(Upload on November 4 2022) [ 日本語 | English ]

Population (個体群)

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

  1. In statistics, the universe of items under study is called the population. I will distinguish this concept as the statistical population.
  2. In ecology (生態学), a population is a defined group of organisms of one species living in a particular area at a particular time. I will distinguish this concept as the biological population (Krebs 2008)

    In sociology, the whole number of people or inhabitants in a country or region is called the population.

Hypothetical population (Ideal population)
Real population

[ minimum viable population | population interactions ]
[ community |ecosystem ]


[minimum viable population]

Population density (個体群密度)

Number of individuals (個体数): basic parameter to obtain population density

Density estimation (密度推定)

Random encounter and staying time model, REST (Nakashima et al. 2018)
Catch per unit effort (CPUE, 単位努力量)
indirect measure of the abundance of a target species
estimating absolute abundance of closed populations in the presence of successive removals

Habitat (生息地・生育地)

An area or a place where a plant or animal species gets the resources, such as food, water, and space it needs to reproduce.
Often a habitat is defined for a whole living organisms in the community (群集).
More fine-scaled habitat is called microhabitat.
ST → Habitat for Trillium smallii Maxim. is generally the floor of deciduous forests.
→ Habitat for Ex.">mangrove.

Habitat creation for environmental conservation (保全)

Provide a conservation benefit to the species

Increase the population
Protect, enhance or restore habitat
Buffer protected areas
Test or implement new conservation strategies

Minimum viable populations (MVP)

The minimum number of individuals to ensure that a given population is not extinct.

Original definition (Shaffer 1981)

A minimum viable population for any given species in any given habitat is the smallest isolated population having a 99% chance of remaining extant for 1000 years despite the foreseeable effects of demographic, environmental, and genetic stochasticity, and natural catastrophes.
Key point: Probability of extinction within a given time
Theoretical controversy

99% (90%, or 95%)
1000 years (100-1000 years)

MVP Practical problems

How and what do we measure to obtain the probability?

→ often estimated by computer simulations for population viability analyses (PVA)

Dispersion (分散・分布)

Regular distribution       Random distribution      Contagious distribution

(Morisita 1959)

Morisita's Iδ index (Iδ指数)
Iδ: > 1 ⇒ contagious dist., = 1 ⇒ random dist., < 1 ⇒ regular dist.
mean crowding (m*-m) (平均込合度)

Population dynamcis (個体群動態)

(Chapman 1931, Kostitzin 1937)

Environmental resistance (環境抵抗)
Def. Birth rate (出生率), B = Bp - (Si + Sd)

Bp: biotic potential or intrinsic coefficient of natality
Si: density-independent suppression of natality
Sd: density-dependent suppression of natality or limiting coefficient of natality

Def. Mortality (death rate), D = Mi + Md

Mi: density-independent mortality
Md: density-dependent mortality or complementary coefficient of mortality

⇒ Actual growth rate, r = B - D = {Bp - (Si + Sd)} - (Mi + Md)

= Bp - (Si + Mi) - (Sd - Md)
= rm - hNα

Innate capacity for increase, rm = Bp - (Si + Mi) (Andrewartha & Birch 1954)

≡ partial potential, ≡ coefficient of multiplication

Coefficient of limitation, h = (Sd - Md)/(hNα)

≡ Verhulst-Pearl factor, if α = 1

Def. Environmental resistance ≡ Si + Sd + Mi + Md

Def. density-independent environmental resistance, Si + Mi

≡ physical environmental resistance, ≡ intrinsic coefficient of mortality

Def. Density-dependent environmental resistance, Sd + Md

≡ biotic environmental resistance

Life table (生命表)

= mortality table or actuarial table
representing survivorship of a certain population
Cohort: a group of individuals having a statistical factor as age in common in a demographic study (prerequisite for making life table)

Age distribution (齢分布)

Age (齢): population structure and size

Population: growth and regulation - homeostasis
Population fluctuation (or dynamics) = (immigration + birth) - (emigration + death)

Survival curve or survivorship curve (生存曲線)
1945 Morris et al.: "Green river project"

outbreak of Choristoneura fumiferana → population dynamics analysis and modeling

1949 Baltensweiler et al.

analysis of periodical fluctuation of Zeiraphera diniana

1966 Klomp

life tables of Bupalus piniarius and cinnabar moth (Tyria jacobaeae)

1950 Jenkins, et al.

population fluctuation of Lagopus lagopus scoticus

Opportunistic and equilibrium populations

1967 MacArthur & Wilson: proposed r, K-strategies

selection occurs through breeding system (交配システム)
K-strategist (K戦略者): high density, advantages near K = avoiding competition → advantages on species producing competitively-strong progeny

= species producing large, non-prolific progeny → K-selection
Ex. perennial herbs, woody plants

r-strategist (r戦略者): dilutive environments, species of which r (intrinsic rate of natural increase) is high has advantages to occuply spaces quickely → r-selection

Ex. annual herbs

r, K-selection: the survival types and results of species under the given environments
r, K-strategy: species that applies r or K strategies

→ species applying both the strategies are present


opportunistic: on or over K (controversial)
K-strategist: density dependent control, stable environment
r-strategist: density independent control, unstable environment

Pianka (1978), Krebs (2008)

Fugitive species (逃亡種, sensu Hutchinson) ≈ r-strategist Ex. Inula salicina L.

r-strategist ↔ K-strategist
Opportunist species ↔ Equilibrium species
Temporal habitat ↔ Permanent habitat

The changes between r-K strategists are gradual and thus useless to classify them strictly

Ex. dead body = food: unpredictable and temporal (ephemeral) → meat fly = r-strategist, carrion beetle = K-strategist: nurturing on the body (non-prolific)

High compression → advantages on K-strategists

Ex. dung (as well as dead body): each group applies specific strategy under the homogenous environments in most cases

Evolution of reproductive tactics (繁殖戦術の進化)
1) Reproductive effort (繁殖努力) → optimal reproductive effort

individual investment to the present reproductive act
ratio of reproductive organs to the whole organs in an individual at a given time
vxmx = vx*

vx*, residual reproductive value (残存繁殖能力)
vx, reproductive value (繁殖価)

2) Expenditure per progeny by the parent (子一匹あたりの親の支出) vs. expenditure of progeny (子の支出)
3) Evolution of clutch size on bird (一腹卵数)

Clutch size = number of eggs laying per nurturing
Climate, food qulity and quantity → determining clutch size

Clutch size interpreted by a cline along latitude
1. day length hypothesis (日長仮説)

high latitude → long day length → feeding for long time (counter: nocturnal birds also proportionally change the clutch sizes with incrsaeing latitude)
1966 Cody:

2. prey diversity hypothesis (豊富な餌仮説)

1965 Perrins 1965: average clutch size of great tit populations

3. Spring bloom hypothesis (one of the competition hypothesis)
4. Predator hypothesis
5. Hypothesis on hazard of migration and residual reproductive value
Table 5.2 Estimated maximal instantaneous rates of increase (rmax, per captia per day) and mean generation times (in days) for a variety of organisms

Species (Taxon): rmax ↔ Generation time (T)
Escherichia coli (Bacterium): ca 60.0 ↔ 0.014
Paramecium aurelia (Protozoa): 1.24 ↔ 0.33-0.50
Paramecium caudatum (Protozoa): 0.94 ↔ 0.10-0.50
Tribolium confusum (Insect): 0.120 ↔ ca 80
Calandra oryzae (Insect): 0.110(0.08-0.11) ↔ 58
Rhizopertha dominica (Insect): 0.085(0.07-0.10) ↔ ca 100
Ptinus tectus (Insect): 0.057 ↔ 102
Gibbium psylloides (Insect): 0.034 ↔ 129
Trigonogenius globulus (Insect): 0.032 ↔ 119
Stethomezium squamosum (Insect): 0.025 ↔ 147
Mezium affine (Insect): 0.022 ↔ 183
Ptinus fur (Insect): 0.014 ↔ 179
Eurostus hilleri (Insect): 0.010 ↔ 110
Niptus sexpunctatus (Insect): 0.006 ↔ 215
Rattus norwegicus (Mammal): 0.015 ↔ 150
Microtus aggrestis (Mammal): 0.013 ↔ 171
Canis domesticus (Mammal): 0.009 ↔ ca 1000
Magicicada septendecim (Insect): 0.001 ↔ 6050
Homo sapinens (Mammal): 0.0003 ↔ ca 7000

Table 5.4 Some of the correlates of r and K selection (Pianka 1970)
r selectionK selection
ClimateVariable and/or unpredictable; uncertainFairly constant and/or predictable; more certain
MortalityOften catastrophic, non-directed, density independentMore direct, density dependent
SurvivorshipOften Type IIIUsually Types I and II
Population sizeVariable in time, non-equilibrium; usually well below carrying capacity of environment; unsaturated communities or portions thereof; ecologic vacuums; recolonization, each yearFairly constant in time, equilibrium, at or near carrying capacity of the environment; saturated communities; no recolonization necessary
Intra-and interspecific competitionVariable, often laxUsually keen
Selection favors1 rapid development
2 high maximal rate of increase, rmax
3 early reproduction
4 small body size
5 single reproduction
6 many small offspring
1 slower development
2 greater competitive ability
3 delayed reproduction
4 larger body size
5 repeated reproduction
6 fewer larger progeny
Length of lifeShort, usually less than 1 yearLonger, usually more than 1 year
Leads toProductivityEfficiency
Stage in successionEarlyLate, climax

Breeding (増殖)

Intrinsic rate of natural increase (内的自然増加率)

Def. r ≡ intrinsic rate of natural increase (内的自然増加率)

= Malthusian parameter (マルサス係数)

Population interactions (個体群間相互作用)

Relationships between individuals and groups of individuals, estimated by benefits (+, positive), or detriments (-, negative) to either population or both. No benefits and detriments (0, neutral) to either population could be included.
Intraspecific: between members of the same population or species

Competition: Various
Cooperation: +/+
Cannibalism: +/-

Interspecific: between members of two or more populations

Predation:_____ +/-
Parasitism:____ +/-
Mutualism:____ +/+
Commensalism: +/0

Assembly rules

  1. Environmentally mediated patterns, i.e., correlations between species due to their shared or opposite responses to the physical environment (環境)
  2. Assembly rules, patterns due to interactions between species, such as competition, allelopathy, facilitation, mutualism, and all other biotic interactions that we know about in theory, and actually affect communities in the real world

(van der Maarel & Franklin 2013)

Interactions between bird and tree

(Nishi & Tsuyuzaki 2004)

Species Jungle Crow (Corvus macrorhynchos) Rhus trichocarpa
Characteristics Canopy seed storage thoroughout year Staying even in snow perido
Advantage The seeds are for food resource in winter Seeds are dispersed to favorable habitats by crow

Founder effect (創始者効果)

1942 Mayr E
Loss of genetic variation that occurs when a new population is established by a small number of individuals from a large population

A population bottleneck may also cause a founder effect

founder effect
Bottleneck effect (瓶首効果)
sharp reduction in the size of a population due to catastrophic disturbances

Population theory (人口学)

= population statistics, demography
Malthus, Thomas Robert (1766-1834, Engand)
1798 "An essay on the principle of population" (人口論), anonymous

population = increase in geometric progression (等比級数的) vs
food = increase in arithmetical progression (等差級数的)
→ predicting food shortage

requirement of birth control to save poor population

1803 2nd edition (Donald Winch)

moral restraint

1826 6th edition
⇒ Malthusianism (マルサス主義)

affected evolution theory proposed by Darwin

Mamdani, Mahmood (1947-, Uganda)
1972 The myth of population control - family, caste and class in an Indian village (人口抑制の論理)

children: work for the family + old age insurance for the poor →
voluntary family planning will not be accepted until technological change reduces the need for family laborers

1984 International conference on population (Mexico City)
1994 International conference on population and development, ICPD

Population fund (UNFPA), programme of action – adopted at the ICPD (Cairo)