Food chain length: ecosystem size and production are both important

Posted on March 26, 2010

Food chain length (FCL), the number of trophic levels between primary producers and the top predators, is a key ecosystem descriptor.  Although FCL varies greatly between ecosystems, there have been differing opinions as to the cause of this variation.  Contending hypotheses propose that FCL is limited by the amount of available energy in the system or by the size of the ecosystem, but interpretations of aquatic data have been complicated by the use of total productivity in lieu of available energy, and by low contrast in the size of studied lakes.  Sampling of 15 ponds (c. 1,000 – 27,000 m2 in area) inMatsuyama,Japan allowed FCL to be estimated by reference to stable isotope data on fish, insect larvae and animal plankton.  The edible size fraction of phytoplankton was used as an indicator of resource availability, and for each pond the total productivity and volume (ecosystem size) were also measured.  Both available resources and ecosystem size were significantly correlated with FCL.  This result lends support to a third hypothesis (the so-called productive space hypothesis), which reflects the capacity of an ecosystem to support extra feeding levels – for example, if maximum FCL is limited by energy transfer inefficiencies, then predators will have to forage over a wider area to meet their energy requirements in low energy habitats.

Reference:  Hideyuki Doi, Kwang-Hyeon Chang, Takamitsu Ando, Ippei Ninomiya, Hiroyuki Imai and Shin-ichi Nakano.  2009.  Resource availability and ecosystem size predict food-chain length in pond ecosystems.  Oikos 118, 138-144.

Posted in: ecosystems, food webs