glycogen hydrolysis in a frog is $2.5\,\text{times}$ greater at $30\,^\circ\text{C}$ than at $20\,^\circ\text{C}$, the $Q_{10}$ value for that specific reaction is exactly $2.5$

    • Low Temperature Effects: Exposure to cold slows down molecular movement and metabolic reaction rates, but cold temperatures do not denature enzymes.

• Mammalian Thermoregulation and Homeostasis:

  • Thermoregulation is governed by complex negative feedback systems to maintain physiological stability.

  • Hypothalamus: Located in the brain, a specialized cluster of neurons functions as the body's internal thermostat. It senses deviations in blood temperature relative to a set point and activates physiological heat-loss (e.g., sweating, vasodilation) or heat-gain (e.g., shivering, vasoconstriction) mechanisms.

  • Thyroxin: A hormone secreted by the thyroid gland that acts directly to regulate basal metabolic rate and support thermal homeostasis.

• Ectothermic Adaptations to Extreme Cold:

  • Certain ectotherms living in subzero environments produce chemical cryoprotectants ("antifreeze" compounds).

  • Cryoprotectants lower the freezing point of cellular fluids and prevent destructive ice crystal formation inside cells.

  • Allows overwintering frogs, terrestrial arthropods (and their eggs), and specialized Arctic and Antarctic fishes to survive body temperatures significantly below $0\,^\circ\text{C}$.

Community Interactions, Trophic Networks, and Regulatory Cascades

• Interspecific Relationships and Coevolution:

  • Interspecific Interactions: Ecological relationships occurring between individuals of different species within a community.

  • Coevolution: Reciprocal evolutionary changes occurring between two interacting species where each exerts powerful selective pressure on the other.

    • Predator-Prey Examples: Mutual evolutionary selection for speed between cheetahs and antelopes.

    • Mutualistic Examples: Specialized physical adaptations evolving concurrently between flowering plants and their specific animal pollinators.

• Trophic Structure and Energy Loss:

  • Trophic structure describes the feeding hierarchy and pathways of energy transfer within a community.

  • Food Chain: Linear pathway transferring chemical energy from primary producers through herbivores (primary consumers) to carnivores (secondary/tertiary consumers).

  • Chain Length Constraints: Food chains are generally limited to $4\text{ or }5$ trophic links. This limitation is directly caused by severe energy losses between trophic steps, leaving insufficient energy to support viable populations of higher-level carnivores.

• Community Regulation: Bottom-Up vs. Top-Down Control:

  • Dominant Species: Species possessing the highest total biomass (the cumulative weight of all individuals in a population) or highest overall abundance in a community. Typically primary producers. Removal of a dominant species causes systemic restructuring from the bottom up.

  • Keystone Species: Species that exert exceptionally strong regulatory control over community structure and species diversity disproportionate to their actual abundance or total biomass.

• Classic Keystone Case Studies:

  • Pisaster Starfish Experiments (Robert Paine):

    • Conducted in rocky intertidal zones in Washington state.

    • Removal of the predatory starfish Pisaster resulted in competitive monopolization of space by mussels, leading to local competitive exclusion and dramatic loss of overall community biodiversity.

    • Demonstrated that top predator keystone species maintain ecological balance via natural homeostatic feedback mechanisms.

  • Wolves in Yellowstone National Park:

    • Reintroduction of wolves initiated a widespread trophic cascade.

    • By preying on and altering the grazing habits of elk, vegetation (willows, aspens) recovered along riverbanks.

    • Revegetation stabilized soil, reduced erosion, altered the physical flow of rivers, and restored habitat for songbirds, beavers, and aquatic organisms.

Ecosystem Energetics and Trophic Efficiency

• Thermodynamics in Ecosystems:

  • First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed. Solar radiation entering the biosphere can be quantitatively tracked through biological conversions until released as heat.

  • Second Law of Thermodynamics: Energy transformations increase entropy and are inefficient. Energy converted to heat during cellular respiration cannot be reused or converted back into chemical energy by living organisms and is permanently lost from the ecosystem to space.

• Primary vs. Secondary Productivity:

  • Primary Productivity: The rate at which light energy or inorganic chemical energy is converted into organic compounds by autotrophs. Primarily limited by light availability, water, and temperature.

  • Secondary Production: The rate at which consumer organisms convert chemical energy from consumed food into their own new biological biomass over a given time frame.

  • Efficiency: Biological energy transfer into secondary production is generally inefficient compared to primary production processes.

• The 10% Trophic Efficiency Rule:

  • On average, approximately $10\%$ of the chemical energy stored at one trophic level is converted into biological biomass at the next trophic level.

  • The remaining $90\%$ of incoming energy is lost through cellular respiration (heat loss), unabsorbed organic waste (feces), and metabolic maintenance.

  • Human Agricultural Implications: Eating lower on the food chain (directly consuming primary producers) maximizes trophic energy conversion, drastically increasing the efficiency of global food production to alleviate human hunger.

• Constructing Ecological Pyramids:

  • Pyramids of Energy: Must be drawn to scale and presented as stepped bars (never smooth triangles). Correct standard terms must be used: producer, first consumer, second consumer (rather than vague numerical trophic levels).

  • Pyramids of Biomass: Represent total dry weight of living organisms at each level. Biomass in terrestrial systems diminishes along food chains due to carbon loss via $CO_2$, water, and metabolic excreta such as urea.

  • Pyramids of Numbers: Graphic representation of the exact number of individual organisms present at each distinct trophic level.

Ecotoxicology: Biological Magnification

• Mechanisms of Biomagnification:

  • Occurs when non-biodegradable, fat-soluble toxic compounds are ingested by organisms within an ecosystem.

  • Because these substances cannot be metabolized or excreted, they accumulate within the fatty tissues of animals (bioaccumulation).

  • While usable biomass and energy decrease exponentially up successive trophic levels, fat-soluble toxins become progressively concentrated at higher trophic levels.

• Quantitative Case Study: DDT Trophic Concentration:

  • The historical application of the synthetic pesticide DDT demonstrated extreme biological magnification across trophic levels:

    • DDT in Water: $0.000003\,\text{ppm}$

    • DDT in Zooplankton: $0.04\,\text{ppm}$

    • DDT in Small Fish: $0.5\,\text{ppm}$

    • DDT in Large Fish: $2\,\text{ppm}$

    • DDT in Fish-Eating Birds (Apex Predators): $25\,\text{ppm}$

  • Magnification Factor: Represents a $10,000,000\,\text{times}$ ($10\,\text{million}\text{ times}$) increase in toxin concentration from the abiotic water background to top avian predators, leading to eggshell thinning and population crashes.

Biogeochemical Cycles and Human Perturbations

• Biogeochemical Reservoir Model:

  • Chemical elements cycle through four major environmental reservoirs defined by organic/inorganic composition and direct biological accessibility:

    • Organic Available: Living organisms and detritus. Moves to inorganic reservoirs via respiration, decomposition, and excretion; converted to organic unavailable via fossilization. Assimilation and photosynthesis pull inorganic materials back into this pool.

    • Organic Unavailable: Peat, coal, and oil reserves. Converted to inorganic available nutrients through weathering, erosion, and fossil fuel combustion.

    • Inorganic Available: Atmosphere, soil, and water reservoirs. Accessible via photosynthetic and nutrient uptake pathways. Moves to unavailable inorganic pools via sedimentary rock formation.

    • Inorganic Unavailable: Minerals locked inside solid rock formations. Made available over geological timescales via weathering and erosion.

• The Carbon Cycle:

  • Autotrophs fix atmospheric or aquatic carbon dioxide into carbohydrates and carbon compounds.

  • In aquatic ecosystems, carbon exists as dissolved $CO_2$ and hydrogen carbonate ions ($HCO_3^-$).

  • $CO_2$ diffuses into autotrophs from water or air and diffuses out during cellular respiration.

  • Peat Formation: Formed when dead organic matter is prevented from fully decomposing due to acidic and/or anaerobic conditions in water-logged soils.

  • Fossil Fuel Formation: Partially decomposed organic matter from past geological eras compressed in porous rocks converted into coal, crude oil, or natural gas.

  • Limestone Formation: Marine organisms (e.g., reef-building corals, mollusks) construct hard skeletal structures out of calcium carbonate ($CaCO_3$), which fossilize over time into limestone rock.

  • Combustion: Burning fossil fuels and biomass rapidly oxidizes carbon back into atmospheric $CO_2$

• Human Alteration of Nitrogen Cycles:

  • Human activities—primarily industrial fertilizer manufacturing, expanded legume agriculture, and fossil fuel burning—have doubled global rates of fixed nitrogen.

  • Excess nitrogen oxides ($NO_x$) pollute the atmosphere, contributing to atmospheric warming, stratospheric ozone depletion, and acid rain.

  • Agricultural Biotechnology Innovation (UC Davis, 2022): Researchers utilized CRISPR gene editing to modify rice so that plants emit biochemical signal molecules that upregulate bacterial nitrogen fixation in the rhizosphere, allowing plants to self-fertilize and eliminate synthetic fertilizer inputs.

Atmospheric Physics, Climate Change, and Ozone Dynamics

• Greenhouse Effect Dynamics:

  • Primary Greenhouse Gases: Carbon dioxide ($CO_2$) and water vapor ($H_2O$) exert the largest warming effect.

  • Secondary Greenhouse Gases: Methane ($CH_4$) and nitrogen oxides ($NO_x$) have lower overall atmospheric concentrations but retain heat effectively.

  • Impact Determinants: The total impact of any greenhouse gas depends on its gas-specific capacity to absorb long-wave radiation and its atmospheric concentration.

  • Mechanism: The Earth's surface absorbs short-wave solar radiation and re-emits energy as longer wavelength infrared radiation (heat). Greenhouse gases retain this heat by absorbing long-wave radiation, keeping the lower atmosphere warm.

• Atmospheric $CO_2$ Trends and Global Temperature:

  • Historical $CO_2$ Monitoring Data:

    • 1958: $316\,\text{ppm}$

    • May 2013: $400\,\text{ppm}$ (surpassing historical highs for millions of years)

    • 2020: $413\,\text{ppm}$

  • Temperature Projection: Climate models indicate that a doubling of baseline atmospheric $CO_2$ will drive a $2\,^\text{o}\text{C}$ increase in global average surface temperatures, leading to polar ice cap melting and coastal inundation.

  • Ocean Acidification: Increased atmospheric $CO_2$ dissolves into marine environments, forming carbonic acid and decreasing oceanic pH, directly threatening coral reef ecosystems and calcifying organisms.

  • Arctic Peat Combustion: Severe warming has led to widespread burning of ancient Arctic peat deposits (reported in 2020), releasing vast locked reserves of carbon back into the atmosphere.

• Methane Cycle Dynamics:

  • Produced naturally in anaerobic conditions by methanogenic archaeans (e.g., wetlands, digestive tracts, underground deposits).

  • Atmospheric methane undergoes chemical oxidation, eventually breaking down into carbon dioxide and water vapor.

• Stratospheric Ozone Layer ($O_3$) vs. Greenhouse Effect:

  • Ozone Function: Stratospheric ozone ($O_3$) filters harmful ultraviolet radiation ($UV\text{-}B$) from incoming solar rays.

  • Depletion: Thinning of the ozone layer was recognized globally starting around 1975 ( showing signs of recovery following international agreements).

  • Crucial Conceptual Distinction: Stratospheric ozone depletion is a completely separate environmental issue from the enhanced greenhouse effect and does not cause global warming.

Conservation Biology, Restoration Ecology, and Sustainability

• Three Levels of Biodiversity:

  1. Genetic Diversity: Variation in gene pools within species. Low genetic diversity leaves populations vulnerable to extinction from single disease events (e.g., wild cheetah populations suffered extreme historical bottlenecks, rendering them more genetically uniform than selectively bred laboratory rodents).

  2. Species Diversity: The variety and relative abundance of species present within ecological communities. The IUCN reports that $13\%$ of the $9,040$ known bird species ($1,183\,\text{species}$) are threatened with extinction.

  3. Ecosystem Diversity: The range of habitats and ecological processes across biomes. Rainforest land equivalent to the size of West Virginia is destroyed annually.

• Four Major Threats to Global Biodiversity:

  1. Habitat Destruction: The single greatest cause of biodiversity decline. Responsible for $73\%$ of all species extinctions/threats listed by the IUCN. Human actions have damaged $93\%$ of the world's coral reefs.

  2. Introduced/Invasive Species: Non-native species introduced by human transfer explode in population size due to an absence of natural predators and abundant resources (e.g., Africanized honeybee, Zebra mussel, Burmese python).

  3. Overexploitation: Harvesting wild species at rates faster than populations can recover (e.g., extinction of the Great Auk; severe population crashes of African elephants due to illegal ivory trade).

  4. Food Chain Disruption: Extinction or collapse of key species destabilizing entire trophic webs.

• Evolutionary Adaptation Case Study: Elephant Tusklessness:

  • African elephants possess a sex-linked gene controlling tusklessness.

  • Under natural conditions, males require tusks for combat and breeding success, selecting strongly against tuskless males.

  • Heavy poaching selects heavily against tusked animals, drastically shifting survival odds.

  • Quantitative Shift: Unpoached baseline female tusklessness is approximately $4\%$. In heavily poached areas (e.g., Gorongosa in Mozambique, Selous in Tanzania), tusklessness in older surviving females rises up to $60\%$.

  • When tuskless females pass the sex-linked gene to offspring ($50\%$ of daughters inherit tusklessness), the gene rapidly proliferates throughout the heavily poached population.

• Restoration Ecology and Bioremediation:

  • Bioremediation: The deployment of living organisms (plants, fungi, microbes) to extract or detoxify pollutants in degraded environments.

  • Metal Accumulation: Specialized plants absorb toxic heavy metals from contaminated soils.

  • Mycofiltration: Specialized fungi break down complex toxic environmental chemicals and synthetic polymers.

  • Plastic Degradation: Insect larvae (e.g., specialized beetle larvae) have been discovered capable of digesting and surviving exclusively on polystyrene (Styrofoam) via gut microbes.

• The Three Spheres of Sustainability:

  • Sustainability requires balancing three intersecting pillars (University of Michigan model):

    • Environmental: Resource stewardship, pollution prevention (air, water, land), waste management.

    • Social: Standard of living, equal opportunity, education, community strength, environmental justice.

    • Economic: Economic growth, fair profit, cost savings, research and development.

  • Intersections: Social-Environmental (Environmental Justice), Environmental-Economic (Energy Efficiency, Sustainable Subsidies), Economic-Social (Fair Trade, Workers' Rights).

• Carbon Footprints and Evolutionary Game Theory:

  • Carbon Footprint: The total measure of fossil fuel combustion and greenhouse gas emissions associated with an individual's lifestyle.

  • Social Cheating Parallels: Refusal to lower one's carbon footprint mirrors "cheating" behaviors in social animal populations. Evolutionary models demonstrate that when social cheating exceeds critical threshold limits, cooperative social structures and systems completely collapse.

Ecological Methodologies and Experimental Design

• Quadrat Sampling and Chi-Squared ($\chi^2$) Association Testing:

  • Used to test for statistically significant associations (positive or negative presence/absence correlation) between two species within an ecosystem.

  • Sampling Protocol: Quad-frame sampling sites must be chosen strictly using random number generation to avoid bias. The presence or absence of target species is systematically recorded across quadrat samples in areas where environmental variables change.

• Constructing Sustainability Mesocosms:

  • Mesocosm: An experimental, enclosed system that simulates natural ecological conditions to test long-term sustainability.

  • Design Specifications: Sealed glass vessels are preferred over open tanks because matter entry/exit is entirely prevented, while solar light energy can enter and heat energy can escape.

  • System Selection: Aquatic mesocosms demonstrate significantly higher experimental stability and success rates compared to sealed terrestrial mesocosms.