4. The table below gives rough estimates of food chain lengths from various fiel

Question

4. The table below gives rough estimates of food chain lengths from various field studies and is taken from the Ricklefs textbook. Community Net primary production (kcal/m²/year) 500 Consumer ingestion (kcal/m2/year) 0.1 Trophic level transfer efficiency (%) 25 Number of trophic levels in food chain 7.1 8000 10.0 10.0 20 20 5.1 Open ocean Coastal marine Temperate grassland | Tropical forest 2000 1.0 4.3 8000 10.0 5 3.2 a) Based on Ricklefs' analysis, what factor appears to consistently control the length of food chains in different ecosystems? b) Explain the ecological basis for this relationship? c) Describe one other factor that has been argued to control food chain length in some ecosystems. This factor does not necessarily have to be supported by the data in this table. 5. Use the figures below to show the expected relationship between variables influencing key ecological tradeoffs in plants and animals. For each figure provide a 1-3 sentence description of why the relationship is in a particular direction.

Explanation / Answer

4. a) The length of food chain, irrespective of the ecosystem, will be controlled by the same factors. In the given cases, these factors are consumer ingestion and trophic level transfer efficiency. These two together decide the number of trophic levels.

b) The above relationships can be explained as follows -

Consumer ingestion shows the amount of energy consumed from the net primary production (NPP), by one consumer. So, this shows us the number of consumers required to consume all of the NPP and complete the food chain. Trophic level transfer efficiency decides the efficiency with which this energy is tranferred from one trophic level to the next. So, consumer ingestion along with trophic level transfer efficiency, shape how many consumers are required to consume NPP and therefore decide the number of trophic levels required. Furthermore, it can be seen from the data that when consumer ingestion is low and trophic level transfer efficiency is high, the number of trophic levels is high (example - open ocean), and vice versa (example - tropical forest).

c) Temperature is one of the factors that controls the food chain length. This is because at extreme temperatures, the NPP cannot be very high and the species richness is comparatively very low in extreme hot or cold climates. Because of these factors the number of consumers filling different trophic levels will be affected, in totality affecting the food chain length. On the other hand, at moderate temperatures, the species richness is very high, which will affect the food chain length. This can further be understood by comparing the food chain lengths in a frozen dessert and the plains.

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