Urban Adaptations
100: Why do city hawksbeard plants produce more non-dispersing seeds?
Because seeds that fly far land on concrete/pavement and cannot grow; heavy seeds land in the "soil island" nearby.
100: What major physical difference did scientists notice in UCSD Juncos vs. Mountain Juncos?
They have less white in their tail feathers (and are generally bolder).
100: What do we call the differences in traits between individuals in a population?
Variation.
100: In the city, is a seed that flies far "favorable" or "unfavorable"?
Unfavorable (it leads to death on the pavement).
100: If a trait makes an organism more likely to survive and have babies, we say it increases their ________.
Fitness. (In biology, fitness isn't about the gym; it's about reproductive success!)
200: In the rat study, what "selective pressure" caused city rats to evolve differently?
Environmental factors like diet (human food), toxins (rodenticide), or habitat fragmentation.
200: True or False: The UCSD Juncos moved to the city and then decided to change their tails.
False. Individuals don't choose to evolve; the environment selected those who already had helpful traits.
200: For a trait to be passed down, it must be ______, meaning it's in the DNA.
Heritable
200: What does a "shift" in a histogram mean for a population over time?
It means the average trait in the population has changed (Evolution has occurred).
200: Which "system" in the Junco's body connects their bold behavior to their physical feather traits?
The Endocrine System. (Hormones like CORT regulate both the "fight or flight" behavior and can be linked to pigment/feather color.)
300: What happens to the "heavy seed" trait frequency in a city population over generations?
The frequency increases (becomes more common).
300: Which hormone levels were lower in the bold UCSD Juncos compared to the shy ones?
CORT (Corticosterone), the stress hormone.
300: This term describes an organism's ability to survive and reproduce in its environment.
Fitness.
300: What happened to the "white outer tail feather" percentage in the UCSD population?
It decreased (UCSD Juncos have less white in their tails than their mountain ancestors)
300: Does natural selection act on the individual's genotype (DNA) or its phenotype (physical trait)?
Phenotype. (The environment "sees" and selects the physical trait; the DNA just hitches a ride to the next generation.)
400: Explain why "dispersing" (flying) seeds are a disadvantage in a paved city.
They land on inhospitable surfaces (concrete) and die, meaning those "flying" genes aren't passed on.
400: How does the "longer breeding season" in the city affect the Junco population?
It allows them to have more offspring per year, increasing the frequency of "urban-friendly" traits quickly.
400: The four components of Natural Selection are Variation, Inheritance, Selection, and ______.
Time (or Differential Survival/Reproduction).
400: If a trait is "neutral," what would you expect to see in the data over many years?
The frequency would remain relatively stable or change randomly, as there is no pressure for or against it.
400: Explain why the UCSD Juncos don't fly away as easily as the Mountain Juncos when a human approaches.
Lower CORT levels / Selection for Boldness. (In a city with constant human foot traffic, being "scared" all the time wastes energy. The bolder birds spent more time eating and mating, passing those "bold" genes on.)
500: If a city park is replaced with a massive community garden (all soil, no concrete), what do you predict will happen to the hawksbeard seed traits over the next 20 years?
The frequency of dispersing (flying) seeds would likely increase again. Without the "pavement penalty," seeds that can travel further to colonize the new, large patches of soil would have a survival advantage.
500: Explain how the "exploratory behavior" of the UCSD Junco provides a competitive advantage specifically in an urban environment compared to a forest
In cities, food sources (trash, bird feeders) are patchy and unpredictable. Bold/exploratory birds find these new food sources faster than "shy" birds, allowing them to survive winter and produce more offspring.
500: Why is "differential reproductive success" considered the most important part of the natural selection process?
Because survival doesn't matter for evolution unless the organism passes its genes to the next generation. An organism that lives 100 years but has 0 babies has a biological fitness of zero.
500: In the rat study, if scientists found city rats and country rats had identical DNA but different behaviors, could we still call it "evolution"? Why or why not?
No. Evolution is defined as a change in the inherited (genetic) traits of a population over time. If the DNA hasn't changed, the behavior is likely "learned" or "plasticity," not evolved.
500: How can a single environmental change (like city noise or lights) lead to a change in both a physical trait AND a behavioral trait simultaneously?
Through pleiotropy or linked systems (like the endocrine system). For example, lower CORT levels help a bird stay calm in noisy cities (behavior), but those same hormone levels also control how much melanin is deposited in feathers (physical trait).