User:Williamkearney98/River ecosystem

Trophic Level Dynamics
Trophic levels is a sub unit of a food web in which explains the transfer of energy from one part of the ecosystem to another. This a is very important concept when understanding the roles that each organism plays with in a food web.

Trophic levels can be illustrated as numbers determining how far the organism is along the food chain.

All functions, including all life within an ecosystem are centered off one external source of energy, solar radiation. Portions of this solar radiation is consumed by producers (plants) and turned into organic substances to be used by inorganic substances (consumers). Plants release portions of this energy back into the ecosystem through a catabolic process. Animals then consume the large amounts of potential energy that is being released from the producers. This system is always followed by death of the consumer organism which then returns nutrient back into the ecosystem to allow suitable growth windows for the plants, and the cycle returns again. This classification of breaking down the cycles into levels has made for understanding ecological succession much more informative for ecologist when observing the transfer of energy within a system.
 * 1) Level One: Producers, plants that can generate their own food using solar radiation including algae, phytoplankton, mosses and lichens.
 * 2) Level Two: Consumers, organism often known as animals that consume their energy from eating producers, for example zooplankton, small fish, and crustaceans.
 * 3) Level Three: Decomposers, organisms that breakdown the dead matter of consumers and producers and return the nutrients back into the system. Examples of these organisms are bacteria and fungi.

Top-Down and Bottom-Up Affect
A common question with trophic level dynamics is the ability to regulate resources and production. The usage and interaction between resources have a large impact on the structure of the food webs as a whole. Temperature plays a role in food web interactions including top-down and bottom-up forces within ecological communities. Bottom-up regulations within a food web is when a resource is available at the base or bottom of the food web, increases productivity which then will climb the chain and influence the biomass availability to higher trophic organism. Top-down regulations is when the predator populations increase which limits the amount of the prey population available, this limits the availability of energy for lower trophic levels within the food chain. Numerous biotic and abiotic factors have the ability to alter the importance of top-down and bottom-up interactions.

Trophic Cascade
Another example of food web interactions is a concept called trophic cascade. Understanding trophic cascade has allowed for ecologist to better understand structure and dynamics of food webs within an ecosystem. This idea of trophic cascade allows for keystone predators to structure an entire food web in terms of how they interact with their prey. Trophic cascade can cause a drastic change in the energy flow with in a food web. For example if a top predator often called keystone species consumes organism below them in the food web, it will change the preys density and behavior. This affects the abundance of an organism that is consumed further down the chain or also know as cascading down the tropic levels. Empirical evidence shows that trophic cascade is much more prevalent in terrestrial food webs rather than aquatic food webs.

Food Chain
A food chain is a system of links that makes up a food web and represents the order in which organisms are consumed from one trophic level to the next. Each link in a food chain correlates to one trophic level in the ecosystem. The numbered steps it takes for the initial source of energy starting from the bottom to reach the top of the food web is known as the food chain length. While food chain length can fluctuate, aquatic ecosystems start with primary producers that are consumed by primary consumers which are consumed by secondary consumers, and those in turn can be consumed by tertiary consumers so on and so forth until the top of the food chain has been reached.

Primary Producers
Primary producers start every food chain. Their production of energy and nutrients comes from the sun through photosynthesis. Algae contributes to a lot of the energy and nutrients at the base of the food chain along with terrestrial litter-fall that enters the stream or river. Production of organic compounds like carbon is what gets transfered up the food chain. Primary producers are consumed by herbivorous invertebrates that act as the primary consumers. Productivity of these producers and the function of the ecosystem as a whole are influenced by the organism above it in the food chain.

Primary Consumers
Primary consumers are the invertebrates and macro-invertebrates that feed upon the primary producers. They play an important role in initiating the transfer of energy from the base trophic level to the next. They are known as regulatory organisms as they are depended on and control rates of nutrient cycling, and mixing of aquatic and terrestrial plant materials. They are also relied upon for the transportation and nutrient retention of some of those nutrients and materials. There are many different functional groups of these invertebrate that include grazers, organism that feed on algal biofilm that collects on submerged objects, shredders are those that feed on large leaves and detritus and helps breakdown large material, filter feeders are macro-invertebrates that rely on stream flow to deliver them fine particulate organic matter (FPOM) suspended in the water column, and gatherers who also feed on FPOM that is found on the substrate of the river or stream.

Secondary Consumers
The secondary consumers in a river ecosystem are the predators of the primary consumers, this includes mainly insectivorous fish. Consumption of the invertebrate insects and macro-invertebrates is the net step of energy flow up the food chain. These predatory consumers can effect all trophic levels below it and can shape an ecosystem depending on the abundance of these secondary consumers. When fish are at high abundance and eat lots of invertebrates, then algal biomass and primary production in the stream is greater, and when secondary consumers are not present, then algal biomass may decrease due to the high abundance of primary consumers. Energy and nutrients that starts with primary producers continues to make its way up the food chain and depending on the ecosystem, may end with these predatory fish.

Food Web Complexity
Diversity, productivity, species richness, composition and stability are all interconnected by a series of feedback loops. Communities can have a series of complex, direct and/or indirect, responses to major changes in biodiversity. Food webs can include a wide array of variables, the three main variables ecologists look at regarding ecosystems include species richness, biomass of productivity and stability/resistant to change. When a species is added or removed from an ecosystem it will have an effect on the remaining food web, the intensity of this effect is related to species connectedness and food web robustness. When a new species is added to a river ecosystem the intensity of the effect is related to the robustness or resistance to change of the current food web. When a species is removed from a river ecosystem the intensity of the effect is related to the connectedness of the species to the food web. An invasive species could be removed with little to no effect, but if important and native primary producers, prey or predatorial fish are removed you could have a negative trophic cascade. One highly variable component to river ecosystems is food supply (biomass of primary producers). Food supply or type of producers is ever changing with the seasons and differing habitats within the river ecosystem. Another highly variable component to river ecosystems is nutrient input from wetland and terrestrial detritus. Food and nutrient supply variability is important for the succession, robustness and connectedness of river ecosystem organisms.