1 Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 1 BIOS 3010: Ecology Lecture 3: Birth and Death • Lecture summary: – Population increase & decrease. – Unitary & modular organisms. – Life cycles. – Life tables. – Reproduction. – Survivorship. – Demographic transition. Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 2 2. Population increases and decreases: • Populations increase in size through births (B) and immigration (I). • Populations decrease in size through deaths (D) and emigration (E). • Thus, N now = N then + B - D + I - E – to describe the distribution and abundance of individuals in populations now and in the future. – .... but what is an individual? Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 3 3. Unitary and Modular organisms: • Individuals vary according to age, stage, size, weight, maturity, sex, etc. – Unitary organisms are highly determinate in growth form with only a single “module” (e.g. a mouse). – Modular organisms are made up of repeated modules, such as leaves or branches of a plant (Fig. 4.2 ): – Modules with the potential for independent existence are called ramets and the genetically distinct entity made up of the ramet modules is called a genet .
Transcript
1
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 1
BIOS 3010: Ecology Lecture 3: Birth and Death
• Lecture summary: – Population increase &
decrease. – Unitary & modular
organisms. – Life cycles. – Life tables. – Reproduction. – Survivorship. – Demographic transition.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 2
2. Population increases and decreases:
• Populations increase in size through births (B) and immigration (I).
• Populations decrease in size through deaths (D) and emigration (E).
• Thus, Nnow = Nthen + B - D + I - E
– to describe the distribution and abundance of individuals in populations now and in the future.
– .... but what is an individual?
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 3
3. Unitary and Modular organisms:
• Individuals vary according to age, stage, size, weight, maturity, sex, etc. – Unitary organisms are highly determinate in growth form
with only a single “module” (e.g. a mouse).
– Modular organisms are made up of repeated modules, such as leaves or branches of a plant (Fig. 4.2):
– Modules with the potential for independent existence are called ramets and the genetically distinct entity made up of the ramet modules is called a genet.
2
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 4
4. Life cycles:
• Semelparous (sometimes called monocarpic in plants) - a single bout of reproductive activity per individual
• Iteroparous (sometimes called polycarpic in plants) - multiple bouts of reproductive activity per individual (see Fig. 4.10). – In order to follow these life cycles in detail we construct
life tables from which survivorship curves can be drawn and patterns of birth among different age classes are described in fecundity schedules.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 5
5. Life Tables:
• Cohort life table (Table 4.1) - describes the fate of a single cohort of individuals (a group of individuals born within the same short interval of time - as in annual plants and animals).
• Actual numbers (data = ax values) are transformed to proportional data for comparison (lx) which are then used to calculate the proportion dying in each stage (dx) and the mortality rate (qx) as dx/lx. – dx values can be summed but do not represent stage
specific intensity of mortality, whereas qx values do, but they can't be summed.
– These two useful properties are combined in k-values, where kx = log10ax - log10ax+1 (same as log10(ax/ax+1)).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 6
6. Fecundity Schedules: • The last 3 columns of Table 4.1 represent the fecundity schedule, or
age-specific egg production for the common field grasshopper. The raw data for egg production are listed under Fx and this gives mx eggs per surviving individual in each stage (22,617/1,300 = 17) and lxmx eggs as a proportion of the original cohort in the stage.
• The basic reproductive rate Ro: – Cohort life table data can be reduced to a single value, the basic
reproductive rate Ro which is the mean number of offspring produced per original individual by the end of the cohort.
• This can be calculated in two ways: – Ro = Σ Fx/ao or, Ro = Σ lxmx
• Compare Table 4.1 (3e) where Ro = 0.51 (population declined) with Table 4.1 (4e) where Ro = 2.41 (population increased).
• This means that when Ro <1 the population will decline and when Ro >1 the population will increase.
3
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 7
7. Survivorship Curves:
• The life table data of Table 4.1 are plotted in Fig. 4.7 as mortality (qx & kx) and survivorship (log10lx) curves to show how both change with time. – Survivorship curves were classified by Pearl and later
Deevey into types I (convex or "late loss"), II (straight or "constant loss") & III (concave or "early loss") – Fig. 4.8.
– Age-specific mortality is shown in Fig. 4.20 where most mortality occurs in post-reproductive plants.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 8
8. Rate of increase for overlapping generations:
• For overlapping, or continuously breeding generations, generation time is represented as time T and so the population reproductive rate is represented by the "continuous" intrinsic rate of natural increase (r)
• r is related to the "discrete" basic reproductive rate (Ro) by:
r = lnRo/T
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 9
9. Human populations and the “demographic transition”
• Human populations are subject to the same processes of birth, death, immigration and emigration in both more developed and less developed countries (Figs 4.23 & 4.24)
• The “demographic transition” occurs when declines in birth rates associated with increased per capita wealth lag behind declines in death rates (Figure 11.20 from Miller, 2000).
4
Dr. S. Malcolm BIOS 3010: Ecology Lecture 3: slide 10
Figure 4.2 (3rd ed., see Fig. 4.1)
– Plants (left) & animals (right): hierarchy of modularities
