Explain the concept of struggle for existence.

Explanation

### Step-by-Step Solution:

1. **Definition of Struggle for Existence**:
The concept of "Struggle for Existence" is a principle within the theory of natural selection, which was proposed by Charles Darwin. It refers to the competition among living organisms for limited resources necessary for survival and reproduction.

2. **Types of Struggles**:
There are three main types of struggles that organisms face in their environment:

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