Population Attributes : These are certain characteristics of a population. Four of them are as follows :

1. Population size or density.
2. Population interaction.
3. Due to natality or birth rate, population increases continuously. It is the production of new individual by birth, hatchingkor by asexual mode, etc. It is expressed as the number of birth per 1000 individuals.
4. Death rate or mortality, is the number of deaths in the population during a given period.

Mutualism : It is an interaction that confers benefits to both the interacting species. For example :
Mycorrhizae : Represent a close mutual association between fungi and the roots of higher plants. Fungi help the plants in absorption of nutrients, especially phosphorus' while the plants provide food for the fungus.