Autochthonous and allochthonous production

All biotic communities depend on a supply of energy for their activities. In most terrestrial systems this is contributed in situ by the photosynthesis of green plants - this is autochthonous production. Exceptions exist, however, particularly where colonial animals deposit feces derived from food consumed at a distance from the colony (e.g. bat colonies in caves, seabirds on coastland) - guano is an example of allochthonous organic matter (dead organic material formed outside the ecosystem).

In aquatic communities, the autochthonous input is provided by the photosynthesis of large plants and attached algae in shallow waters (littoral zone) and by microscopic phytoplankton

Figure 17.2 Interannual variation in net primary productivity (NPP) in a grassland in Queensland, Australia (above-ground NPP), a cropland in Iowa, USA (total above- and below-ground NPP) and a tropical savanna in Senegal (above-ground NPP). Black horizontal lines show the mean NPP for the whole study period. (After Zheng et al., 2003.)

in the open water. However, a substantial proportion of the organic matter in aquatic communities comes from allochthon-ous material that arrives in rivers, via groundwater or is blown in by the wind. The relative importance of the two autochthonous sources (littoral and planktonic) and the allochthonous source of organic material in an aquatic system depends on the dimensions of the body of water and the types of terrestrial community that deposit organic material into it.

A small stream running through a wooded catchment derives most of its energy input from litter shed by surrounding vegetation (Figure 17.4). Shading from the trees prevents any significant growth of planktonic or attached algae or aquatic higher plants. As the stream widens further downstream, shading by trees is restricted to the margins and autochthonous primary production increases. Still further downstream, in deeper and more turbid waters, rooted higher plants contribute much less, and the role of the microscopic phytoplankton becomes more important. Where large river channels are characterized by a flood plain, with associated oxbow lakes, swamps and marshes, allochthonous dissolved and particulate organic may be carried to the river channel from its flood plain during episodes of flooding (Junk et al., 1989; Townsend 1996).

The sequence from small, shallow lakes to large, deep ones shares some of the characteristics of the river continuum just discussed (Figure 17.5). A small lake is likely to derive quite a large proportion of its energy from the land because its periphery is large in relation to its area. Small lakes are also usually shallow, so internal littoral production is more important than that by phytoplankton. In contrast, a large, deep lake will derive only limited organic matter from outside (small periphery relative to lake surface area) and littoral production, limited to the shallow margins, may also be low. The organic inputs to the community may then be due almost entirely to photosynthesis by the phytoplankton.

autochthonous and allochthonous production ...

... vary in systematic ways in lakes, rivers and estuaries

North American Photosynthesis

Figure 17.3 Seasonal development of maximum daily gross primary productivity (GPP) for deciduous and coniferous forests in temperate (Europe and North America) and boreal locations (Canada, Scandinavia and Iceland). The different symbols in each panel relate to different forests. Daily GPP is expressed as the percentage of the maximum achieved in each forest during 365 days of the year. (After Falge et al., 2002.)

Figure 17.3 Seasonal development of maximum daily gross primary productivity (GPP) for deciduous and coniferous forests in temperate (Europe and North America) and boreal locations (Canada, Scandinavia and Iceland). The different symbols in each panel relate to different forests. Daily GPP is expressed as the percentage of the maximum achieved in each forest during 365 days of the year. (After Falge et al., 2002.)

Figure 17.4 Longitudinal variation in the nature of the energy base in stream communities.

Figure 17.4 Longitudinal variation in the nature of the energy base in stream communities.

Allochthonous InputAllochthonous Input
Figure 17.5 Variation in the importance of terrestrial input of organic matter and littoral and planktonic primary production in contrasting aquatic communities.

Estuaries are often highly productive systems, receiving allochthonous material and a rich supply of nutrients from the rivers that feed them. The most important autochthonous contribution to their energy base varies. In large estuarine basins, with restricted interchange with the open ocean and with small marsh peripheries relative to basin area, phytoplankton tend to dominate. By contrast, seaweeds dominate in some open basins with extensive connections to the sea. In turn, continental shelf communities derive a proportion of their energy from terrestrial sources (particularly via estuaries) and their shallowness often provides for significant production by littoral seaweed communities. Indeed, some of the most productive systems of all are to be found among seaweed beds and reefs.

Finally, the open ocean can be described in one sense as the largest, deepest 'lake' of all. The input of organic material from terrestrial communities is negligible, and the great depth precludes photosynthesis in the darkness of the sea bed. The phytoplank-ton are then all-important as primary producers.

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Responses

  • sophia bader
    What is autochthonous production in ecology?
    7 months ago
  • Maire
    What is the difference between allochthonous and autochthonous input in aquatic ecosystem?
    7 months ago
  • Aloisia
    What are allochthonous nutrients?
    6 months ago
  • mustafa
    What are the difference between autochtonous and allocht?
    5 months ago
  • Eija Salli
    What is autochthonous inputs in ecosystem?
    5 months ago
  • thomas
    What are the main difference between allochthonous and autochthonous input in aquatic ecosystems?
    5 months ago
  • RALF
    What are the autochthonous microoganism of aquatic environment?
    5 months ago
  • Eric
    What are authoctonous and allochtonouus organisms?
    5 months ago
  • poppy grubb
    What is the difference between autochthonous and allochtonous in aquatic ecosystem?
    5 months ago
  • Sandra
    What is the difference between autochthonous &allochtonous inputs in aquatic ecosystems?
    5 months ago
  • Adelfo
    What is the difference between autochthonous and allochthonous inputs ecosystem?
    5 months ago
  • kerstin
    What is autochthonous energy?
    2 months ago
  • Raakel
    What is allochthonous energy?
    2 months ago
  • Emilia
    What are autothonous and allothonous organisms?
    2 months ago

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