Elena

Litchman

Species-abundance distributions (SADs) describe the spectrum of commonness and rarity in a community. Beyond the universal observation that most species are rare and only a few common, more-precise description of SAD shape is controversial. Furthermore, the mechanisms behind SADs and how they vary along environmental gradients remain unresolved. We lack a general, non-neutral theory of SADs. Here, we develop a trait-based framework, focusing on a local community coupled to the region by dispersal. The balance of immigration and exclusion determines abundances, which vary over orders-of-magnitude. The local trait-abundance distribution (TAD) reflects a transformation of the regional TAD. The left-tail of the SAD depends on scaling exponents of the exclusion function and the regional species pool. More-complex local dynamics can lead to multimodal TADs and SADs. Connecting SADs with trait-based ecological theory provides a way to generate more-testable hypotheses on the controls over commonness and rarity in communities.

Few microbiome-based solutions for agricultural productivity, food processing and human nutrition have been successfully commercialized. A systems-based approach that considers the ecology of microbial communities may help finetune extant tools to increase their reliability while promoting innovation and greater adoption.

A complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold-adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6 degrees C and chlorophyll > 9 mu g L-1. Water was incubated in triplicate at -0.5 degrees C, 2.6 degrees C, and 6 degrees C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature-nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature-nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

Mathematica code for "A general framework for species-abundance distributions: linking traits and dispersal to explain commonness and rarity", Ecology Letters. Requires: Wolfram Mathematica (tested on v13.1) EcoEvo package (tested on v1.6.4) This research was supported by the Simons Foundation grant 343149, NSF grant DEB 17-54250 and NASA grant 80NSSC18K1084. Copyright: Creative Commons Attribution 4.0 International Open Access

Mathematica code for "A general framework for species-abundance distributions: linking traits and dispersal to explain commonness and rarity", Ecology Letters. Requires: Wolfram Mathematica (tested on v13.1) EcoEvo package (tested on v1.6.4) This research was supported by the Simons Foundation grant 343149, NSF grant DEB 17-54250 and NASA grant 80NSSC18K1084. Copyright: Creative Commons Attribution 4.0 International Open Access