10.12 Population Interaction

. Population Interaction Organisms belonging to different populations interact for food, shelter, mating or for other necessities. Interaction may be intra specific (interaction within the members of same species) or inter specific (among organisms of different species). Intra specific association is observed for all livelihood processes like feeding, territoriality, breeding and protection. Interspecific associations or interactions can be: Neutral: where different species live together but do not affect each other. Positive: it is a symbiotic relationship in which no organism in association is harmed and either one or both may be benefitted. It is of two types – Mutualism and Commensalism. Negative: One or both of the interacting organisms will be affected as in case of competition, predation, parasitism. The common types of interspecific inter actions are: growth is represented by S shaped growth curve. Biotic potential or Reproductive capacity (r) It is the maximum reproductive capacity of an organism under optimum environmental conditions. Carrying capacity (K) The maximum number of organism that a region can support without environmental degradation is called carrying capacity. Environmental resistance Is the sum total of the environmental limiting factors, both biotic and abiotic, which together act to prevent the biotic potential of an organism from being realized. Table . Differences between r- selected and K selected species r selected species (r - Reproductive capacity) K selected species (K - Carrying capacity) Smaller sized organisms Larger sized organisms Produce many offspring Produce few offspring Mature early Late maturity with extended parental care Short life expectancy Long life expectancy Each individual reproduces only once or few times in their life time Can reproduce more than once in lifetime Only few reach adulthood Most individuals reach maximum life span Unstable environment, density independent Stable environment, density dependent XII Std Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Organisms and Populations sex ratio and age distribution. The proportion of different age groups of males and females in a population is often presented graphically as age pyramid, its shape indicated whether a population is stationary, growing or declining. Ecological effects of any factors on a population are generally reflected in population density. Population grow through births and immigration and decline through deaths and emigration. When resources are unlimited, the growth is usually exponential but when resources become progressively limiting the growth pattern turns logistic. In either case, growth is ultimately limited by the carrying capacity of the environment. The intrinsic rate of natural increase is a measure of the inherent potential of a population to grow. Population of the same or different species in a habitat do not live in isolation but interact in many ways. These interactions may be intra specific or interspecific. They may be positive, negative or neutral in nature.