The process where plant and animal communities in an area change over time due to large-scale changes or destruction. Its speed is influenced by geographical location and occurs faster in areas in the middle of large continents.
Stages in Ecological Succession: Involves directional changes in vegetation.
Pioneer Community: The first plant to colonize an area.
Climax Community: Final stage, stable and mature. It is more complex and long-lasting.Successional Stages/Seres: Progressive series of
changes where one community replaces another.
Transitional communities are also replaced (seral
community) and characterized by increased
productivity, nutrient shift, organism diversity, and
food web complex.
Primary Succession.
Occurs in areas where no previous community existed i.e. bare, often harsh environments (rock outcrops, sand dunes).
Pioneer species: Hardy species like microbes, mosses, and lichens (symbiotic association of Fungi and algae).
Pioneers alter the habitat through growth and development.
Relatively slow, starting from barren conditions.
Secondary Succession
Follows complete or partial destruction of an existing community by natural events like floods, droughts, fires or by human interventions like deforestation, agriculture etc.
- Well-developed soil already present at the site.
- Hardy grasses initially, followed by herbaceous plants and eventually trees.
- Faster, as it builds upon existing soil and community remnants.
Autogenic succession: brought about by biotic
components (living inhabitants) of that community itself.
Allogenic succession: brought about by the abiotic
components (fire, flood) of the ecosystem.
Succession in Plants
Xerarch Succession: Occurs on land with low
moisture content (e.g., bare rock)
Pioneers: Colonizing plants adapted to arid conditions
Progression: Succession leads to mesophytic
habitat (moderate water)
Hydrarch Succession: takes place in water bodies
(ponds, lakes)
Pioneers: Phytoplankton in primary succession
Progression: Phytoplankton → Floating
angiosperms → Rooted hydrophytes
→ Sedges/
grasses → Trees.
HOMEOSTASIS (FEEDBACK CONTROL MECHANISMS)
Tendency for a biological system to resist changes and maintain equilibrium, through which ecosystems can self-regulate species’ structure and functional processes.
For example: In a pond ecosystem, if the zooplankton population increases, it leads to phytoplankton scarcity, causing zooplankton starvation, and if the zooplankton population decreases, phytoplankton increases, causing the zooplankton population to rise. Thus, the negative feedback mechanism (an increase in one factor leadsbto a decrease in another) induced by the limiting resource (here, food scarcity) maintains stability in an ecosystem.
Homeostasis in Organisms
Maintenance of stable equilibrium through physiological functions, like sweating for cooling, migration for temperature regulation etc.
Conform: Bodily changes in the internal environment of the organisms influenced by the changes in the surroundings. For example: most animals cannot maintain a constant body temperature, their body temperature changes with the ambient temperature outside.
Regulation: Most birds and mammals perform homeostasis, i.e., keep their internal environment constant through behavioural (e.g. animals migrating to under tree shade to avoid summer heat) and physiological means(e.g. increase in metabolism to keep the body warm) to ensure thermoregulation.
Regulatory Challenges: Thermoregulation and
osmoregulation are energetically expensive; small
animals face challenges due to the high surface-
to-volume ratio; small animals are rare in polar
regions due to energy expenditure.
Migration: Movement to more hospitable areas temporarily (e.g., migratory birds).
Suspension:
Formation of spores in bacteria, fungi, and lower plants.
Escape Strategies: Hibernation(Winter Sleep) in polar bears during winter; Aestivation(Summer Sleep) in snails and fish to avoid summer-related problems; Diapause(Suspending Growth) in zooplankton during unfavourable conditions.
Seed Formation: Higher plants use seeds for stress survival and dispersal.
ENERGY FLOW THROUGH THE FOOD CHAIN
Trophic level represents energy flow in an ecosystem. A trophic level is a position occupied by an organism in a food chain.
Unidirectional Energy Flow: Energy in an ecosystem flows in a unidirectional manner, typically from the lower trophic levels to the higher ones. This means that energy is transferred from producers (plants or autotrophs) to consumers (herbivores, carnivores, etc.) and rarely moves in the opposite direction.
Energy Loss in Trophic Levels: At each trophic level, there is a significant loss of energy, primarily in the form of heat, during the process of metabolism and other life activities. This is often represented by the ecological pyramid, where the energy decreases as you move up the trophic levels.
The trophic level interaction involves three concepts, namely:
- Food Chain
- Food Web
- Ecological Pyramids
Food Chain
Feeding relationship between species based on who eats whom.
Types of Food chains
Grazing food chain: Starts from live plants.
Grasses → Grasshopper → Frog → Snake → Eagle;
Diatoms → Crustaceans (Krills, Prawns, Lobsters,
Crabs, Barnacles, Copepods) → Herrings (small
Fish).
Detritus food chain: Starts from dead organic matter. Some detritivores are Earthworms, Millipedes, and Woodlice.
On Earth, the grazing food chain is dominant in the marine ecosystem.
In the terrestrial ecosystem, the detritus food
chain is more dominant.
Food Web
Interconnected networks of food chains are known as food web.
Types of Biotic Interactions in a Food Web Net Positive Outcome
Mutualism: When both the species benefit from the association. E.g. coral and zooxanthellae.
Commensalism: When one species benefits while the other is neutral, E.g. the relationship between trees and epiphytic plants.
Antagonism Outcome (Compensatory Interaction)
Parasitism: Beneficial to one species (parasite) and harmful to the other species (host).
Predation: One species (predator) benefits, while the second species (prey) is harmed.
Predators may be bigger or smaller than prey.Parasite is smaller in size than the host.Predators intend to kill their prey.Parasite doesn’t intend to kill the host. The Predator’s energy requirement is more.Parasite’s energy requirement is less.
Non-Symbiotic (both do not live together).Symbiotic (both live together).
Negative Outcome
Competition: Adversely affects both species.
Amensalism: One species is inhibited, while the other species is unaffected, E.g: Bread mould and fungi Penicillium; a large tree shades a small plant, retarding the growth of the small plant, while the small plant has no effect on the large tree.
Ecological Pyramids
Graphical presentation of the relationship betweenvarious trophic levels. Horizontal bars depict specific trophic levels, with the length of the bar indicating the total number of individuals, biomass, or energy at each trophic level.
Categories of Ecological Pyramids
Pyramid of Numbers: Represents the number of
individuals at each trophic level. Generally, numbers decrease as you move up the pyramid.
Pyramid of Biomass: Depicts total biomass (dry
weight) of organisms at each trophic level. Generally, biomass decreases as you move up due to energy loss.
Pyramid of Energy or Productivity: Represents
energy flow through trophic levels. Generally, energy availability decreases moving up the pyramid, hence the pyramid is always upward.
Movement of Non-Degradable Pollutants in Ecosystems
Non-degradable pollutants (persistent pollutants) cannot be easily broken down by detritivores. For instance, Chlorinated Hydrocarbons (Perfluoro Chlorides) are particularly damaging and long-lasting.
The movement of these pollutants involves:
Bioaccumulation: Bioaccumulation is the gradual buildup of pollutants in an organism. It occurs when the rate of substance loss through breakdown or excretion is slower than the rate of accumulation. Persistent organic pollutants like DDT pose a high risk of bioaccumulation due to their long-lasting nature.
Biomagnification: Biomagnification is the progressive increase in pollutant concentration at each trophic level over time(progressive bioaccumulation). For this pollutants require a long biological half-life (long-lived) and insolubility in water but solubility in fats (e.g., DDT). Pollutants soluble in water get excreted, while those soluble in fats are retained for a long time.
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