(i) Population attributes are certain characteristics of a population. Some of them are as follows:
(a) Population size or density is the number of individuals of a species per unit area or volume.
(b) Birth rate or natality is expressed as the number of births per 1000 individuals of a population per year, e.g. if in a pond, there are 20 lotus plants last year and through reproduction 8 new plants ate added Birth rate = 8/20=0.4 offspring per lotus per year
(c) Death rate or mortality is expressed as the number of deaths per 1000 individuals of a population per year, i.e. if 4 individuals in a population of 40 fruits flies died during a specified time interval (say a week). Death rate =4/40=0.1 individuals per fruitfly per week
(d) Sex ratio is expressed as the number of females and males per 1000 individuals of a population in a given time, e.g. 60% females and 40% males in population.
(e) Age pyramid When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid.
(ii) Population density is the number of people living per unit of an area.
Three ways of measuring population density of a habitat.
(a) Per cent cover for trees with larger canopy.
(b) Number caught per trap for fishes.
(c) Pug marks or fecal pellets for tiger census.