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

PLOS ONE, Dec 2019

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.

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

Citation: Doi H, Vander Zanden MJ, Hillebrand H ( Shorter Food Chain Length in Ancient Lakes: Evidence from a Global Synthesis Tamara Natasha Romanuk, Dalhousie University, Canada 0 1 Institute for Chemistry and Biology of the Marine Environment, Carl-von-Ossietzky University Oldenburg , Schleusenstrasse 1, Wilhelmshaven, Germany , 2 Institute for Sustainable Sciences and Development, Hiroshima University 1-3-1 Kagamiyama , Higashi-Hiroshima, Japan, 3 Center for Limnology , University of Wisconsin , Madison, Wisconsin , United States of America 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. - Food chain length (FCL), which is a measure of the number of trophic levels in an ecosystem between primary producers and the top predator, has been recognized as a fundamental ecosystem attribute. FCL influences community structure, species diversity, and population stability by altering the organization of trophic interactions [12]. Defining the factors that determine FCL has been an important research focus for ecologists. Numerous widely cited hypotheses have been proposed. The productivity hypothesis predicts that energy availability limits FCL [12], due to limited efficiency in energy transfer up the food chain, such that the available energy diminishes at higher trophic levels. The ecosystem size hypothesis predicts that FCL increases with increasing ecosystem size, such as lake volume and island area [3]. The productive-space hypothesis [4] is a combination of the productivity and the ecosystem size hypotheses. This argues that total ecosystem production (per-unit-area productivity 6 ecosystem size) reflects the productive capacity of the ecosystem to support higher trophic levels. The dynamic stability hypothesis argues that long food chains tend to be dynamically unstable in the face of disturbance, such that food webs should be shorter in more highlydisturbed systems [56]. Ecosystem history may set important evolutionary constraints on ecological processes and properties of ecosystems [78]. Food webs are affected by evolutionary processes such as speciation, and effective evolutionary time ultimately affects the probability of species evolving to fill the available niche space [9]. In addition, a long evolutionary history may provide more opportunities for food web disturbances. Previous studies have shown that FCL varies greatly among systems [3,1013]. However, the role of ecosystem age and the historical signal on FCL has not been examined. How might FCL vary as a function of ecosystem age? First, older ecosystems might be expected to have longer food chains, as speciation and colonization should increase overall biodiversity, and thus the increase the potential to assemble longer food chains [11]. On the other hand, speciation could lead to an increase in herbivores and other low trophic position species. This might be expected since shorter food chains are expected to be more dynamically stable [14]. There are numerous examples of evolutionary adaptations towards lower trophic position, for example, the filter feeding apparatus of baleen whales, which evolved from the teeth of toothed whales [15]. If speciation simply increases the number of herbivorous species or increases the frequency of intraguild predation [16], older ecosystems could end up with shorter, not longer, food chains. Here we investigate patterns of FCL using a global lake dataset. Lakes in our data set vary in size by .5 orders of magnitude, and in age from a few to 107 years, depending on whether they are tectonic, glacial or impounded lakes. Ancient lakes (typically .1 million year) have a long evolutionary history and consequently higher species diversity, often with a large number of endemic species. In the present study, we used stable nitrogen isotope-based estimates of FCL from reservoirs, glacial, and ancient lakes. Our data se (...truncated)


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Hideyuki Doi, M. Jake Vander Zanden, Helmut Hillebrand. Shorter Food Chain Length in Ancient Lakes: Evidence from a Global Synthesis, PLOS ONE, 2012, Volume 7, Issue 6, DOI: 10.1371/journal.pone.0037856