Food web - Wikipedia
How food chains and food webs represent the flow of energy and matter. and are more realistic representation of consumption relationships in ecosystems. from plant-eating insects to meat-eating animals to fungi that feed on debris and wastes. . This is also the amount of energy per year that's made available to the . Study how food chains and food webs work with BBC Bitesize KS3 Science. some common terms used to describe living things in their environment. a paragraph in your Science Journal com- in the food you eat, in the water you drink, and even deep in the ocean. For thousands of years, people did not know about bacteria. . archaebacteria live in harsh environments where few kinds of . as shown in Figure 7. Concept Map Copy and complete the follow -.
Heterotrophs consume rather than produce biomass energy as they metabolize, grow, and add to levels of secondary production. A food web depicts a collection of polyphagous heterotrophic consumers that network and cycle the flow of energy and nutrients from a productive base of self-feeding autotrophs.
Feeding connections in the web are called trophic links. The number of trophic links per consumer is a measure of food web connectance. Food chains are nested within the trophic links of food webs. Food chains are linear noncyclic feeding pathways that trace monophagous consumers from a base species up to the top consumerwhich is usually a larger predatory carnivore.
Trophic species are functional groups that have the same predators and prey in a food web. Common examples of an aggregated node in a food web might include parasitesmicrobes, decomposerssaprotrophsconsumersor predatorseach containing many species in a web that can otherwise be connected to other trophic species.
Trophic level A trophic pyramid a and a simplified community food web b illustrating ecological relations among creatures that are typical of a northern Boreal terrestrial ecosystem. The trophic pyramid roughly represents the biomass usually measured as total dry-weight at each level.
Plants generally have the greatest biomass. Names of trophic categories are shown to the right of the pyramid. Some ecosystems, such as many wetlands, do not organize as a strict pyramid, because aquatic plants are not as productive as long-lived terrestrial plants such as trees. Ecological trophic pyramids are typically one of three kinds: Basal species, such as plants, form the first level and are the resource limited species that feed on no other living creature in the web.
Basal species can be autotrophs or detritivoresincluding "decomposing organic material and its associated microorganisms which we defined as detritus, micro-inorganic material and associated microorganisms MIPand vascular plant material.
The top level has top or apex predators which no other species kills directly for its food resource needs. The intermediate levels are filled with omnivores that feed on more than one trophic level and cause energy to flow through a number of food pathways starting from a basal species.
The trophic level is equal to one more than the chain length, which is the number of links connecting to the base. The base of the food chain primary producers or detritivores is set at zero. The technique has been improved through the use of stable isotopes to better trace energy flow through the web.
Food chains & food webs (article) | Ecology | Khan Academy
This realization has made trophic classifications more complex. The basis of trophic dynamics is the transfer of energy from one part of the ecosystem to another. Omnivores, for example, are not restricted to any single level. Nonetheless, recent research has found that discrete trophic levels do exist, but "above the herbivore trophic level, food webs are better characterized as a tangled web of omnivores. Ecologists use simplified one trophic position food chain models producer, carnivore, decomposer.
Using these models, ecologists have tested various types of ecological control mechanisms. For example, herbivores generally have an abundance of vegetative resources, which meant that their populations were largely controlled or regulated by predators.
This is known as the top-down hypothesis or 'green-world' hypothesis. Alternatively to the top-down hypothesis, not all plant material is edible and the nutritional quality or antiherbivore defenses of plants structural and chemical suggests a bottom-up form of regulation or control. Links in a food-web illustrate direct trophic relations among species, but there are also indirect effects that can alter the abundance, distribution, or biomass in the trophic levels.
For example, predators eating herbivores indirectly influence the control and regulation of primary production in plants.
Food chains & food webs
Although the predators do not eat the plants directly, they regulate the population of herbivores that are directly linked to plant trophism. The net effect of direct and indirect relations is called trophic cascades.
Trophic cascades are separated into species-level cascades, where only a subset of the food-web dynamic is impacted by a change in population numbers, and community-level cascades, where a change in population numbers has a dramatic effect on the entire food-web, such as the distribution of plant biomass.
Ecological efficiency The Law of Conservation of Mass dates from Antoine Lavoisier's discovery that mass is neither created nor destroyed in chemical reactions.
Interactions and interdependence within the environment
In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. Energy flow diagram of a frog. The frog represents a node in an extended food web. The energy ingested is utilized for metabolic processes and transformed into biomass. The energy flow continues on its path if the frog is ingested by predators, parasites, or as a decaying carcass in soil. This energy flow diagram illustrates how energy is lost as it fuels the metabolic process that transform the energy and nutrients into biomass.
An expanded three link energy food chain 1. The transformity of energy becomes degraded, dispersed, and diminished from higher quality to lesser quantity as the energy within a food chain flows from one trophic species into another.
Energy flow is directional, which contrasts against the cyclic flows of material through the food web systems. Biomass represents stored energy.
However, concentration and quality of nutrients and energy is variable. Many plant fibers, for example, are indigestible to many herbivores leaving grazer community food webs more nutrient limited than detrital food webs where bacteria are able to access and release the nutrient and energy stores.
These polymers have a dual role as supplies of energy as well as building blocks; the part that functions as energy supply results in the production of nutrients and carbon dioxide, water, and heat. Excretion of nutrients is, therefore, basic to metabolism. Different consumers are going to have different metabolic assimilation efficiencies in their diets. Each trophic level transforms energy into biomass.
Energy flow diagrams illustrate the rates and efficiency of transfer from one trophic level into another and up through the hierarchy. This is because energy is lost to the environment with each transfer as entropy increases. As this example illustrates, we can't always fully describe what an organism—such as a human—eats with one linear pathway.
For situations like the one above, we may want to use a food web that consists of many intersecting food chains and represents the different things an organism can eat and be eaten by. In this article, we'll take a closer look at food chains and food webs to see how they represent the flow of energy and nutrients through ecosystems.
Some organisms, called autotrophs, also known as self-feeders, can make their own food—that is, their own organic compounds—out of simple molecules like carbon dioxide. There are two basic types of autotrophs: Photoautotrophs, such as plants, use energy from sunlight to make organic compounds—sugars—out of carbon dioxide in photosynthesis. Other examples of photoautotrophs include algae and cyanobacteria. Chemoautotrophs use energy from chemicals to build organic compounds out of carbon dioxide or similar molecules.
This is called chemosynthesis. For instance, there are hydrogen sulfide-oxidizing chemoautotrophic bacteria found in undersea vent communities where no light can reach.
Autotrophs are the foundation of every ecosystem on the planet. That may sound dramatic, but it's no exaggeration! Autotrophs form the base of food chains and food webs, and the energy they capture from light or chemicals sustains all the other organisms in the community. When we're talking about their role in food chains, we can call autotrophs producers. Heterotrophs, also known as other-feeders, can't capture light or chemical energy to make their own food out of carbon dioxide.
Instead, heterotrophs get organic molecules by eating other organisms or their byproducts. Animals, fungi, and many bacteria are heterotrophs. When we talk about heterotrophs' role in food chains, we can call them consumers. As we'll see shortly, there are many different kinds of consumers with different ecological roles, from plant-eating insects to meat-eating animals to fungi that feed on debris and wastes.
Food chains Now, we can take a look at how energy and nutrients move through a ecological community. Let's start by considering just a few who-eats-who relationships by looking at a food chain. A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. Let's look at the parts of a typical food chain, starting from the bottom—the producers—and moving upward.
At the base of the food chain lie the primary producers. The primary producers are autotrophs and are most often photosynthetic organisms such as plants, algae, or cyanobacteria. The organisms that eat the primary producers are called primary consumers. Primary consumers are usually herbivores, plant-eaters, though they may be algae eaters or bacteria eaters. The organisms that eat the primary consumers are called secondary consumers. Secondary consumers are generally meat-eaters—carnivores.
The organisms that eat the secondary consumers are called tertiary consumers. These are carnivore-eating carnivores, like eagles or big fish. Some food chains have additional levels, such as quaternary consumers—carnivores that eat tertiary consumers. Organisms at the very top of a food chain are called apex consumers.
We can see examples of these levels in the diagram below. The green algae are primary producers that get eaten by mollusks—the primary consumers. The mollusks then become lunch for the slimy sculpin fish, a secondary consumer, which is itself eaten by a larger fish, the Chinook salmon—a tertiary consumer.