D4.3.12 Evolution as a consequence of climate change (HL) Notes

Evolution as a Consequence of Climate Change

1. Evolution is a process where populations change over generations due to genetic variations and environmental pressures.
2. Climate change is altering habitats, creating new challenges for survival.
3. Organisms must adapt or face extinction.

The Tawny Owl: A Case Study

1. Tawny owls ( Strix aluco) in Finland exhibit two plumage colors: brown and grey.
2. This coloration is a heritable trait, with brown being dominant over grey.
3. Snow cover plays a critical role in their survival:
   1. Grey owls blend into snowy landscapes, reducing predation risk.
   2. Brown owls are more visible in snow, making them easier targets for predators.

Tawny Owl and Snow Cover

1. In cold northern climates, where the snow is often present, light-colored owls are more camouflaged against the snowy background, making them harder for predators to spot.
2. In contrast, dark-colored owls stand out against the snow, making them more visible and less likely to survive.
3. This means that in snowy environments, light-colored owls have a higher fitness, as they are better able to evade predators.

How Climate Change Alters Fitness

1. Over the past 30 years, winters in Finland have become milder, with less snow.
2. As climate change leads to warmer temperatures in winter and a decrease in snow cover, the white morph becomes less advantageous.
3. Without snow, the white morph becomes more visible against the darker, forested backgrounds, which reduces its fitness.
4. In contrast, the brown morph becomes better camouflaged in areas with less snow, giving it a higher chance of survival.
5. This environmental shift has reversed the selective pressure:
   1. Brown owls now have a higher survival rate because their plumage blends better with snow-free environments.
   2. Grey owls are less camouflaged without snow, increasing their vulnerability.

Evidence of Evolution in Tawny Owls

1. Studies show a rise in the frequency of brown owls as snow cover decreases.
2. This change demonstrates how climate-driven environmental shifts can influence natural selection.

Natural Selection and Evolutionary Change in Response to Climate Change

1. The example of the tawny owl illustrates natural selection at work.
2. The fitness of the color morphs changes in response to changes in the environment (in this case, snow cover).
3. As snow cover decreases due to warmer winters, the brown morph becomes better adapted to its environment and is more likely to survive and reproduce.
4. Over time, this shift in fitness could lead to an evolutionary shift in the population, with more brown morphs and fewer white morphs.
5. This example shows how climate change can alter selective pressures and lead to evolutionary changes in species.
6. As the environment changes, natural selection acts on the available genetic variation within a population, favoring individuals that are better suited to the new conditions.