Ecosystems and Ecological Succession

• An ecosystem is a community of living organisms that shapes its environment.

Learning Objectives

• To describe the basic components of the ecosystem.
• To explain the interactions between organisms within an ecosystem.
• To explain the flow of energy within an ecosystem.
• To differentiate the ecological succession.
• To analyze the biogeochemical cycle within an ecosystem.

Assessments

• Attitude: Group cooperation.
• Skill: Project, presentation.
• Knowledge: Worksheet, summative test.

Components of Ecosystem

• Biotic components are living organisms that shape their environment.
  • Examples: Producers, consumers, and decomposers.
• Abiotic components are nonliving influences on organisms.
  • Examples: Soil, air, water, wind, temperature, and the sun.

Interactions Within an Ecosystem

• Predation involves predator and prey.
• Competition is the interaction of two or more organisms vying for the same limited resources.
  • Competition is divided into intraspecific and interspecific competition.
• Mutualism is a mutually beneficial interaction between two different species.
• Commensalism is the interaction between organisms where one organism benefits while the other is unaffected.
• Parasitism involves one organism (parasite) living on or in another organism (host).

Energy Flow Within an Ecosystem

• Energy moves through different trophic levels.
• Food chains and food webs are ways to visualize energy flow.
• Ecological pyramids represent the structure of the food chain within an ecosystem.

Food chain

• The trophic levels are:
  • Level 1: Producer
  • Level 2: Primary Consumer
  • Level 3: Secondary Consumer
  • Level 4: Tertiary Consumer
  • Level 5: Quaternary Consumer
• An example food chain is grass (producer) --> grasshopper -->frog --> python --> eagle (apex predator).

Food web

• The trophic levels are:
  • Level 1: Producer
  • Level 2: Primary consumer
  • Level 3: Secondary Consumer
  • Level 4: Tertiary Consumer
  • Level 5: Quaternary Consumer
• An example food web is plants (producer) --> grasshopper -->scorpion --> fox, and plants --> grasshopper --> squirrel --> eagle (apex predator).

Ecological pyramids

• Pyramid of energy
  • Producers: 10,000 J
  • Primary Consumers: 1,000 J
  • Secondary Consumers: 100 J
  • Tertiary Consumers: 10 J
• Pyramid of numbers: Oak Tree (producer) --> insects (primary consumers) --> woodpeckers (secondary consumers).
• Pyramid of biomass
  • Clover (producer) --> snail (primary consumer) --> thrush (secondary consumer) --> sparrowhawk (tertiary consumer).

Succession

• Ecosystems are dynamic and constantly changing.
• Sometimes, ecosystems change from being very simple to being relatively complex; this process is known as succession.
• During succession, biotic conditions (living factors) and abiotic conditions (non-living factors) change over time.
• Newly formed or exposed land (with no species present) is gradually inhabited by an increasing number of species.

Primary succession

• New uninhabited land can be created by erupting volcanoes that cool and leads to the formation of new rock surfaces or new rocky islands in the sea, or by sea-level dropping or the drying up of a lake, leaving areas of bare rock.
• Seeds and spores that are carried by wind land on the exposed rock and begin to grow.
• The first species to colonize the new land (often moss and lichens) are known as pioneer species.
• Dead organic matter (humus) forms a basic soil as pioneer species die and decompose.
• Small plants and grasses that are adapted to survive in shallow, relatively nurtrient poor soild land on the basic soil and begin to grow.
• The new soil becomes deeper and more nutrient-rich as small plants and shrubs die and decompose.
• The roots of these plants and shrubs form a network that helps hold the soil in place and prevent it from being washed away.
• Larger plants and shrubs, as well as small trees, that require deeper, more nutrient-rich soil, can now begin to grow; they also require more water, which can be stored in deeper soils.
• Large trees can grow once the soil is sufficiently deep, contains enough nutrients and can hold enough water.
• Final species to colonise the new land become the dominant species of the now complex ecosystem.
• The final community formed, containing all the different plant and animal species that have now colonised the new land, is known as the climax community.
• Primary Succesion Stages:
  • Bare rock
  • Lichens
  • Small annual plants and lichens
  • Grasses and perennials
  • Grasses, shrubs and shade-intolerant trees such as pines
  • Shade-tolerate trees such as oak and hickory
• All of these stages can take hundreds of years.

Secondary Succession

• Occurs in areas where the soil is already present.
  • Examples: Abandoned agricultural fields, logged forests, or areas affected by a fire or natural disturbance that does not completely remove the soil.
• Begins with the colonization of fast-growing and opportunistic plant species, such as grasses and herbaceous plants.

Biogeochemical Cycle

• Natural process where elements like carbon, nitrogen, and phosphorus move through living organisms at the atmosphere, oceans, and the Earth crust, sustaining life and maintaining ecological balance.

Carbon Cycle

• Involves processes, such as combustion of fossil fuels, respiration, decomposition, photosynthesis, and dissolving.
• Can include exchanges between the atmosphere, plant biomass, animal biomass, dead tissue, fossil fuels, and oceans.
• Reactions reverse to buffer pH change, reducing hydrogen ions, but also reducing the availability of carbonate ions.

Phosphorus Cycle

• Nutrients (such as nitrogen and phosphorus) are recycled through food webs in natural ecosystems.
• Nutrients pass from producers to primary consumers and from primary consumers to secondary consumers.
• Microorganisms ensure that nutrients stored within dead organisms and in waste products are recycled and made available to producers.
  • This process is known as decomposition.

Saprobionts

• True decomposers.
• Mainly come from the fungi and bacteria kingdoms.
• Secrete enzymes onto their food (dead organisms and waste material), which then digest the material externally (extracellular digestion).
• The products of this external digestion (saprobiotic nutrition) are then absorbed.
• Mineral ions, such as ammonium and phosphate ions, which are important for the growth and function of producers (e.g. plants), may be released as products during saprobiotic nutrition.

Nitrogen Cycle

• Involves nitrogen fixation, feeding, death and excretion, ammonification, nitrification, and denitrification.
• Nitrogen-fixing bacteria (Azotobacter and Rhizobium species) converts gaseous nitrogen into ammonium ions (NH4+).
• Nitrifying bacteria (Nitrosomonas and Nitrobacter species) converts Ammonium ions into nitrite (NO2-) and nitrate (NO3-).
  • Nitrite/Nitrate are highly soluble and can be absorbed by roots.
• Denitrifying bacteria (e.g. Thiobacillus denitrificans) use nitrates for respiration and return gaseous nitrogen to the atmosphere.
• Other bacteria and fungi are involved in saprobiotic decomposition e.g. decay of dead biomass or excreta.

Water Cycle

• Involves condensation, precipitation, absorption of water through plant roots, evaporation, surface run-off, transpiration, and percolation.

Sulphur Cycle

• Dilute sulfuric acid is used as a catalyst in many organic reactions and to clean the surface of metals.
• Concentrated sulfuric acid is used in car batteries, making fertilizers, soaps, and detergents.
• Also used to make acid drain cleaners and in the production of paints and dyes.

Explore the roles of decomposers and interspecific competition within ecosystems. Understand energy loss through trophic levels. Differentiate between primary and secondary succession, focusing on pioneer species and climax communities.