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Application of Graph Theory and Ecosystems. Discrete Methods Group Project 2007 Erika Mizelle, Kaiem L. Frink, Elizabeth City State University 1704 Weeksville Road Elizabeth City, North Carolina 27909. Abstract.

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Application of Graph Theory and Ecosystems

Discrete Methods Group Project 2007

Erika Mizelle, Kaiem L. Frink,

Elizabeth City State University

1704 Weeksville Road

Elizabeth City, North Carolina 27909


The word graph (graf) comes from the Greek word graphein and is a noun. It is a diagram indicating any sort of relationship between two or more things by means of a system of dots, curves, bars, or lines. The word ecosystem (e’ko sis’tem) is from the Greek word oikos meaning habitat + system. It is defined as a community of organisms and their nonliving environment.

introduction of graph theory
Introduction of Graph Theory

Applications of graph theory are primarily, but not exclusively, concerned with labeled graphs and various specializations of these. Graphs can be used in almost any field of study for various different reasons. This paper will discuss how graph theory and its applications can be used in ecosystems and DNA sequencing.

leonhard euler 1707 1783 leonhard euler theory
Leonhard Euler (1707-1783) Leonhard Euler Theory

Notable IndividualLeonhard Euler (1707-1783) Leonhard Euler was the son of a Calvinist minister from the vicinity of Basel, Switzerland. At 13 he entered the University of Basel, pursing a career in theology, as his father wished. At the University of Basel, Johann Bernoulli of the famous Bernoulli family of mathematicians tutored Euler. His interest and skills led him to abandon his theological studies and take up mathematics. Euler obtained his masters degree in philosophy at the age of 16. In 1727 Peter the Great invited him to join the Academy at St. Petersburg. In 1736, Euler solved a problem known as the Seven Bridges of Konigsberg. In 1741 he moved to the Berlin Academy, where he stayed until 1766. He then returned to St. Petersburg, where he remained for the rest of his life.

examples of graphs
Examples of Graphs
  • Figure 1.1 Figure 1.2Simple Graph Directed Graph
transportation networks
Transportation networks

Transportation networks. The map of a bus line route forms a graph. The nodes (vertices) could represent the different cities or states that the bus visits.

communication network
Communication network.

Communication network. A collection of computers that are connected via a communication network can be naturally modeled as a graph in a few different ways. First, we could have a node for each computer and an edge joining k and m if there is a direct physical link connecting them.

information networks
Information networks
  • Information networks. The World Wide Web can be naturally viewed as a directed graph, in which nodes correspond to Web pages and there is an edge from p to q if p has a hyperlink to q.
social networks
Social networks.

Social networks. Given any collection of people who interact for example friends, we can define a network whose nodes are people, with an edge joining two nodes if they are friends.

dependency networks
Dependency networks.
  • Dependency networks. It is natural to define directed graphs that capture the interdependencies among a collection of objects. For example, given the list of courses offered by a college or university, we could have a node for each course and an edge from y to z if y is a pre-requisite for z.
  • These are only mere examples of graphs there are plenty more to discuss but that will not cover in this paper.

Applications of graph theory are primarily, but not exclusively, concerned with labeled graphs and various specializations of these. Many applications of graph theory exist in the form of network analysis. These split broadly into two categories. First, analysis to determine structural properties of a network, such as the distribution of vertex degrees and the diameter of the graph. A vast number of graph measures exist, and the production of useful ones for various domains remains an active area of research. Secondly, analysis to find a measurable quantity within the network, for example, for a transportation network, the level of vehicular flow within any portion of it. Graph theory applications is also used in the studies of molecules in chemistry and physics.

circuits and paths
Circuits and Paths

Circuits and Paths

A Euler circuit in a graph G is a simple circuit containing every edge of G. An Euler path in G is a simple path containing every edge of G

euler s theorems
Euler's Theorems

Theorem 1: If a graph has any vertices of odd degree, then it CANNOT have an EULER CRCUIT and if a graph is connected and every vertex has even degree, then it has AT LEAST ONE EULER CIRCUIT.

Theorem 2: If a graph has more than 2 vertices of odd degree, then it CANNOT have an EULER PATH and if a graph s connected and has exactly 2 vertices of odd degree, then it has AT LEAST ONE EULER PATH. Any such path must start at one of the odd-degree vertices and end at the other.

Theorem 3: The sum of the degree of all the vertices of a graph is an even number (exactly twce the number of edges). In every graph, the number of vertices of odd degree must be even.

dna sequencing
DNA Sequencing
  • Deoxyribonucleic acid, or DNA is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all living organisms. The main role of DNA is the long-term storage of information and it is often compared to a set of blueprints, since DNA contains the instructions needed to contruct other components of cells, such as proteins and RNA molecules. The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in regulating the use of this genetic information.

How is DNA Sequencing Done

  • i)chromosomes, which range in size from 50 million to 250 million bases, must first be broken into much shorter pieces.
  • ii)Each short piece is used as a template to generate a set of fragments that differ in length form each other by a single base.
  • iii)The fragments in a set are separated by gel electrophoresis. New fluorescent dyes allow separation of all four fragments in a single lane on the gel.
  • iv)The final base at the end of each fragment is identified. This process recreates the original sequence of As, Ts, Cs, and Gs for each short piece generated in the first step. Automated sequencers analyze the resulting electropherograms, and the output is a four-color chromatogram showing peaks that represent each of the four DNA bases. After the bases are “read”, computers are used to assemble the short sequences into long continuous stretches that are analyzed for errors, gene-coding regions, and other characteristics.

Euler Paths and DNA Sequencing

Euler helped changed the DNA world. With Euler’s Paths, Circuits and Theorems, it changed the repeat problem faced in DNA..

  • Even a single misassembly forces biologists to conduct total genome screening for assembly errors. Euler bypasses the “repeat problem,” because the Eulerian Superpath approach transforms imperfect repeats into different paths in the de Bruijn graph. As a result, Euler does not even notice repeats unless they are long perfect repeats.


  • Ecosystems (ecological systems) are functional units that result from the interactions of abiotic, biotic, and cultural components. Like all systems they are a combination of interacting, interrelated parts that form a unitary whole. All ecosystems are “open” systems in the sense that energy and matter are transferred in an out. In this paper food webs will be used instead of the ecosystem as a whole, to show how graph theory is incorporated into this study.
food chain
Food Chain
  • A food web extends a food chain concept from a simple linear pathway to a complex network of interactions. The best way to understand this concept is through visualization. Below is a pitcure of a food web.
food chain1
Food Chain

In the graph Figure 4, this is an example of a Directed graph that pertains to the ecosystem. As you can see this graph displays everyday natural animal and insects consumption. For example the Grasshopper eats the Preying Mantis. The arrows indicate in which direction the consumption takes place. This is a common yet easy way to understand how the ecosystem and graph theory are closely related.


So that in conclusion the Graph Theory Applications in Relation to the Study of Ecosystems and DNA 2007 Team has arrived to the decision that Euler’s Path was fundamental in DNA sequencing. Elulers Path allowed for no repeats in DNA sequencing, which means that they were not even identifiable in the sequence. Graph Theory is fundamental when identifying possible correlations between mathematical modeling. Graph theory can be compared to an If else statement in Computer Science.

Graph Theory is essential when identifying highways and ecosystems path. Graph Theory is also incorporated within our everyday life with the Flow of Energy for example. The Graph Theory Applications in Relation to the Study of Ecosystems and DNA 2007 team obtain our goal of gaining an enhanced knowledge of Graph Theory, Euler path, ecosystems and conducting useful and meaningful research.

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  • International Congress of Mathematicians Madrid 2006 Retrieved February 28, 2007, from the World Wide Web: