Life tables and population growth

Reference no: EM1389189

When answering these questions, you will do some simple calculations (you can use a spreadsheet program like Excel or show your work in this document). Due to rounding, your answer may not exactly match the correct answer, but we have made the multiple choice options such that there is an obvious choice if you have calculated things correctly.

Setup: You have been assigned the task of studying the ecology of an isolated population of a rare tropical turtle, to assess its long-term prospects for survival. The turtle breeds throughout the year in a lake that has formed in the crater of a dead volcano. Distinctive patterns of growth in their shells allow you to determine the age (in years) of each turtle, and other aspects of their shell shape tell you whether they are male or female.

During the first year on the job (2012), you perform a mark-release-recapture study to estimate the number of individuals of each age. For this study, you visit the site on one date, capture turtles with the help of a small field crew, determine the age and sex of each turtle, and scratch unique numbers into the shell on the underside of each turtle (this does not harm them in any way). You then return to the site on a second date, capture turtles again, again noting the age and sex of each, and also checking to see if it was a turtle you had marked on the first date. From this study, you obtain the following data:

Table 1. Mark-release-recapture data.

Turtle age (years)	First visit # Marked & released	Second visit Total Captured (marked and unmarked)	Second visit Total recaptures (marked only)
0	75	63	7
1	50	40	10
2	55	45	25
3	59	56	38
4	42	35	20
5	38	42	24
6	12	18	9
7	15	14	12
8	8	7	7
9	0	0	0

Question 1:

Based on these results (Table 1), what is the estimated number of individuals in the population in 2012 (round to the nearest whole number)? HINT: calculate the number of individuals in each cohort first.

a) 674 individuals

b) 1250 individuals

c) 745 individuals

d) 152 individuals

In a separate study (also in 2012), you put small radio-signaling devices on a subset of a closely-related turtle species that live in the same crater (again, these do not cause them any problems), so that you can track their movements in real time. It is known that these turtles only lay their eggs in a particular patch of loose soil more than 100m away from the lake, and the only time they go to this patch is to lay eggs. Thus, by tracking individuals, you can tell when and where each has laid eggs, allowing you to count the number of eggs laid by each female. From these results (and the sex ratios of the hatchlings emerging from each nest), you obtain the age-specific fecundity estimates (m_x = average # female offspring per female of age x) shown in the life table below (Table 2). The number of individuals in this turtle species within each age cohort is provided in the table (it is not the same as the number of individuals in each age cohort of question 1!)

Table 2. Life-table for closely related species.

Age (x)	N_x	l_x	m_x
0	725		0.000
1	300		0.000
2	165		0.455
3	99		0.825
4	87		1.104
5	53		1.088
6	40		0.973
7	19		0.825
8	10		0.410
9	0		---

Question 2:

By adding to the above life table (Table 2), what is the estimated net reproductive rate, R₀, of this turtle species?

a) 0.51 individuals/individual

b) 10.5 individuals/individual

c) 0.77 individuals/individual

d) 1.41 individuals/individual

Question 3:

Using the life table (Table 2), what is the estimated generation time?

a) 1.08 years

b) 10.5 years

c) 3.9 years

d) 4.8 years

Question 4:

In another closely related species of turtle (general reproductive dynamics are the same as the first two turtle species in question 1 and questions 2 & 3), we find that the value for the net reproductive rate (R₀) is 0.95 and the generation time is 2.5 years. Solving for l or r as you think appropriate, what is the per capita rate of growth for this population?

a) 0.02 individuals/individual/year

b) -0.35 individuals/individual/year

c) 0.51 individuals/individual/year

d) -0.02 individuals/individual/year

Question 5:

You also compute the per capita rate of growth of the population represented by Table 2, and obtain a value of -0.173 individuals/individual/year. Based on this value, which of the following describes this population?

a) growing

b) declining

c) stable

d) none of the above

Question 6:

Given the total population size of the population in Table 2 (in year 2012), using the per capita growth rate in question 5, and assuming that this growth rate does not change, what is the expected population size of these turtles in year 2022?

a) 474 individuals

b) 230 individuals

c) 4730 individuals

d) 0 individuals

Reference no: EM1389189

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