Population and its characteristics-Population Growth.pptx

This ppt contains details about Population ecology including the characteristics of a populations like Natality, Mortality, Population growth, Population density etc

1. Dr. B.Elia , M.Sc., Ph.D Lecturer in Zoology P.R. Govt College (A) Kakinada-533001 ANDHRA PRADESH POPULATION ECOLOGY

2. POPULATION ECOLOGY The word population is derived from the Latin word ‘ Populus ’ which means people. Wynne Edwards (1965)-a population is self regulating system. Characteristics of a Population Birth rate or Natality Death rate or Mortality Population density Population growth Population dispersal Population Dispersion or Internal distribution patterns

3. Birth rate or Natality : It can be defined as the average number of new individuals produced by that population in a unit of time. The maximum birth rate or potential natality is the maximum number of new individuals which could be produced per unit of time under ideal ecological conditions. It means maximum birth rate is solely determined by the physiological factors such as the number of sexually mature males and females Proportion of females in the population Number of eggs produced per female in one unit of time. The maximum birth rate remains almost constant for a given population

4. The actual or ecological birth rate or realized natality is the actual number of new individuals added to the population in a given time. This is considerably less than the maximum birth-rate, because all the females are not equally fertile, all the eggs that are produced do not hatch and all the larvae hatched out do not attain adulthood. The ecological birth rate of a population can be expressed by the formula B= N n /t Where B= natality rate per unit of time; N n =number of new individuals added to the population by natality and t=unit time. Similarly the natality rate per individual in the population per unit of time can be expressed by the formula B= N n / N t

5. Death rate or Mortality Refers to number of individuals dying per unit of time. Mortality can be expressed as 1) Potential mortality 2) Realized mortality The potential mortality or the minimum mortality is the number of deaths which would occur under ideal conditions due to physiological changes of old age. This is constant for a given population. The realized mortality or actual death rate varies depending upon physical factors and on the size, composition and density of population.

6. Population density: can be defined as the number of individuals per unit area or per unit volume. The unit measurement varies for different types of populations. Population density is expressed in two ways 1. The crude density-is the total number of individuals or biomass per unit of total area or total volume 2) Ecological density-is the number of individuals or the biomass per unit of that area or volume which is actually inhabited by those individuals The formula for determining the density of population is D=n/a/t Where D=density, n=the number of individuals, a=area, t=time unit

7. The study of density indicates the successful nature of population and suggests the future of birth-rate and death-rate, it has been found that increased density slows down the population growth. The density of population depends upon the birth rate, death rate, rate of reproduction, migration etc.

8. Population growth S-shaped growth curve J-shaped growth curve

9. Population growth

10. Population growth

11. Population dispersal-is the movement of individuals or their reproductive products into and out of population area. The ability to move is a feature of animals but plants disperse through water or air or by the dispersal of their seeds, fruits or spores. i ) Emigration ii) Immigration iii) Migration

12. Age distribution

13. Population Dispersion or Internal distribution patterns Dispersion is the mode of distribution of individuals within a population. It greatly affects the internal structure and other characteristics of the population. Individuals in a population exhibit three different patterns of distribution. They are 1) Uniform 2) Random 3) Clumped

14. 1. Uniform distribution: Individuals are more or less evenly spaced. This pattern occurs only in those populations where competition between the individuals is severe or where there is positive antagonism. 2. Random distribution: Individuals of a population neither aggregate to form clumps nor they are evenly spaced. They are irregularly scattered in the range of distribution. Random distribution is rarely seen. It occurs only where the environment is uniform and the individuals do not have a clumping tendency. It follows the random or bell shaped distribution

15. 3. Clumped distribution: The clumped or aggregation is the common pattern of distribution of individuals. Individuals exhibit varying degree of clumping but in a particular population they form groups of specific size. In animals it is represented by a pair and in plants by a vegetative one. The groups could be the same or of varying size and could be distributed randomly or aggregated. Therefore, the clumped distribution could be of three types.

16. i ) Random clumped ii) Uniformly clumped iii) Aggregated clumped

17. All the three types of clumped distribution are found in nature The clumping is caused by the aggregation of individuals and depends upon the i ) local habitat differences ii) daily and seasonal weather changes iii) reproductive processes iv) social attraction

18. Clumping in plants depends upon the first three factors, where as social attraction is found in animals along with other three factors. Therefore the degree of clumping in a population depends upon the specific nature of habitat, the weather, type of reproductive pattern and the degree of sociality. Clumping may be because of social aggregations eg . Honey bees, Wasps, and termites

19. R-selected and K-selected species Individual organisms and their populations can grow or reproduce only if they acquire more energy that is required for their maintenance. Maintenance energy consists of the resting or basal rate metabolism and a multiple of this to cover minimum activity needed for survival under field conditions. This existence energy is calculated in field from time to time as it varies according to activity of sedentary and active species. The net energy required for reproduction is the energy required for survival of race for future generations i.e., the energy devoted to reproductive structures, mating activities, production of offspring and parental care. For animals the ratio is between useful energy in food, minus, the energy of cost of searching for food and feeding.

20. This can be brought to an optimum level. By 1. Minimizing time by efficient searching 2. Maximizing net energy by selecting large food items and easily convertable energy sources. The ratio of reproductive energy to maintenance energy varies not only with the size of organisms and with life history patterns but also with population density and high reproductive potential. This mode is called R-selection.

21. Crowded conditions favour organisms with lower growth potential but better capabilities for using and competing for scarce resources. This mode is called K-selection.

22. R-selection 1. Selection at or near intrinsic growth rate ‘r’, characterized by high rates of reproduction under conditions of low competition. 2. R-selection tends to dominate in early seral stages of ecological succession. K-selection under carrying capacity, ‘K’, conditions are mostly high levels of competition. The K-selected species are generally dominating the stable and mature seral stages of ecological succession. The allotment of energy by an organism shows the balance it strikes, between the cost of production and survivorship.

23. The first priority is given to survival and maintenance of the individual (The respiratory component) with additional energy allocated to growth and reproduction (Production component). Larger the organism, larger the metabolic costs of maintainence when compared to smaller organisms with smaller structure for maintainence .

24. The characteristics of R-selection The R-selected species are subjected to unpredicatable climatic conditions like storms, floods etc. The population of R-selected species is variable in time, generally large. Competition is very less as these are in early stages of ecological succession where very few species are established. The R-selection favours rapid development of species as well as populations. It favours early reproduction These animals have smaller body size and have many offsprings The R-selected species have short life span.

25. The characteristics of K-selection These animals exist in later, more mature and stable stages of ecological succession. Stable and predictable weather conditions favours these species They have delayed periods of reproduction These animals exhibit larger body sizes and beget fewer off springs They have longer life span generally above one year Example 1) When compared to herbivores, predators spend more of their energy in maintenance activity like foraging for food, defending territories and so on. 2) Large homeotherms allot larger percentage of energy for maintenance of body temperature as compared to arthropods.

26. Regulation of Population or Density stabilizing factors No animal population increases indefinitely. Its number is influenced by some factors outside the population itself, or by some factors acting within the population. Those factors influencing the population from outside are termed density independent factors Those influencing the population from within the population are termed density dependent factors.

27. Density Independent factors The limiting effects of space, weather, and food are considered to be the density independent factors. The amount of space available for additional individuals is inversely proportional to the space already occupied. Thus the greater the population density, lesser the space available per individual. If all favourable space is occupied, addition of new individuals to the population are formed into inferior cover where they receive less protection and become more exposed to the attacks of predators.

28. II. Density dependent Factors The density dependent factors that have a stabilizing effect on population size are 1. Competition, 2. Reproductivity , 3. Predation, 4. Emigration, 5. Disease, 6. Social Behaviour or territoriality, 7. Social dominance and hierarchy, 8. Home range, 9. Endocrine balance and cycles.

29. 1. Competition: Competition is the active demand for the same ecological resources by two or more individuals of same species or of different species, thus contributing to the density and diversity of a population. The role of competition in regulating population size is directly effective by causing mortalities through fighting, nest destruction, and loss of food supplies.

30. 2. Reproductivity : Reduction in the amount of food available decreases rate of reproduction. Ex: In cultures of Paramecium, a decrease in the volume of culture fluid for the same initial number of individuals or an increase in the initial number of individuals for a given volume of fluid, decreases the rate of binary fission.

31. 3. Predation: The variations in the population level of predators follows variations in the population of prey species. But it is not certain whether the number of predators depends simply on the abundance of prey or whether the predators by their feeding regulate the number of prey animals. Under certain conditions predators greatly affect the number of the species on which they feed.

32. 4. Emigration: The pressure of over population is relieved by mass emigration of individuals from particular localities and also by their death. Emigrations under natural conditions occur when there is overcrowding, in certain animals. 5 . Disease : The infectious disease in some form is a common cause of mortality. But it is less important as a stabilizing factor because it reduces the population size in an important manner only when epidemics occur.

33. 6. Social Behaviour or Territoriality : Social behaviour or territoriality limits the number and reproductive activity and excludes the surplus. The right to food, the right to space and the right to reproduce are the greatest competitive situations in each individual animal. Territoriality exists when an individual animal claims a certain area and defends it against others of the same species and perhaps even against others of the different species. It is most conspicuous during the breeding season.

34. 7. Social Dominance and Hierarchy : There is a tendency among many animals to band together in flocks or herds. Among vertebrates, such animal aggregations have some form of social organization. Two opposing forces are at work in these social groups. One is a mutual attraction towards one another. At the same time the animals exhibit a degree of social intolerance, a negative reaction against crowding. This limits the size of a herd or a flock.

35. 8. Home Range: Home Range is the area over which an animal habitually travels while engaged in its usual activities. Among some species, home range and territory are the same. Among others only a part or none of it is defended. The two sexes may have the same or different home range. But the home ranges of both sexes may overlap and the home range of the male may overlap those of several females.