Ecology Organisms And Populationsdiversity Of Living Organisms

Ecology The Branch of science that deals with the interrelationship amongst organism and interaction between organism and their environment.The term coined by Ernest Huckel. Ecology is basically concerned with four levels of biological organisation – organisms, populations, communities and biomes

Ecosystem It is composed of Biotic and Abiotic factors in which cyclic interaction takes place and flow of energy is always unidirectional.

Organism Organism are the basic unit in the study of ecology. it is composed of both plants and animal. at this level we understand physiology, behaviour, distrubution and adaptation in relation to the environment conditions.

Species Similar organism having potential for interbreeding and produce fertile off springs constitute a particular species.

Population A group of individuals of the same species living in a defined geographical are, They share/compete for resources and can potentially interbreed Includes groups formed by both sexual and asexual reproduction

Population Attributes:

• Birth rates and death rates (per capital)
• Sex ratio
• Age distribution
• Population density

Population Measurements:

• Birth rate example: 8 new lotus plants/20 existing plants = 0.4 offspring per lotus per year
• Death rate example: 4 dead fruit flies/40 total = 0.1 individuals per fruit fly per week

Population Growth

(i) Natality refers to the number of births during a given period in the population that are added to the initial density. (ii) Mortality is the number of deaths in the population during a given period. (iii) Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration. (iv) Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

So, if N is the population density at time t, then its density at time t +1 is

$N_{t+1}=N_t +[(B+I)-(D+E)]$

Growth Model#

1. Exponential Growth Defined:

• Exponential growth occurs when a population increases at a rate proportional to its current size. This happens when resources (food, space) are unlimited.

$dN/dt=(b-d)\times N$

Let $(b-d)=r,$ then

$dN/dt=rN$

$N_t=N_{0}\quad e^{rt}$

where

$N_t$= Population density after time t

$N_{0}$= Population density at time zero

$r$ = intrinsic rate of natural increase

$e$ = the base of natural logarithms (2.71828)

• The equation $dN/dt = rN$ models this, where:
• $dN/dt$ represents the change in population size over time.
• $N$ is the current population size.
• $r$ is the intrinsic rate of natural increase (b - d, where b is the per capital birth rate and d is the per capital death rate).

Logistic growth

Verhulst-Pearl Logistic Growth describes a population growth model where the rate of population increase slows as the population size approaches the carrying capacity (K) of its environment. Unlike exponential growth, which assumes unlimited resources, logistic growth incorporates resource limitation, leading to a sigmoid (S-shaped) curve when population size (N) is plotted against time (t). The initial phase shows exponential growth, followed by a deceleration phase as the population nears its carrying capacity, eventually leveling off at K.

$dN/dt=rN (\frac{K-N}{k})$

POPULATION INTERACTION#

• Mutualism: An interaction between two species where both species benefit.

• Competition: An interaction between two species where both species are negatively affected (lose resources, etc.).

• Parasitism: A symbiotic relationship where one organism (the parasite) benefits at the expense of another organism (the host). The parasite typically lives on or in the host, and often does not immediately kill it.

• Predation: A biological interaction where one organism (the predator) kills and consumes another organism (the prey).

• Commensalism: A symbiotic relationship in which one species benefits and the other species is neither harmed nor helped.

• Amensalism: An interaction between two species where one species is harmed and the other species is neither harmed nor benefited.

1.Predation is a biological interaction where one organism, the predator, kills and consumes another organism, the prey. This transfer of energy from prey to predator is a fundamental process in most ecosystems.

Examples: Tiger eating a deer: The tiger (predator) kills and eats the deer (prey).

2.Competition, in the context of ecology, is a process where the fitness (measured by the intrinsic rate of increase, ‘r’) of one species is significantly reduced due to the presence of another species. This reduction in fitness isn’t necessarily tied to limited resources.

Examples: Interspecific competition with limited resources: Flamingoes and fish in shallow South American lakes compete for zooplankton. If zooplankton becomes scarce, the species that is more efficient at acquiring it will thrive, potentially at the expense of the other. This is classic resource competition.

3.Parasitism: A symbiotic relationship where one organism (the parasite) benefits at the expense of another organism (the host). The parasite typically lives on or in the host, deriving nutrients and shelter.

Examples: Human liver fluke: A trematode that requires an intermediate snail and fish host to complete its life cycle. It harms its final (human) host.

4.Commensalism is a type of symbiotic relationship where one species benefits, and the other species is neither harmed nor helped. The benefit to the one species can be in the form of food, shelter, or transportation.

Example: Cattle egrets and grazing cattle. The cattle egret benefits by feeding on insects stirred up by the cattle’s movement. The cattle are neither helped nor harmed by the presence of the egrets.

5.Mutualism is a type of symbiotic relationship where two different species interact in a way that benefits both of them. Each species receives something advantageous from the interaction.

Example: Lichens are a classic example. They are a symbiotic partnership between a fungus and a photosynthetic organism (algae or cyanobacteria). The fungus provides a protective structure and absorbs water and minerals from the environment. The algae or cyanobacteria, in turn, produce food (sugars) through photosynthesis, which nourishes the fungus. Both organisms rely on each other for survival.