Living organisms are connected to others because of a number of reasons but the main reason is that they together make the food chain. A food chain is the network of the organisms linked together on the basis of their food. For example, lion eats goats, goats eat grass and other plants(which are also living) and we eat meat as well as grass. In this way one organism is the food of the other organism. If the population of one organism starts depleting then the other organism which eats the depleting specie will also start depleting and the cycle expands. Another way through which living organisms are linked with others is through their relationships like Mutualism, parasitism etc. Lichens and fungi make a beneficial relation with each other and similarly, other other organisms make such relations.