Biotic Structure
Biotic structure describes the way organisms interact within an ecosystem. The opposite of biotic is abiotic, which includes the physical and chemical factors present in the environment. Every organism in a species has a limit of tolerance, zone of stress, and optimum range for the abiotic factors present in its environment. Ecosystems can be simplified into three basic groups of organisms: producers, consumers, and decomposers. Some organisms can be in more than one category.
The definition of an ecosystem is a group of living organisms existing in a network of interactions with each other and their environment. The three feeding relationships are the food chain, the food web, and trophic levels. Non-feeding relationships can be defined as symbiotic or competitive.
Arctic marine food web. Research in the Beaufort Sea suggests that ice algae at the base of the marine food web may have already been profoundly affected by warming over the last few decades. - Arctic Climate Impact Assessment (ACIA)
Food Chains and Food Webs
Food webs illustrate the relationship between animals and what they feed on in the biotic community. Food webs also show how material and energy is transfered and lost within the ecosystem.
Each organism is a source of energy and material for another organism. The path in which biomass is moved can be illustrated in a food chain or food web. Grouping organisms into trophic levels is helpful when attempting to understand how much energy has been lost from the capture of the energy from the sun or from chemicals by primary producers. Primary producers, or autotrophs, can be any species that produce organic material from energy and/or from inorganic sources to be used by other organisms. In the deep sea, primary producers do not have access to sunlight; therefore, they utilize energy from chemicals and are called chemoautotrophs.
Food Chains
A food chain is different from a food web because it illustrates only one energy and nutrient path in an ecosystem. Each platform is a trophic level with one organism that begins with one primary producer and ends with a secondary or tertiary consumer. A typical food chain might go like this: algae-copepod-fish-squid-seal-orca. In this example the orca feeds on the seals and the seals feed on the squid which feed on fish which feed on copepods. The base of the food chain is formed by algae which are eaten by copepods.
Food Webs
Food webs are more intricate than food chains and illustrate the feeding relationships between a number of organisms at different trophic levels in an ecosystem. Food chains are useful to illustrate relationships in a simple way, and food webs are more accurate as they can illustrate more relationships. Another aspect evident in a food web is the diversification of prey by predators in order to survive the loss of one species.
Trophic Levels
Trophic levels are the platforms in the food chain that indicate a position for a particular organism. In a very basic way, a trophic level will indicate whether an organism is a foundation species, primary consumer, or secondary consumer. Information about whether the organism eats plants or animals can also be obtained. Most often trophic levels are used to determine how much energy is lost from the primary producers up to the tertiary consumers. For each trophic level in the food chain, energy is lost due to the laws of thermodynamics. Levels can be diagrammed to form a triangle with the apex formed by tertiary consumers, or apex predators. The primary producers yield the most profit from the energy of the sun. By the time this energy has been transferred up to the higher trophic levels much of it has been lost to the environment.
Symbiosis
Symbiosis is a term most often used to describe two organisms living in a close association that benefits both of their survival. For example, clownfish live in sea anemones that have dangerous stinging tentacles, to which the clownfish are immune because they are protected by an outer layer of mucus.
Pederson cleaning shrimp with their host corkscrew anenome, Utila, Honduras 2005.
The clownfish is therefore protected by the sea anemone, and in turn, acts as bait to lure fish into the stinging anenome. Another example of symbiosis is the goby fish often found living in a burrow with a shrimp. The shrimp makes a burrow for the fish and even does some housekeeping. The fish in turn warns the blind shrimp of impending danger by touching its tail so they can both swim deeper inside their burrow.
Symbiosis usually involves a symbiont (for example, the smaller clownfish) and a host (the anenome which is larger). A microscopic symbiont like bacteria in a termite's gut is usually called an endosymbiont. In ecological terms, symbiosis can mean more than just a mutually beneficial relationship. The four basic types of symbiosis are: parasitism, mutualism, commensalism, and amensalism. With parasitism, the relationship is good for one organism and bad for the other. A mutual symbiotic relationship is when both organisms benefit, commensalism is when only one benefits (and the other is indifferent), and amensalism is when one is harmed and the other is indifferent.
Depending on how the symbiotic relationship occurs, it is categorized into ectosymbiosis or endosymbiosis. Since "ecto" means on the outside, an ectosymbiotic relationship indicates that both organisms are separate. An endosymbiotic relationship is when one organism lives inside the cells of the other organism or simply inside the other organism. Most interactions are more complex than simple categorical interactions of competition, mutualism, parasitism, and commensalism. The type of interactions can also change during the lifetime of an individual organism due to its development and the environment.
Competition
Species better adapted to their environment are able to survive and produce offspring. In biological terms, fitness refers to the number of offspring an organism is able to produce (versus the most well known term indicating greater physical strength). Charles Darwin explained that the competition between species is what results in organisms that are better adapted to their environment. Whenever there are limited resources, species or even organisms within a species are forced to compete in order to survive. Competition occurs in predator-prey relationships when both are trying to survive.
Since Darwin wrote about evolution, some details have been fine-tuned. Scientists no longer believe that competition is the only relationship driving evolution. The symbiotic relationships observed in animals like the blenny and the shrimp are evidence that evolution is driven by cooperation, integration, and mutual dependence instead.
Predators
The common definition of a predator is one that hunts and kills other organisms for food. It could be claimed that herbivores are predators due to some similarities in their style of seeking and eating food. For example, an animal that eats part of a plant would be a herbivore and one that hunts for single-celled algae might be a herbivore, or predator.
Resting nurse shark off Boynton Beach, Florida 2005.
Most predators are carnivores, although some are omnivores meaning they also eat plants. A predator like the great white shark is called an apex predator because no other animal (except humans) hunts it for food. A keystone predator is one that keeps the entire ecosystem in balance and if it were removed the ecosystem would collapse. Scientists generally use the Volterra-Lotka equations to study predator-prey relationships with a mathematical model.
Share your thoughts
Feedback & Citation
Sea Life News :: ScienceDailyCommon fungicide wreaks havoc on freshwater ecosystems
A new study on chlorothalonil, one of the world's most common fungicides, shows it was lethal to a wide variety of freshwater organisms.
Sulfur finding may hold key to Gaia theory of Earth as living organism
Is Earth really a sort of giant living organism as the Gaia hypothesis predicts? A new discovery may provide a key to answering this question. This key of sulfur could allow scientists to unlock heretofore hidden interactions between ocean organisms, atmosphere, and land -- interactions that might provide evidence supporting this famous theory.
Hidden lives of elephant seals: Record-setting dive more than a mile deep
The same researchers who pioneered the use of satellite tags to monitor the migrations of elephant seals have compiled one of the largest datasets available for any marine mammal species, revealing their movements and diving behavior at sea in unprecedented detail.
Ancient sea reptile with gammy jaw suggests dinosaurs got arthritis too
Imagine having arthritis in your jaw bones ... if they're over 2 meters long! A new study has found signs of a degenerative condition similar to human arthritis in the jaw of a pliosaur, an ancient sea reptile that lived 150 million years ago. Such a disease has never been described before in fossilized Jurassic reptiles.
Arctic seabirds adapt to climate change
The planet is warming up, especially at the poles. How do organisms react to this rise in temperatures? Biologists have now shown that little auks, the most common seabirds in the Arctic, are adapting their fishing behavior to warming surface waters in the Greenland Sea. So far, their reproductive and survival rates have not been affected. However, further warming could threaten the species.
The gut could reveal effect of climate change on fish
As sea temperatures rise, stocks of some fish species can decline while others may grow, reveals new research looking at gastrointestinal function in fish.
New species of fish in Sweden
Reticulated dragonet have been found in Väderöarna -- "Weather Islands" -- off the west coast of Sweden. It is not often that a new species of fish is discovered in Sweden.
Roadmap towards sustainable pole-and-line-caught tuna
New research offers a blueprint for the long-term sustainability of tuna caught using the pole-and-line method.
First satellite tag study for manta rays reveals habits and hidden journeys of ocean giants
Using the latest satellite tracking technology, conservationists have completed a ground-breaking study on a mysterious ocean giant: The manta ray.
First forecast calls for mild Amazon fire season in 2012
Forests in the Amazon Basin are expected to be less vulnerable to wildfires this year, according to the first forecast from a new fire severity model.
What do marine snails and insulin have in common? New approach to treat diabetes?
The cone snails are predators of the sea. They capture fish by injecting a venom into the prey that consists of a cocktail of different substances. The single components of the snails' venom, so-called conopeptides, are known for their extraordinary pharmacological properties and potential.
Protein analysis investigates marine worm community
Techniques used by researchers to analyze a simple marine worm and its resident bacteria could accelerate efforts to understand more complex microbial communities such as those found in humans.
Whale population size, dynamics determined based on ancient DNA
Researchers compare ancient, modern whale DNA to investigate discrepancies between genetic data and historical estimates.
One-quarter of grouper species being fished to extinction
Groupers, a family of fishes often found in coral reefs and prized for their quality of flesh, are facing critical threats to their survival. Scientists report that 20 species are at risk of extinction if current overfishing trends continue, and an additional 22 species are near "threatened" status.
Encyclopedia of Life reaches historic one million species pages milestone
The Encyclopedia of Life has surged past one million pages of content with the addition of hundreds of thousands of new images and specimen data. Launched in 2007 with the support of leading scientific organizations around the world, the Encyclopedia of Life provides global access to knowledge about life on Earth by building a web page for each of the 1.9 million recognized species.
Antarctic octopus study shows West Antarctic Ice Sheet may have collapsed 200,000 years ago
Scientists have found that genetic information on the Antarctic octopus supports studies indicating that the West Antarctic Ice Sheet could have collapsed during its history, possibly as recently as 200,000 years ago.
Plastic trash altering ocean habitats
A 100-fold upsurge in human-produced plastic garbage in the ocean is altering habitats in the marine environment, according to a new study.
Bats, whales, and bio-sonar: New findings about whales' foraging behavior reveal surprising evolutionary convergence
Though they evolved separately over millions of years in different worlds of darkness, bats and toothed whales use surprisingly similar acoustic behavior to locate, track, and capture prey using echolocation, the biological equivalent of sonar. Now researchers have shown that the acoustic behavior of these two types of animals while hunting is eerily similar.
Dolphin speaker to enhance study of dolphin vocalizations and acoustics
To gain new insights into how dolphins communicate, researchers in Japan created a prototype of an extremely broadband "dolphin speaker" capable of projecting dolphins' communication sounds, whistles, burst-pulse sounds, as well as detection sounds such as echolocation clicks.
Built-in ear plugs: Whales may turn down their hearing sensitivity when warned of an impending loud noise
Toothed whales navigate through sometimes dark and murky waters by emitting clicks and then interpreting the pattern of sound that bounces back. The animals' hearing can pick up faint echoes, but that sensitivity can be a liability around loud noises. Now researchers have discovered that whales may protect their ears by lowering their hearing sensitivity when warned of an imminent loud sound.
Help us continue to share the wonders of the ocean with the world, raise awareness of marine conservation issues and their solutions, and support marine conservation scientists and students involved in the marine life sciences. Join the MarineBio Conservation Society or make a donation today. We would like to sincerely thank all of our members, donors, and sponsors, we simply could not have achieved what we have without you and we look forward to doing even more.
