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Life cycle (生活環)·life history (生活史)






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

Life history stage (growth stage)

≈ life cycle (on ecology)
A system of interrelated adaptive traits forming a set of reproductive tactics
There are various definitions on each life history stage, depnding on research objectives. This page is for terrestrial seed-plant community ecology.

Stage

Growth stages on terrestrial seed plants. Note that the definitions of seedling and junenile are totally fuzzy.
  • Seed: a structure that encapsulates the embryo. The seeds are often in dormant and makes a seedbank
    ↓ germination
  • Seedling (実生): a young plant reproduced by means of seeds (not by sprouts). On forestry, seedling often means young trees less than the defined height, 1.0-1.3 m. For monitoring tree growth on Mount Koma, we define trees less than 30 cm high for trees.
  • Sapling
    1. young tree, that does not produce any flowers and fruits even if the environmental conditions are appropriate
    2. in the case of the research on Mount Koma, the height of saplings ranges from 0.3 m to 1.3 m (= DBH). A sapling of Magnolica kobus
    3. plants having a DBH greater than 0 and less than the minimum adult DBH defined in the tree parameters
  • Juvenile: an immature (non-flowering) individual resembling an adult except reproductive activity, i.e., seedlings and saplings
    ↓ growth / competition
  • Adult: the mature stage. In the case of terrestrial plants, it is recognized by theproduction of reproductive organs, such as flowers and fruits. See an adult Robinia pseudoacacia
    ↓ seed dispersal
    Time has passed …
  • Dead: an individual makes neither photosynthesis nor respiration
seedling seedling [Left] A Picea mariana seedling emerged on a petri dish with three-layered filter paper in an incubator. The length is about 2 cm. [Right] A P. mariana seedling on burned ground surface after the 2004 wildfire (森林火災) at Poker Flat near Fairbanks, Alaska, on July 30 2007 (by Narita K).
索引

Examples

Annuals (一年生)
completing its life cycle from germination to the production of seeds within one growing season
  1. From seed dispersal to seedling emergence
  2. Seedling establishment
  3. Seedling development
  4. Sapling, or juvenile
  5. Pole development
  6. Maturation
It can be grouped into semelparous.
Perennials (多年生, based on age)
living more than two years
  1. Viable seeds in soil
  2. Seedlings
  3. Juvenile plants
  4. Immature plants
  5. Mature virginile plants
  6. Plants in the initial phase of generative period
  7. Plants in the period of life culmination
  8. Senescing plants
  9. Senile plants
  10. Plants in the dormant state
Trillium

(DeGasperis & Motzkin 2007)

Windows of opportunity
Timing for establishing the life-history stage

Grime's triangle (グライムの三角形)

The combination of three strategies of plants:


                    
Disturbance
                    


       
High
Low

Productivity            
Low                         
   -
Stress tolerators (S)

                          
High                  
Ruderals (R)
Competitors (C)





Competitors (C)
Plants have high competition ability when low stress and disturbance are given. The high competition ability is evaluated by fast growth rate and high productivity
Stress tolerators (S)
Plants adapt to high stress and low disturbance, by slow growth rates, long-lived leaves, and high nutrient retention rate. These are represented by species growing in alpine, arid, or sprpentine habitats
Ruderals (R)
Species favor disturbance with low stress, and are fast-growing. Plants that have adapted this strategy are often found colonizing recently disturbed land, and are often annuals
 CSR
⇒ Application to Succession (遷移)
(☛ Q. an example)

Phenology (フェノロジー)

periodic plant and animal life cycle events

Ex. seed germination, leaf flushing, flower production, defoliation

Spring ephemeral (春植物)

Producing flowers immediately after snowmelt and completing the life-cycle by early summer

be perennial that can reproduce by underground organs in each spring soon after snow melting
be able to utlize excess light before the leaf flushing of canopy trees →
be distributed in deciduous forests

Spring ephemerals
Fig. Seasonal changes in light intensity on the forest floor of deciduous and evergreen forests
Representative species
Adonis ramosa (フクジュソウ), Adoxa moschatellina (レンプクソウ), Allium monanthum (ヒメニラ), Amana edulis (アマナ), A. erythronioides (ヒロハノアマナ), Anemone debilis (ヒメイチゲ), A. flaccida (ニリンソウ), A. nikoensis (イチリンソウ), A. pseudoaltaica (キクザキイチゲ), A. soyensis (エゾイチゲ), Erythronium japonicum (カタクリ), Trillium smallii (コジマエンレイソウ), Soldanella alpina L. (イワカガミダマシ, alpine snowball)
Five species often shown in my lectures for international students

Trillium kamtschaticum (オオバナノエンレイソウ)
Anemone raddeana (アズマイチゲ)
Corydalis ambigua (エゾエンゴサク)
Scopolia japonica (ハシリドコロ)
Gagea lutea (キバナノアマナ)

[ reproduction ]

Sex (性)

vegetative stage = often immature stage ↔ reproductive stage = mature stage, anyway
sex ratio: polygamy (多系), vegetative propagation, monogamy

Sexual form

Case. Plants
Hermaphrodite and monoecy (synoecious)

protandry (adj. protandrous)
protogyny (adj. protogynous)

hermaphrodite flower, bisexual flower

adichogamous flower
dichogamous flower

monoecism, or monoecy
Dioecism, dioecy

androgynodioecious, triecious: (♂)/(♀)/(♂♀)
androdioecious: (♂)/(♂♀)
gynodioecious: (♀)/(♂♀)

Case. Animals
Hermaphrodite (雌雄同体): an individual produces both male and female gametes (monoecy or monoecious is not used for animals)

Ex. earthworms, snails, slugs and many tunicates and mollusks

Dioecy (雌雄異体)

Recombination system, res (組換システム)

Maximum res: open res (開放型組換), restricted res (制限型組換), colsed res (閉鎖型組換)
Maximum replication

Open res: wide allogamy
Restricted res: predominant autogamy
Closed res: agamospermy

Table 1.1. Components of the recombination system in plants
1. Factors controlling the amount of recombination per gernerations; control operative at meiosis

a. chromosome number
b. frequency of corssing-over
c. hybrid sterility

2. Factors controlling the amount of recmbination per generation; controlling operative at fertilization

d. brdding system
e. pollination system
f. dispersal potential
g. seed number and germination behavior
h. population size
i. crossability barriers and external mechanisms

3. factor controlling the amount of recombination per mechanisms

j. length of generation

☛ cytogenetics

Sex determination (性決定)

Sex chromosome (性染色体)
Sex transformation (性転換)
protogyny (雌性先熟)
protandry (雄性先熟)
Trans
Fig. 1. The size advantage hypothesis represented by fish. Expected female offspring production (blue line) increases with body size if large females can lay more eggs. Expected male offspring production (red line) may increase strongly with body size if, for instance, large males breed with many more females than do small males. Sex change is favored when the size-(or age) specific fertility curves of the sexes cross. Female-to-male sex change ((a) protogyny) is favored when the fertility of an average male increases more rapidly than the fertility of an average female. Male-to-female sex change ((b) protandry) is favored when fertility of an average female increases. (Munday et al. 2006)

Sex ratio (性比)

1871 Darwin: polygamy (一夫多妻) = polygyrous + polyandeous

Q. why many sexually reproducing species evolve a 1:1 ratio of males to females

Th. Sex ratio theory (性比理論) (Fisher 1930): key principle ⇒

Rare type advantage: when one sex becomes rare, parents who produce more of that sex gain a reproductive advantage
This frequency‑dependent selection pushes the population toward a 1:1 sex ratio, which becomes evolutionarily stable

⇒ A variety of exceptions to equal sex ratio

unequal costs: the cost differs between males and females
local resource competition (with rare type advantage)
local mate competition (common in invertebrates)

Sexual selection (性淘汰)

Def. natural selection arising from differences in mating success

Secondary sexual traits Ex. peacock tails, deer antlers
⇒ evolved by sexual selection

Intrasexual selection (同性間淘汰)

through competition between members of one sex for mates
Ex. the development of fighting equipment such as antlers, horns, tusks and enlarged canines in male mammals

Intersexual selection (異性間淘汰)

through preference for particular traits in the other sex
Ex. the extravagant tails or head plumes of male birds of paradise or peacocks
☛ handicap hypothesis, runaway hypothesis
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