Question

In your own words, compare and contrast the ways in which demographers track both continuously growing (e.g. humans) and discretely growing (e.g. most bird species) populations of organisms considering the exponential and geometric growth models that they have developed. How are these 2 different types of populations similar and how are they different in terms of: how they are surveyed, their yearly population #’s patterns, their population growth dynamics, . . .?

Answer 1

geometric growth

• in this type of growth every individual reproduce
• the intial growth is low as the number of individuals is intially small later on there will b rapid growth at exponential rate
• the growth is depentent on 3 factors in this population - r - intrinsic rate of natural increase, b is the birth rate, d is the death rate and population size is N
• dN / dt = (b - d ) N , (b-d) = r
• the r in this equation is a very important parameter for accessing the impacts of any biotic or abiotic factor on population growth
• this type of growth pattern results in a J shaped curve when we plot N in relation to time t
• exponential growth equation - Nt = N0 ert , Nt is the population density at time t , N0 is the population density at time 0
• if any species is growing exponential under unlimited resources it can reach big population density in a short time
• by surveying per capita birth dates and per capita death rates we can find the growth rate of a population
• this geometric growth cannot be sustained for long
• limited resource availability causes slowing down of growth leading to a stationary phase

logistic growth

• carrying capacity(K) - beyond which level , nature can't support the population with resources
• in this type of growth only the fittest individuals can survive and make new generations
• intially a lag phase is observed due to limited esource availability followed by phases of increase and decrease and finally population density until the given population reaches  the maximum capacity
• this type of growth rate results in sigmoid curve
• equation dN / dt = rN(K - N)