Chapter 6
Structure and Organism of Single Species population
At the end of the lesson, you should be able to:
1. Discuss the structure and organisms in a single species population
2. Describe the population ratios in relation to the key features of population and population dynamics
3. Provide examples for the structure and organisms in a single species population
You have learned on the previous module that a population is a group of people or animals of a
particular kind that live in a place. The previous module also discuss the key features of population
dynamics which are size, density and dispersion. In addition to, key features of population such as birth
rate, death rate and growth rate were tackled. With this, we can now have a look at different concepts
involving population ecology.
Carrying capacity was mentioned during the previous discussion as well as on the given video whereas,
carrying capacity was defined as the number of species a certain area can sustain based on the
availability of resources. The question now is how does this affects the growth or death of a population?
In population ecology we have this concept called resource partitioning. For us to better understand this
concept, lets take an example. For instance, at home, your mother bought a whole fried chicken for the
seven members of your family. Applying the concept of resource partitioning, the mother should divide
the chicken into seven equal parts and distribute it to the seven members allowing them to have a taste
of it. In a natural setting, since in a given area, there are instances that different organisms tend to
compete for the same resources where predators dominate the prey, it can be said that resource
partitioning is not applied causing the number of some species to prosper while the other species don’t.
This event may tend to affect others factors of population ecology. Lets take a look at them one by one.
Population Ratios
Population ratios are used to describe the degree of balance between two elements of the population,
e.g., Males vs. females, children versus women of reproductive age. The ratio is normalized to refer to a
standard unit of people, usually 100 persons.
Sex ratio: The sex ratio is the ratio of males to females in the population (normalized to 100). We
calculate two sex-ratios: At birth, and in the total population.
The sex ratio at birth is fairly standard, around 105. Due to higher mortality among males, the sex ratio
in the total population switches to 95-97. For populations with high levels of sex-selective outmigration
(such as male soldiers leaving a country for war), particularly in certain age groups (e.g. aged 15-29), the
sex ratio may be even smaller.Ranges for sex ratios:
Sex ratio at birth: 105 except for African populations, where it is 102-103
Sex ratio for total population: 101.5
