Phenotypic plasticity maintains biodiversity

Background/Question/Methods

Theoretical and empirical work suggests that a variety of mechanisms promote biodiversity. There is increasing evidence that trait variation between and within species, as well as trade-offs among traits, can influence species coexistence, e.g. by altering vulnerability to predation and predator selectivity. However, few studies have considered both interspecific (genetic) and intraspecific (genetic or phenotypic plasticity) trait variation simultaneously. We combined both types of trait variation to identify their joint influence on the maintenance of biodiversity, i.e. species richness, evenness of community composition and functional diversity. We used a multispecies predator-prey model with functionally different predator and prey species. Prey species differed in their maximum growth rate and vulnerability to predation and predator species in their half saturation constant and selectivity for prey items. Additionally, individual prey and predator species exhibited a variable amount of phenotypic plasticity which enabled them to change their trait values in response to altered predation pressure and resource levels. We altered the initial species richness, the strength of phenotypic plasticity and the speed of phenotypic changes to identify their interacting effects on biodiversity and the relative importance of intra vs. interspecific trait variation.

Results/Conclusions

Biodiversity was strongly influenced by the degree and the speed of phenotypic plasticity as well as initial species richness. Intermediate phenotypic variation allowed species to make clear adjustments to their trait values in order to reduce predation pressure and/or enhance growth rates and therefore maintain higher average fitness over time. This prevented many species from prompt extinction and promoted permanent or greatly prolonged coexistence of numerous functional different predator and prey species at high biomass levels. Despite some functional redundancy, functional diversity and final species richness were high as often found in natural systems. High phenotypic variation generated large overlap in the trait values attainable by all species, increasing competition and leading to slow competitive exclusion of species. Although final species richness increased with initial species richness biodiversity maintained low because of strongly reduced functional diversity. Low phenotypic variation led to strong fitness differences among species and yielded fast exclusion independent of initial species richness which, in turn, strongly reduced biodiversity. Increased speed of phenotypic plasticity stabilized predator-prey dynamics and enhanced biodiversity whereas too slow phenotypic adjustment prevented species coexistence. Our results suggest that phenotypic plasticity may strongly promote the maintenance of biodiversity.