Botany Oraganism and Population - Class 12 JKBOSE History

Organisms and Population

Introduction to Ecology

Ecology is derived from two Greek words: "Oikos" meaning home and "Logy" meaning study. It is the branch of biology that deals with the study of interactions among organisms and between organisms and their environment. The environment includes both biotic (living) and abiotic (non-living) components.

• First authentic use of the term "Ecology": By Reiter.
• Father of Indian Ecology: Ramdeo Mishra.
• Biotic components: Living organisms such as plants, animals, bacteria.
• Abiotic components: Light, temperature, water, soil, air.

Ecological Hierarchy

Ecological hierarchy refers to the ascending or descending arrangement…

Organisms and Population

Introduction to Ecology

Ecology is derived from two Greek words: "Oikos" meaning home and "Logy" meaning study. It is the branch of biology that deals with the study of interactions among organisms and between organisms and their environment. The environment includes both biotic (living) and abiotic (non-living) components.

• First authentic use of the term "Ecology": By Reiter.
• Father of Indian Ecology: Ramdeo Mishra.
• Biotic components: Living organisms such as plants, animals, bacteria.
• Abiotic components: Light, temperature, water, soil, air.

Ecological Hierarchy

Ecological hierarchy refers to the ascending or descending arrangement of ecological units based on size and complexity. The smallest and basic unit is the organism, followed by population, community, and biome.

• Order (Ascending): Organism → Population → Community → Biome
• Organism: Basic and smallest unit of ecology.
• Population: Group of individuals of the same species in a particular area at a particular time.
• Community: Different populations interacting in an area.
• Biome: Large ecological area with distinct climate and organisms.

Population: Definition and Key Points

A population is a group of individuals of a particular species living in a specific area at a specific time, sharing common resources and capable of interbreeding.

• Key features:
  • Same species
  • Same area
  • Same time
  • Share resources (food, shelter)
  • Interbreed among themselves
• Ecological concept: Population can form by both sexual and asexual reproduction.
• Genetic concept: Population forms only by sexual reproduction.

Habitat and Ecological Niche

A habitat is the specific place where an organism lives, including both biotic and abiotic components. An ecological niche refers to the functional role or profession of an organism within its habitat.

• Habitat: The address or residence of an organism.
• Niche: The activities, role, and range of resources an organism utilizes in its habitat.
• Niche explains: Range of tolerance and resource utilization by an organism.

Population Attributes: Birth Rate and Death Rate

Birth rate and death rate are crucial in determining population size. Birth rate increases population size, while death rate decreases it. These rates are always expressed per capita (average per individual).

• Birth rate: Number of births per capita (average per person) in a given time.
• Death rate: Number of deaths per capita in a given time.
• For individuals: Use "birth" and "death".
• For populations: Use "birth rate" and "death rate".

Formula for Birth Rate:

Where:

• $\Delta n$ = Change in population size (final - initial)
• $n$ = Initial population
• $\Delta t$ = Time period

Example Calculation:

• Initial lotus plants: 20
• Added after 1 year: 8
• Final: 28
• Birth rate: $(28-20)/(20 \times 1) = 8/20 = 0.4$ per lotus per year

Formula for Death Rate:

• Negative value indicates decrease in population size.

Population Age Pyramids

At any given time, a population consists of three age groups: pre-reproductive (juvenile), reproductive (adult), and post-reproductive (old). The graphical representation of these groups is called the population age pyramid.

• Pre-reproductive: Juvenile stage (before reproduction)
• Reproductive: Adult stage (capable of reproduction)
• Post-reproductive: Old age (after reproduction)

Types of Age Pyramids:

• Expanding Population: Pre-reproductive group > reproductive and post-reproductive; population size increases (triangular graph).
• Stable Population: Pre-reproductive ≈ reproductive; population size remains constant (bell-shaped graph).
• Declining Population: Pre-reproductive < reproductive; population size decreases (urn-shaped graph).

Population Growth and Regulation

Population size is not constant; it changes due to various factors. Four main factors regulate population size: natality (births), mortality (deaths), immigration (entry), and emigration (exit).

• Natality (B): Number of births added to initial density.
• Mortality (D): Number of deaths during a given period.
• Immigration (I): Number of individuals of the same species entering from elsewhere.
• Emigration (E): Number of individuals leaving the habitat.

Population size equation:

Where:

• $N_{t+1}$ = Final population size
• $N_t$ = Initial population size

Population Growth Models

Population growth can be described by two models: exponential and logistic.

Exponential Growth Model:

• Occurs under ideal conditions (abundant resources, no environmental resistance).
• Growth is geometric.
• Graph is J-shaped.
• Equation:$$\frac{dn}{dt} = r n$$Where $r$ is the natural rate of increase ($r = B - D$), $n$ is population size.
• Exponential form:$$n = n_0 e^{rt}$$
• Followed by bacteria.

Logistic Growth Model:

• Occurs under realistic conditions (limited resources, environmental resistance).
• Graph is S-shaped (sigmoid).
• Phases: Lag phase (slow increase), log phase (rapid increase), deceleration phase (gradual decrease), asymptote (constant at carrying capacity).
• Carrying capacity ($K$): Maximum number of individuals an environment can support indefinitely.
• Equation:$$\frac{dn}{dt} = r n \left(\frac{K - n}{K}\right)$$
  • $(K - n)/K$ represents environmental resistance.

Population Interactions

Organisms do not live in isolation; they interact to form communities. Interactions are of two types: interspecific (between different species) and intraspecific (within the same species).

• Interspecific interactions: Between individuals of different species.
• Intraspecific interactions: Between individuals of the same species.

Types of Interspecific Interactions:

• Mutualism (+, +): Both species benefit (e.g., lichen: algae and fungi; mycorrhiza: fungi and higher plant roots).
• Competition (-, -): Both species are harmed; occurs for limiting resources.
• Predation (+, -): Predator benefits, prey is harmed (e.g., lion eating deer, sparrow eating seeds).
• Parasitism (+, -): Parasite benefits, host is harmed (e.g., lice on humans, tapeworm in humans).
• Commensalism (+, 0): One benefits, other unaffected (e.g., orchid on mango branch, barnacles on whale).
• Amensalism (-, 0): One is harmed, other unaffected (e.g., Penicillium secreting penicillin inhibiting Staphylococcus).

Competition and Gause’s Principle

Competition occurs when closely related species compete for the same limiting resources. It can also occur between unrelated species for the same resource.

• Key objections to classical definition:
  • Competition can occur between unrelated species (e.g., flamingo and fish for zooplankton).
  • Resources need not always be limiting (e.g., goats outcompeting tortoises in Galapagos Islands).
• Best definition: Competition is a process where the reproductive fitness (biotic potential) of one species is significantly lower in the presence of another.

Gause’s Competitive Exclusion Principle:

• Two closely related species competing for the same resource cannot coexist indefinitely.
• One will be eliminated (the competitively inferior), the other survives (the superior).
• Example: Paramecium aurelia (superior) survives, Paramecium caudatum (inferior) is eliminated when grown together.

Roles of Predators

Predators play important roles in ecosystems beyond just killing prey.

• Energy transfer: Predators act as conduits (channels) for energy transfer across trophic levels in food chains.
• Population control: Predators regulate prey population size (e.g., prickly pear cactus controlled by introducing its natural predator, moth).
• Maintaining species diversity: By reducing competition among prey species, predators help maintain species diversity (e.g., removal of Pisaster fish led to extinction of 10 invertebrate species due to increased competition).

Parasitism: Types and Examples

Parasitism involves one species (parasite) benefiting at the expense of another (host). Most parasites harm their hosts.

• Ectoparasites: Live on the external surface of the host (e.g., lice on humans, ticks on dogs, Cuscuta on hedge plants).
• Endoparasites: Live inside the host’s body (e.g., tapeworm, liver fluke, Plasmodium causing malaria).
• Brood parasitism: Found in birds; parasitic bird (e.g., cuckoo/koel) lays eggs in the nest of host bird (e.g., crow). Host incubates eggs, often unable to distinguish them due to evolutionary mimicry in size and color.

Life History Variation

Different organisms exhibit variations in their life cycles and reproductive strategies to adapt to environmental conditions.

• Some organisms produce one offspring per reproductive event (e.g., humans), others produce many (e.g., dogs).
• Some reproduce only once in their lifetime, others reproduce seasonally or continuously throughout the year.
• These variations help organisms accommodate different environmental conditions and are termed life history variations.