Ecology: the Science of Interactions. IV-03. Demographic Tables, Pyramids, and Survival Curves

IV-3. Demographic Tables, Pyramids, and Survival Curves
As we have already noted, the most important static characteristics of a population are its sex structure (the ratio of individuals of different sexes) and age structure (the ratio of individuals of different ages). These parameters are conventionally described using demographic tables. The first such table was constructed by the founder of demography, John Graunt, in the 17th century based on mortality data for London residents, which church parishes collected in order to promptly detect the onset of plague epidemics.
Demographic tables are convenient for observing the dynamics of birth and mortality rates in different age and (or) sex groups. One method for constructing them (Table IV-3.1) involves observing the fate of a particular group of individuals (a cohort) born within a short time interval and recording the age at death of all cohort members.
Table IV-3.1. Demographic Table of the Population of the Acorn Barnacle (Balanus glandula)—a Representative of the Barnacles (Cirripedia) (Connell, 1970, after Hilyarov, 1990)

Proportion of individuals surviving to the beginning of the age interval	Number of living individuals at the time of census	Proportion of individuals surviving to the beginning of the age interval	Number of individuals that died during the interval	0	Expected lifespan of those individuals who survived to this age, years
0	142	1000	80	0,563	1,58
1	62	0,437	28	0,452	1,97
2	34	0,239	14	0,412	2,18
3	20	0,141	4,5	0,225	2,35
4	15,5*	0,109	4,5	0,290	1,89
5	11	0,077	4,5	0,409	1,45
6	6,5*	0,046	4,5	0,692	1,12
7	2	0,014	0	0,000	1,50
8	2	0,014	2	1,000	0,50
9	0	0,0	-	-	-

IV-3. Demographic Tables, Pyramids, and Survival Curves
As we have already noted, the most important static characteristics of a population are its sex structure (the ratio of individuals of different sexes) and age structure (the ratio of individuals of different ages). These parameters are conventionally described using demographic tables. The first such table was constructed by the founder of demography, John Graunt, in the 17th century based on mortality data for London residents, which church parishes collected in order to promptly detect the onset of plague epidemics.
Demographic tables are convenient for observing the dynamics of birth and mortality rates in different age and (or) sex groups. One method for constructing them (Table IV-3.1) involves observing the fate of a particular group of individuals (a cohort) born within a short time interval and recording the age at death of all cohort members.
Table IV-3.1. Demographic Table of the Population of the Acorn Barnacle (Balanus glandula)—a Representative of the Barnacles (Cirripedia) (Connell, 1970, after Hilyarov, 1990)

Number of deaths in each age group	Mortality per 1,000 persons	0‑1	Mortality per 1000 individuals
0-1	173 400	1 651	9,52
1-4	685 900	340	0,5
5-9	876 600	218	0,25
10-14	980 300	234	0,24
15-19	1 164 100	568	0,49
20-24	1 136 100	619	0,54
25-29	1 029 300	578	0,56
30-34	933 000	662	0,71
35-39	739 200	818	1,11
40-44	627 000	1 039	1,66
45-49	622 400	1 664	2,67
50-54	615 100	2 574	4,18
55-59	596 000	3 878	6,51
60-64	481 200	4 853	10,09
65-69	413 400	6 803	16,07
70-74	325 600	8 421	25,86
75-79	235 100	10 029	42,66
80-84	149 300	10 824	72,5
85 and older	119 200	18 085	151,7

Demographic tables can be simpler, containing only the number of individuals in certain age-sex categories. Demographic pyramids are constructed based on demographic tables. Age intervals are plotted on the vertical axis, and the number of males (in the case of human pyramids - men) is plotted on the left as a bar chart, and the number of females is plotted on the right. This makes the difference in mortality in different age categories and sexes apparent. For example, data for constructing the demographic pyramid of Ukraine are given in Table IV-3.3. ( source ). Table IV-3.3. Demographic table of the population of Ukraine as of January 1, 2016 (excluding territories occupied by Russia and terrorist organizations supported by Russia).

Women	Men	Women		Women	Men	Women
0	211 339	197 833		51	268 174	312 280
1	238 053	224 436		52	282 787	334 969
2	242 884	228 566		53	286 276	343 840
3	251 286	236 070		54	295 213	356 263
4	242 525	228 012		55	302 282	369 718
5	239 790	225 895		56	283 130	354 777
6	247 658	232 081		57	276 830	352 682
7	246 292	231 359		58	260 318	338 471
8	226 677	214 535		59	254 431	337 497
9	220 970	210 041		60	232 462	315 462
10	205 415	193 481		61	233 782	324 457
11	205 494	194 605		62	208 379	296 363
12	196 088	185 961		63	212 821	309 520
13	188 378	177 020		64	208 929	306 173
14	180 933	170 616		65	202 140	302 258
15	186 068	175 950		66	201 406	312 895
16	188 132	178 596		67	164 310	259 283
17	199 667	191 300		68	140 031	229 249
18	209 887	199 416		69	129 849	222 131
19	228 717	216 345		70	81 538	146 446
20	239 365	225 479		71	89 398	168 292
21	249 004	234 132		72	77 468	149 507
22	262 351	248 210		73	95 195	189 839
23	281 119	266 380		74	122 876	245 425
24	299 627	284 254		75	119 964	245 102
25	313 751	298 618		76	118 369	258 565
26	326 933	312 701		77	116 399	261 038
27	346 300	332 604		78	113 614	254 250
28	357 229	343 228		79	87 444	195 204
29	377 924	365 398		80	66 546	151 397
30	365 389	355 317		81	46 057	105 479
31	373 599	363 325		82	35 102	84 951
32	377 596	368 473		83	39 273	103 169
33	343 652	334 841		84	37 704	97 200
34	329 211	327 713		85	41 419	110 758
35	336 112	334 930		86	27 468	84 095
36	316 073	316 770		87	25 154	80 296
37	311 492	316 567		88	20 900	63 381
38	299 213	307 561		89	15 911	52 720
39	314 648	324 098		90	11 919	41 260
40	305 622	319 800		91	8 390	31 390
41	296 250	312 008		92	5 399	19 405
42	288 153	304 467		93	3 881	13 776
43	295 105	315 155		94	3 580	10 578
44	292 515	311 807		95	3 562	9 192
45	288 882	309 322		96	1 038	2 675
46	262 769	286 474		97	998	2 995
47	265 315	291 439		98	859	1 852
48	259 160	289 260		99	345	821
49	264 886	298 893		50	1 848
50	259 215	297 676

Demographic tables can also be simpler, containing only the numbers of certain sex-age categories. Demographic pyramids are constructed based on demographic tables. Age intervals are plotted on the vertical scale; on the left side, in the form of a bar chart—the number of males (in the case of human pyramids—men), and on the right—females (women). This makes the difference in mortality between different age categories and different sexes clearly visible. For example, data for constructing the demographic pyramid of Ukraine are presented in Table IV-3.3. (source).
Table IV-3.3. Demographic Table of the Population of Ukraine as of January 1, 2016 (without the territories occupied by Russia and terrorist organizations supported by Russia)

Demographic pyramids help to vividly imagine the history of a population. Consider such a pyramid for the population of Ukraine (Fig. IV-3.1). You can see, for example, how it reflects the decline in birth rates during World World II. The "echo" of these events manifested even after a generation and, to a lesser extent, after two generations, when the distant consequences of the war were compounded by a decline in the standard of living associated with incompetent governance of Ukraine in the first (unfortunately, not only the first) years of its independence. The number of people who by their age are children and grandchildren of those born during the war turns out to be smaller than the number of those in nearby age groups. The decline in the number of newborns is, probably, a consequence of Russia's aggression and the deterioration of the country's economic situation.

Fig. IV-3.1. Demographic Pyramid of the Population of Ukraine (without occupied territories) as of 2016 (based on data from Table 4.3.3)
Furthermore, demographic tables provide material for constructing survival curves. This method of graphical representation of the dependence of the proportion of individuals remaining alive on their age was proposed in the 1920s by Robert Pearl. He distinguished three main types of survival curves (Fig. IV-3.2).

Fig. IV-3.2. Three Types of "Ideal" Mortality Curves according to Pearl
Curve Type I (Drosophila type) has a convex form. It describes a situation when high mortality is observed at mature age. This is characteristic of Drosophila, mayflies, and other insects that soon after emerging from the pupa leave offspring and die. The survival curves of large mammals approximate Curve Type I. Curve Type II (Hydra type) is characteristic of organisms with uniform mortality at any age. On the graph, this corresponds to a straight line. Such curve types are characteristic of fish, reptiles, birds, herbaceous perennial plants, etc., with the sole caveat that the count is made from organisms that have already passed the most vulnerable stages of their development. Curve Type III (oyster type) has a concave form. It is characteristic of organisms that mainly die at the early stages of their life. Oysters lead a sessile lifestyle as adults, while their larvae are planktonic. It is during this period that they are most vulnerable. For individuals that successfully pass the larval stage, the chance of survival greatly increases. This type of survival curve is characteristic of many animals with high fecundity and no parental care.
Real survival curves are a combination of these types. The human curve is convex, relatively close to the first type, but can have different forms in different cases (Fig. IV-3.3).

Fig. IV-3.3. Types of Survival Curves in Primitive and Developed Society