BIOTIC POTENTIAL AND ENVIRONMENTAL RESISTANCE

Population
It is a group of organisms of the same species living in an area at the same time.
Birth rate is the ratio of total live births to total population in a specified community or area over a specified period of time. The birthrate is often expressed as the number of live births per 1,000 of the population per year.
Death rate is the ratio of total deaths to total population in a specified community or area over a specified period of time. The death rate is often expressed as the number of deaths per 1,000 of the population per year. Also called fatality rate.

Population Density
It is a measurement of population per unit area or unit volume; it is a quantity of type number density. It is frequently applied to living organisms, and most of the time to humans.

Environmental resistance
Environmental resistance is the limiting effect of environmental conditions on the numerical growth of a population.
Environmental resistance factors are things that limit the growth of a population. They lower the chances for reproduction, affect the health of organisms, and raise the death rate in the population.  They include biotic factors like predators, disease, competition, and lack of food, as well as abiotic factors like fire, flood, temperature, wrong amount of sunshine ,and drought.

Environmental Resistance Factors

Food supply
As  the population increases, the food supply, or the supply of another necessary resource , may decrease. When necessary resources, such  as  food , decrease, some individuals will die.  Overall, the population cannot reproduce  at the same rate, so the birth rates drop. This will cause the population growth rate to decrease.

Competition
When populations become crowded, organisms compete for food,water, space, sunlight and other essentials. 

Predation
Populations in nature  are often controlled  by  predation. The  regulation of a population by predation takes place within a  predator-prey  relationship, one of the best-known mechanism of population control.

Parasitism and Disease
Parasites and disease can limit the growth of a population. A parasite lives in or on another organism  (the host)  and consequently harms it.

Natural disasters 
Natural  disasters such as droughts,  floods,  hurricanes, and fires, can all influence whatever  populations are in the area at  the  time. Not only  do these occurrences kill individuals in all populations,  they also disrupt  the availability of resources for survivors.

Biotic Potential

The biotic potential of a population is how well a species is able to survive.
While environmental resistance acts like a hill pushing back against population growth, biotic potential is what urges a population to grow. Biotic potential has to do with how well a species can survive, including how well adapted it is to the environment and its rate of reproduction. Some species produce a lot of young very often (while others produce fewer babies less often), but invest a lot of energy raising and protecting them. So while the biotic potential of a species causes the population to increase, environmental resistance keeps it from increasing relentlessly.

When the population is small, environmental resistance factors are, well, not as big of a factor. There may be plenty of resources around so the population can keep growing quickly. It's kind of like pushing a piece of gravel uphill rather than a boulder. But, as competition get stiffer and resources start to become limited, population growth starts to slow.