lesson 2: what could be causing the trout population to change?

invasive species could enter the great lakes because their native rivers emptied into them. the great lakes were all interconnected, so it was easy for them to spread.

the trout population dropped in 1920. It increased again in 1950.

possible reasons why the trout population had decreased:

  • overhunting
  • invasive species
  • climate change
  • lack of food
  • predators
  • disease
  • electrocution
  • pollution

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Timberlines

For about 80-100 years, trees in the alps have been moving further up the mountain.

plants have moved up at a rate of 4 meters every 10 years. At higher elevations, the number of trees increased. timberline is the edge of a treeā€™s habitat. Trees cannot survive beyond this line.

Ā Climate change could be a reason for this, as seedlings cannot survive when the foothills are warm and dry. seedlings that get dispersed higher have a better chance of survival, so this is why the timberline is moving up. ^^It is due to reproduction and climate change.^^

Humboldt penguins

Humboldt penguins originally lived in the southern hemisphere but began appearing in the northern hemisphere. people first noticed Humboldt penguins in the northern hemisphere in 1976. Penguins cannot fly, they only swim.

scientists believe that fishermen caught penguins and kept them as pets. when they arrived in the northern hemisphere, they thought it was a good place for the penguins to live, and released them there. ^^They moved due to an interaction with other organisms.^^

California red-legged tree frogs

California red-legged tree frogs live in wetlands and streams in central California. They live in thick vegetation next to deep pools of water. They need an aquatic environment so they can reproduce. Scientists found that these frogs can no longer be found in 70% of their original habitats. They are only found in 10% of their native habitats.

Humans introduced bullfrogs to the native habitats of the red-legged frogs. Bullfrogs are an invasive species. They prey on red-legged tree frogs. red-legged frogs live in swampy areas and lay their eggs in shallow water. These habitats have been destroyed by urbanization. ^^So it is due to reproduction, environment, and other organisms.^^

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