Species loss and nitrogen pollution alter litter decomposition dynamics in coastal salt marshes.

Litter decomposition is a central ecosystem function because dead plant biomass plays a critical role in carbon storage, the nitrogen (N) cycle, and as food/habitat for animals and microorganisms. In the face of global change, interactions between organisms that participate in litter decomposition are likely to change due to species loss and N pollution. To understand how these global change factors may interact to alter litter decomposition, we manipulated the detritivore community and N concentrations in a coastal salt marsh for 2 years. We chose to manipulate densities of a dominant, detritivorous snail (Melampus bidentatus) because its population size is expected to decline due to climate change, yet its impact on litter decomposition has not been tested in the field. We measured litter decomposition rates, detritivore densities, and the N concentrations of sediment and litter. We found that endogenous N enrichment (N added live plants before decomposition), exogenous N enrichment (N added to decomposing plants) and higher densities of Melampus increased litter decomposition rates. Linear mixed models further revealed that snails, other detritivores, and soil NH4+ were the best predictors of litter mass loss in the middle stages of decomposition. Notably, exogenous N added to litter already enriched with N further increased mass loss but did not increase litter %N. Our study reveals how global change in the form species loss and N pollution can have palpable impacts on carbon cycling and ecosystem function.

Ecosystem services consideration in the remediation process for contaminated sites.

In 2009, the U.S. Environmental Protection Agency's Science Advisory Board recommended activities to advance consideration of ecosystem services (ES) to enhance existing remediation and redevelopment processes in the U.S. This article examines advancements in the decade since, focusing on providing those involved in cleanup of contaminated sites a basic understanding of ES concepts and guidelines for considering ES at cleanup sites using a new, four-step transferable framework. Descriptions, including activities for site teams and case study applications of ES tools, are presented for each step: (1) identify site-specific ES; (2) quantify relevant ES; (3) examine how cleanup activities affect ES; and (4) identify, select, and implement solutions (e.g., Best Management Practices). The goal of this article is to provide site cleanup stakeholders, including project managers, contractors, and site responsible parties, with a stronger foundation and shared understanding to consider ES during the cleanup process for their given site. Anticipated outcomes include identifying ES benefits to inform management and tradeoff analyses, a reduction in unintended impacts on ES during site operations, and attention to developing a robust suite of ES relevant for site reuse.

Global change in marine coastal habitats impacts insect populations and communities.

Salt marsh and mangrove coastal ecosystems provide critical ecosystem services, but are being lost at an alarming rate. Insect communities in these ecosystems are threatened by human impacts, including sea level rise, habitat loss, external inputs including nutrients, metals, and hydrocarbons, as well as weather events, such as hurricanes. While some disturbances are felt throughout the food web (e.g. hurricanes), others are mediated by impacts on the dominant plants (e.g. nutrient subsidies). The impacts of these disturbances on insects/spiders and their rate of recovery is dependent on trophic level, life history, and diet breadth. While we understand impacts of single disturbances relatively well, we have very little understanding of how multiple disturbances interact to affect insect communities.

Digest: Be honest with me: Do parasites play a role in divergence of sexual signals?

Do local parasite assemblages correlate with the divergence of sexual signals across subspecies? Hund et al. found that locally relevant sexual signals were associated with the most costly local parasites, indicating sexual signals communicate information about local parasite costs and suggesting a potential role in speciation.

Putting the genes into community genetics.

As part of the long-term fusion of evolutionary biology and ecology (Ford, 1964), the field of community genetics has made tremendous progress in describing the impacts of plant genetic variation on community and ecosystem processes. In the "genes-to-ecosystems" framework (Whitham et al., 2003), genetically based traits of plant species have ecological consequences, but previous studies have not identified specific plant genes responsible for community phenotypes. The study by Barker et al. (2019) in this issue of Molecular Ecology uses an impressive common garden experiment of trembling aspen (Figure 1) to test for the genetic basis of tree traits that shape the insect community composition. Using a Genome-Wide Association Study (GWAS), they found that genomic regions associated with phytochemical traits best explain variation in herbivore community composition, and identified specific genes associated with different types of leaf-modifying herbivores and ants. This is one of the first studies to identify candidate genes underlying the heritable plant traits that explain patterns of insect biodiversity.