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Trophic level (栄養段階)

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

[ trophic level | food web ]

Trophic level (栄養段階)

Fig. Food web and trophic levels in the Arctic. Consider why the arctic ecosystem is fragile.
Producer, P (= Autotroph)
organisms that produce their own energy, i.e., peforming photosynthesis (or chemosynthesis)

productivity (生産力)

Consumer, C (≈ Heterotroph)
organisms that gets their food from other living organisms to obtain energy

Macroconsumer organisms (herbivores, carnivores, detritivore)

Decomposer, D (≈ Saprotroph)
organisms that obtain energy through the decomposition of dead or decaying organisms

bacteria, fungi, worms, etc.

[cycle of matter]

Food web (食物網)

= Food chain (食物連鎖)
P → C1 → C2 → C3 → C4 → C5
__↘ ↓________________
D ← ← ← ← ← ← ← ← ← ←
______________food chain
Ex. Mount Usu (有珠山)
┏━ Sparrow hawk (ハイタカ)
____eats small birds, ratsd, squirrels, snakes, etc.
__Japanese rat snake (アオダイショウ)
____eats rats, birds, lizards, frogs, and others, including eggs
┗━ Great tit (シジュウカラ)
______┃ ┃eats insects (polyhagous)
______┃ ┗━━━━━━━━━━━┓
_Gypsy moss larva____________Nut weevils
______eats leaves of deciduous tree__ eats acorns and chestnuts (perforator)
_Oak leaf (ミズナラ葉)__________Acorn (堅果)
The optimal length of food chain probably exists

Food size → determined by the oral organs of animals
→ The number of food chains is usually 5 to 6, depending on the energy flow ↔ the minimum number exists, as well as the maxmum

Trophic cascade (栄養カスケード)
indirect interactions that control entire ecosystems, occurring when a trophic level is suppressed
Ex. top-down cascade, bottom-up cascade, subsidy cascade
                             top-down  bottom-up  subsidy
Second consumer        ×               ⇓             ⇓
First consumer              ⇑              ⇓             ×
Producer                       ⇓               ×             ⇑

Ecological pyramid (生態ピラミッド)

The structure of ecosystems is visualized by ecological pyramids that were proposed by Elton. Ecological pyramids show the amounts of various parameters across trophic levels. The major three parameters are: number (1), biomass (2) and energy (3).
  1. Eltonian or number pyramid (個対数ピラミッド, 数のピラミッド): usually numbers decreased with increasing trophic levels, as shown by a grassland in summer (Fig. A). However, there are many excpetions, i.e., showing inverse pyramids. For example, a few large tree support numerous insects in (Elton 1927)
  2. Biomass pyramid (現存量ピラミッド): measuring the amount of energy converted into living tissue at the different trophic levels. We usually see the pyramid shown by Sliver Spring in Fig. A, becasue of the high biomass of producers. However, there are few expections, as showin by English Channel in Fig. A. The cause is the high productivity of the phytoplankton. The phytoplankton are consumed rapidly by the primary consumers, and thus, minimizing their biomass at any time.
  3. Energy pyramid (生産量またはエネルギーピラミッド): shown by energy flow through the trophic levels (Lindemann 1942). The energy pyramids are upright with no exceptions → predicting low primary productivity cannot support the ecosystem.
Fig. A. Ecological pyramids depict the (a) biomass, (b) number of organisms, and (c) energy in each trophic level.