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)