Organisms and Populations

• Population is defined as the group of organisms of the same species in the same area.
• many ecosystems coming together is called biome
• the habitat of a species is the place where it lives and the conditions it needs to survive
• the population that occupies a very small area and is smaller in size is called local population
• a group of such closely related local populations is called metapopulation
• population density is the number of a species per unit area or volume
• The number of births of new individuals per unit of population per unit time is called birth rate
• The number of loss of individuals per unit time due to death or due to different environmental changes, competition, predation etc is called death rate
• sex ratio is the number of females to male per 1000 individuals of a population is a given time
• natality refers to the number of births during a given period in the population that are added to the initial density
• mortality is the number of deaths in the population during a given period
• immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration
• Emigration is the number of individuals of the population who left the habitat and moved elsewhere during a given time period
• age pyramid is the age distribution of per cent of individuals of a given age or age group plotted for the population
• exponential growth shows a J-shaped curve, it is due to the unlimited availability of resources
• logistic growth shows the sigmoid curve. A habitat has enough resources to support a maximum possible number (K).
• predation in which only one species is benefitted and the other gets killed
• competition in which both organisms compete for the same resources, both are harmed
• commensalism in which one species is benefitted and the other is unaffected
• mutualism in which both the species are benefitted
• amensalisme in which one species is harmed, whereas the other is unaffected
• protocooperation is the interaction between two different species in which both are mutually benefitted, but can sustain their lives individually
• parasitism in which only one species is benefitted, the other species host is harmed or loses life. They may be endo or ecto parasites
• brood parasitism is an example of parasitism in which parasite lays eggs in the nest of host for the latter to incubate them
• gause’s competitive exclusion principle states the two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually by the superior one
• Organisms that feed on plant sap and other plant parts are called phytophagous