Question

1. stickleback fish in marine and freshwater environments

in the ocean, three - spined stickleback fish develop
heavy armor plates that protect them from large
predators. however, when some populations
moved into freshwater lakes, their environment
changed drastically. freshwater environments had
fewer large predators, and were nutrient - poor,
making growth and reproduction more difficult.
sticklebacks with fewer armor plates could grow
faster, mature sooner, and escape small predators
by swimming faster. over generations, freshwater
populations evolved to have fewer or no armor
plates, while marine populations still retain heavy
armor. the graph tracks this change over time.
unit 7: natural selection
biology by: rachel taylor
directions: for each example, identify and explain the trait variation with the initial advantage, describe the environmental change
that took place, and identify and explain the trait variation with the advantage after the environmental change. then, interpret each
graph by describing the data.

example	variation with initial advantage	environmental change (selective pressure)	variation with advantage after environmental change	graph interpretation
elephants	(handwritten text, partially unclear)	(handwritten text, partially unclear)
cod fish	(handwritten text, partially unclear)	(handwritten text, partially unclear)	cod populations evolve to mature at smaller sizes	(handwritten text, partially unclear)
stickleback fish
cane toads

Explanation:

For the Stickleback fish example:

• Variation with initial advantage: In marine environments, heavily armored sticklebacks were protected from large predators, giving them a survival/reproductive advantage.
• Environmental change (selective pressure): Movement to freshwater lakes with fewer large predators, nutrient - poor conditions, and different predation (small predators, need for faster growth/escape).
• Variation with advantage after environmental change: Lightly armored (or less armored) sticklebacks could grow faster, mature sooner, and escape small predators by swimming faster, so they had a survival/reproductive advantage in freshwater.
• Graph interpretation: The bar graph shows that in marine populations, the percentage of heavily armored sticklebacks is high (around 85 - 90%) and lightly armored is low (around 10 - 15%). In freshwater populations, the percentage of heavily armored is low (around 30 - 35%) and lightly armored is high (around 70 - 75%), indicating a shift in armor trait frequency due to natural selection.

Answer:

Example	Variation with initial advantage	Environmental change (selective pressure)	Variation with advantage after environmental change	Graph interpretation