The abiotic factors of an ecosystem are those components of it that are not alive. These can be thought of as the core elements upon which the entire structure of the ecosystem depends. Whatever organisms exist in a given ecological community must adapt to its prevailing abiotic factors, which can be strikingly extreme in deserts.
Limited water is a defining feature of desert ecosystems and their most profound environmental constraint. Typically, deserts receive less than 508 millimeters (20 in.) of rain per year. This means that animals and plants looking to survive in the desert must be able to live with little water for extended periods of time. For example, cacti have evolved to store water in their stems to help them through dry spells.
Deserts typically go through huge fluctuations in temperature during a 24-hour period. Because there is little moisture, deserts lack the insulating protection of both humidity and cloud cover. A desert that is hot during the day may drop to well below zero degrees at night, once the heat of the sun has left. Organisms that cannot adapt well to rapid temperature fluctuations have trouble surviving in the desert.
The type of soil in an ecosystem determines what plants can grow, which in turn defines which animals can survive. Desert soil types vary greatly, influencing a given location’s drainage as well as evaporation. Water may seep deeply in sandy or gravelly substrate, but barely penetrate hard-packed clay or exposed bedrock. Depending on the substrate and the intensity of precipitation or flow, rainfall or runoff may sink quickly into desert soil or form sudden flash floods producing significant erosion.
Desert sunlight can be intense courtesy of prevailing cloud-free conditions and, in the subtropics, the position of the sun. Barren flats such as pebbly desert pavement or “reg” may be blindingly bright. In other desert landscapes, more convoluted terrain, such as sand dunes and mountain ranges, or more substantial plant cover, such as forests of tree-sized cacti, ensure more complex patterns of light and shadow. The degree and intensity of sunlight in a given spot helps shape its microclimate and thus profoundly affects plants and animals.