Abstract
It is well-established that when equilibrium is attained for two species competing for the same limiting resource in a stable, uniform environment, one species will eliminate the other due to competitive exclusion. While competitive exclusion is observed in laboratory experiments and ecological models, the phenomenon seems less common in nature, where static equilibrium is prevented by the fluctuating physical environment and by other factors that constantly change species abundances and the nature of competitive interactions. Trait-based models of phytoplankton communities appear to be useful tools for describing the evolution of large assemblages of species with aggregate group properties such as total biomass, mean trait, and trait variance, the latter representing the functional diversity of the community. Such an approach, however, is limited by the tendency of the trait variance to unrealistically decline to zero over time. This tendency to lose diversity, and therefore adaptive capacity, is typically solved by fixing the variance or by considering exogenous processes such as immigration. Exogenous processes, however, cannot explain the maintenance of adaptive capacity often observed in the closed environment of chemostat experiments. Here we present a new method to sustain diversity in adaptive trait-based models of phytoplankton communities based on a mechanism of trait diffusion through subsequent generations. Our modeling approach can therefore account for endogenous processes such as rapid evolution or transgenerational trait plasticity.
Highlights
Phytoplankton are a group of mainly single-celled primary producers widespread in aquatic ecosystems
We develop the method in the idealized context of a simple nutrientphytoplankton-zooplankton (NPZ) chemostat system and apply it to examine the consequences of different levels of trait diffusivity for the ecological dynamics and adaptive capacity of a phytoplankton community
We have presented here a modeling approach that addresses the problem of maintaining phytoplankton functional diversity based on the mechanism of trait diffusion through subsequent generations
Summary
Phytoplankton are a group of mainly single-celled primary producers widespread in aquatic ecosystems. Given that phytoplankton community composition and diversity play important roles in the functioning of aquatic ecosystems (Ptacnik et al, 2008; Eggers et al, 2014) and global climate (Falkowski et al, 1998), it is important to understand the factors that drive assembly and dynamics of such communities. Recent modeling approaches have begun to resolve more complex community structures by explicitly incorporating different functional groups of phytoplankton, significant challenges remain (Anderson, 2005), in particular concerning the formulation of valid models for describing plankton diversity and the adaptive responses of phytoplankton communities to a changing environment. It is neither feasible nor effective to account explicitly for all these different types in plankton models, because this would require far too many equations and free parameters
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