What is the difference between direct and indirect struggle for existence? Give examples.

Direct struggle – any relationship in which between individuals of one or different species in the composition of their populations physical contact is expressed to one degree or another. Direct struggle can be either intraspecific or interspecific. Examples of direct intraspecific struggle can be: rivalry between rook families for breeding sites, between wolves for prey, between males for territory. The direct interspecific struggle includes the relationship between a predator and a prey, a parasite and a host, flowering plants and pollinating insects, nodule bacteria and legumes, sharks and fish, sticking, etc. Indirect struggle is any relationship between individuals of different populations using common food resources, territory, environmental conditions without direct contact with each other. Indirect struggle can also be intraspecific, interspecific and with abiotic environmental factors. Examples of indirect struggle can be the relationship between individual birch trees in a thickened birch grove (intraspecific struggle), between polar bears and Arctic foxes.