Life Table for Lacerta vivipara in the Netherlands[table]
Year | Number alive | Survivorship | Fecundity | Survivorship × Fecundity = Average Number of Offspring Produced per Female of Age x
0 | 1000 | 1.000 | 0.00 | 0.00 1 | 763 | 0.763 | 1.70 | 1.30 2 | 308 | 0.308 | 2.94 | 0.91 3 | 158 | 0.158 | 4.13 | 0.65 4 | 57 | 0.057 | 4.88 | 0.28 5 | 10 | 0.010 | 6.50 | 0.07 6 | 7 | 0.007 | 6.40 | 0.04 7 | 2 | 0.002 | 6.30 | 0.01
[/table]Data are from Strijbosch and Creemers, 1988.Using the life table, how would you describe the population dynamics of L. vivipara?

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Question restatement: Using the life table for Lacerta vivipara, determine the population dynamics of the species.
Option analysis:
- Option a: 'The population is decreasing.' At first glance, the number alive declines each year (from 1000 to 763 to 308, etc.), which might suggest a decline. However, to assess population dynamics you must consider not just yearly survivorship but lifetime reproductive output. The column 'Survivorship × Fecundity' gives the average number of offspring produced per female of age x, and when you sum these across all age classes, you obtain the net reproductive rate.
- Option b: 'The table does not provide this information.' This is inaccurate because the table provides both survivorship (l_x) and fecundity (m_x), and the product l_x m_x yields the lifetime reproductive output per female. From these data you can infer population growth or decline.
- Option c: 'The population is increasing.' This is supported by calculating the lifetime reproductive output. Compute R0 = sum over all ages of l_x m_x. Using the values given: 0.00, 1.30, 0.91, 0.65, 0.28, 0.07, 0.04, 0.01 sum to approximately 3.26. Since R0 > 1, each female, on average, leaves about 3.26 daughters that survive to reproduce, implying the population would grow over the long term (assuming constants such as density independence and stable age structure).
- Option d: 'The population is stable.' This would require R0 ≈ 1 or a precise balance between births and deaths across ages. With R0 ≈ 3.26, stability is not supported by the data; the population would not be expected to remain constant.
Additional nuance: Although the number alive declines steeply across years, the total lifetime reproduction is greater than replacement, which drives population growth rather than decline. The transient drop in numbers alive in early years does not contradict a growing population if lifetime fecundity is high enough and there are no strong density-dependent effects eroding survival or fecundity.
In summary, while observed counts of individuals decrease with age, the cumulative reproductive output per female indicates an increasing population rather than a decreasing or stable one, and the option stating the population is increasing best aligns with the life-table data. The other options misinterpret either the meaning of the table, fail to consider lifetime reproduction, or contradict the calculated net reproductive rate.

BIO 112-004 - Spring 2025: Biological Concepts and Methods I I (Lecture)

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