BottomUp Forces

A major theme of this article is the contrary actions of bottom-up and top-down forces in food webs and chains. The former are fundamental and the backbone of all ecological nature; matter and energy are transferred from the bottom up, to consumers from producers, in every web and chain. The decomposition of Polonius in Act IV, Scene III of Shakespeare's Hamlet is a classical example of this bottom-up foundation:

King Claudius: Now, Hamlet, where's Polonius?

Hamlet: At supper.

King Claudius: At supper! where?

Hamlet: Not where he eats, but where he is eaten. A certain convocation of [politic] worms are e'en at him. Your worm is your only emperor for diet. We fat all creatures else to fat us, and we fat ourselves for maggots. Your fat king and your lean beggar is but variable service, two dishes, but to one table; that's the end.

Figure 1 David Lavigne's 'Simplified Foodweb for the Northwest Atlantic', which illustrates the fact of huge, reticulate, and interwoven feeding relationships among species from tiny to large in this area. The title is meant to be ironic and illustrates that even in simplification the trophic relationships in this ecosystem are elaborate and complex. One approach to study of such complicated systems is aggregation of species of similar ecological functions; another is consideration of small chains or webs of few species isolated from the rest in the ecosystem. From http://www.visualcomplexity.com/vc/project.cfm?id=47.

Figure 1 David Lavigne's 'Simplified Foodweb for the Northwest Atlantic', which illustrates the fact of huge, reticulate, and interwoven feeding relationships among species from tiny to large in this area. The title is meant to be ironic and illustrates that even in simplification the trophic relationships in this ecosystem are elaborate and complex. One approach to study of such complicated systems is aggregation of species of similar ecological functions; another is consideration of small chains or webs of few species isolated from the rest in the ecosystem. From http://www.visualcomplexity.com/vc/project.cfm?id=47.

Table 1 An early representation of the differences between aquatic and terrestrial herbivores in consumption rates of primary productivity by herbivores

Number

Percent of net

Type of

of trophic

P to first-order

system

levelsa

Characteristics of autotrophs

biophages

References

Mature

3

Trees, large amount of nonphotosynthetic

1.5-2.5

Bray (1964)

deciduous

structure, long generation time, low biotic

forest

potential

1-7-year-old

3

Herbaceous annual plants, medium biotic

12

Wiegert and Evans (1967) (data

South

potential

from Odum etal., 1962)

Carolina

fields

30-year-old

3

Perennial forbs and grasses, medium biotic

1.1

Wiegert and Evans (1967)

Michigan

potential

field

African

3

Perennial grasses, small amount of

28-60

Wiegert and Evans (1967) (data

grasslands

nonphotosynthetic structure rapid growth rate when environmental conditions are favorable

from Lamprey, 1964; Petrides and Swank, 1965)

Managed

3b

Perennial grasses, small amount of

30-45

Wiegert and Evans (1967) (data

rangelandb

nonphotosynthetic structure rapid growth rate when environmental conditions are favorable

from Lewis et al., 1956)

Ocean

4

Phytoplankton, small, numerous, high biotic

60-99

Riley (1956); Macfadyen (1964)

waters

potential, short generation time

aAboveground (terrestrial) or open water (aquatic) - does not normally Include food chains containing first-order saprophages. bGrass, cattle, man.

Reproduced from Wiegert RG and Owen DF (1971) Trophic structure, available resources and population density in terrestrial versus aquatic ecosystems. Journal of Theoretical Biology 30(1): 69-81.

aAboveground (terrestrial) or open water (aquatic) - does not normally Include food chains containing first-order saprophages. bGrass, cattle, man.

Reproduced from Wiegert RG and Owen DF (1971) Trophic structure, available resources and population density in terrestrial versus aquatic ecosystems. Journal of Theoretical Biology 30(1): 69-81.

Matter and energy flow from the producer, Polonius, to the consuming maggots and on to the fish that consume them. This is a saprotrophic chain with carrion as the producer. The first link in most saprotrophic chains is usually a one-way affair without feedback. Usually, neither the supply of carrion nor that of plant detritus is affected by the species that consume these dead resources. The basal link of these chains lacks top-down effects. Carrion flies lack influence upon the abundance of carrion. Similarly, the animals, bacteria, and fungi that decompose dead plant biomass lack direct influence upon the supply of this resource. Food chains without top-down effect on the supply of the resource are called processing chains.

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