Microbial communities feature an immense diversity of species and the extent of this diversity correlates with outcomes ranging from ecosystem stability to medical prognoses. Yet the mechanisms underlying microbial diversity are not well understood; simple resource-competition models do not allow for coexistence of a large number of species. However, it was recently shown that  metabolic trade-offs  can lead to unlimited diversity in a chemostat model . Do such trade-offs permit diversity under more realistic, intermittent conditions of nutrient supply? Here, we demonstrate that in serial dilution culture, metabolic trade-offs allow for high diversity. Unlike the chemostat case, diversity depends on the amount of nutrient supplied to the community. The form of this dependence varies with the precision of trade-offs and the presence of cross-feeding, immigration, or evolution . The large variation seen in this simple model suggests that real ecosystems may not obey a single universal relationship between nutrient supply and diversity. To connect to real microbial communities, we validate our model framework against previously published Escherichia coli batch and chemostat experiments and outline potential future experiments to test the model's multispecies predictions.
Microbial communities feature an immense diversity of species and the extent of this diversity correlates with outcomes ranging from ecosystem stability to medical prognoses. Yet the mechanisms underlying microbial diversity are not well understood; simple resource-competition models do not allow for coexistence of a large number of species. However, it was recently shown that assuming the existence of metabolic trade-offs - in allocating a limited enzyme production capacity - can lead to unlimited diversity , when nutrients are steadily supplied . Do such trade-offs permit diversity under more realistic, intermittent conditions of nutrient supply? Here, we demonstrate that in serial dilution culture, metabolic trade-offs allow for high diversity. Unlike the constant environment case, diversity depends on the concentration of nutrients supplied to the community. These changes in diversity are driven by an "early-bird" effect in which species specialized for nutrients that are initially more abundant gain a population advantage over other species. We explore the interplay of this effect with different environmental factors and diversity-supporting mechanisms, such as immigration and cross-feeding, and find a variety of ensuing relationships between nutrient supply and diversity . The large variation seen in this simple model suggests that real ecosystems may not obey a single universal relationship between nutrient supply and diversity. To connect to real microbial communities, we validate our growth model against previously published Escherichia coli batch and chemostat experiments and outline potential future experiments to test the model's multispecies predictions.
A
assuming the existence of
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- in allocating a limited enzyme production capacity -
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in a chemostat model
, when nutrients are steadily supplied
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chemostat
constant environment
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amount of nutrient
concentration of nutrients
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The form of this dependence varies with the precision of trade-offs and the presence of
These changes in diversity are driven by an "early-bird" effect in which species specialized for nutrients that are initially more abundant gain a population advantage over other species. We explore the interplay of this effect with different environmental factors and diversity-supporting mechanisms, such as immigration and
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immigration, or evolution
and find a variety of ensuing relationships between nutrient supply and diversity
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model framework
growth model