The number and kinds of organism is not constant. How do you explain this statement?

The number and kinds of organisms is never constant. Populations are constantly affected by various factors. These factors include:

1. Season: Some organisms, plants and animals alike, are present in the ecosystem only during certain time. For example Mayfly, Mayflies spend a year awaiting their birth, and then most die after living just one day.

2. Extinction: Some species might be wiped out due to human or environmental activities.

3. Human activities: Deforestation causes a loss of a great number of organisms, hunting reduces the number of organisms.