Lesson 2 – Components of Ecosystem

Definition of Core Terms

• Environment
  • Sum total of all forces, materials and influences surrounding us at a given point in time and space.
• Ecology
  • Scientific study of relationships of living organisms to each other and to their natural environment.
• Ecosystem
  • Basic, self-sustaining, self-regulatory structural & functional unit of the biosphere.
  • Coined by A. G. Tansley (1935).
  • Includes both living (biotic) and non-living (abiotic) components that influence and depend on one another.

Classification of Ecosystems

• Natural Ecosystems (no direct human manipulation)
  • Terrestrial: Forest, Grassland, Desert
  • Aquatic: Pond, Lake, River, Marine
• Artificial Ecosystems (human-made or heavily modified)
  • Zoological parks, Botanical gardens, Aquaria, Crop fields, Gardens, Tree plantations converted from forests

Major Components of an Ecosystem

• Abiotic (Non-living)
  • Inorganic substances: $C,~N,~CO<em>2,~H</em>2O$, etc.
  • Organic substances: proteins, lipids, carbohydrates, humic acids, etc.
  • About $40$ chemical elements required for life.
  • Macronutrients (needed in large amounts): $C,~H,~O,~N,~K$.
  • Micronutrients (trace elements): $Cu,~Mn,~Se,~Zn,~B,~Mo,$ etc.
  • Physical factors
  • Climatic: light, temperature, wind, rainfall, humidity, atmospheric gases
  • Edaphic: soil texture, mineral composition, organic matter, soil water & air
  • Topographic: altitude, slope steepness & aspect, distance from sea, presence of rivers
• Biotic (Living)
  • Autotrophs (self-nourishing) – green plants, photosynthetic bacteria
  • Heterotrophs (other-nourishing)
  • Macro-consumers / phagotrophs – herbivores, carnivores, omnivores
  • Micro-consumers / saprotrophs – bacteria & fungi that decompose organic matter

Levels of Biological Organisation

• Organism – fundamental unit; interacts directly with environment.
• Species – largest group of organisms capable of interbreeding & producing fertile offspring; e.g. genus $Panthera$ contains $P.\;tigris,~P.\;onca,~P.\;pardus$.
• Population – number of individuals of the same species in a defined area & time (e.g. lions in Gir Forest).
• Community – all populations of different species living in a particular area.
• Ecosystem – community + abiotic environment.

Habitat vs. Ecological Niche

• Habitat
  • Physical place where an organism lives (its “address”).
  • Characterised by soil, moisture, temperature, light, predators, etc.
  • Host’s body = habitat for parasites.
• Ecological Niche
  • Organism’s “profession” or functional role within its habitat.
  • Involves how it obtains resources, interacts, and alters its surroundings.
  • Fundamental niche – full potential range of conditions.
  • Realised niche – portion actually occupied when constrained by competition.
  • Example: Sunflower niche = absorb light/water/nutrients, give shelter & food to bees/ants, release $O_2$.

Species Interactions Overview

• Interactions rated as $+, -, 0$ (positive, negative, neutral effect on each partner).
• Two broad categories
  • Positive interactions – beneficial to at least one, harmful to none.
  • Negative interactions – one or both are harmed.

Positive Interactions

• Mutualism (Obligatory) $+ / +$
  • Partners cannot survive naturally without each other.
  • Examples:
  • Rhizobium in legume root nodules $\leftrightarrow$ plant (N-fixation vs. carbohydrates).
  • Lichen = algae (photosynthate) + fungus (water & shelter).
• Proto-cooperation (Facultative Mutualism) $+ / +$ but non-obligatory.
  • Sea anemone on hermit crab (transport vs. protection).
  • Ants “milk” aphids/mealybugs for honeydew; ants protect/shelter them.
  • Insect- or bird-pollinated flowers (nectar/pollen vs. cross-pollination).
  • Egyptian plover or cattle egret removes ectoparasites from large mammals.
  • Cleaner fish at “cleaning stations.”
• Commensalism $+ / 0$
  • One benefits; other unaffected.
  • Continuous contact: Epiphytes (orchids, ferns) on tree branches.
  • Non-continuous: Remora or pilot fish on sharks (feeds on leftovers); clown fish lives among sea-anemone tentacles.

Negative Interactions

• Predation $+ / -$
  • Predator kills & consumes prey.
  • Classic carnivory: wolves–moose, lions–deer, owls–mice.
  • Plant predators: Venus flytrap, pitcher plant.
• Parasitism $+ / -$ (host harmed, usually not immediately killed)
  • Endoparasites (inside): tapeworms, flukes, protozoa, pathogenic bacteria.
  • Ectoparasites (outside): ticks, lice, some fungi.
• Competition $- / -$
  • Intraspecific: large fish eating small fish of same species.
  • Interspecific: lions vs. tigers for prey; plants competing for light in rainforest understory.
• Amensalism (implied under competition + parasitism though not explicitly named) would be $- / 0$.

Neutral Interaction

• Neutralism $0 / 0$
  • Species co-occur with no measurable effect on each other (e.g. rabbits, deer, frogs living in same grassland).

Law of Limiting Factors

• Definition: Any factor in least supply (relative to need) limits biological processes.
• Liebig’s Law of the Minimum
  • Growth controlled not by total resources but by scarcest one.
  • Typically a micro-nutrient such as $Cu,~Mn,~Zn,~Mo,~B$.
• Implications
  • Limits growth, survival, reproduction; causes competition.
  • Especially evident: water availability, sunlight in dense forests, trace elements in soil.

Synergism

• Combined effect of two+ agents exceeds sum of individual effects.
  • Greek origin: “working together.”
• Ecological example: multiple predator species whose combined hunting decreases prey more than expected.
• Pharmacology: synergistic drugs enhance combined efficacy.
• In contrast, antagonistic predator interactions can reduce feeding rates & persistence.

Adaptations & Evolutionary Processes

• Natural Selection (Darwin, 1859)
  1. More offspring produced than can survive.
  2. Heritable phenotypic variation exists.
  3. Individuals with advantageous traits survive & reproduce more.
  4. Over time & reproductive isolation ⇒ new species.
  • Leads to “survival of the fittest.”
• Co-evolution
  • Reciprocal evolutionary change in interacting species (predator–prey, mutualist, competitor).
  • Examples:
  • Fruit-eating birds & fleshy-fruited plants: plants evolve conspicuous, odourless pulp; birds evolve seed-tolerant guts & dispersal behaviour.
  • Parasite/host arms races; flowering plants & pollinators.

Extinction

• Definition: Irreversible loss when last individual dies; “functional extinction” when survivors cannot reproduce.
• Statistics
  • >99\% of all species ever lived are extinct.
  • Average species lifespan ≈ $10$ million years (varies widely).
• Immediate vs. Gradual Causes
  • Sudden: toxic pollution, rapid habitat destruction.
  • Gradual: competitive exclusion, climate shifts.
• Key Drivers
  • Habitat destruction, fragmentation, land-use change
  • Over-hunting & poaching
  • Invasive species
  • Disease & epidemics
  • Climate change / global warming
  • Glaciation, volcanic activity, sea-level change
  • Lack of evolvability, food scarcity
• Notable Extinctions
  • Dodo $(Raphus~cucullatus)$
  • Hawaiian mamo $(Drepanis~pacifica)$
  • Passenger pigeon $(Ectopistes~migratorius)$
  • Tasmanian wolf/thylacine $(Thylacinus~cynocephalus)$
• Effects
  • Disruption of food chains & ecosystems
  • Loss of biodiversity; degradation of ecosystem services
  • Economic losses (food crops, timber, medicines, genetic resources)
  • Diminished recreational & aesthetic value
  • Estimated $\ge 5$ million years required to restore biodiversity lost this century.

Ethical, Philosophical & Practical Implications

• Maintaining biodiversity safeguards ecosystem stability & human well-being.
• Responsible resource use & conservation combat limiting factors & extinction.
• Understanding niches, interactions & limiting nutrients guides sustainable agriculture, forestry & wildlife management.
• Synergistic or antagonistic predator dynamics inform biological control & pest-management programmes.
• Natural selection & co-evolution highlight importance of genetic diversity for future adaptation, breeding, and medicine.

Numerical / Statistical References & Formulae

• Approximate number of chemical elements required for life: $\approx 40$
• Macro vs. micro nutrient demand: macro needed in gram-level quantities; micro in trace ($\mu$g–mg) amounts.
• Species average lifespan: $\sim 10$ million years.
• Extinction proportion: > 99\% of all historic species.

Quick Comparison Chart of Interactions (Sign Convention)

• Mutualism: $+/+$
• Proto-cooperation: $+/+$ (facultative)
• Commensalism: $+/0$
• Predation: $+/-$
• Parasitism: $+/-$ (host not killed immediately)
• Competition: $-/-$
• Neutralism: $0/0$

Connections to Coursework & Real-World Application

• Builds on earlier lecture foundations of biosphere organisation & energy flow.
• Provides conceptual base for later topics (e.g., productivity, nutrient cycling, conservation biology).
• Real-world relevance in agriculture (crop nutrient limitation), forestry (shade tolerance & competition), climate policy (extinction risk), public health (parasite control), and pharmacology (drug synergy).

Possible Exam Prompts Embedded in Text

• Define ecology, ecosystem, niche, neutralism; illustrate with examples.
• Differentiate mutualism vs. commensalism; predation vs. parasitism.
• Explain Liebig’s Law & provide at least two limiting micronutrients.
• Describe three negative interactions with ecological consequences.
• Discuss Darwin’s four postulates & application to modern biodiversity crises.
• Evaluate causes & effects of recent extinctions using named species.
• Outline relationship among species, population & community within an ecosystem.