Paper : 12 Principles of Ecology Module : 20 Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV Development Team Principal Investigator: Prof. Neeta Sehgal Department of Zoology, University of Delhi Co-Principal Investigator: Prof. D.K. Singh Department of Zoology, University of Delhi Paper Coordinator: Prof. D.K. Singh Department of Zoology, University of Delhi Content Writer: Dr. Haren Ram Chiary and Dr. Kapinder Kirori Mal College, University of Delhi Content Reviewer: Prof. K.S. Rao Department of Botany, University of Delhi 1 Principles of Ecology ZOOLOGY Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV Description of Module Subject Name ZOOLOGY Paper Name Zool 12, Principles of Ecology Module Name/Title Community Module Id M20, Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification : Part-IV Keywords Succession, Primary succession, secondary succession, Sera, Climax community, Hydrosere, Lithosere, theories of climax community Contents 1. Learning Objective 2. Introduction 3. History of study of succession 4. Ecological succession and types: Primary and secondary succession 5. Stages of Primary and secondary succession 6. Process of succession in Hydrosere 7. Process of succession in Lithosere 8. Theories of climax community 9. Summary 2 Principles of Ecology ZOOLOGY Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV 1. Learning Outcomes After studying this module, you shall be able to • Understand the meaning of succession and the history of study of succession. • Briefly study the types of succession • Learn about the general pattern of Primary and secondary succession • Evaluate different stages of Hydrosere succession and Lithosere succession • Understand different theories of Climax community 2. Introduction More or less but communities are regularly changing over time and thus, are dynamic entities. Each community has its own developmental history with its particular prevailing environment and time. The source of studying the growth and development of ecological community can be a barren area. The development of the community initiates on arrival of the propagules or their parent organisms to the area of study. Out of all the immigrating organisms or popagules only few of them survives, grow and gets established at the new site. The first developmental stage of the community is called as the pioneering community which is made up of those few successfully survived and established organisms or their propagules. As more and more new species immigrates to this site the competition for the resources becomes more intense between them. Due to the activities of the survived species and physiography and constant change in the climatic conditions, the prevailing environment conditions keeps on changing. The nature works on the principle of “survival of the fittest” and thus, supports only those organisms which adapts and fits best to the changing environment conditions. Until the community becomes incomplete accordance with the environment and become a relatively stable community, the process of development and change in community continues. The changes occurring during the entire process of community development is ordered and highly directional. This highly directional and sequences changes in the community are called as succession. 3 Principles of Ecology ZOOLOGY Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV 3. History of the Study of Succession Europeans have already described the coastal dunes related succession when, in 1899, Henry Cowles’s got inspired from this study and started his study on sand dunes along Lake Michigan. He defined the laws essential to the changing patterns of the community and influenced many ecologists of new generation. He viewed plant communities and documented that these communities differ in the underlying physical environment and species composition and are dynamic in nature. The plant communities in sand dunes were studied at different ages in order to reflect the pattern of changes in the community over time. Since then, many other ecologists along with Cowles studied the succession process by using the chrono-sequence approach. This temporal approach to study succession process is difficult to follow for centuries or decades and thus replaced by another approach that uses spatial differences between communities to infer the occurrence of succession. Spatial differences means locations of different ages are compared to understand the process of succession. Sere is defined as the stage in the succession sequence. Ecologists identified animals as the factors that affect the rate and direction of succession along with different patterns of succession. All the taxonomical groups such as rodents, fish, protozoans and insects and all type of ecosystems such as marine or aquatic etc are being investigated to study succession. 4. Ecological succession and types: Primary and secondary succession In ecology, the community structure evolves over time and the process of this progress is termed as Ecological Succession. Over a period of time, the replacement of one population or community by another is called as succession. The sequence of change in the type of community sequentially relates different community types and describes the landform or soil or total site succession and vegetation succession. Ecological succession is majorly categorized into primary and secondary succession. Based on the association between individual with their biotic and abiotic factors, ecologists 4 Principles of Ecology ZOOLOGY Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV suggested two types of succession process (a) primary and (b) secondary succession. Primary Succession: The establishment of a community in an area never been habituated by organisms or where no prior existence of life is evidenced. The presence of complete lifeless empty area may be because of greater natural disasters such as lava flow, sand dunes or via glacier newly introduced rocks etc. Over a period of time few living organisms manage to sustain life in these empty areas and with continuous succession variety of life-forms begins to grow in the area. Secondary succession: The more common type of succession is secondary succession where the existed life forms of community are partially destroyed by small scale disturbances, for example forest wildfire. For a period of time, with remaining nutrients in environment the area remains empty but gradually life begins to reappear and communities changes over time. In both type of succession the sizes, intensities and frequency of change in species vary within communities while altering the area or habitat leading to mixture of species exploiting the prevailing conditions of community. The species evolved life histories in a partially predictable sequential way and leads to gradual progressive changes in species composing the community. Initially in the unfavourable environmental conditions of this disturbed habitat only few species from the surrounding areas invade and then they modify the habitat by alterations such as soil component compositions, amount of sunlight or shades on grounds etc. The first community established in an originally completely lifeless land is called Pioneer community and the plants and animals are called Pioneer plants or animals. After these successive changes in habitat environment a stable community is achieved termed as Climax dominated by few prominent species. The community with this stable state of equilibrium is termed as Climax Community. Thus, Climax community is characterized by stable environment conditions limiting any further admission of other species in the community. At each successive community the replacing species are more complex. Other than climax community other communities at the time of succession undergo small scale environmental disturbances thereby offering species diversity with equal probability of each species to become dominant. 5 Principles of Ecology ZOOLOGY Community: Community characteristics, types of biodiversity, diversity index, abundance, species richness, vertical and horizontal stratification: Part IV 5. Stages of Ecological succession A process of ecological changes where established communities are replaced by more evolved natural communities is called as succession. Depending on the type of area over which succession has to take place mainly two types of succession occurred: primary and secondary succession. 1. Primary succession When completely lifeless bare area starts succession it is called as Primary succession. 2. Secondary succession When succession starts from an area which has been once occupied by vegetation but become vegetation free due to some disturbances, the mechanism called as denudation or secondary succession. The disturbances can be because of strong winds, fire, rains and cultivation. The stages of ecological process of primary succession includes following stages: 1. Nudation Nudation is a stage occurred