Introduction to Ecology and Evolution
Study guide – key concepts, definitions, and connections
1. What Is Ecology?
| Sub‑field |
Focus |
Typical Questions |
| Population Ecology |
Dynamics of a single species (size, age structure, birth‑death rates) |
How does a rabbit population fluctuate over time? |
| Community Ecology |
Interactions among species (predation, competition, mutualism) |
What roles do wolves and deer play in a forest? |
| Ecosystem Ecology |
Flow of energy and nutrients through abiotic and biotic components |
How does carbon move from plants to soil microbes? |
| Landscape Ecology |
Spatial patterns across habitats (patches, corridors) |
How does fragmentation affect pollinator movement? |
| Global Ecology (Biosphere) |
Planet‑scale processes (climate, biogeochemical cycles) |
How does deforestation influence atmospheric CO₂? |
Core Ecological Principles
- Hierarchy of Organization – individual → population → community → ecosystem → biosphere.
- Energy Flow – unidirectional; governed by the law of thermodynamics; primary production → consumers → decomposers.
- Matter Cycling – closed loops (e.g., nitrogen, phosphorus).
- Limiting Factors – abiotic (temperature, water) and biotic (predation, competition) constraints on population growth.
- Carrying Capacity (K) – maximum sustainable population size given resource limits.
- Density‑Dependent vs. Density‑Independent Regulation – feedback mechanisms that depend on (or are independent of) population density.
Key Models
- Exponential Growth: ( N(t) = N_0 e^{rt} ) (r = intrinsic rate of increase).
- Logistic Growth: ( N(t) = \frac{K}{1 + \left(\frac{K-N_0}{N_0}\right)e^{-rt}} ).
- Lotka‑Volterra Predator‑Prey Equations:
[
\begin{aligned}
\frac{dN}{dt} &= rN - aNP \
\frac{dP}{dt} &= baNP - mP
\end{aligned}
]
(N = prey, P = predator; a = attack rate, b = conversion efficiency, m = predator mortality).
2. What Is Evolution?
| Concept |
Definition |
Example |
| Variation |
Heritable differences among individuals. |
Beak length in finches. |
| Selection |
Differential survival/reproduction based on traits. |
Dark moths survive better in polluted forests. |
| Inheritance |
Transmission of genetic information across generations. |
DNA replication, epigenetic marks. |
| Time |
Cumulative change over generations. |
Development of antibiotic resistance. |
Mechanisms of Evolutionary Change
| Mechanism |
How It Works |
Typical Outcome |
| Natural Selection |
Fitness differences → allele frequency shifts. |
Adaptation to local environment. |
| Genetic Drift |
Random sampling of alleles, strongest in small populations. |
Loss of genetic variation, fixation of neutral alleles. |
| Gene Flow (Migration) |
Movement of individuals/genes among populations. |
Homogenization of allele frequencies. |
| Mutation |
New genetic variants arise spontaneously. |
Source of raw material for evolution. |
| Sexual Selection |
Preference for certain traits influences reproductive success. |
Elaborate plumage in birds of paradise. |
Evolutionary