Principles of Ecology Final Exam Notes
Exam 1:
Foundations of Ecology
Definition: Ecology = study of relationships between organisms and their environment.
Biology: the study of life
Economics: the study of how individuals and groups interact to make choices about the use and exchange of scarce resources
Key Influencers:
Ernst Haeckel: coined "ecology" from Greek oikos (house).
Rachel Carson: Silent Spring, ecological effects of pesticides.
Wangari Maathai: Greenbelt Movement, reforestation in Kenya.
Akira Miyawaki: microforests, high density of native plants in small area
Foundations:
Evolution and natural selection form foundation
Evolution: change in gene frequencies over time
Core Concepts:
Multidisciplinary fields involving biology, physics, chemistry, statistics, genetics, etc.
Human impacts (biodiversity loss, climate change) are now inseparable from ecological systems.
Systems: interconnected sets of elements that are coherently organized in a way that achieves something; digestive system, football team, etc.
Feedback loops:
Balancing (Negative): keeps a stock at a given value or within a range of values; opposes whatever direction of change is imposed on the system; an example is body temp, sweating to cool when it's hot and shivering to warm up when it's cold
Reinforcing (Positive): generates more input to a stock with increasing amounts (and less input with decreasing amounts); snowballing
Dynamic equilibrium: forward and reverse processes occur at the same rate, so the overall levels remain constant over time
Scientific Method in Ecology
Observe → Ask Questions → Hypothesize → Experiment → Collect Data → Analyze → Revise Hypothesis
Use of models: simplified systems to explain/predict ecological phenomena (e.g., niche models).
Levels of Ecological Organization
Organism: How it interacts with the environment.
Population: Size, structure, dynamics.
Community: Species interactions.
Ecosystem: Energy/nutrient flow.
Landscape: Spatial patterns.
Biosphere: Global processes.
Evolution as a Basis for Ecology
Ecology is medium we use to study environmental forces that drive evolution
Darwin & Wallace: Natural Selection — traits favorable to survival become more common.
Darwin: competition drives evolution; descent with modification
Wallace: environmental pressures drive evolution
Lamarck: individuals changed to meet environmental needs and passed acquired characteristics to offspring
Mendel: Inheritance patterns → Modern Synthesis = Evolution + Genetics.
Law of segregation – each individual has two alleles for each gene; a parent passes on one of these two alleles to their offspring.
Law of independent assortment – alleles are transmitted independently to the gametes, i.e., having Y doesn’t mean have S
Hardy-Weinberg Equilibrium:
Predicts allele frequencies under no evolution.
Assumptions: random mating, no mutation, no migration, no natural selection, large population
Evolutionary Mechanisms
Special creationism: living things created to exactly suit particular niche
Blending Hypothesis
Offspring would have some intermediate level of a trait found in both parents. Tall parent + short parent = medium height offspring
Drives of Evolution: natural selection, genetic drift, gene flow, mutation
Natural Selection:
Adaptation to the environment.
Disruptive: Average phenotype less successful than the extremes; extremes more common
Stabilizing: Extreme phenotypes less successful than the average; average more common
Directional: Exceptional phenotype has greater survival and reproduction; population shifts in that direction
Genetic Drift: random change in allele frequency
Bottleneck: chance event kills/prevents reproduction in large amount of population; loss of diversity
Founder effect: establishment of new population; loss of diversity
Gene Flow: movement of alleles between populations.
Mutation: new genetic variation.
Sexual Selection: traits for mating success.
Darwin’s postulates:
Variability: Individuals within a species vary
Heritability: Some variations passed to offspring
Adaptation: individuals vary in their ability to survive and reproduce
Selection: Most favorable traits in the environment are more likely to survive
Speciation:
Allopatric: split by vicariance and subject to selection
Sympatric: sub-population arises within parent population; genetically distinct species
Heritability: increases with increased VG
Equation: h2 = VG / (VG + VE)
If VG = 0, not heritable
Biogeography
Species Range:
Fundamental: where it can live.Realized: where it does live.
Factors: microclimate, dispersal, competition, barriers (e.g., Grand Canyon, Isthmus of Panama).
Dispersal: a process that can maintain gene flow between populations; permanent, one way movement of individuals from parent habitat somewhere else
Migration: regular, cyclical movement of a species through its environment
Vicariance: geographic separation → speciation; a process that disrupts gene flow
Island Biogeography (MacArthur & Wilson)
Equilibrium between immigration and extinction rates.
Influenced by island size (target effect) and distance (rescue effect).
Edge effect: less edge area means higher population stabilitydue to reduced habitat fragmentation and increased resources available within the interior
Species-Area Curve: S=cAz
S = number of species, A = area, c = constant, z = slope of the line
Ecosystem Services
Ecosystem Services: Benefits ecosystems provide to humans.
Regulating (climate), provisioning (water), cultural, and supporting services.
Valuation Controversies: ethics of monetizing nature.
Term Project: With U.S. State Dept. — assign economic value to wildlife & wild spaces.
Population Genetics & Heritability
Phenotype = Genotype + Environment + Random Noise.
Heritability (h²) = genetic variance / total phenotypic variance.
High h² = strong genetic basis, low h² = more environmental influence.
Heritable traits:
Discrete: trait received as one of two distinct forms
Quantitative: trait has continuous distribution
Climate & Abiotic Factors
Milankovitch Cycles: affect long-term climate (eccentricity, precession, tilt)
Changes in earth’s movement on climate
Eccentricity - orbital shape (around sun)
Precession - axial rotation (towards sun)
Obliquity - axial tilt (towards sun)
Coriolis Effect & Ekman Transport: drive global wind/water patterns → gyres, upwelling.
Ekman Transport: water deflected 45° from wind direction; Each water layer transfers energy and is deflected 90° from wind’s direction
Gyres: circular motion in oceans
Upwelling: surface water pushed offshore, deeper water takes its place
Northern hemisphere deflects right
Southern hemisphere deflects left
Wind Pattern: heating warms air, air rises, air moves to poles, cooler air moves in, cooler air sinks, repeat
Soil formation = rock + rain + vegetation interactions.
Biomes
Defined by climate, soil, vegetation, and animal life
Climate: physical/chemical features of an environment
Terrestrial Biomes: tundra, taiga, temperate forest, grassland, desert, tropical rainforest, etc.
Marine Biomes: coral reefs, intertidal zones, pelagic and benthic zones.
Extinction
Background Extinction: normal rate (1-10 species/year).
Mass Extinction: 5 historical, humans driving a potential sixth.
Biodiversity Hotspots: areas with high endemism + high threat (e.g., California Floristic Province).
Exam 2:
Trade-offs in Organismal Performance
Organisms face trade-offs between:
Fecundity (number and investment in offspring)
Growth (size, defense)
Longevity (lifespan)
Example: Eastern Fence Lizards show differences in energy intake (MEI) based on temperature and population origin.
Temperature and Performance
All organisms have a narrow temperature range where performance peaks.
Acclimation: short-term physiological adjustments.
Adaptation: long-term physiological/genetic changes.
Evolution: changes in allele frequencies over generations.
Homeostasis
The ability to maintain stable internal conditions.
Key concepts:
Ectotherm: heat from the environment.
Endotherm: heat from internal metabolism.
Poikilotherm: variable body temperature.
Homeotherm: constant internal temperature.
Stenotherm: narrow thermal tolerance.
Heat Balance Equation
HS = Hm ± Hcd ± Hcv ± Hr - He
Metabolism, conduction, convection, radiation, evaporation.
Mechanisms of Temperature Regulation
Anatomy:
Insulation (fur, feathers, blubber)
Coloration
Countercurrent heat exchange (rete mirabile)
Thermal inertia (whales)
Physiology:
Bradycardia (diving reflex)
Vasoconstriction
Sweating / Evaporative cooling
Behavior:
Basking, migration, hibernation
Water Balance in Animals
Equation: Water = Wd + Wf + Wa – We – Ws
Ingestion, food metabolism, absorption vs. evaporation and secretion.
Adaptations include behavior, physiology, and habitat use.
Water Balance in Plants
Transpiration: water loss through stomata.
Evapotranspiration: balance between water gain and environmental loss.
Trade-off: water conservation vs. photosynthesis efficiency.
Potential Evapotranspiration (PET): atmospheric demand for water.
Photosynthesis
CO₂ + H₂O → CH₂O + O₂ (uses light energy)
Reduces carbon; stores energy in chemical bonds.
Respiration
Opposite of photosynthesis.
Oxidizes sugars to release stored energy.
Metabolic Strategies
Photosynthetic autotrophs (e.g., plants, cyanobacteria)
Chemosynthetic autotrophs (e.g., sulfur bacteria)
Heterotrophs (e.g., animals, fungi)
Photosynthetic Pathways
C3: common, less efficient in hot/dry areas.
C4: spatial separation of fixation and synthesis (e.g., corn).
CAM: temporal separation (e.g., cacti), open stomata at night.
Energy Trade-offs
Even abundant resources can’t be fully utilized due to physiological constraints.
Pmax: max photosynthesis rate.
Isat: light level needed to reach Pmax.
Animal Functional Response
Type I: linear increase then plateau (e.g., filter feeders)
Type II: decelerating intake (common)
Type III: sigmoidal curve; low response at low prey density.
Optimal Foraging Theory (OFT)
Predicts how organisms maximize net energy gain.
Trade-offs: foraging time vs. handling time.
Applied to both animals and plants (e.g., root/shoot allocation).
Life Cycles
Asexual vs. Sexual reproduction.
Types: Gametic (humans), Zygotic (fungi), Sporic (ferns).
Key Traits
Age at maturity, number/size of offspring, lifespan.
Trade-offs: investing in current vs. future reproduction.
r/K Selection
Plant Life Strategies (Grime’s Model)
Ruderals: tolerate disturbance. (r-selected)
Stress-tolerators: conserve in poor conditions.
Competitors: thrive in resource-rich, stable areas. (k-selected)
Population Growth Models
Geometric growth: pulsed reproduction.
Exponential growth: continuous reproduction.
Nt = N₀λᵗ (geometric), dN/dt = rN (exponential)
Logistic growth: includes carrying capacity K.
dN/dt = rN(1 - N/K)
Density Factors
Density-dependent: effects intensify as population grows (e.g., disease, competition).
Density-independent: unrelated to density (e.g., weather).
Factors Influencing Distribution
Direct environment (light, temp)
Indirect effects (predators, symbiosis)
Microclimate
Biotic interactions (competition)
Fundamental vs. Realized Niche
Fundamental: potential range.
Realized: actual due to competition, predation.
Patterns of Distribution
Random, Regular, Clumped
Random: organisms indifferent to other individuals and environment
Regular: organisms antagonistic with other individuals and resources are depleted
Clumped: organisms attracted to other individuals or individuals attracted to a common resource
Small-scale vs. large-scale patterns.
Abundance
Inverse relationship between body size and population density.
Dispersal Types
Range expansion (e.g., invasive species)
Within-range movement
Metapopulation dispersal: multiple subpopulations connected by migration.
Source-Sink Dynamics
Source: high-quality habitat, exports individuals.
Sink: poor-quality, needs immigration to persist.
Types
Intraspecific: within the same species.
Interspecific: between different species.
Lotka-Volterra Competition Model
Adds competition coefficients (α) to logistic growth.
Predicts outcomes: coexistence or competitive exclusion.
Niche Partitioning
Species evolve to use different resources to reduce overlap.
Examples: warblers, barnacles, Anolis lizards.
Types of Exploitation
Herbivory, Predation, Parasitism, Amensalism
Parasites: obligate, facultative, accidental
Obligate: needs host to complete life cycle
Facultative: does not require host to complete life cycle
Accidental: hosts that are not the natural target, unable to complete life cycle
Predator-Prey Cycles
Modeled using Lotka-Volterra:
dNh/dt = rhNh – pNhNp (prey)
dNp/dt = cpNhNp – dpNp (predator)
Stabilizing Factors
Refuges, alternative prey, time lags, predator inefficiency.
Refuges
Space, numbers, morphology, size, behavior.
Community Diversity
Species richness: number of species.
Evenness: relative abundance of each.
Diversity Indices
Shannon-Wiener Index: accounts for richness & evenness.
Simpson’s Index: probability two individuals are same species.
Rank-Abundance Curves
Visualize abundance and evenness.
Flat slope = high evenness, steep = dominance by few species.
Environmental Complexity
More complex environments → more niches → greater diversity.
Exam 3:
Ecological Disturbance
Disturbance is an event of intense environmental stress occurring over a relatively short period, causing large changes in the affected ecosystem.
Disturbance occurs at the community level of ecological organization.
Types of Disturbance
Disturbances can be categorized as:
Natural
Anthropogenic
They also vary along a spatial continuum from:
Small-scale
Large-scale
Intermediate Disturbance Hypothesis (Joseph Connell, 1975)
Species diversity is highest in communities experiencing intermediate levels of disturbance.
High disturbance: Favors dominance by a few weedy and fast-growing species.
Low disturbance: Favors dominance by a few competitively superior/dominant species.
Intermediate disturbance: Provides a balance where a wide variety of species can become established, but competitive exclusion is prevented.
The hypothesis predicts that:
High levels of disturbance reduce diversity.
Low levels of disturbance allow competition to reduce diversity.
Species diversity will be highest at intermediate levels of disturbance.
Sousa (1979) studied the diversity of marine algae and invertebrates on different sized boulders to test this hypothesis.
Succession
Succession is the process of change in plant, animal, and microbial communities in an area following a disturbance (or the creation of a new habitat).
Communities are not static; they change constantly in response to:
Disturbances (e.g., hurricanes, fires).
Environmental change (e.g., climatic shift).
Internal dynamics (e.g., pathogens).
Henry Cowles (1899) described succession by observing different ages of plant communities on sand dunes, proposing they were different stages of ecological development.
Types of Succession
Primary succession: Community development on new or newly exposed geological substrate.
Secondary succession: Development after a disturbance removes the community of organisms but not the soil and organics.
Groups of Organisms in Succession
Pioneer species (early successional species): The first species to colonize an open area after a disturbance.
These species tend to be hearty plants with -fixing bacteria and deep roots.
Pioneering species typically grow fast, disperse well, and have a shorter life span, emphasizing energy into reproduction over sustaining growth.
These are also known as r-selected species.
r-selected species attributes:
Rapid Development
Early Reproduction
Small Body Size
Small Offspring Size
Many Offspring
Semelparity Reproduction Type
Unpredictable Environment
Influence Per capital rate of increase (r)
Climax species (late successional species): The last assemblage of species to establish themselves in a habitat.
The community remains in a stable state until a disturbance resets the system.
These species tend to be slow-growing, long-lived, and highly efficient competitors.
These are also known as K-selected species.
K-selected species attributes:
Slow Development
Delayed Reproduction
Large Body Size
Large Offspring Size
Few Offspring
Iteroparity Reproduction Type
Stable Environment
Influence Carrying Capacity (K)
Intermediate species: Species that fall in between being weedy/fast-growing and dominant/slow-growing.
Succession: Return Time
How long does succession take?
Sometimes relatively quickly: Marine boulders – 1.5 years
Sometimes slowly: Taiga – 1,500 years
This depends on the type of community.
Stages of Succession
Primary succession: Organisms arrive by waiting for their arrival.
Secondary succession: Organisms arrive via seed banks and metapopulations.
Metapopulations: Source and Sink dynamics.
Rescue effect if source population wiped out.
Example: Japanese tsunami debris spreading species over long distances.
Mechanisms of Succession
Facilitation: Pioneer species modify the environment in such a way that it becomes less suitable for themselves and better for later successional species.
Inhibition: Earlier occupants modify the environment in a way that makes it less suitable for both early and late successional species. Late successional species can only get a foothold in an area if space is opened up by the death of earlier successional species. Late successional species eventually dominate because they are long-lived and are able to resist biotic and physical stress that wipes out earlier successional species.
Tolerance: All species tolerant of the conditions in a particular environment (even climax species) can be present in a pioneer community. Less emphasis on earlier species modifying the environment for later species; the final species composition of the climax community simply reflects the environment’s selection of all species that can tolerate environmental conditions.
Most ecologists and research support the facilitation and/or inhibition models.
Autogenic vs. Allogenic Succession
Autogenic succession: Biotic elements of a community are driving succession to a stable, unchanged equilibrium.
Allogenic succession: Abiotic elements (disturbances, weather) prevent a community from reaching equilibrium.
Community Stability and Disturbance
Communities are in constant change due to disturbances.
Communities can have both stability and exposure to disturbances via:
Resistance: The ability of a community to maintain structure/function in the face of disturbances.
Resilience: The ability of a community to bounce back after a disturbance.
Persistence: Communities of species move back and forth in response to disturbance in succession. Although there is variance in the recovery of a community, in general, the community persists.
Phase shift: If underlying environmental conditions change (e.g., addition of nutrients), the community composition will change (e.g. Kaneohe Bay, Hawaii).
Altered Stable State: If a pulse event occurs (e.g., removal of keystone predator), the community changes but can change back if the pulse dissipates (e.g., the return of keystone predator).
Ecosystem Ecology
Ecosystem: Interactions of all members (biotic) of an area (community), with consideration of how members interact with the environment, how energy flows, and how matter cycles through the environment.
Ecosystem ecology is the study of ecosystems from a systems approach.
Systems approach: Examination of a complex scenario/phenomenon by:
Describing arching features of the system
Decomposing the system into small parts
Studying the parts and synthesizing to describe the whole
Ecosystem-based Management
Ecosystem-based management: Create policy that recognizes a species does not survive in isolation, must account for interactions (positive and negative) at all levels that sustain a species.
Ecosystem Energetics
Ecosystem energetics: How does energy move through an ecosystem?
An ecosystem is fueled by the Net Primary Productivity (NPP)
NPP is the energetic output from a plant or ecosystem.
It’s all the energy available after accounting for the plant’s/ecosystem’s own energy demands.
NPP = GPP – R
(GPP is gross primary productivity, R is respiration. Unit is energy (or mass) per unit time)
The accessibility of energy from NPP is determined by the consumption efficiency (CE) of the herbivores.
Energy Pyramid: Visualizes the transfer (and loss) of energy through an ecosystem. Lots of energy at lower levels, consumed by higher levels with losses at each transfer.
Energy pyramids are similar to those for biomass or number of individuals, but shape of the pyramid can be different in different ecosystems.
Species Interactions
Some species have evolved close, sometimes beneficial relationships with other species for part or their entire life.
Commensalism
Commensalism: Interaction between two species where one gains fitness benefits; the other is unaffected.
Latin com mensa means “same table.”
The time period of commensalism ranges from a brief interaction to a long-lived relationship.
Phoresy: One species attaches to another species for transportation.
Inquilinism: One species uses a second species for housing/support.
Metabiosis: One species uses something created by the second species after the second species has died or moved on. Includes species that can only exist after modification of the habitat by another species (ecosystem engineer via facilitation).
Obligate: One or both partners require commensal/mutualistic relationship for survival.
Facultative: Species can live without commensal/mutualistic partner.
Mutualism
Mutualism: Relationship between two species, sometimes intimate, where both benefit and gain fitness success.
The opposite of competition.
Evolutionarily, the first mutualistic relationship occurred between mitochondria and plastids (chloroplasts) with prokaryotes (The Endosymbiotic Theory).
Obligate mutualism: Complete dependence.
Facultative mutualism: May co-exist without other.
Dispersive Mutualism: One disperses other.
Defensive Mutualism: One protects the other.
Trophic Mutualism: One provides food.
Resource – Resource Mutualism: Mycorrhizal fungi and plant roots – both gain resources (Fungi increase the roots capacity to take up inorganics, and the roots serve as food for the fungi).
Resource – Service Mutualism: One species receives resources, and the other gains a service (e.g., pollination).
Service – Service Mutualism: Both species gain a beneficial service from the other. (e.g., clownfish and anemone; pistol shrimp and watchman goby).
Sustainability
Communities of species are interacting with biotic features and influenced by the transfer of energy and matter.
In the face of ecological and environmental challenges, organisms in an ecosystem are trying to sustain life, and a healthy ecosystem keeps species in check – living sustainably.
Sustainability: Meeting the needs of the present without compromising the ability of future generations to meet their own needs.
Accomplish sustainability in part by utilizing renewable resources – resources able to reproduce and replenish over time (relatively short time period).
Opposite to renewable resources are finite (non-renewable) resources – things that can’t be replenished or take a very, very long time to be replenished.
Ecological footprint: Estimate of how much land is needed to sustainably provide all the resources a population uses and assimilates all the waste it generates.
Ecosystem Services
Ecosystem services: Benefits provided to humans by nature, for FREE!
Valuation of ecosystem services of a nascent urban park in east Los Angeles, California: This study found that the value of ES measured at AHP was between 3,074 and $80,608/ha/year across the four land cover types. Applied methods which only considered the park's tree population (excluding grasses, shrubs, etc.) place the value of ES from trees between 53 and $6,193/ha/year.
Current global efforts to support biodiversity and ecosystem services
The Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) is an independent intergovernmental body, established by member States in 2012. The objective of IPBES is to strengthen the science-policy interface for biodiversity and ecosystem services for the conservation and sustainable use of biodiversity, long- term human well-being and sustainable development.
What does IPBES do?
Assessments on specific themes & methodological themes at regional/global scale.
Policy Support to identify tools and facilitate their use.
Build capacity to equip states, experts, & stakeholders with data and tools
Communication & Outreach to ensure the widest reach & impact of work
Restoration Ecology
To restore generally means to bring back, return to a previous condition, or repair so it is again in its original condition.
Restoration Ecology: The study of restoring degraded, damaged, or destroyed habitats by taking direct (human) actions.
Ecological restoration: The process of intentional action to begin or accelerate the recovery of a habitat in terms of integrity, health, and sustainability.
Importantly, restoration is not a trade-off to conservation.
Urban Reforestation
Simply, planting trees in urban environments.
Urban reforestation includes urban farming and horticulture.
Benefits of urban reforestation:
Improves air quality (NO2, O3, PM 2.5, SO2 reduction)
Cools the urban climate (reduces urban heat island effect).
Alters the soil conditions through decontamination of chemicals and waste (phytoremediation, estimated to cost $5-$40 per ton of soil decontaminated).
Beautification and noise abatement.
Food and shelter for urban wildlife.
Food security and economic value via urban gardening
The estimated value of ES provided from the 98-acre Ascot Hills Park is $110,664 to $2,901,874 annually (Wilson and Willette, 2022).
Challenges to urban reforestation
Competition for land
Maintenance and upkeep
The lollipop tree dilemma
Use of native or non-native plants
Supports urban wildlife
Microforest & Miyawaki method
Dr. Akira Miyawaki was a botanist who developed a distinct approach to reforestation.
Extremely high density of a range of native species in a tiny area.
200 years of growth in 20 years.