Gross density: Defined as the number of individuals or biomass/unit of total space e.g. Specific or Ecological Density: Defined as the number or biomass/unit of habitat space (available area or volume that can actually be colonized by the population). Sampling methods: Usually, a small part of the population is counted and this sample is used to estimate the total population.
Vocalization frequency: The number of pheasant calls heard/15 minutes in the early morning has been used as an index of pheasant population size. It is not constant for a population and varies with population size, age, composition and physical environmental conditions. The shape of the survival curve can be used to point to the critical periods in the organisms' lives.
Age distribution data can be organized in the form of age polygons or pyramids where the relative width of successive horizontal bars indicates the number of individuals or the percentage in different age classes. Dispersal is the movement of individuals or their disseminules (seeds, spores, larvae, etc.) within or outside the population. Forest floor spiders and molluscs (Mulinia lateralis) of the intertidal mudflats of the northeastern coast of N.
Fertility rates (the number of children born to the average woman in the population during her entire reproductive life) have fallen sharply in all parts of the world over the past 50 years.
Preindustrial phase: A balance between birth and death rates till the late 18th century characterizes it. The birth and death rates are high around 30 to 50 per thousand and
For the progress and well-being of people in less developed countries, population growth must be controlled and an effort must be made to achieve Zero Population Growth (ZPG). In China the fertility rate has decreased from 6 in 1970 to 1.8 in 1990 and if the decline in fertility follows a pattern of Bangladesh and China, the world population may show a decline by the end of the 21st century. The global transformation in human health in the 20th century led to an increase in life expectancy, which can be defined as the average age a newborn baby can expect to reach in any given society.
For example, in 1900 the average Indian could live less than 23 years, the life expectancy has increased to almost three times in 2000. The increase in life expectancy is attributed to better nutrition, improved sanitation and medical facilities. He observed changes in birth and death rates in industrialized societies over the past 200 years.
Demographer, Frank Notestein (1945) also observed a typical pattern of declining death and birth rates due to improved living conditions accompanied by economic development. He called this pattern the demographic transition from high birth and death rates to lower birth and death rates. The general model of demographic transition shown in Figure 1.7 is used to explain the relationship between population growth and economic development.
Pre-industrial phase: A balance between birth and death rates until the late 18th century characterizes it. Towards the end of the industrial stage, the fertility level falls close to replacement levels, but population growth continues due to population momentum. Most of the developed countries are in the third stage of transition and a few developing countries are entering this stage.
The decline in the birth rate continues until it equals the death rate and thus reaches zero.
Postindustrial stage: It is characterized by stability of the population. The decline in birth rates continues further till it equals the death rate and thus reaching the zero
The specific growth rate is defined as the average rate of change in the number of organisms/time/unit of the population or organisms initially present. As can be seen from the graph, the number of individuals added to the population at the beginning of the exponential curve will be quite small; but within a very short time the. These species can grow exponentially if resources are unlimited, but their growth slows as they approach the carrying capacity of the environment.
The resistance increases and the rate of logistic growth decreases as the population approaches the carrying capacity of the environment. Reed (1930) of John Hopkins University, for the growth of the population of the United States. The fluctuations are basically in response to the extrinsic factors such as weather and intrinsic factors inherent in the population that influence the behavior of the organisms in the population.
Pioneers, colonizers later stages of succession Climate variable and unpredictable constant and predictable STATUS OF THE LOGISTICS THEORY. According to Wilson and Puffer (1933), the logistic formula should not be considered a fixed law of population growth, allowing extrapolation of the curve for forecasting purposes. The intensity and duration of the predation after initial decline of hare due to food shortages.
As a result of interaction between some of the above factors, cyclical fluctuations are caused in the populations. Density-dependent influences change as population density varies and the proportion of organisms affected changes with density. For example, a harsh winter can damage the potato crop leading to a shortage of potatoes for the people.
The suffering of the people is the result of their own density and the shortage of potatoes, but weather (severe winter) is the main cause of decrease in production of potatoes. Extrinsic influences: These factors affect the population from outside and are not part of the population. However, due to the delay in the development process, the population continuously decreased, reducing the intensity of larval competition and allowing an increasing number of larvae to survive.
Diseases and Parasites: Parasites act as density-dependent regulators, as the virulence and rate of spread of infectious diseases increases with population density. Internal influences: It includes the factors resulting from the activities of individuals in the population. In chickens, too, a dominant male has access to all the females in the group and redundant males are only on the periphery of the group.
Genetic feedback: As an animal population increases in density, the quality of the population deteriorates, preventing unlimited growth.
