Explanation:

- Correct Answer: Option 3 - Charles Elton

- Charles Elton was a pioneering English ecologist known for founding the field of animal ecology.

- In 1927, he introduced the concept of the "pyramid of numbers," illustrating the decreasing number of organisms at each trophic level in a food chain.

- Option 1 - Arthur Tansley

- Arthur Tansley was a British ecologist who introduced the term "ecosystem."

- His work mainly focused on plant communities and ecosystems.

- Option 2 - Eugene Odum

- Eugene Odum was an American ecologist who emphasized ecosystem ecology.

- He is known for his work on ecological energy flow and ecosystem dynamics.

- Option 4 - Ernst Haeckel

- Ernst Haeckel was a German biologist who coined the term "ecology" and focused more on biological evolution.

- His work laid foundations for future ecological and evolutionary studies, but not specifically related to food web structures.