Montaña Co-Authors New Study on Relationship Between Body Size-Trophic Position Among Fishes in Cambodia

Carmen G. Montaña, Ph.D., of the Department of Biological Sciences at SHSU, is the co-author of a new study investigating the relationship between Body Size-Trophic Position among fishes of the lower Mekong River, Cambodia. The study was the result of team collaboration, including lead author Chouly Ou (Cambodia), Carmen G. Montaña (Venezuela), and Kirk O. Winemiller (USA).The study has been published in the journal Royal Society Open Science (an open access journal from the Royal Society of London). See http://rsos.royalsocietypublishing.org/content/4/1/160645 for the full study.

The team's research study took place in the Mekong River, Cambodia, which is the third richest river in fish species diversity in the world after the Amazon River, in South America, and the Zaire River in Africa. It examined the relationship between body size and trophic position of fishes inhabiting four rivers in northern Cambodia: The Mekong, Seking, Sesan, and Srepok rivers. A better understanding of the relationship between body size and trophic position in tropical rivers has immediate resource management and is critical for numerous ecological applications in community based research. 

Study findings showed that fishes in the Lower Mekong River are extremely diverse in terms of body size, habitat use and feeding ecology. As in many other tropical freshwater rivers, this high diversity is attributed to several factors including historical biogeography, hydrological seasonality which affects habitats and food web dynamics, and the greater niche diversification in tropical regions compared to temperate regions. 

Overall, the findings showed that Body Size significantly predicted Trophic Position within the orders Siluriformes and Perciformes, but not for Cypriniformes, the most species-rich and ecologically diverse order in the Lower Mekong River. Cypriniformes, a species-rich order that dominates freshwater systems in Asia and North America, has many detritivorous, algivorous and omnivorous species in the Lower Mekong that span a wide range of adult body sizes, including members of pelagic and benthic habitat guilds.

An important finding of the study is that results contradict a broadly accepted model, the Fishing-Down-the-Food-Web by Pauly et al. (1998), which proposes that fish body size positively correlates with trophic position, so the removal of larger fishes from a system results in a reduction in average food chain length, a model based on marine systems. In tropical river-floodplain ecosystems (i.e., the Mekong River), body size is not a useful surrogate for examining the vertical trophic position because fish assemblages are ecological diverse and these tropical freshwater systems contain diverse large body size detritivores and insectivores. When commercial fisheries remove large herbivorous and detritivorous fishes from these food webs, the diet of predatory fishes may shift and consequently affect secondary production.