By:Dafeng Hui(Department of organic Sciences, Tennessee State University)©2012ptcouncil.net Education

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Food net is one important conceptual tool for showing the feeding relationship among types within a community, revealing species interactions and community structure, and also understanding the dynamics of power transfer in an ecosystem.

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Introduction

Food web is critical ecological concept. Basically, food web represents feeding relationship within a community (Smith and also Smith 2009). It additionally implies the transfer of food energy from its resource in plants through herbivores come carnivores (Krebs 2009). Normally, food network consist the a variety of food chain meshed together. Every food chain is a descriptive diagram including a collection of arrows, every pointing native one species to another, representing the flow of food power from one feeding team of organisms to another.

There space two varieties of food chains: the grazing food chain, start with autotrophs, and the detrital food chain, start with dead organic issue (Smith & smith 2009). In a grazing food chain, energy and nutrients relocate from plants to the herbivores spend them, and also to the carnivores or omnivores preying ~ above the herbivores. In a detrital food chain, dead organic matter of plants and animals is broken down through decomposers, e.g., bacteria and also fungi, and moves to detritivores and then carnivores.

Food web offers vital tool for investigating the eco-friendly interactions that specify energy flows and also predator-prey partnership (Cain et al. 2008). Number 1 shows a simplified food web in a desert ecosystem. In this food web, grasshoppers feeding on plants; scorpions food on grasshoppers; kit foxes prey on scorpions. When the food net showed below is a an easy one, many feed network are complex and show off many varieties with both solid and weak interactions amongst them (Pimm et al. 1991). For example, the predators the a scorpion in a desert ecosystem might be a golden eagle, one owl, a roadrunner, or a fox.


The idea to apply the food chain to ecology and also to analyze its consequences was an initial proposed by Charles Elton (Krebs 2009). In 1927, he known that the size of this food chains to be mostly minimal to 4 or 5 links and the food chain were not isolated, however hooked together right into food network (which he referred to as "food cycles"). The feeding interactions represented by the food internet may have profound results on types richness the community, and also ecosystem productivity and stability (Ricklefs 2008).

Types of Food WebsFood webs describe the relationship — web links or relationships — among varieties in an ecosystem, yet the relationships vary in their prominence to power flow and dynamics of species populations. Some trophic relationship are an ext important than others in dictating how energy flows v ecosystems. Some relations are more influential on species populace change. Based upon different methods in which types influence one another, Robert Paine propose three types of food webs based on the species of a rocky intertidal zone top top the coastline of Washington (Ricklefs 2008, number 2). Connectedness network (or topological food webs) emphasize feeding relationships amongst species, depicted as links in a food internet (Paine 1980). Power flow webs quantify power flow native one species to another. Thickness of an arrowhead reflects the stamin of the relationship. Practical webs (or communication food webs) represent the prominence of each species in preserving the truth of a community and reflect influence on the expansion rate of various other species" populations. As shown in number 2, limpets Acmaea pelta and A. Mitra in the neighborhood consume considerable food power (energy flow web), however removal of these consumers has actually no detectable affect on the abundance of their sources (functional web). The many effective regulate was exerted by sea urchin Stronglocentrotus and also the chiton Katharina (Ricklefs 2008).


Figure 2:Three species of food net diagrams based on types of a rocky intertidal zone ~ above the coast of Washington.
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Applications the Food network

Food web are built to describe types interactions (direct relationships).


The fundamental purpose of food web is to describe feeding connection among species in a community. Food webs can be built to explain the varieties interactions. All varieties in the food webs have the right to be differentiated into basal varieties (autotrophs, such as plants), intermediate types (herbivores and also intermediate level carnivores, such as grasshopper and scorpion) or height predators (high level carnivores such as fox) (Figure 1).

These feeding teams are referred as trophic levels. Basal species occupy the lowest trophic level as major producer. They transform inorganic chemical and also use solar power to create chemical energy. The second trophic level consists of herbivores. This are first consumers. The continuing to be trophic levels encompass carnivores that consume animals at trophic levels below them. The second consumers (trophic level 3) in the desert food web encompass birds and scorpions, and tertiary consumers comprising the 4th trophic level incorporate bird predators and foxes. Group all varieties into different functional teams or tropic levels helps united state simplify and also understand the relationships amongst these species.


Indirect interaction occurs when two species do not interact with each various other directly, yet influenced by a 3rd species. Species can affect one an additional in many different ways. One instance is the keystone predation room demonstrated through Robert Paine in an experiment carried out in the rocky intertidal region (Cain et al. 2008; blacksmith & blacksmith 2009; Molles 2010). This study verified that predation deserve to influence the compete among species in a food web. The intertidal ar is home to a variety of mussels, barnacles, limpets, and also chitons (Paine 1969). All these invertebrate herbivores space preyed ~ above by the predator starfish Pisaster (Figure 3). Starfish was fairly uncommon in the intertidal zone, and considered less vital in the community. Once Paine manually gotten rid of the starfish from speculative plots if leaving other areas undisturbed as regulate plots, he uncovered that the number of prey species in the speculative plots dropped from 15 at the start of the experiment to 8 (a loss of 7 species) 2 years ~ the starfish removal while the full of prey types remained the exact same in the control plots. He reasoned that in the lack of the predator starfish, number of of the mussel and also barnacle varieties (that were premium competitors) to exclude, the other varieties and reduced in its entirety diversity in the community (Smith & blacksmith 2009). Predation by starfish lessened the diversity of mussel and opened up room for other types to colonize and persist. This form of indirect communication is dubbed keystone predation.


(a) The rocky intertidal zone the the Pacific Northwest coastline is lived in by a variety of species including starfish, barnacles, limpets, chitons, and mussels. (b) A food net of this community shows the the starfish preys top top a variety of invertebrate species. Removed of starfish from this neighborhood reduced the diversity that prey types due to enhanced competition.

another interesting examine demonstrated indirect interaction among types in both aquatic and also terrestrial ecosystems (Figure 4). In a study carried out near Gainesville, Florida, Knight and her colleagues (2009) investigated the results of fish in ponds on plant seed production. Lock measured and compared abundances the both larval and also adult dragonfly in and also around four ponds that had actually been stocked v fish and also four ponds the lacked fish (Knight et al. 2009). They found that ponds with fish develop fewer larval and adult dragonflies 보다 ponds without fish, as fish food on larval dragonflies. As dragonfly population decreases, the populaces of their prey, consisting of bees, flies, and butterflies, decrease. This prey species are pollinators that the plants. Therefore, flowers in the vicinity of ponds without fish get fewer pollinator visits 보다 flowers close come ponds stocked through fish. Due to the fact that the manufacturing of seeds is pollen-limited, fewer pollinator visits an outcome in lower seeds production. This examine demonstrates, via a complex trophic cascade, that including fish come a pond enhances the reproductive success of a plant on floor (Ricklefs 2008).


Figure 4:An communication food net shows that fish have actually indirect results on the populations of several types in and around ponds.
The hard arrows represent direct effects, and also the dashed arrows indirect effects; the ptcouncil.net of the impact is indicated by + or -. Fish have actually indirect effects, through a trophic cascade, on number of terrestrial species: dragonfly adults (-), pollinators (+), and plants (+)
Food network illustrate power flow from primary producers to main consumers (herbivores), and also from major consumers to an additional consumers (carnivores). The structure of food webs suggests that productivity and abundance of populations at any type of given trophic level are regulated by the productivity and also abundance of populaces in the trophic level below them (Smith & smith 2009). This phenomenon is speak to bottom-up control. Correlations in diversity or productivity between consumers and also their sources are considered as proof for bottom-up control. For example, plant population densities regulate the abundance of herbivore populations which in turn regulate the densities of the carnivore populations. Thus, the biomass of herbivores usually rises with major productivity in terrestrial ecosystems.

Top-down control occurs as soon as the population density of a customer can control that the its resource, because that example, predator populaces can manage the diversity of prey varieties (Power 1992). Under top-down control, the abundance or biomass of reduced trophic levels counts on impacts from consumer at greater trophic levels. A trophic cascade is a form of top-down interaction that explains the indirect effects of predators. In a trophic cascade, predators induce impacts that cascade down the food chain and influence biomass of organisms at least two web links away (Ricklefs 2008). Nelson Hairston, Frederick Smith and Larry Slobodkin very first introduced the principle of top-down control with the commonly quoted "the human being is green" proposition (Power 1992; smith & smith 2009). Castle proposed that the human being is green since carnivores depress herbivores and keep herbivore populaces in check. Otherwise, herbivores would certainly consume many of the vegetation. Indeed, a bird exclusion study demonstrated the there to be significantly more insects and also leaf damage in plots without birds compared to the regulate (Marquis & Whelan 1994).


Food webs have the right to be provided to reveal various patterns of energy transfer in terrestrial and aquatic ecosystems.


patterns of energy flow through different ecosystems might differ markedly in terrestrial and also aquatic ecosystems (Shurin et al. 2006). Food network (i.e., energy flow webs) can be provided to expose these differences. In a review paper, Shurin et al. (2006) provided evidence because that systematic difference in power flow and also biomass partitioning in between producers and herbivores, detritus and also decomposers, and greater trophic levels in food webs. A dataset synthesized through Cebrian and colleagues ~ above the fate of carbon resolved by primary productivity throughout different ecosystems was offered to show various patterns in food chains between terrestrial and aquatic ecosystems (Figure 5). Top top average, the turnover rate of phytoplankton is 10 come 1000 times much faster than the of grasslands and also forests, thus, much less carbon is save on computer in the life autotroph biomass pool, and also producer biomass is spend by aquatic herbivores in ~ 4 time the terrestrial rate (Cebrian 1999, 2004; Shurin et al. 2006). Herbivores in terrestrial ecosystems are much less abundant but decomposers are much an ext abundant than in phytoplankton overcame aquatic ecosystems. In many terrestrial ecosystems with high standing biomass and reasonably low harvest of major production through herbivores, the detrital food chain is dominant (Smith & blacksmith 2009). In deep-water aquatic ecosystems, with their low standing biomass, quick turnover that organisms, and also high price of harvest, the grazing food chain may be dominant.


Figure 5:Differences in pathways the carbon flow and pools in between aquatic and also terrestrial ecosystems.
The thickness that the arrows (flows) and also the area of the crate (pools) correspond to the magnitude. The size of the pools space scaled as log units since the differences cover four orders that magnitude. The C’s indicate intake terms (i.e. CH is usage by herbivores). Ovals and also arrows in grey show unknown quantities.

As a diagram tool, food web has been authorized to be effective in illustrating types interactions and testing study hypotheses. It will proceed to be an extremely helpful for us to know the associations of types richness/diversity with food web complexity, ecosystem productivity, and stability.


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