Question

5. Define the following terms and give one example of each. (4 marks)

1. density-dependent factor:  

       - example:

2. density-independent factor:  

      

       - example:

Answer 1

Sol. a. Density dependent factor is factor whose influence varies with the density of the population. Density dependent factors affect a higher proportion of individuals when population densities are higher and a lower. For instance, birth rates may decrease as populations increase since resources become more reduced and density dependent competition for those resources increases. Density-dependent mortality may also occur as population densities increase and competition for resources increases, reducing offspring production or survival. Example: Competition, predation, disease.

Sol.b. Density-independent factors are physical factors such as weather, drought, chills,floods, and disturbances like fire. For example, in herd freezes a considerable percentage of organisms such as birds or plants are usually killed, no matter how large the population size, since most individuals are susceptible. However, even physical factors such as weather can sometimes act in density dependent manner. In an environment where there are many beara and limited number of dens, some individuals will not have a den. In such a situation, a cold winter could kill a high percentage of bears. Example: Weather, drought, freezes, floods, and disturbances.