ecosystems are rich in
biodiversity. This is the
Gambia River in
Senegal's
Niokolo-Koba National Park. of
Baja California desert,
Cataviña region,
Mexico External and internal factors Ecosystems are controlled by both external and internal factors. External factors, also called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem. On broad geographic scales,
climate is the factor that "most strongly determines ecosystem processes and structure". Climate determines the
biome in which the ecosystem is embedded. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of energy available to the ecosystem. Other external factors that play an important role in ecosystem functioning include time and potential
biota, the organisms that are present in a region and could potentially occupy a particular site. Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present. The
introduction of non-native species can cause substantial shifts in ecosystem function. Unlike external factors, internal factors in ecosystems not only control ecosystem processes but are also controlled by them. Other factors like disturbance, succession or the types of species present are also internal factors.
Primary production biomass, it is only a rough indicator of primary production potential and not an actual estimate of it. Primary production is the production of
organic matter from inorganic carbon sources. This mainly occurs through
photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass,
soil carbon and
fossil fuels. It also drives the
carbon cycle, which influences global
climate via the
greenhouse effect. Through the process of photosynthesis, plants capture energy from light and use it to combine
carbon dioxide and water to produce
carbohydrates and
oxygen. The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP). About half of the gross GPP is respired by plants in order to provide the energy that supports their growth and maintenance. The remainder, that portion of GPP that is not used up by respiration, is known as the
net primary production (NPP).
Ecosystem respiration is the sum of
respiration by all living organisms (plants, animals, and decomposers) in the ecosystem.
Net ecosystem production is the difference between
gross primary production (GPP) and ecosystem respiration. In the absence of disturbance, net ecosystem production is equivalent to the net carbon accumulation in the ecosystem. Energy can also be released from an ecosystem through disturbances such as
wildfire or transferred to other ecosystems (e.g., from a forest to a stream to a lake) by
erosion. In
aquatic systems, the proportion of plant biomass that gets consumed by
herbivores is much higher than in terrestrial systems.
Decomposition The carbon and nutrients in
dead organic matter are broken down by a group of processes known as decomposition. This releases nutrients that can then be re-used for plant and microbial production and returns carbon dioxide to the atmosphere (or water) where it can be used for photosynthesis. In the absence of decomposition, the dead organic matter would accumulate in an ecosystem, and nutrients and atmospheric carbon dioxide would be depleted. Newly shed leaves and newly dead animals have high concentrations of water-soluble components and include
sugars,
amino acids and mineral nutrients. Leaching is more important in wet environments and less important in dry ones. Animals fragment detritus as they hunt for food, as does passage through the gut.
Freeze-thaw cycles and cycles of wetting and drying also fragment dead material. The rate of decomposition is governed by three sets of factors—the physical environment (temperature, moisture, and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself. Resilience thinking also includes humanity as an integral part of the
biosphere where we are dependent on
ecosystem services for our survival and must build and maintain their natural capacities to withstand shocks and disturbances. Time plays a central role over a wide range, for example, in the slow development of soil from bare rock and the faster
recovery of a community from disturbance. This can range from
herbivore outbreaks, treefalls, fires, hurricanes, floods,
glacial advances, to
volcanic eruptions. Such disturbances can cause large changes in plant, animal and microbe populations, as well as soil organic matter content. Disturbance is followed by succession, a "directional change in ecosystem structure and functioning resulting from biotically driven changes in resource supply." The frequency and severity of disturbance determine the way it affects ecosystem function. A major disturbance like a volcanic eruption or
glacial advance and retreat leave behind soils that lack plants, animals or organic matter. Ecosystems that experience such disturbances undergo
primary succession. A less severe disturbance like forest fires, hurricanes or cultivation result in
secondary succession and a faster recovery.
Nutrient cycling Ecosystems continually exchange energy and carbon with the wider
environment. Mineral nutrients, on the other hand, are mostly cycled back and forth between plants, animals, microbes and the soil. Most nitrogen enters ecosystems through biological
nitrogen fixation, is deposited through precipitation, dust, gases or is applied as
fertilizer. Macronutrients which are required by all plants in large quantities include the primary nutrients (which are most limiting as they are used in largest amounts): Nitrogen, phosphorus, potassium. Secondary major nutrients (less often limiting) include: Calcium, magnesium, sulfur.
Micronutrients required by all plants in small quantities include boron, chloride, copper, iron, manganese, molybdenum, zinc. Finally, there are also beneficial nutrients which may be required by certain plants or by plants under specific environmental conditions: aluminum, cobalt, iodine, nickel, selenium, silicon, sodium, vanadium. Phosphorus enters ecosystems through
weathering. As ecosystems age this supply diminishes, making phosphorus-limitation more common in older landscapes (especially in the tropics). , featuring various
Adansonia (baobab) species,
Alluaudia procera (Madagascar ocotillo) and other vegetation
Biodiversity plays an important role in ecosystem functioning. Ecosystem processes are driven by the species in an ecosystem, the nature of the individual species, and the relative abundance of organisms among these species. Ecosystem processes are the net effect of the actions of individual organisms as they interact with their environment.
Ecological theory suggests that in order to coexist, species must have some level of
limiting similarity—they must be different from one another in some fundamental way, otherwise, one species would
competitively exclude the other. Despite this, the cumulative effect of additional species in an ecosystem is not linear: additional species may enhance nitrogen retention, for example. However, beyond some level of species richness, == Study approaches ==