Ecology

About this course

Ecology from population models to the biosphere — growth, life tables and regulation, species interactions, community structure and succession, energy flow and nutrient cycles, and climate and human forcing.

What you will be able to do

• Model population growth with exponential, logistic and life-table methods
• Analyse predator–prey and competitive interactions and relate them to the niche
• Explain how community structure changes on islands and during succession
• Trace energy flow and nutrient cycling through an ecosystem
• Relate the distribution of biomes to climate and assess human forcing of ecosystems

What this course covers

• Sun to plant: the one-percent ceiling
• Why one percent is a theorem, not a failure
• The trophic pyramid and the ten-percent rule
• Transfer efficiency as a product of three fractions
• The ten-percent rule as a log-scale geometric mean
• Chain length and the inverted biomass pyramid
• Worked example: forest production to wolf territory
• Exponential population growth and doubling time
• R as rate per head: meaning and limits
• K as rate reaching zero, not a physical wall
• Logistic growth model
• Human population curve and demographic transition
• Sustainable harvest and the collapse cliff
• Worked deer-herd example: four ecological conversions
• Lotka-Volterra predator-prey equations
• Neutral cycles versus limit cycles
• Holling's functional response
• Dual regulation of the hare cycle
• Rosenzweig-MacArthur isoclines and the paradox of enrichment
• Fitting the lynx–hare cycle to the model
• Worked example: voles and weasels
• Solar insolation by latitude and season
• Hadley cell and the 30-degree desert belt
• Global circulation belts and continental modifiers
• Whittaker's biome plane
• Limits of mean annual temperature as a classifier
• Thornthwaite water balance
• Mountain as a folded latitude and the tree line isotherm
• Species–area power law and loss rate
• Diversity indices: Shannon and Simpson
• Extinction debt and law limitations
• Keystone species and trophic cascades
• May vs. Tilman: stability of parts vs. steadiness of whole
• Food webs and May's stability criterion
• Worked example: applying S = CA^Z and diversity indices
• Lotka-Volterra Competition Equations and Four Outcomes
• Alpha as a Summary Coefficient: Strengths and Limits
• Gause's Competitive Exclusion Principle
• Tilman's R* Rule and Resource Competition
• The Niche: Fundamental, Realized, and Limiting Similarity
• Synthesis: Five-Line Master Summary
• Worked Example: Two Grasses
• Biogeochemical cycles: boxes, arrows, and residence time
• Exchange time vs. perturbation lifetime of CO₂
• Why the airborne fraction is near one-half
• The Keeling curve and the two-box model
• Nitrogen cycle doubled by human fixation
• Phosphorus: a one-way cycle with no gaseous reservoir
• Hubbard Brook: forest nitrogen held by uptake, not storage
• Worked example: emissions to ppm, date of 500 ppm, and two timescales
• The Life Table: Survivorship, Mortality, and Expectancy
• Cohort vs. Period Life Tables
• Net Reproductive Rate R₀, Generation Time T, and Intrinsic Rate r
• Effect of Breeding Timing on r (Cole's Result)
• The Leslie Matrix and Stable Age Structure
• Population Momentum
• Gompertz's Law and the Human Lifespan
• Elasticity and the Juvenile Survival Lever
• Extinction rate and species-area debt
• Limits of the vertebrate extinction count
• Logistic harvest, maximum sustainable yield, and fixed-catch collapse
• Why the Grand Banks collapsed despite effort-based fishing
• Climate velocity and the species-climate race
• Mechanism vs. trend: why these numbers are not Malthusian projections
• Human appropriation of net primary production and the Living Planet Index
• Island Equilibrium Theory: Two Lines and a Crossing
• Why the Two Lines Curve: Distance and Area Parameters
• Tests of the Theory: Simberloff's Islets and Krakatau
• Conservation Implications: Turnover, Relaxation, and Reserve Design
• Succession and Nitrogen Fixation at Glacier Bay
• The Climax as a Matrix's Stationary Vector
• Intermediate Disturbance and the Landscape Mosaic
• Olson's exponential decay of litter
• Soil carbon pools and their residence times
• Steady-state store: input over K
• Carbon-to-nitrogen ratio and the line at 20
• Two-pool soil feedback and the permafrost
• Meentemeyer's regression: K from climate and lignin
• Worked example: warming a woodland floor
• SIR model and epidemic threshold
• Final size equation
• R₀ as a ratio of rates and intervention logic
• Herd immunity threshold and endemic dynamics
• Anderson–May host regulation by pathogens
• Aggregated worm burdens and negative binomial distribution
• Mutualism as Lotka-Volterra with reversed signs
• Daisyworld: feedback without foresight
• Earth's energy balance and the greenhouse
• Ice-albedo feedback and snowball hysteresis
• Lake phosphorus: two states and hysteresis
• Self-reinforcing feedbacks and the fold as a theorem
• Carbon budget: cumulative warming and time paths
• Worked example: planet arithmetic on one page
• Ricker Map: Discrete-Generation Dynamics
• Why the Ricker Map Overshoots the Logistic
• Regulation vs. Stability: Not the Same Word
• Delayed Logistic and the π/2 Threshold
• Distinguishing Cycles, Chaos, and Weather Noise
• Allee Effect: Threshold and the Harvest Cliff
• Killing-Power Accounting: Key Factor vs. Regulating Factor

Syllabus

1. Population Dynamics

   1. L1 · Exponential and Logistic Growth
   2. L2 · Life Tables and Age Structure
   3. L3 · Density Dependence and Regulation

2. Species Interactions

   1. L4 · Predator-Prey
   2. L5 · Competition and the Niche
   3. L6 · Parasites, Pathogens and Mutualists

3. Communities

   1. L7 · Community Structure
   2. L8 · Islands and Succession

4. Ecosystems

   1. L9 · Energy Flow
   2. L10 · Nutrient Cycles
   3. L11 · Decomposition and Soil

5. Climate, Humans and the Biosphere

   1. L12 · Climate and Biomes
   2. L13 · Humans as a Forcing
   3. L14 · The Integrated Biosphere