lecture recording on 17 September 2025 at 08.55.41 AM
Office Hours, Exam Logistics, and Study Guidance
Monday plan: the instructor will be on campus during class time as an extended office hour period to answer questions about the exam and the study guides; students can pop in organically without emailing first.
Normal office hours remain in effect; the instructor will be on campus from roughly 8 ext{ to } 11 and can address questions then.
Wednesday exam specifics:
You will have the entire class period to complete it.
Scantron answer sheets will be provided; bring pencils.
Plan for using a pencil: generally, you should have some 2 ext{ pencils}; if the policy changes, Friday updates will follow.
Study guides (extra credit):
More guides are coming; currently finishing chapter 22; chapter 23 study guide will follow.
For extra credit, plan on submitting handwritten study guides, in an organized fashion, on exam day Wednesday morning.
You’ll hand the completed guide to the instructor; it will be checked during the exam, and the notebook (or other format) will be returned after the exam and answer sheet are handed in, enabling continuation of the next study guides.
The instructor hopes for a quick turnaround so students can begin the next exam’s study guides promptly; it's acknowledged to be a fair amount of work.
Study-guide format and expectations:
Handwritten only; must be neat and organized; do not include superfluous decorations on loose sheets.
Number questions and vocab terms clearly; you may rewrite questions or statements if you wish, but you are not obligated to rewrite the question/statement itself.
The teacher will stop the program if the process becomes too time-consuming or disorganized.
For the vocabulary section, you must write the vocabulary term and its definition.
For questions/statements, you only need to answer; rewriting is optional.
End of chapter 22 focus: evolution scenarios and the pace of evolution.
Chapter 22: Evolution and the Pace of Evolution
Evolutionary pace can vary: some changes are slow, some rapid; adaptive radiation is a form of rapid speciation.
Adaptive radiation: rapid speciation that produces a cluster of mostly related species with diverse ecological adaptations.
Triggered when environments dramatically change (e.g., formation of volcanic islands) or when a key innovation evolves within a lineage.
Examples of key innovations: traits that unlock access to new resources or habitats.
Key innovations and their ecological impact:
Lungs in fish: likely evolved from swim bladders; swim bladders regulate buoyancy by gas adjustment, enabling deeper or shallower movement.
Evolution of lungs allowed fishes to move into hypoxic or even temporarily anoxic environments by gulping air from the surface; this opened avenues for terrestrial life (tetrapods) and movement into environments previously inaccessible.
Wings: evolved independently in birds and insects (convergent evolution); enabled exploitation of aerial environments with new food sources and reduced predation risk in some contexts.
In both cases, key innovations can drive rapid speciation and niche expansion.
Stepwise view of adaptive radiation:
An ancestral species colonizes a cluster of islands (e.g., Galápagos or Hawaiian Islands).
The ancestral population spreads to multiple islands; populations on different islands experience different selective pressures.
Over time, populations diverge due to local adaptation, leading to multiple species.
The color-coding in illustrations represents different species derived from the ancestral lineage.
Some lineages may colonize additional islands, creating allopatric contexts; others may co-occur on a single island, leading to competition.
Allopatry and sympatry in diversification:
Some new species colonize other islands or become geographically separated (allopatry) and diverge due to differing selective pressures.
Alternatively, multiple new species can arise on the same island, with competition driving divergence (or colonization of new islands followed by sympatry).
Competition drives resource partitioning to reduce overlap; natural selection favors traits that minimize competition (character displacement).
Resource partitioning and character displacement:
When two species overlap in resource use, traits that allow exploitation of different resources become advantageous.
Example: differences in beak size enabling access to different seed sizes reduces competition and increases fitness for each population.
Over time, traits shift toward reduced competition, improving fitness for the individuals exploiting different resources.
The two key ideas illustrated for character displacement:
Before displacement: two species compete for overlapping resources; high competition reduces fitness for individuals in the overlap.
After displacement: natural selection favors individuals with traits that use different resources; trait frequencies shift toward the extremes, reducing overlap.
Three-spined sticklebacks as a case study:
British Columbia sticklebacks show divergence in ecological niches and body/morphology to minimize competition, including specialized gill structures and streamlined bodies for pelagic open-water feeding vs. bottom-dwelling, rocky-margin feeding.
This divergence reduces competition and supports coexistence in shared habitats.
Darwin’s finches and adaptive radiation evidence:
Darwin’s finches showcase rapid diversification to exploit different food sources, leading to distinct beak morphologies and feeding strategies.
Lake Victoria cichlids as a dramatic example:
Diversified rapidly with notable color pattern variation and morphological differences tied to feeding strategies.
Key innovation: evolution of a second set of jaws (pharyngeal jaws) and changes in snout shape, enabling processing of different food items.
Species richness reached around 400 species, but up to 70\% of them were extinct by the 1990s due to the introduction of the perch predator, illustrating how competition and predation drive extinction risk.
Adaptive radiation is often depicted as a branching diagram (phylogeny) showing rapid speciation from a common ancestor to multiple extant species.
Additional case studies:
Lake Victoria ciliates (cichlids) highlight the role of jaw diversification in rapid adaptive radiation.
Comparative notes on other radiations (e.g., Darwin’s finches) illustrate similar patterns of resource-driven divergence.
Pace of evolution: gradualism (accumulation of small changes) versus punctuated equilibrium:
Gradualism (often described as slow, continuous change): accumulation of small changes over thousands to millions of years; key innovations are not necessary for major shifts.
Punctuated equilibrium: long periods of little to no evolutionary change (stasis) punctuated by bursts of rapid change in relatively short timescales.
Visual representation: a graph with time on the x-axis and evolutionary change on the y-axis demonstrates extended plateaus (stasis) with sudden vertical or steep segments for rapid change.
Stasis and range shifts:
Environments that remain stable can foster evolutionary stasis; conversely, range shifts allow species to stay within favorable conditions as climates shift, reducing selection pressures and slowing apparent evolutionary change.
If a species can migrate to keep its environment stable (e.g., moving north to maintain temperature) it may exhibit less selective pressure for rapid adaptation.
Climate-driven range shifts can modify selection pressures and alter rates of evolution.
Ocean currents, larval dispersal, and climate effects on marine life:
Some sessile adults rely on larval dispersal via water currents; future predictions suggest shifts in ocean currents could transport larvae to new areas with different temperatures and light, affecting survival and distribution.
Corals rely on zooxanthellae (photosynthetic algae) for nutrition, which also colors corals; these symbiotic relationships complicate adaptation, as both partners must cope with environmental changes.
Coral reefs and ocean chemistry under climate change:
Coral bleaching and symbiosis with zooxanthellae tie coral health to the presence of symbiotic algae; loss of zooxanthellae weakens corals as they lose a primary energy source.
Ocean acidification (driven by increased atmospheric CO₂) reduces calcium carbonate (CaCO₃) availability, which corals and other shelled organisms require to build skeletons and shells.
Mechanism: CO₂ dissolves in water forming carbonic acid; increased carbonic acid lowers carbonate ion availability for CaCO₃ precipitation, effectively softening shells/skeletons and impacting reef growth.
Additional context: doom-and-gloom discussion and conservation framing:
Evolution and diversification have occurred for hundreds of millions of years, with long-term trends showing net diversification, but mass extinctions punctuate this history.
There have been five major mass extinctions historically: the Ordovician, Devonian, Permian, Triassic, and Cretaceous events.
These events saw extensive losses of life, with near-total declines in some groups and drastic reductions in biodiversity.
The present moment is described as a potential sixth mass extinction, largely driven by human activity; while background extinction rates are ongoing, the current rates are elevated relative to typical baselines.
This topic is often framed within conservation biology, exploring how human activities alter environments and disproportionately affect different groups of organisms.
Biodiversity and the long-term record:
A broad view shows biodiversity increasing over the last 6\times 10^2\text{ million years}, with a larger number of families including many related