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RETROGRESSIVE CHANGES, CONCEPT OF CLIMAX COMMUNITIES AND RESILIENCE OF COMMUNITIES.pptx

The document discusses ecological succession, emphasizing the concepts of climax and retrogressive communities. It details progressive and retrogressive changes in species diversity and biomass, exemplified by case studies like the spruce forest in Alaska. Additionally, it covers community resilience, highlighting factors such as biodiversity, keystone species, and human impact, with examples from both plant and animal kingdoms.

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RETROGRESSIVE CHANGES, CONCEPT OF CLIMAX COMMUNITIES AND RESILIENCE OF COMMUNITIES SUBMITTED TO, DR. AGHIL SOORYA DEPARTMENT OF BOTANY SUBMITTED BY, HASNIYA.K.M ROLL NO. :09 II MSc BOTANY
INTRODUCTION • Ecological succession is the steady and gradual change in a species of a given area with respect to the changing environment. • It is a predictable change and is an inevitable process of nature as all the biotic components have to keep up with the changes in our environment. • These changes lead finally to the equilibrium of the community with the environment called a climax community. Climate community marks the endpoint of succession. • An intermediate stage in the successional process towards the climax community is known as seral community and the temporary stage is called the seral stage.
Progressive Succession: Progressive succession is a succession where the community becomes complex and contains more species and biomass over time. Retrogressive Succession: Retrogressive succession is a succession where the community becomes simplest and contains minimum or fewer species and less biomass over time.
Retrogressive changes • It is a type of succession in which the community becomes more simplistic and contains fewer species and less biomass over time. • In certain cases, a situation occurs in which a community depreciate and a new simpler community develops. • Some retrogressive succession is allogenic in nature. • For example, introduction of grazing animals into grassland resulting in degenerated rangeland.
When the depletion of glaciers occurred on the slopes and flat terrains in Alaska, succession proceeds from the formation of simpler community to complex communities (herb and shrub stage) and finally reaches to climax community, the spruce forest. Along with spruce tree, some mosses and small trees were also found in the forest. But during the course of time there was sudden invasion of sphagnum mosses. It has the ability to hold large amount of water. As a result it absorbed large amount of water from the soil and leads to death of spruce tree. Another example: Pedersen Glacier, Alaska, ~1930s and 2005
The spruce beetle is a bark beetle that attacks the White spruce trees in Interior Alaska. Of all the insects that affect spruce in Alaska, the spruce beetle causes the most damage. Spruce beetle-killed trees in Alaska Spruce trees in Alaska
Climax or stable community • Climax community (Clements 1916) is the more or less stable final stage of ecological succession. It is almost self perpetuating, and is in equilibrium with the physical environment so long as the environment remains unperturbed. • Climax community is in steady-state or dynamic equilibrium because its net annual organic production, energy level, and density of populations are kept almost constant. • The annual production and input of organic matter will be counterbalanced by consumption and output. So, there is no net accumulation of organic matter and energy.
Forest Desert Grassland Coral reef
Climax community cont.. According to Clements, climax has the following three principle characteristics: (a) Unity: Climax is a unit. All the species are taken as an organised unit to show the climate. In other words, climax is a unit, which acts as the index of climate of an area. (b) Stability: The form of the climax community is stable with the climate. The climax community cannot be replaced through competition. (c) Origin and Organism Concept: Climax community is interpreted as a super organism. This community takes birth, grows and develops like an organism. Climax communities undergo changes with the changes of time and climate.
Characteristics of climax community • Climax communities maintain species diversity for an extended period. • They contain multiple specialized ecological niches. • They maintain high levels of organism interactions. • Climax communities recycle nutrients while maintaining a relatively constant biomass. • They can withstand a lot of environmental stress. • They have a lot of species diversity, and energy is transferred through complicated food webs rather than simple food chains. • Organisms in the climax stage are replaced by organisms that are similar to them. As a result, the balance of species is maintained.
Types of climax community (1) Climatic climax • A climatic climax exists when there is only one climax, and the location’s climate influences the climax community’s development. • For example, the growth of a Maple-beech climax community in moist soil. (2) Edaphic Climax • When a location has many climax communities, each of which is influenced by local substrate circumstances such as soil moisture, soil nutrients, terrain, slope exposure, fire, and animal activity, the term “edaphic climax” is used.
(3)Catastrophic Climax • Climax vegetation is vulnerable to catastrophic occurrences, such as wildfire Chaparral vegetation. • For example, is the ultimate vegetation in California. (4) Disclimax (disturbance climax) or Anthropogenic Subclimax • When a man or his domestic animals maintain a stable community that is not the climatic or edaphic climax for the particular place, it is referred to as disclimax (disturbance climax) or anthropogenic sub climax (man-generated). • Overgrazing by livestock, for example, could result in a desert community of bushes and cacti where the local climate would allow grassland to thrive.
(5) Preclimax and post climax community • Preclimax describes a society with life forms that are lower than those found in the projected climatic climax. In contrast, post- climax describes one with higher life forms than those in the expected climatic climax. • Preclimax strips form in less moist and hotter locations than the surrounding climate, whereas postclimax strands form in more moist and colder areas. Pre climax Post climax
There are three theories about the climax community. (a) Mono-climax theory (b) Poly-climax theory (c) Climax-pattern hypothesis
(a) Monoclimax theory • Federic Clements created the monoclimax (or climatic climax) theory. • According to the mono climax theory of succession, each region has a single climax community toward which all other assemblies are progressing. • The area climate determines the climax. Differences in topography, soil parent material, biotic component, and other factors are overcome through succession and environmental modification processes. • A uniform plant community would cover the entire area. • Subordinate communities are the communities that exist in that area in addition to the climax community. • Pro-climax, post-climax, pre-climax, sub-climax, and disclimax are subordinate communities.
(b) Theory of Polyclimax • Tansley (1939) proposed this theory, which was later backed up by Daubenmire (1966). • According to the hypothesis, a region’s climax vegetation comprises a mosaic of vegetation climaxes influenced by soil moisture, soil nutrients, terrain, slope exposure, fire, and animal activity. • According to the poly climax theory, many forms of vegetation known as climax communities can be found in a particular location, each of which is influenced by factors other than the local climatic conditions. • So, depending on the nature of the element in stabilization, the climax stages may be labeled topographic climax, biotic climax, edaphic climax, fire climax so on.
(c) The climax pattern theory • The climax pattern theory, developed by R.H. Whittaker (1953), is a version of the poly climax idea. • A natural community is adapted to the entire pattern of environmental factors in which it exists, according to Whittaker (1953); the significant factors are the genetic structure of each species, climate, site, soil, biotic factors (animal activity), fire, and wind, availability of plant and animal species, and dispersal chances. • According to this hypothesis, Climax communities are patterns of populations that fluctuate depending on the overall environment. • As a result, there is no fixed number of climax communities, and no one element affects a climax community’s structure stability.
Resilience of community • Community resilience is the sustained ability of a community to use available resources (energy, communication, transportation, food, etc.) to respond to, withstand, and recover from adverse situations. • This allows for the adaptation and growth of a community after disaster strikes. • Communities that are resilient are able to minimize any disaster, making the return to normal life as effortless as possible. • A stressor may be caused by natural disturbances or human impacts (anthropogenic stressors) that affect the environment.
Some examples of factors like natural disturbances and human impacts that cause disturbances to ecosystems include:
Key factors of community resilience: 1. Biodiversity: High species diversity tends to increase the resilience of both plant and animal communities. In diverse ecosystems, there is a greater chance that some species can adapt or thrive even when conditions change. 2. Keystone Species: Certain species in both plant and animal communities can have a disproportionately large impact. These “keystone species” can significantly influence the community’s structure and function. Their presence often enhances resilience. 3. Habitat Connectivity: The connectivity of habitats is essential for the movement and migration of species. It allows them to find new areas to inhabit or resources to exploit when conditions change. This is crucial for resilience, especially in the face of climate change.
4. Ecosystem Health: The overall health of the ecosystem, including factors like water quality, soil quality, and climate stability, affects the resilience of both plant and animal communities. Healthy ecosystems are better at absorbing shocks. 5. Adaptive Capacity: The ability of individual species within a community to adapt to changing conditions is vital for resilience. Some species may possess traits or behaviors that enable them to survive and reproduce in a new environment. 6. Human Impact: Human activities, such as habitat destruction and pollution, can reduce the resilience of plant and animal communities. Conservation efforts aim to mitigate these impacts and increase resilience through restoration and protection.
Examples: In the plant kingdom, an example of community resilience can be observed in a forest ecosystem after a wildfire. While individual trees may be damaged or destroyed, the forest as a whole often exhibits resilience. Some tree species have adapted to survive and even thrive in fire-prone environments. Additionally, the remaining plants and shrubs can help prevent soil erosion, and their seeds can quickly germinate and regrow, gradually restoring the forest ecosystem. This demonstrates how plant communities adapt and recover collectively in the face of natural disturbances.
Examples: An example of community resilience in the animal kingdom is seen in honeybee colonies. When a hive faces. Challenges such as disease, predators, or harsh environmental conditions, worker bees cooperate to protect and repair the hive. They adapt to changing circumstances by adjusting their behavior and resources, ensuring the survival and vitality of the entire colony. This demonstrates how animal communities can exhibit resilience in the face of various challenges.
Examples: One example of community resilience is how a neighborhood comes together after a natural disaster, such as a hurricane. Residents may collaborate to help each other evacuate, provide shelter, share resources, and support one another during the recovery process. This demonstrates the strength and resilience of the community in the face of adversity.
Reference 1. Mishra, D.D. (2008). Fundamental Concepts in Environmental Studies. S.Chand & Company Pvt Ltd. 2. Sharma, P.D., & Sharma, P.D. (2012). Ecology and Environment. Rastogi Publications. 3. Smith, T.M., & Smith, R.L. (2006). Elements of Ecology, 6th edn. 4. https://www.turito.com/learn/biology/concept-of-climax- community.
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