This is determined by the topography, geology, and climate of an area, all of which may be modified over time by the organisms that live there. The organic community with the physical environment makes up an ecosystem. When we look closer we realize that the same species are not involved. There may be closely related or quite unrelated plants and animals occupying similar ecological niches. A group of ecosystems with similar biological features is called a biome .
Light is the primary resource for which plants compete, followed by water and nutrients.
Antagonism is commonly between plants and other kinds of organisms, although it can be between plants. Allelopathy occurs when one plant produces chemicals that inhibit the growth of other plants. We don't know how common this phenomenon is, although there is great interest in the use of cover crops for weed suppression in the field. Parasitism involves mostly viral , bacterial and fungal pathogens , but there are a few parasitic angiosperms. These interactions are not just features of wild areas.