For example, two animal predators may consume different prey items, so they are less likely to compete with one another, allowing higher total biomass of predators in the system. In the case of plants, all species may utilize the same suite of resources (space, light, water, soil nutrients, etc.)
The sperm and egg have 1/2 the amount because when the sperm fertilizes the egg, it equals out to the regular amount of chromosomes. That is why we have half chromosomes from our dad and half chromosomes from our mom, equaling out to normal amount of chromosomes.
