Q.Animals that can move from fresh water to sea called as.....

A population is a group of interbreeding organisms of one species occupying a defined space and functioning as part of a biotic community; unlike an individual organism, it has emergent group-level attributes that only make sense at the population scale. These include population density (size relative to space and time, measurable as abundance, numerical density, biomass density or ecological density), natality (birth rate, expressed as crude birth rate or $b = \dfrac{\text{births per unit time}}{\text{average population}}$) and mortality (death rate, $d = \dfrac{\text{deaths per unit time}}{\text{average population}}$, which rises with crowding due to predation, disease and competition), age distribution, and dispersion — the tendency of populations to spre …