Boitechnology

In behavioral ecology, the marginal value theorem (MVT) considers an optimally foraging animal exploiting resources distributed in patches and that must decide when to leave a patch to start searching for a fresh one. The animal is assumed to have evolved to optimize a cost/benefit ratio: searching for and manipulating food is costly, while food is a benefit. The decision taken by animals appears to be based on an expected transit time among patches and an observed intake rate within each patch. Examples include bees visiting flowers, birds eating berries, or even mobile phone shop owners (in which case the “resource” being exploited is paying customers).

The theorem predicts that individuals will stay longer:
as the distance between patches increases,
when the environment as a whole is less profitable.

Plants have also been shown to obey the predictions of the marginal value theorem. Plant roots traveling through soil will slow their growth rate in order to remain in patches of higher soil resources for longer periods of time in exactly the same way as animals.

The MVT has been criticised on the grounds that few foragers are optimal (typical limiting factors include inability to assess exploitation rate and lack of knowledge of distant patch existence). Nevertheless, it predicts behavior that is compatible with many types of real forager behavior.

The theorem was first formulated by R. A. Fisher in his 1930 book The Genetical Theory of Natural Selection.[1] Fisher held that “It is not a little instructive that so similar a law should hold the supreme position among the biological sciences”. However, for forty years it was misunderstood, it being read as saying that the average fitness of a population would always increase, and models showed this not to be the case. The misunderstanding can be seen largely as a result of Fisher’s feud with the American geneticist Sewall Wright primarily about adaptive landscapes.

The American George R. Price showed in 1972 that Fisher’s theorem was correct as stated, and that the proof was also correct, given a typo or two[3] (see Price equation). Price showed the result was true, but did not find it to be of great significance. The sophistication that Price pointed out, and that had made understanding difficult, is that the theorem gives a formula for part of the change in gene frequency, and not for all of it. This is a part that can be said to be due to natural selection.

More recent work (reviewed in Grafen 2003) builds on Price’s understanding in two ways. One aims to improve the theorem by completing it, i.e. by finding a formula for the whole of the change in gene frequency. The other argues that the partial change is indeed of great conceptual significance, and aims to extend similar partial change results into more and more general population genetic models.

Due to confounding factors, tests of the fundamental theorem are quite rare. For an example of this effect in a natural population, see (Bolnick, 2007).[4]

In population genetics, R. A. Fisher’s fundamental theorem of natural selection was originally stated as:
“The rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time.”[1]

Or, in more modern terminology:
“The rate of increase in the mean fitness of any organism at any time ascribable to natural selection acting through changes in gene frequencies is exactly equal to its genetic variance in fitness at that time”.[2]

Cells can be subdivided into the following subcategories:
Prokaryotes: Prokaryotes lack a nucleus (though they do have circular DNA) and other membrane-bound organelles (though they do contain ribosomes). Bacteria and Archaea are two divisions of prokaryotes.
Eukaryotes: Eukaryotes, on the other hand, have distinct nuclei and membrane-bound organelles (mitochondria, chloroplasts, lysosomes, rough and smooth endoplasmic reticulum, vacuoles). In addition, they possess organized chromosomes which store genetic material.

Viruses are considered by some to be alive, yet they are not made up of cells. Viruses have many of the features of life, but by definition of life, they are not alive.
The first cell did not originate from a pre-existing cell. There was no exact first cell since the definition of cell is not that precise. This is an intellectual game that comes from making strict logical symbols out of the biological definitions.
Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell.

The generally accepted parts of modern cell theory include:
The cell is the fundamental unit of structure and function in living things.
All cells come from pre-existing cells by division.
Energy flow (metabolism and biochemistry) occurs within cells.
Cells contain hereditary information (DNA) which is passed from cell to cell during cell division
All cells are basically the same in chemical composition.
All known living things are made up of cells.
Some organisms are unicellular, i.e., made up of only one cell.
Others are multicellular, composed of a number of cells.
The activity of an organism depends on the total activity of independent cells.

All organisms are made up of one or more cells.
Cells are the fundamental functional and structural unit of life.
All cells come from pre-existing cells.
The cell is the unit of structure, physiology, and organization in living things.
The cell retains a dual existence as a distinct entity and a building block in the construction of organisms.

Drawing of the structure of cork

The cell was first discovered by Robert Hooke in 1665. He examined very thin slices of cork and saw billions of tiny pores that he remarked looked like the walled compartments of a honeycomb. Because of this association, Hooke called them cells, the name they still bear. However, Hooke did not know their real structure or function. [1] Hooke’s description of these cells (which were actually non-living cell walls) was published in Micrographia.[2]. His cell observations gave no indication of the nucleus and other organelles found in most living cells.

The first man to witness a live cell under a microscope was Antonie van Leeuwenhoek, who in 1674 described the algae Spirogyra and named the moving organisms animalcules, meaning “little animals”.[3]. Leeuwenhoek probably also saw bacteria.[4] Cell theory was in contrast to the vitalism theories that had been proposed before the discovery of cells.

The idea that cells were separable into individual units was proposed by Ludolph Christian Treviranus[5] and Johann Jacob Paul Moldenhawer[6]. All of this finally led to Henri Dutrochet formulating one of the fundamental tenets of modern cell theory by declaring that “The cell is

The observations of Hooke, Leeuwenhoek, Schleiden, Schwann, Virchow, and others led to the development of the cell theory. The cell theory is a widely accepted explanation of the relationship between cells and living things. The cell theory states:
All living things are composed of one or more cells.
The cell is the most basic unit of life.
All cells come from pre-existing cells.

The cell theory holds true for all living things, no matter how big or small, or how simple or complex. Since according to research, cells are common to all living things, they can provide information about all life. And because all cells come from other cells, scientists can study cells to learn about growth, reproduction, and all other functions that living things perform. By learning about cells and how they function, you can learn about all types of living things.

Credit for developing cell theory is usually given to three scientists: Theodor Schwann, Matthias Jakob Schleiden, and Rudolf Virchow. In 1839, Schwann and Schleiden suggested that cells were the basic unit of life. Their theory accepted the first two tenets of modern cell theory (see next section, below). However the cell theory of Schleiden differed from modern cell theory in that it proposed a method of spontaneous crystallization that he called “Free Cell Formation”[8]. In 1858, Rudolf Virchow concluded that all cells come from pre-existing cells, thus completing the classical cell theory.

Cell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 1600s was made possible by advances in microscopy. This theory is one of the foundations of biology. The theory says that new cells are formed from other existing cells, and that the cell is a fundamental unit of structure, function and organization in all living organisms.

The Bishop–Cannings theorem is a theorem in evolutionary game theory. It states that (i) all members of a mixed evolutionarily stable strategy (ESS) have the same payoff (Theorem 2), and (ii) that none of these can also be a pure ESS[1] (from their Theorem 3). The usefulness of the results comes from the fact that they can be used to directly find ESSes algebraically, rather than simulating the game and solving it by iteration.

The logic of (i) also applies to Nash equilibria (all strategies in the support of a mixed strategy receive the same payoff).[citation needed]

The theorem was formulated by Tim Bishop and Chris Cannings at Sheffield University, who published it in 1978.

A review is given by John Maynard Smith in Evolution and the Theory of Games, with proof in the appendix[2]