Community Ecology III

Good afternoon welcome back to Bio 1.
Last lecture before Midterm 2, scheduled for Wednesday at this time and place.
Students must bring a writing implement; scientific calculators are permitted, but graphing calculators are not.
Excitement for students to excel on the upcoming exam.

Office hours available this afternoon and tomorrow.
Tutoring session scheduled for tomorrow afternoon as additional support resources.

Today's lecture integrates ecology and evolution themes into a cohesive whole.
Focus on situations where ecology influences evolutionary trajectories of organisms.

Discussion around toxic defensive compounds in plants, exemplified by milkweed sap.
Inquiry into the driver of selection for plant production of these compounds and the patterns of phenotypic change that result.
- Key terms discussed include:
  - Directional selection
  - Defensive processes
  - Predation
  - Herbivory (specifically, the predation of plants).

By the end of the lecture, students should be able to:
1. Explain how species interactions can lead to evolutionary change.
2. Understand the impact on speciation.

Exploration of how species interactions shape evolutionary trajectories.
Previous discussions on how competition drives character displacement, forcing organisms to utilize different resources or parts of the environment.

Graphical representation of a niche:
- X-axis: Variable (e.g., food size, specifically seed size).
- Y-axis: Frequency of organism's usage of food of that size.
Conceptual populations:
- Black population uses primarily medium-sized seeds.
- Blue population enters, leading to competition for these seeds.

Organisms may adapt behaviors to alleviate competition (e.g., birds may shift to smaller seeds).
- If behavioral flexibility is not present, individuals with extreme trait values (e.g., those who are adept at eating tiny seeds) will experience greater reproductive success.
Over time, populations diverge; species occupying complementary niches to minimize competitive pressures.
This phenomenon is categorized under character displacement:
- Applicable to resources like food or reproductive traits where mistakes can happen (e.g., reproductive character displacement).

Definition: The evolution of one organism influences the evolution of another with which it interacts.
- Two key types of co-evolution discussed:
1. Mutualism: Co-evolutionary trait matching.
2. Predation interactions: Evolving arms race scenarios.

Description of character displacement:
- Outcomes from competition for the same limiting resources driven by natural selection.
- Observed where two populations show similar traits in allopatry but diverge in sympatria due to competition.
Real-life example using Galapagos finches (Geospiza species):
- When isolated, populations show similar beak sizes (10-11 mm).
- Upon overlapping in habitat, G. fuliginosa develops smaller beaks, while G. fortis develops larger beaks, evidencing character displacement through resource competition.

Character displacement related to mating mistake avoidance.
Example using fly species (Costalis and Prunosa):
- Males exhibit clear and orange wing morphs with different preferences in sympatry.
- In allopatry, no strong selection for wing coloration.
- In sympatry, divergence occurs: Costalis predominantly orange-winged and Prunosa clear-winged to ensure reproductive compatibility.

When populations interact competitively, ecological pressures can facilitate the emergence of distinct traits.
Example: Two species of toads produce two types of tadpoles (omnivorous and carnivorous).
- Proposed activity: Students analyze proportions of tadpole types in allopatry vs. sympatry to assess character displacement.
Observations lead to conclusions on adaptive evolutionary changes in response to resource availability and reproductive strategies.

Case study of mutualism: orchids and their pollinators (e.g., specific moths).
Darwin's Hypothesis: Evolution of long nectaries aligns with the long-tongued moth pollinator's requirements, leading to mutual dependence.
Adaptations:
- Plant evolves longer nectaries to ensure pollinator effectiveness.
- Pollinators evolve traits that allow them to access nectar while ensuring pollen transfer.

Example: Ant-acacia mutualism
- Acacia species provide resources (nectar, food bodies) to ants in exchange for protection from herbivores.
- Description of morphological adaptations: swollen thorns and nutrient-rich secretions to incentivize mutualist ants.
- Evidence supporting co-adaptive evolution between the acacias and ants based on their reliance on each other for survival.

Discussion of antibiotic resistance as a crucial example of co-evolution in medical biology.
- Graph showing the time period each antibiotic remained effective before resistance emerged, influenced by bacteria’s rapid generation time.

Example involving toxic newts (Taricha species) and their snake predators.
- Geographic variation in newt toxicity and the correlation with predator tolerance levels.
- Details on how toxin levels affect sodium ion channels and associated trade-offs for the snakes.
Importance of ecological context: availability of alternative prey may affect predator-prey co-evolutionary dynamics.

Definition: The diversification of organisms when niche space opens up, leading to the emergence of new species.
- Example: Adaptive radiation among Hawaiian honeycreepers from a single ancestor.
- Discussion of the distinct beak shapes and behaviors that evolved to fill diverse niches without competition.
Consideration of insights regarding evolutionary processes that influence biodiversity.

Discussion surrounding character displacement, trait matching, and evolutionary arms races as driving mechanisms for diversification.
Recognizing adaptive radiation as a result of ecological dynamics leading to new niche exploitation.
Final remarks leading into upcoming midterm exam preparations.