Population and Natural resources
Population ecology
Ecology is the study of the interaction between organisms and their physical environment.
it involves examining how individuals in a particular population interact with each other
and how the population as a whole interacts with its environment.
The levels of ecological organizations include:
Individuals- population- community- ecosystem- biosphere- biome
A population is a group of individuals of the same species with common characteristics living and interbreeding within a given area.
Population ecology is the study of the process of interaction and changes that affect the distribution and abundance of population in the environment.
Population size, density, and dispersal
Population size(N) is the total number of individuals present in a particular habitat.
Locating and counting each individual is very difficult, so scientists use sampling techniques; counting individuals in the sample area and estimating the larger population in the habitat.
Different sampling methods can be used to determine the size and density of a population.
The quadrat ( for plant species)
This method is used to study immobile organisms such as plants and small, slowly moving organisms.
The formula for Calculating Population Size Using Quadrats:
Population size = (Number of individuals counted in sample area / Area of the sample) x Total area of the study area.
The mark-recapture (for animals)
This method is used to study the population size of animals that move from one place to another.
Steps
Capture a sample of animals; mark them and release them back into the environment.
Capture a sample of animals again; check how many of them are marked and unmarked
Estimate total population size using marked and unmarked ratios.
The formula for Calculating Population Size using Mark-Recapture:
N = No of marked(1st catch) \ No of marked(2nd catch) X Total no of second catch( marked and unmarked)
Studying human population
A census is a systematic collection of information from individuals in the population.
It is also the complete enumeration of the members of a given population.
There are two methods of conducting census:
De Facto method of census
Government fixes one date for conducting the census throughout the country.
De Jure method of census
Government fixes enumeration period of two or three weeks.
Advantage of using De Jure over De Facto is that it’s accurate because only permanent residents are counted.
Population Density
Population density is the number of individuals within a specific area or volume.
It is the measurement of the size of a population as a percentage the total land are occupied by the people.
Population density like other population properties is dynamic( changes over time).
Birth rate and immigration +ve=increase population density
(immigration=double m;so increase population)
Death rate and emigration _ve=decreases population density
(emigration= single m; population loss)
Density(D)=Total population size/Total area
Population dispersal
Refers to how the individuals in a population are distributed in a space at a given time.
There are three dispersal patterns of species:
Uniform dispersion: individuals of a population are spaced more or less evenly.
Random dispersion: individuals are distributed randomly, without a predictable pattern.
Clumped dispersion: individuals are clustered in groups.
Population Growth
Refers to the increase in the number of individuals in a population.
Population growth rate is the percentage rate of change within a specified number of individuals in a population.
It is the average annual rate change of population size during a specified period of time.
It measures how fast the size of the population is changing.
There are two ways(models) of describing population growth
Exponential growth model
Describes population increases with out any limit to their growth.
Represents growth without any environmental constriants, thus increase exponentially.increases