Unitary and modular organisms

Our 'ecological fact of life', though, implies by default that all individuals are alike, which is patently false on a number of counts. First, almost all species pass through a number of stages in their life cycle: insects metamorphose from eggs to larvae, sometimes to pupae, and then to adults; plants pass from seeds to seedlings to photosynthesizing adults; and so on. The different stages are likely to be influenced by different factors and to have different rates of migration, death and of course reproduction.

Second, even within a stage, individuals can differ in 'quality' or 'condition'. The most obvious aspect of this is size, but it is also common, for example, for individuals to differ in the amount of stored reserves they possess.

Uniformity amongst individuals is especially unlikely, moreover, when organisms are modular rather than unitary. In unitary organisms, form is highly determinate: that is, barring aberrations, all dogs have four legs, all squid have two eyes, etc. Humans are perfect examples of unitary organisms. A life begins when a sperm fertilizes an egg to form a zygote. This implants in the wall of the uterus, and the complex processes of embryonic development commence. By 6 weeks the fetus has a recognizable nose, eyes, ears and limbs with digits, and accidents apart, will remain in this form until it dies. The fetus continues to grow until birth, and then the infant grows until perhaps the 18th year of life; but the only changes in form (as opposed to size) are the relatively minor ones associated with sexual maturity. The reproductive phase lasts for perhaps 30 years in females and rather longer in males. This is followed by a phase of senescence. Death can intervene at any time, but for surviving individuals the succession of phases is, like form, entirely predictable.

In modular organisms (Figure 4.1), modular organisms on the other hand, neither timing nor form is predictable. The zygote develops into a unit of construction (a module, e.g. a leaf with its attendant length of stem), which then produces further, similar modules. Individuals are composed of a highly variable number of such modules, and their program of development is strongly dependent on their interaction with their environment. The product is almost always branched, and except for a juvenile phase, effectively immobile. Most plants are modular and are certainly the most obvious group of modular organisms. There are, however, many important groups of modular animals individuals differ in their life cycle stage and their condition unitary organisms

Duckweed LifecycleModular Organism

Figure 4.1 Modular plants (on the left) and animals (on the right), showing the underlying parallels in the various ways they may be constructed. (opposite page) (a) Modular organisms that fall to pieces as they grow: duckweed (Lemna sp.) and Hydra sp. (b) Freely branching organisms in which the modules are displayed as individuals on 'stalks': a vegetative shoot of a higher plant (Lonicera japonica) with leaves (feeding modules) and a flowering shoot, and a hydroid colony (Obelia) bearing both feeding and reproductive modules.

(c) Stoloniferous organisms in which colonies spread laterally and remain joined by 'stolons' or rhizomes: a single plant of strawberry (Fragaria) spreading by means of stolons, and a colony of the hydroid Tubularia crocea. (above) (d) Tightly packed colonies of modules: a tussock of the spotted saxifrage (Saxifraga bronchialis), and a segment of the hard coral Turbinaria reniformis. (e) Modules accumulated on a long persistent, largely dead support: an oak tree (Quercus robur) in which the support is mainly the dead woody tissues derived from previous modules, and a gorgonian coral in which the support is mainly heavily calcified tissues from earlier modules. (For color, see Plate 4.1, between pp. 000 and 000.)

((a) left, © Visuals Unlimited/John D. Cunningham; right, © Visuals Unlimited/Larry Stepanowicz; (b) left, © Visuals Unlimited; right, © Visuals Unlimited/Larry Stepanowicz; (c) left, © Visuals Unlimited/Science VU; right, © Visuals Unlimited/John D. Cunningham;

(d) left, © Visuals Unlimited/Gerald and Buff Corsi; right, © Visuals Unlimited/Dave B. Fleetham; (e) left, © Visuals Unlimited/Silwood Park; right, © Visuals Unlimited/Daniel W. Gotshall.

Figure 4.1 Modular plants (on the left) and animals (on the right), showing the underlying parallels in the various ways they may be constructed. (opposite page) (a) Modular organisms that fall to pieces as they grow: duckweed (Lemna sp.) and Hydra sp. (b) Freely branching organisms in which the modules are displayed as individuals on 'stalks': a vegetative shoot of a higher plant (Lonicera japonica) with leaves (feeding modules) and a flowering shoot, and a hydroid colony (Obelia) bearing both feeding and reproductive modules.

(c) Stoloniferous organisms in which colonies spread laterally and remain joined by 'stolons' or rhizomes: a single plant of strawberry (Fragaria) spreading by means of stolons, and a colony of the hydroid Tubularia crocea. (above) (d) Tightly packed colonies of modules: a tussock of the spotted saxifrage (Saxifraga bronchialis), and a segment of the hard coral Turbinaria reniformis. (e) Modules accumulated on a long persistent, largely dead support: an oak tree (Quercus robur) in which the support is mainly the dead woody tissues derived from previous modules, and a gorgonian coral in which the support is mainly heavily calcified tissues from earlier modules. (For color, see Plate 4.1, between pp. 000 and 000.)

((a) left, © Visuals Unlimited/John D. Cunningham; right, © Visuals Unlimited/Larry Stepanowicz; (b) left, © Visuals Unlimited; right, © Visuals Unlimited/Larry Stepanowicz; (c) left, © Visuals Unlimited/Science VU; right, © Visuals Unlimited/John D. Cunningham;

(d) left, © Visuals Unlimited/Gerald and Buff Corsi; right, © Visuals Unlimited/Dave B. Fleetham; (e) left, © Visuals Unlimited/Silwood Park; right, © Visuals Unlimited/Daniel W. Gotshall.

(indeed, some 19 phyla, including sponges, hydroids, corals, bryo-zoans and colonial ascidians), and many modular protists and fungi. Reviews of the growth, form, ecology and evolution of a wide range of modular organisms may be found in Harper et al. (1986a), Hughes (1989), Room et al. (1994) and Collado-Vides (2001).

Thus, the potentialities for individual difference are far greater in modular than in unitary organisms. For example, an individual of the annual plant Chenopodium album may, if grown in poor or crowded conditions, flower and set seed when only 50 mm high. Yet, given more ideal conditions, it may reach 1 m in height, and produce 50,000 times as many seeds as its depauperate counterpart. It is modularity and the differing birth and death rates of plant parts that give rise to this plasticity.

In the growth of a higher plant, the fundamental module of construction above ground is the leaf with its axillary bud and the attendant internode of the stem. As the bud develops and grows, it produces further leaves, each bearing buds in their axils. The plant grows by accumulating these modules. At some stage in the development, a new sort of module appears, associated with reproduction (e.g. the flowers in a higher plant), ultimately giving rise to new zygotes. Modules that are specialized for reproduction usually cease to give rise to new modules. The roots of a plant are also modular, although the modules are quite different (Harper et al., 1991). The program of development in modular organisms is typically determined by the proportion of modules that are allocated to different roles (e.g. to reproduction or to continued growth).

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Responses

  • crystal
    Are there unitary plants and modular animals?
    5 years ago
  • DODA
    Is coral unitary or modular?
    5 years ago
  • BLADUD GARDNER
    What are modular and unitary organism give an examples of each?
    4 years ago
  • kiros abrha
    What is diffrence b/n module unitary?
    3 years ago
  • lillian
    What do u mean by unitary and midular population?
    3 years ago
  • aki-petter
    How can you obtain the species size for unitary organism?
    3 years ago
  • sari
    What is unitary organism in ecology?
    3 years ago
  • richard
    What affects unitary organisms?
    3 years ago
  • virpi haataja
    What methods used to get the population size of unitary organism?
    3 years ago
  • Scott
    What is the difference between unitary and modular organisms?
    2 years ago
  • derek fraser
    What is difference between unitary population and modular population?
    2 years ago
  • Jessica
    What is unitary pulation?
    2 years ago
  • leyton
    Why does animals considered as unitary organism?
    2 years ago
  • Asmara
    What is unitary and moduler populations?
    2 years ago
  • francesca
    What are the effects of intraspecific competition on individual unitary organisms?
    2 years ago
  • kandy walker
    What do you understand by modular type of growth?
    2 years ago
  • Principio
    What is moduler population?
    2 years ago
  • hagosa
    How unitary organisms are determinate?
    1 year ago
  • linda
    What is the differnc between unitary and modular?
    1 year ago
  • veronica
    Are ramets applied to unitary organisms?
    1 year ago
  • kerry milne
    Is clonal bamboo unitary organism?
    1 year ago
  • Ines Baecker
    What is bad about an organism modular body plan?
    9 months ago
  • NORMA
    Are modular or unitary organisms more plastic?
    6 months ago
  • Paul Eberhardt
    Which of the following represents a modular organism?
    5 months ago
  • bucca
    What is the dxampls of modular orgnism?
    4 months ago
  • BASSO COCCI
    What are the distinguishing features of modeular anda unitary organism?
    3 months ago
  • Jukka-Pekk
    Why unitary organisms genetically unique?
    3 months ago
  • eliisa
    What is the differemce between unitary and modular organisms?
    3 months ago
  • Keira
    What is the deference between modular and unitary organisms?
    3 months ago
  • anthony
    Are modular populations single organisms?
    1 month ago
  • Alfie
    Is grass unitary or modular?
    4 days ago

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