Shorter Food Chain Length in Ancient Lakes: Evidence from a Global Synthesis

Food webs may be affected by evolutionary processes, and effective evolutionary time ultimately affects the probability of species evolving to fill the niche space. Thus, ecosystem history may set important evolutionary constraints on community composition and food web structure. Food chain length (FCL) has long been recognized as a fundamental ecosystem attribute. We examined historical effects on FCL in large lakes spanning >6 orders of magnitude in age. We found that food chains in the world’s ancient lakes (n = 8) were significantly shorter than in recently formed lakes (n = 10) and reservoirs (n = 3), despite the fact that ancient lakes harbored much higher species richness, including many endemic species. One potential factor leading to shorter FCL in ancient lakes is an increasing diversity of trophic omnivores and herbivores. Speciation could simply broaden the number of species within a trophic group, particularly at lower trophic levels and could also lead to a greater degree of trophic omnivory. Our results highlight a counter-intuitive and poorly-understood role of evolutionary history in shaping key food web properties such as FCL

Occurrence and biomagnification of polychlorinated naphthalenes and non- and mono-ortho PCBs in Lake Ontario sediment and biota

Biota and surface sediments collected from Lake Ontario were analyzed for polychlorinated naphthalenes (PCNs) and non- and mono-ortho-substituted polychlorinated biphenyls (n/m-o-PCBs) to compare bioaccumulation behavior of these classes of dioxin-like chemicals in a food web from the Great Lakes. Mean ΣPCN concentrations (tri-octaCN) ranged from 14 ± 9 pg/g in plankton to 3500 ± 3200 pg/g (wet weight) in lake trout, while sediments contained from 21 to 38 ng/g (dry weight). Principal components analysis of PCN congener patterns indicated that chlorine substitution determined which congeners favored accumulation (e.g., CN-42, -52, -60, -66, -67, and -73), while others may be subject to metabolism. The bioaccumulative congeners exhibited similar trophic magnification factors (TMFs; 1.23-1.42) and biomagnification factors (BMFs; 5.5-8.6) to the n/m-o-PCBs for the trout/weighted diet relation, although BMFs for a benthic feeding relationship (slimy sculpin/Diporeia) indicated that the n/m-o-PCBs were more bioavailable through the benthic pathway. PCNs contribute significantly to the burden of dioxin-like compounds in Lake Ontario biota, contributing between 12 and 22% of total PCN + PCB TEQ in lake trout and up to 69% in benthic organisms. © 2008 American Chemical Society