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1. Long-Term Cellulose Enrichment Selects for Highly Cellulolytic Consortia and Competition for Public Goods

   https://doi.org/10.1128/msystems.01519-21  

   Lewin, Gina R.; Davis, Nicole M.; McDonald, Bradon R.; Book, Adam J.; Chevrette, Marc G.; Suh, Steven; Boll, Ardina; Currie, Cameron R. (April 2022, mSystems)

   Mackelprang, Rachel (Ed.)

   ABSTRACT The complexity of microbial communities hinders our understanding of how microbial diversity and microbe-microbe interactions impact community functions. Here, using six independent communities originating from the refuse dumps of leaf-cutter ants and enriched using the plant polymer cellulose as the sole source of carbon, we examine how changes in bacterial diversity and interactions impact plant biomass decomposition. Over up to 60 serial transfers (∼8 months) using Whatman cellulose filter paper, cellulolytic ability increased and then stabilized in four enrichment lines and was variable in two lines. Bacterial community characterization using 16S rRNA gene amplicon sequencing showed community succession differed between the highly cellulolytic enrichment lines and those that had slower and more variable cellulose degradation rates. Metagenomic and metatranscriptomic analyses revealed that Cellvibrio and/or Cellulomonas dominated each enrichment line and produced the majority of cellulase enzymes, while diverse taxa were retained within these communities over the duration of transfers. Interestingly, the less cellulolytic communities had a higher diversity of organisms competing for the cellulose breakdown product cellobiose, suggesting that cheating slowed cellulose degradation. In addition, we found competitive exclusion as an important factor shaping all of the communities, with a negative correlation of Cellvibrio and Cellulomonas abundance within individual enrichment lines and the expression of genes associated with the production of secondary metabolites, toxins, and other antagonistic compounds. Our results provide insights into how microbial diversity and competition affect the stability and function of cellulose-degrading communities. IMPORTANCE Microbial communities are a key driver of the carbon cycle through the breakdown of complex polysaccharides in diverse environments including soil, marine systems, and the mammalian gut. However, due to the complexity of these communities, the species-species interactions that impact community structure and ultimately shape the rate of decomposition are difficult to define. Here, we performed serial enrichment on cellulose using communities inoculated from leaf-cutter ant refuse dumps, a cellulose-rich environment. By concurrently tracking cellulolytic ability and community composition and through metagenomic and metatranscriptomic sequencing, we analyzed the ecological dynamics of the enrichment lines. Our data suggest that antagonism is prevalent in these communities and that competition for soluble sugars may slow degradation and lead to community instability. Together, these results help reveal the relationships between competition and polysaccharide decomposition, with implications in diverse areas ranging from microbial community ecology to cellulosic biofuels production. 

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2. The Ecological Importance of Allelopathy

   https://doi.org/10.1146/annurev-ecolsys-051120- 030619  

   José L. Hierro; Ragan M. Callaway (August 2021, Annual review)

   Allelopathy (i.e., chemical interaction among species) was originally conceived as inclusive of positive and negative effects of plants on other plants, and we adopt this view. Most studies of allelopathy have been phenomenological, but we focus on studies that have explored the ecological significance of this interaction. The literature suggests that studies of allelopathy have been particularly important for three foci in ecology: species distribution, conditionality of interactions, and maintenance of species diversity. There is evidence that allelopathy influences local distributions of plant species around the world. Allelopathic conditionality appears to arise through coevolution, and this is a mechanism for plant invasions. Finally, allelopathy promotes species coexistence via intransitive competition, modifications of direct interactions, and (co)evolution. Recent advances additionally suggest that coexistence might be favored through biochemical recognition. The preponderance of phenomenological studies notwithstanding, allelopathy has broad ecological consequences. 

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3. Interspecific competition affects resource use by three cryptic freshwater species of Hyalella Smith, 1874 (Amphipoda: Hyalellidae)

   https://doi.org/10.1093/jcbiol/ruab019  

   Mercer, Arissa A; Cothran, Rickey D (June 2021, Journal of Crustacean Biology)

   null (Ed.)

   Abstract Species that use the same resources present a paradox for understanding their coexistence. This is especially true for cryptic species because they are phenotypically similar. We examined how competition affects food-resource use in three cryptic species of Hyalella Smith, 1874, a freshwater-amphipod genus. We hypothesized that competitively inferior species would use high-quality algae patches when alone and competitively superior species would displace inferior species to low-quality patches. We compared use of foraging patches varying in algal content (i.e., quality) when species were alone or with another species. Our results showed that the competitively inferior species spent more time on the low-quality patch in the presence of the competitively superior species, but the behavior of the competitively superior species was independent of heterospecifics. This study provides insight into the role of interspecific competition in shaping resource use and patterns of coexistence in nature. 

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4. Extensions and limitations of MacArthur (1958): A review of ecological and evolutionary approaches to competition and diet in the New World wood warblers (Parulidae)

   https://doi.org/10.1093/ornithology/ukac010  

   Sherry, Thomas W; Kent, Cody M (March 2022, Ornithology)

   Abstract The extent to which interspecific competition structures species interactions and coexistence within communities, and the relevant mechanisms, are still debated. We focus on New World wood warblers (Parulidae), beginning with Robert MacArthur’s iconic 1958 paper in which he shows how subtle foraging behaviors, purportedly linked to dietary differences, within spruce trees contribute to the coexistence of 5 spruce-woods warbler species. MacArthur coined the phrase “resource partitioning”, and profoundly impacted the field of Ecology for subsequent decades in diverse ways. To understand what MacArthur got right and what he missed, we reviewed both ecological and evolutionary approaches to questions of the origin and coexistence of competing species in the context of diet. We argue that an important, underappreciated, mechanism of competition among coexisting migratory warbler species, particularly in winter, is diffuse exploitation competition, based in part on our own studies of warbler diets in relation to foraging behavior, substrate use, bird morphology, and other traits. Our review and synthesis of interspecific competition and coexistence in warblers have important consequences, including our questioning of the importance and effectiveness of resource partitioning in birds. We also suggest a novel hypothesis for the success of warblers today in the Caribbean and other habitats, beginning with their relatively recent adaptive radiation and the ecological opportunity on Caribbean islands. 

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5. Germination phenology alters species coexistence outcomes

   https://doi.org/10.1111/1365-2745.14382  

   Diez, Jeff; Schlauch, Jen; DuCharme, Elysa; Collings, Jeremy; Erskine, Sarah (August 2024, Journal of Ecology)

   Species‐specific phenological responses to changing climate are reshuffling the timing of species interactions, however we do not fully understand the consequences of these changes for species' population dynamics and community composition. In this study, we experimentally manipulated the timing of germination for five annual plant species from southern California and used pairwise competition experiments and coexistence theory to quantify how phenological shifts may impact species interactions and coexistence. We found that phenological shifts may help promote coexistence when they confer an advantage for competitively inferior species, but in other cases promote dominance by competitively superior species. Earlier germination generally increased species' performance relative to competitors, but the relative changes in intra‐and inter‐specific interactions caused more complex effects on niche and fitness differences. Phenological differences tended to reduce stabilising niche differences for many species pairs and reduced overall coexistence probabilities. Synthesis. While phenological differences among species have typically been considered a form of niche partitioning, it seems increasingly likely that phenological offsets could destabilise species coexistence. The net effects of changing phenology on species coexistence will depend on the complex combinations of effects on intra‐ and inter‐specific interactions, which remain challenging to predict. 

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