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Population (個体群)

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


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

  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

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.

→ Habitat for Trillium smallii Maxim. is generally the floor of deciduous forests.

→ Habitat for 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 (規則分布)
Random distribution (ランダム分布)
Contagious distribution (集中分布)

Population dynamcis (個体群動態)

Life table

= mortality talbe 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 (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 talbes of Bupalus piniarius and cinnabar moth (Tyria jacobaeae)

1950 Jenkins, et al.

population fluctuation of Lagopus lagopus scoticus

Opportunistic and equilibrium populations


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

1967 MacArthur & Wilson

selection occurs through breeding system (交配システム)
K-strategist: 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: 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
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
Taxon     Species                 rmax              Generation
                                                    time (T)

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

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