POPULATIONINTRODUCTION:

In ecology the population of a certain species in a certain area is estimated using the Lincoln Index. The area that is used to define a sexual population is defined as the area where inter-breeding is potentially possible between any pair within the area. The probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas. Under normal conditions, breeding is substantially more common within the area than across the border.

WHAT IS POPULATION? :

A population is a summation of all the organisms of the same group or species, who live in the same geographical area, and have the capability of interbreeding.

The basics of population ecology emerge from some of the most elementary considerations of biological facts. For example, the basic problem of mitosis, to make two cells from one. For example, in Figure 1 we see a population of Paramecium sp. over a six day period.

Figure:  Changes in a population of Paramecium over a six day period.(Each individual in the population divides once per day.)

POPULATION GENETICS:

In population genetics a sexual population is a set of organisms in which any pair of members can breed together. This means that they can regularly exchange gametes to produce normally-fertile offspring, and such a breeding group is also known therefore as a gamodeme. This also implies that all members belong to the same of species, such as fish.

POPULATION DENSITY:Population density (in agriculture standing stock and standing crop) is a measurement of population per unit area or unit volume. It is frequently applied to living organisms, and particularly to humans. It is a key geographic term.

Biological population densities:

Population density is population divided by total land area or water volume, as appropriate. Low densities may cause an extinction vortex and lead to further reduced fertility. This is called the Allee effect after the scientist who identified it. Examples of the causes in low population densities include:

Increased problems with locating sexual mates Increased inbreeding

Different species have different expected densities. R-selected species commonly have high population densities, while K-selected species may have lower densities. Low densities may be associated with specialized mate location adaptations such as specialized pollinators, as found in the orchid family (Orchidaceae).

METHODS OF MEASURING POPULATION DENSITY:

While arithmetic density is the most common way of measuring population density, several other methods have been developed which aim to provide a more accurate measure of population density over a specific area.

Arithmetic density: The total number of people / area of land (measured in km2 or miles).

Physiological density: The total population / area of arable land. Agricultural density: The total rural population / area of arable land. Ecological optimum: The density of population which can be

supported by the natural resources.

AFFECTS OF POPULATION IN FISHERIES AND WILDLIFE MANAGEMENT:

In fisheries and wildlife management, population is affected by three dynamic rate functions.

i. Natality or birth rate, often recruitment, which means reaching a certain size or reproductive stage. Usually refers to the age a fish can be caught and counted in nets

ii. Population growth rate, which measures the growth of individuals in size and length. More important in fisheries, where population is often measured in biomass.

iii. Mortality, which includes harvest mortality and natural mortality. Natural mortality includes non-human predation, disease and old age.

Care is needed when applying population dynamics to real world fisheries. Over-simplistic modelling of fisheries has resulted in the collapse of key stocks.

POPULATION SIZE:

The population size (usually denoted by N) is the number of individual organisms in a population. The effective population size (Ne) was defined by Sewall Wright.

He defined it as "the number of breeding individuals in an idealized population that would show the same amount of dispersion of allele frequencies under random genetic drift or the same amount of inbreeding as the population under consideration". It is a basic parameter in many models in population genetics. Ne

is usually less than N (the absolute population size).

Virtual Population Analysis:

Virtual population analysis (VPA) is a cohort modeling technique commonly used in fisheries science for reconstructing historical fish numbers at age using information on death of individuals each year.

Minimum Viable Population:

The minimum viable population (MVP) is a lower bound on the population of a species.

Maximum Sustainable Yield:

In population ecology and economics, the maximum sustainable yield or MSY is, theoretically, the largest catch that can be taken from a fishery stock over an indefinite period. Under the assumption of logistic growth, the MSY will be exactly at half the carrying capacity of a species, as this is the stage at when population growth is highest. The maximum sustainable yield is usually higher than the optimum sustainable yield.

Recruitment:

Recruitment is the number of new young fish that enter a population in a given year. The size of fish populations can fluctuate by orders of magnitude over time, and five to 10-fold variations in abundance are usual. This variability applies across time spans ranging from a year to hundreds of years.

The recruitment problem is the problem of predicting the number of fish larvae in one season that will survive and become juvenile fish in the next season. It has been called "the central problem of fish population dynamics" and “the major

problem in fisheries science". Fish produce huge volumes of larvae, but the volumes are very variable and mortality is high. This makes good predictions difficult.

POPULATION PYRAMID:

A population pyramid, also called an age picture diagram, is a graphical illustration that shows the distribution of various age groups in a population, which forms the shape of a pyramid when the population is growing. It is also used in Ecology to determine the overall age distribution of a population.

TYPES OF POPULATION PYRAMID:

Population pyramids for 4 stages of the demographic transition model. A population pyramid showing an unchanging pattern of fertility and mortality.

i. Stationary pyramid: A population pyramid typical of countries with low fertility and low mortality, very similar to a constrictive pyramid.

ii. Expansive pyramid: A population pyramid that is very wide at the base, indicating high birth and death rates.

iii. Constrictive pyramid: A population pyramid that comes in at the bottom. The population is generally older on average, as the country has long life expectancy, a low death rate, but also a low birth rate.

POPULATION DISPERSION :

Population dispersion is the observation of where individuals are found in a habitat. How individuals "disperse" themselves. There are three main types of dispersion, eg. Clumped, Uniform and Random.

i. Clumped Dispersion: Is the tendency for populations to be found in tight clusters, dispersed across a large landscape. In between these population hubs, very few to no individuals are usually found. This sort of a dispersion can be caused by a number of factors. Some species cluster together for protection, while others group around natural resources necessary to their survival.

Figure: Clumped Dispersion.

ii. Regular/Uniform Dispersion:

Is the tendency for populations to be found evenly distributed about their habitat. This is generally caused by a species ability to survive anywhere in their habitat - they use the resources found immediately around them, and spread out as to use all of the available resources.

Figure: Regular Dispersion.

iii. Random Dispersion :Is the tendency for populations to be found randomly about their habitat. In immobile species, this is usually caused by their ability to live anywhere in a given habitat. In motile populations, individuals are able to move about their habitat, so that at any given instance, they can be found anywhere about their environment.

Figure: Random Dispersion.

POPULATION GROWTH FORM:

The growth of population is measured as increase in its size over a period of time and populations show characteristic patterns of growth with time. These patterns are known as population growth forms.

In S - shaped or sigmoid growth the population show an initial gradual increase in population size, followed by an exponential increase and then a gradual decline to near constant level.Sigmoid growth curve is formed of five phases.a) Lag phaseb) Positive acceleration phasec) Logarithmic or exponential phased) Negative acceleration phasee) Stationary phase.a) Lag phase - Period where individuals adapt to the new environment.b) Positive acceleration phase - Period of slow increase in the populationc) Logarithmic or exponential phase - Period of rapid rise in population due to availability of food and requirements in plenty and no competition.d) Negative acceleration phase - Period in which these is a slow rise in population as the environmental resistance increases.e) Stationary phase - Finally, growth rate becomes stable because mortality and natality rates become equal.

STANDING CROP :The total amount or weight, or energy content, of (a portion of) organisms existing in a specific area at a particular time

CARRYING CAPACITY:The carrying capacity of a biological species in an environment is the maximum population size of the species that the environment can sustain indefinitely, given the food, habitat, water and other necessities available in the environment

CONCLUSION:

The development of population ecology owes much to demography and actuarial life tables. Population ecology is important in conservation biology, especially in the development of population viability analysis (PVA) which makes it possible to predict the long-term probability of a species persisting in a given habitat patch, such as a national park. Although population ecology is a subfield of biology, it provides interesting problems for mathematicians and statisticians who work in population dynamics.

REFERENCE:1. http://en.wikipedia.org/wiki/Population2. http://en.wikipedia.org/wiki/Population_density3. http://en.wikipedia.org/wiki/Population_dynamics4. http://act.hdsb.ca/grassroots2005/Grassroots/Population/Population

%20Sampling/Sampling.html5. http://www.extension.iastate.edu/CropNews/

2009/0423elmoreabendroth.htm6. http://en.wikipedia.org/wiki/Population_dynamics_of_fisheries7. http://www.geography.learnontheinternet.co.uk/topics/popn1.html8. http://en.wikipedia.org/wiki/Species_distribution9. http://www.tutorvista.com/content/biology/biology-iv/biotic-

community/population-growth.php10.http://en.wikipedia.org/wiki/Carrying_capacity