Question

 

1. Fossa (a terrestrial mammal in Madagascar) experience a population decline of 20% each time a cyclone hit a particular national park on the African coast, because their prey populations also decline rapidly. Usually, one cyclone hits every 10 years. However, in one unusual year, five cyclones hit this national park and the population was reduced in quick succession to a level that was then easily wiped out by hunters. The primary causes of this population’s extinction were:

a) Over-Exploitation & Demographic Stochasticity

b) Over-Exploitation & Environmental Stochasticity

c) Demographic Stochasticity & Habitat Loss

d) Environmental Stochasticity & Habitat Loss

e) Demographic & Environmental Stochasticity

2. For a decreasing population, which of the following could be true regarding a declining population?

a) Ro= .8 and r = .2
		b) Ro = .5 and r = 0
		c) Ro = 0.8 and r = - 0.2
		d) Ro= - 0.8 and r = - 0.2
		e) Ro= - 0.2 and r = 0.8

Answer 1

1. Answer is (d)

Explanation- Over exploitation means the over use or excessive use of a resource so that it will be scarce in the near future. Demographic stochasticity refers to the sampling variation in births and deaths. Environmental stochasticity means the effect of random environmental fluctuations in growth rate and habital loss means loss of space for living in corresponding habitats. In the question there is no mention of over exploitation. The cyclone comes generally in every 10years. Thus there must be habitat loss in every 10 years. In a particular year the cyclone hit 5times, thus the rate of habitat loss would be more and there is already mention of the fluctuations in the environmental conditions due to cyclone. If we consider the demographic stochasticity, the environment needs to be constant to calculate birth and death processes. So, the primary reasons for the population's extinction will be "environmental stochasticity and habitat loss".

2. Answer is (d).

"Ro" refers to the average number of offsprings produced by an average individual living an average lifespan. It is commonly used to measure the rate of change of a population size. If Ro=1, the population is stable.

If Ro>1, the population is increasing.

If Ro< 1, the population is declodecl.

If the value of Ro is slightly less than 1, we can consider the population to be increasing.

"r" is a measure of the instantaneous rate of change of population size per individual. Increase r value means high birth rate and less death rate which indicates the increase in the population. Decrease r value means less birth rate and high death rate which indicates the declining population.

In the question, the population is declining, so the Ro value will be more negative and r value will be less.

Both the values would be negative.