All organisms on Earth are connected. In an ecosystem, each organism holds a unique position and plays a role that contributes to the functioning of the entire system. An ecosystem includes all organisms living in one geographic region and all the environmental factors, such as temperature and water availability, that affect those organisms. For example, a forest may be one ecosystem while a meadow may be another. Similarly, all life is connected to the global biosphere, which includes all living things and their ecosystems on Earth. All ecosystems share one planet, and global climate (long-term, wide-range weather patterns) plays a major role in determining the location and composition of each ecosystem. Likewise, global disturbances such as climate change, which is a long-term change in weather patterns, can impact every ecosystem.
Ecology is the study of interactions among organisms and between organisms and their environments. Different areas of ecology focus on interactions that occur at different levels, starting with individual organisms. A population is an interbreeding group of individuals of the same species, such as coyotes. The study of interactions among a group of organisms of the same species is called population ecology. The group of all organisms living in a given area is called a community. Community ecology involves the study of the interactions among all species living in an area. Interactions among all organisms and their shared environment is the focus of ecosystem ecology. The next level that is studied by ecologists is a biome, a large ecosystem defined by climatic, physical, and biotic characteristics. It typically includes smaller ecosystems in a wide geographic region sharing similar characteristics, usually average rainfall, average temperature, and major plant types. For example, the American prairie is a grassland biome. The combination of all the world's biomes, including all life on Earth, is the biosphere.
Factors Influencing the Distribution of Organisms
The distribution of organisms around the planet is dependent upon several factors. Scientists classify factors as biotic or abiotic. A biotic factor is a living thing that influences an ecosystem, such as food resources, predators, and pathogens. An abiotic factor is a nonliving thing, such as water, temperature, and minerals, that affects an ecosystem. An ecosystem includes all organisms living in one geographic region and all the environmental factors that affect those organisms.
Both types of factors determine whether an organism is likely to reside in a particular location. Biotic factors include the presence or absence of other organisms. The presence of natural predators may drive a population to either leave an area or become extinct. An absence of natural prey or other nutrient-providing species may have a similar effect. For example, either the presence of a large population of wolves or the absence of plentiful grasses may cause a population of rabbits to leave an area or die out. Competition can also play a role in where a species is found. Competition exists when species fight each other directly or when they use the same resource. A population may be physically capable of thriving in a given environment but be pushed out of an area by another species that is a better at finding resources. For example, if there are no wolves and plenty of grasses, but a large population of grasshoppers consumes the grasses before the rabbits can find them, the rabbit population may leave the area or die out.In addition to biotic factors, the global distribution of species is also dependent on abiotic, or nonliving, factors. Organisms tend to be found in places well suited for their physiological needs and physical constraints. Water is among the most important abiotic factors because water is critical for life. Access to some amount of freshwater, which accounts for only a small percentage of all water on Earth, is important for terrestrial organisms. Temperature is another factor that determines where life is found on Earth. Many organisms survive within a narrow body-temperature range. Depending on its metabolism, an organism has a greater or lesser tolerance for extreme environmental temperature fluctuations. In addition, some organisms are better adapted to cold temperatures, while others thrive at warm temperatures. As a result, more organisms are found in locations with moderate or stable temperatures than in locations with extreme or highly variable temperatures. Sunlight is another important abiotic factor affecting the geographic distribution of life. Photosynthetic organisms require access to sunlight, and these organisms are often the source of energy for ecosystems. Subterranean caves and deep-ocean environments contain organisms that use alternative energy sources, such as feeding on leftovers that sink from shallow depths. Pressure is yet another abiotic factor that can affect living things. In the deep ocean, where pressure is high, only organisms specifically adapted to those conditions can thrive. Similarly, at high mountain altitudes, where air pressure is low and oxygen is scarce, specially adapted organisms are found. Oxygen is important for respiring organisms, but the presence of other critical elements in air, soil, and water can be equally important. For example, organisms also require carbon, nitrogen, and phosphorus to carry out life's processes. Regional variability in each of these factors helps explain the variety of organisms found across different environments around the globe.
Additional factors affect where populations thrive. Some geographic patterns of living things are global. There tends to be greater biodiversity (number and variety of species in a given area) at low and mid-range elevations than at higher elevations. It is suggested this is because there is less habitable area at higher elevations. There tends to be greater biodiversity closer to the ocean's surface than in the deepest depths of the oceans, because of the availability of light. In addition, more biodiversity exists near the equator than near Earth's poles. As in all aspects of biology, there are exceptions to these general trends. For example, a hydrothermal vent is a deep-sea fissure releasing extremely hot fluid that contains hydrogen sulfide. Areas around hydrothermal vents have much greater biodiversity than the surrounding sea floor.