Honors Ecology Unit Study Guide

Introduction to Ecology

Abiotic vs. Biotic Factors
- Biotic Factors: Any living component or previously living organic matter within an ecosystem that affects another organism or shapes the environment.
- Examples include plants, animals, fungi, bacteria, protists, leaf litter, and decomposing carcasses.
- Abiotic Factors: The non-living chemical and physical features of an environment that influence ecosystem function and organism survival.
- Examples include temperature, solar radiation, water availability, soil pH, salinity, dissolved oxygen levels, atmospheric pressure, wind patterns, and mineral nutrients.
Levels of Ecological Organization
- Organism: could be singular or plural
- simiular organism which can interbreed and produce offspring
- Population: group of the same species that interbreed
- Community: all the various populations in an area that interact -multiple species population
- Ecosystem: all the living AND nonliving components of an area
- Biome: groups of ecosystems with a similar climate
- Biosphere: the parts of the Earth where life exists
Fundamental Ecological Vocabulary
- Species: A group of organisms capable of interbreeding in nature and producing fertile, viable offspring.
- Organism: A single, distinct living individual.
- Habitat: The specific physical address or environment in which an organism lives and finds the resources necessary for survival.
- Niche: The complete ecological role, functional position, and set of resource requirements of a species within its ecosystem. It encompasses abiotic tolerances, food sources, activity patterns, and interactions with other organisms.
- Trophic Levels: The hierarchical positions occupied by organisms in a food chain or web, defined by their primary energy source.
- Producer / Autotroph: An organism that synthesizes organic molecules from inorganic carbon sources ( $CO_2$ ) using light energy (photoautotroph) or chemical energy (chemoautotroph). Examples: Phytoplankton, oak trees, nitrifying bacteria.
- Consumer / Heterotroph: An organism that obtains its energy and organic nutrients by consuming other organisms or organic matter. Examples: Mammals, birds, fish, fungi.
- Herbivore: A primary consumer that feeds exclusively on living plant material or producers. Example: Cottontail rabbit.
- Carnivore: A consumer that feeds exclusively on other animals. Example: Cougar.
- Omnivore: A consumer that feeds on both plant and animal matter. Example: Brown bear.
- Scavenger: An animal that feeds on dead animal carcasses killed by other vectors or natural causes. Example: Turkey vulture.
- Detritivore: An organism that ingests non-living organic particulate matter (detritus) internally to extract energy and nutrients. Examples: Earthworms, dung beetles, millipedes.
- Decomposer: An organism, primarily a fungus or bacterium, that breaks down complex organic matter extracellularly by secreting digestive enzymes and absorbing the simplified products, recycling nutrients back into the ecosystem.
- Food Web: A complex network of interconnected food chains representing the multi-directional pathways of energy and matter transfer within an ecosystem.
- Biomass: The total dry mass of living or recently living biological organisms within a given area or volume at a specific time.
Energy Pyramid and Energy Flow Dynamics
- Pyramid Structure: Energy pyramids represent the total energy available at each sequential trophic level. Primary producers occupy the broad base, followed by primary consumers, secondary consumers, and tertiary consumers.
- The $10\text{ }\text{\%}$ Rule: On average, only approximately $10\text{ }\text{\%}$ of the energy stored as biomass in one trophic level is incorporated into biomass at the next higher trophic level ( $\text{Ecological Efficiency} \thickapprox 10\text{ }\text{\%}$ ).
- Energy Loss ( $90\text{ }\text{\%}$ Destination): The remaining $90\text{ }\text{\%}$ of energy is lost as heat generated during cellular respiration, expended on metabolic activity (movement, cell maintenance, thermoregulation), or passed out as unabsorbed waste products (feces and unconsumed biomass).
Reading Food Webs and Food Chains
- Direction of Arrows: Arrows in a food web point from the organism being consumed toward the consumer that receives the energy (e.g., $\text{Grass} \rightarrow \text{Grasshopper} \rightarrow \text{Frog}$ ).
- Determining Trophic Position: Primary producers sit at Trophic Level $1$ ; Primary consumers (herbivores) sit at Trophic Level $2$ ; Secondary consumers sit at Trophic Level $3$ ; Tertiary consumers sit at Trophic Level $4$ . Many organisms occupy multiple trophic levels depending on the specific food chain analyzed.
Types of Symbiotic Relationships
- Mutualism ( $+ / +$ ): A close interaction where both participating species derive a net ecological benefit. Example: Mycorrhizal fungi providing mineral nutrients to tree roots while receiving photosynthetic carbohydrates.
- Commensalism ( $+ / 0$ ): An interaction where one species benefits while the other is neither harmed nor helped. Example: Epiphytic orchids growing on high tree branches to access sunlight without taking nutrients or water from the host tree.
- Parasitism ( $+ / -$ ): An interaction where one species (parasite) benefits by extracting energy/nutrients from a host organism, which is harmed over time. Example: Ticks feeding on the blood of white-tailed deer.
- Competition( $- / -$ ): An interaction where two or more species compete for the same resources such as food, water, or territory, leading to negative effects on both participants. Example: Trees in a dense forest competing for sunlight and nutrients in the soil.
- two types of competition:
- Intraspecific Competition: Competition between individuals of the same species
- Interspecific Competition: Competition between individuals of different species for similar resources

Native, Introduced, and Invasive Species

Definitions and Categorization
- Native Species: A species that naturally occurs, evolves, and persists in a specific geographical ecosystem without human intervention.
- Introduced (Non-Native) Species: A species living outside its native distributional range, brought into a new area through human activity, either intentionally (e.g., crops, biocontrol) or accidentally (e.g., ballast water, cargo transport).
- Invasive Species: An introduced species that establishes self-sustaining populations, spreads aggressively beyond its point of introduction, and causes measurable ecological, economic, or environmental harm.
Determining Native Status
- A species is confirmed native by examining evolutionary history, historical distribution records, fossil evidence, genetic lineage tracking, and its natural co-evolutionary integration with local species assemblages.
Distinguishing Introduced from Invasive Species
- Not all introduced species are invasive. Many non-native species are unable to survive long-term without human assistance, or stay localized without outcompeting native organisms (e.g., cultivated maize, domestic livestock, garden roses).
- An introduced species becomes invasive only when it possesses traits such as high reproductive capacity, rapid growth rate, broad environmental tolerance, generalist feeding habits, and an absence of natural predators or pathogens in the new ecosystem.

Population Ecology

Core Quantitative Concepts and Terminology
- Population: A group of individuals of the same species inhabiting the same geographic region at a specific time.
- Population Size: The absolute total number of individual organisms present in a defined population.
- Geographic Distribution (Range): The spatial boundary or geographic area within which a species' population occurs.
- Population Density: The number of individuals per unit area or volume
- Population Dispersion: The spatial arrangement pattern of individuals within a given area.
- Population Sample: A representative subset of individuals selected from a population used to statistically estimate total population size and parameters.
- Mortality (Death) Rate: The proportion or number of individuals dying within a specified time interval.
- Birth Rate: The proportion or number of new individuals produced via reproduction within a specified time interval.
- Life Expectancy: The mean expected remaining lifespan for an individual at a given age.
- Stable Population: A population with a zero growth rate where total inputs equal total outputsE) $.</li><li>Survivorship Curves: Graphical depictions showing the proportion or percentage of a cohort surviving at each age level across their lifespan.</li><li>Growth Rate ($ r $): The fractional change in population size per unit time, calculated as:$ r = (B + I) - (D + E) $.</li><li>Immigration ($ I $): The movement of individuals into a population from another area.</li><li>Emigration ($ E $): The movement of individuals out of a population to another area.</li><li>Exponential Growth: Unrestricted population growth occurring under ideal, unlimited resource conditions, producing a characteristic J-shaped curve modeled by:$ \frac{dN}{dt} = r N $.</li><li>Logistic Growth: Population growth constrained by limiting factors and resource scarcity, leveling off as the population approaches the carrying capacity, producing an S-shaped curve modeled by:$ \frac{dN}{dt} = r N \begin{pmatrix} \frac{K - N}{K} \begin{pmatrix} $.</li><li>Carrying Capacity ($ K $): The maximum stable population size of a species that a specific environment can sustainably support over an extended timeframe.</li><li>Limiting Factors: Any biotic or abiotic environmental variable that restricts population growth, distribution, or density.</li><li>Biotic Potential: The maximum possible rate of population growth under optimal, unlimited environmental conditions.</li></ul></li><li>Spatial Population Dispersion Patterns<ul><li>Clumped Dispersion: Individuals are grouped together in patches, which can be influenced by resource availability, social behavior, or environmental conditions. Ex: Patches of wheat. </li><li>Uniform/Even Dispersion: spread out evenly Ex: Penguins</li><li>Random Dispersion: randomly dispersed individuals, Ex: Dandelions</li></ul></li><li>Mechanisms Driving Population Dynamics<ul><li>A population increases when inputs exceed outputs</li><li>A population decreases when outputs exceed inputs</li></ul></li><li>Classification of Survivorship Curves<ul><li>Type I Curve: High survival rates throughout early and middle life, followed by a steep decline in survival in old age. Characteristic of species with high parental care and low fecundity. Example: Humans, elephants, large mammals.</li><li>Type II Curve: Constant, linear mortality rate throughout the lifespan regardless of age. Example: Songbirds, small rodents, hydras.</li><li>Type III Curve: Extreme mortality in early development and juvenile stages, with high survival rates for the few individuals reaching maturity. Characteristic of species producing vast offspring quantities with zero parental investment. Example: Oysters, marine invertebrates, oak trees, frogs.</li></ul></li><li>Limiting Factors: Density-Dependent vs. Density-Independent<ul><li>Density-Dependent Factors: Environmental variables whose magnitude and effect vary as a function of population density. They exert stronger regulation as population density increases. Examples: Intraspecific competition for food/space, predation pressure, infectious disease transmission, parasite load, metabolic waste accumulation.</li><li>Density-Independent Factors: Environmental variables that affect population mortality and birth rates regardless of how dense the population is. Examples: Severe weather events (hurricanes, severe freezes), natural disasters (volcanic eruptions, wildfires), human habitat destruction.</li></ul></li><li>Life-History Strategies:$ K $--Strategists vs.$ r $--Strategists<ul><li>$ K $--Strategists (Selected for Carrying Capacity):</li><li>Adapted to stable, predictable environments near carrying capacity ($ K $).</li><li>Characterized by large body size, long lifespans, late sexual maturity, low fecundity, and heavy energetic investment in parental care.</li><li>Show Type I or Type II survivorship curves.</li><li>Regulated predominantly by density-dependent limiting factors.</li><li>Examples: Blue whales, gorillas, elephants.</li><li>$ r $--Strategists (Selected for Rate of Growth):</li><li>Adapted to unstable, unpredictable, or disturbed environments.</li><li>Characterized by small body size, short lifespans, rapid sexual maturity, high fecundity, and zero parental care.</li><li>Show Type III survivorship curves.</li><li>Regulated predominantly by density-independent limiting factors.</li><li>Examples: Mosquitoes, dandelions, marine plankton.</li></ul></li><li>Graphical Comparison of Growth Models<ul><li>Exponential Growth (J-Curve): Depicts unbounded population growth. The slope increases continuously over time because population growth is proportional to current population size. Occurs when resources are abundant and limiting factors are absent (e.g., newly introduced invasive species or initial post-disturbance recovery).</li><li>Logistic Growth (S-Curve): Depicts real-world population growth. Starts with an exponential growth phase, decelerates as resources become depleted and density-dependent factors exert pressure, and oscillates around a horizontal asymptote representing carrying capacity ($ K $).</li></ul></li></ul><h3 id="0d257c42-29c1-4532-bc63-90c1f9c54464" data-toc-id="0d257c42-29c1-4532-bc63-90c1f9c54464" collapsed="false" seolevelmigrated="true">Ecological Interactions</h3><ul><li>Feedback Loops in Ecosystems<ul><li>Negative Feedback Loops: Regulatory pathways that counteract changes in a system, driving the system back toward dynamic equilibrium or stability. Example: Classic predator-prey cycles (as prey density increases, predator density increases, which consumes prey, causing prey density to drop, which subsequently reduces predator density).</li><li>Positive Feedback Loops: Amplifying pathways that accelerate changes in a system, destabilizing balance and pushing the system further away from equilibrium. Example: Global warming melting Arctic sea ice, which lowers global albedo, leading to greater solar radiation absorption and accelerated warming.</li></ul></li><li>Interspecific and Intraspecific Dynamics<ul><li>Intraspecific Competition: Competition for limited resources (food, mates, territory, light) occurring between individuals of the same species. Acts as a key density-dependent factor regulating population size.</li><li>Interspecific Competition: Competition for shared, limited resources occurring between individuals of different species.</li><li>Predation: An interaction where an individual of one species (predator) kills and consumes an individual of another species (prey).</li></ul></li><li>Evolutionary Adaptation: Mimicry<ul><li>Purpose: Increases individual survival and fitness by exploiting predator visual recognition and avoidance systems.</li><li>Mimicry:A form of evolutionary adaptation where one species evolves to resemble another species or object, allowing it to avoid predation by deceiving predators into mistaking it for something else that is unpalatable or dangerous. </li></ul></li><li>Keystone Species<ul><li>Definition: A species that exerts strong control on community structure and composition out of proportion to its physical abundance or biomass.</li><li>Ecological Importance: Removal of a keystone species leads to dramatic altercations in food webs, massive loss of local species diversity, and ecosystem collapse.</li><li>Classic Example: Sea otters in Pacific kelp forests. Sea otters consume herbivorous sea urchins. If otters are removed, urchin populations explode, overgrazing kelp forests into barren ground and driving out resident fish and invertebrate communities.</li></ul></li><li>Trophic Cascades<ul><li>Definition: A powerful top-down ecological process originating at the apex predator level and propagating down through successive lower trophic levels across the food web.</li><li>Mechanisms and Examples:</li><li>Reintroduction of wolves (Canis lupus) to Yellowstone National Park.</li><li>Top level increase: Wolf population restored.</li><li>Trophic level$ 2 $response: Elk populations regulated and forced to alter spatial movement patterns away from open riverbanks.</li><li>Primary producer response: Aspen, willow, and cottonwood stands along riparian zones regenerated.</li><li>Secondary physical cascade: Increased vegetative stability reduced river bank erosion, stabilized channels, and restored habitat for beavers, birds, and aquatic organisms.</li></ul></li></ul><h3 id="e68e92ef-9dae-4ecd-9cfd-bb5a350538fe" data-toc-id="e68e92ef-9dae-4ecd-9cfd-bb5a350538fe" collapsed="false" seolevelmigrated="true">Ecological Succession</h3><ul><li>Primary Succession<ul><li>Definition: The sequential colonization and development of an ecological community in a barren area devoid of initial organic soil or existing biological life.</li><li>Conditions: Starts on bare rock, hardened volcanic lava flows, exposed sand dunes, or retreat paths of glaciers.</li><li>Timeline: Unfolds extremely slowly, often taking hundreds to thousands of years due to the mandatory requirement of soil formation.</li></ul></li><li>Secondary Succession<ul><li>Definition: The re-establishment of an ecological community following a major disturbance that disrupts or clears existing vegetation but leaves the underlying organic soil matrix intact.</li><li>Conditions: Starts post-wildfire, post-agricultural field abandonment, or after severe windstorms/floods.</li><li>Timeline: Proceeds rapidly compared to primary succession, taking decades to a few centuries, because viable soil, seed banks, and root systems remain present.</li></ul></li><li>Pioneer Species<ul><li>Definition: The initial hardy organisms capable of colonizing harsh, nutrient-poor, disturbed, or barren substrates.</li><li>Primary Pioneer Examples: Lichens (symbiotic relationship of fungus and alga/cyanobacterium) and mosses. Lichens produce organic acids that chemically weather bare rock, trapping fine dust to create rudimentary soil.</li><li>Secondary Pioneer Examples: Fast-growing annual weeds, crabgrasses, and nitrogen-fixing herbaceous plants.</li><li>Ecological Importance: They modify the physical environment, build organic matter, stabilize soil matrix, increase moisture retention, and pave the way for mid-successional grasses, shrubs, and canopy trees.</li></ul></li><li>Aquatic Succession<ul><li>Definition: The process by which an aquatic ecosystem (such as a glacial lake) gradually transforms over geological time into a terrestrial ecosystem.</li><li>Process:</li><li>An initially nutrient-poor body of water (Oligotrophic) receives continuous inputs of eroded sediment, biological debris, and leaf litter.</li><li>Nutrient concentration increases (Eutrophication), fueling plant and algal growth.</li><li>Organic detritus accumulates rapidly on the basin floor, filling the body of water from the edges inward.</li><li>Shallowing transforms the lake into a marsh, bog, or wetland, which eventually fills completely to become dry terrestrial land (meadow leading to forest climax).</li></ul></li></ul><h3 id="9e37e570-a742-49f7-896f-2fc2b7735c52" data-toc-id="9e37e570-a742-49f7-896f-2fc2b7735c52" collapsed="false" seolevelmigrated="true">Climate Change and Biodiversity</h3><ul><li>Biodiversity and Its Essential Components<ul><li>Biodiversity Definition: The variety and variability of living organisms across all structural levels of biological organization on Earth.</li><li>$ 1 $. Genetic Diversity: The total range of genetic characteristics and allele variations present within individuals of a single population or species. High genetic diversity increases resistance to diseases and environmental change.</li><li>$ 2 $. Species Diversity: The variety of distinct biological species present within a specific region. Measured via species richness ( absolute count of species) and species evenness (relative abundance distribution of each species).</li><li>$ 3 $. Ecosystem Diversity: The structural variety of ecological habitats, biological communities, energy flows, and abiotic processes operating across biomes.</li></ul></li><li>Spatial Patterns and Specialized Definitions<ul><li>Latitudinal Diversity Gradient: The established global pattern where species richness increases progressively from polar regions toward the equatorial tropics.</li><li>Endemic Species: Species exclusively native to a specific, defined geographic boundary and found nowhere else on Earth (e.g., Lemurs of Madagascar).</li><li>Biodiversity Hotspots: Biogeographic regions that contain exceptionally high concentrations of endemic species ($ > 1,500 $endemic vascular plant species) and are experiencing severe habitat destruction (having lost at least$ 70\text{ }\text{\%} $of their primary natural habitat).</li></ul></li><li>Mechanisms of Climate Change<ul><li>Climate Change: Long-term shifts in global temperatures, weather patterns, and ocean dynamics driven primarily by anthropogenic greenhouse gas emissions alter historical planetary baselines.</li><li>Major Greenhouse Gases ($ \text{GHGs} $): Water Vapor ($ H_2O $), Carbon Dioxide ($ CO_2 $), Methane ($ CH_4 $), Nitrous Oxide ($ N_2O $), and Ozone ($ O_3 $).</li><li>The Greenhouse Effect: GHGs in the troposphere absorb longwave thermal infrared radiation emitted from the solar-heated surface of the Earth and re-emit it in all directions, trapping heat energy within the lower atmosphere.</li><li>Are Greenhouse Gases Bad? Natural greenhouse warming is indispensable; without it, Earth's average global surface temperature would drop to approximately$ -18^\text{o}\text{C} $, rendering the planet frozen and uninhabitable. However, anthropogenic burning of fossil fuels creates hyper-warming, accelerating climate disruption.</li></ul></li><li>Albedo Effect and Snow-Temperature Feedback<ul><li>Albedo: The measure of surface reflectivity for shortwave solar radiation (ranges from$ 0 $to$ 1 $).</li><li>High Albedo: Highly reflective light surfaces such as Arctic snow and ice reflect up to$ 80\text{ }\text{\%} $to$ 90\text{ }\text{\%} $($ 0.80 $to$ 0.90 $) of solar radiation back into space.</li><li>Low Albedo: Dark surfaces such as open oceans absorb up to$ 90\text{ }\text{\%} $($ 0.90 $) of incoming solar energy as heat.</li><li>Snow-Temperature Positive Feedback Loop: Elevated temperatures melt snow/ice$ \rightarrow $exposes low-albedo ocean/land$ \rightarrow $increases absorbed solar heat$ \rightarrow $further elevates ambient temperatures$ \rightarrow $accelerates additional snow/ice melting.</li></ul></li><li>Carbon Sinks and Sequestration<ul><li>Carbon Sink: Natural or artificial reservoirs that accumulate and store carbon-containing chemical compounds for an indefinite period, absorbing more carbon than they release.</li><li>$ 1 $. Oceans: Function as huge sinks by dissolving$ CO_2 $gas directly at the air-sea interface and fixing carbon via marine phytoplankton photosynthesis, storing it deep via the biological carbon pump.</li><li>$ 2 $. Forests and Soils: Terrestrial forests sequester vast amounts of carbon through photosynthesis, locking$ CO_2 $into woody biomass (cellulose and lignin) and storing organic carbon in undisturbed soils.</li></ul></li><li>Impacts of Climate Change on Biodiversity<ul><li>Ocean Acidification: Excess atmospheric$ CO_2 $dissolves into seawater to form carbonic acid ($ H_2CO_3 $), reducing ocean pH and depleting carbonate ions ($ CO_3^{2-} $) required by corals, mollusks, and plankton to build calcium carbonate ($ CaCO_3$$) shells.
- Phenological Mismatches: Disruption of delicate timing synchronization between species, such as migratory bird arrival dates decoupling from insect emergence peaks.
- Range Shifts and Extinction: Species forced to migrate poleward or upward in altitude to track viable climate envelopes faces geographical boundaries or habitat fragments, driving rate-of-change extinctions.