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1. Habitat loss and simplification lower arthropod richness but not diversity

   https://doi.org/10.1002/ecs2.4914  

   Scott, Erin V; Almeida, Ryan; McKlin, Sam; Lippert, Alston Lee; Clary, Jake; Vargas, Carlos; Hidell, Will; Wadgymar, Susana; Smith, Kevin G (June 2024, Ecosphere)

   Habitat loss is rarely truly random and often occurs selectively with respect to the plant species comprising the habitat. Such selective habitat removal that decreases plant species diversity, that is, habitat simplification or homogenization, may have two negative effects on other species. First, the reduction in plant community size (number of individuals) represents habitat loss for species at higher trophic levels who use plants as habitat. Second, when plants are removed selectively, the resulting habitat simplification decreases the diversity of resources available to species at higher trophic levels. It follows that habitat loss combined with simplification will reduce biodiversity more than habitat loss without simplification. To test this, we experimentally implemented two types of habitat loss at the plant community level and compared biodiversity of resident arthropods between habitat loss types. In the first type of habitat loss, we reduced habitats by 50% nonselectively, maintaining original relative abundance and diversity of plant species and therefore habitat and resource diversity for arthropods. In the second type of habitat loss, we reduced habitats by 50% selectively, removing all but one common plant species, dramatically simplifying habitat and resources for arthropods. We replicated this experiment across three common plant species: Asclepias tuberosa, Solidago altissima, and Baptisia alba. While habitat loss with simplification reduced arthropod species richness compared with habitat loss without simplification, neither type of habitat loss affected diversity, measured as effective number of species (ENS), or species evenness as compared with controls. Instead, differences in ENS and evenness were explained by the identity of the common plant species. Our results indicate that the quality of remaining habitat, in our case plant species identity, may be more important for multi‐trophic diversity than habitat diversity per se. 

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2. Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon

   https://doi.org/10.1126/sciadv.aaz4880  

   Walters, D. M.; Cross, W.F.; Kennedy, T.A.; Baxter, C.V.; Hall, R.O.; Rosi, E.J. (May 2020, Science Advances)

   Mercury (Hg) biomagnification in aquatic food webs is a global concern; yet, the ways species traits and interactions mediate these fluxes remain poorly understood. Few pathways dominated Hg flux in the Colorado River despite large spatial differences in food web complexity, and fluxes were mediated by one functional trait, predation resistance. New Zealand mudsnails are predator resistant and a trophic dead end for Hg in food webs we studied. Fishes preferred blackflies, which accounted for 56 to 80% of Hg flux to fishes, even where blackflies were rare. Food web properties, i.e., match/mismatch between insect production and fish consumption, governed amounts of Hg retained in the river versus exported to land. An experimental flood redistributed Hg fluxes in the simplified tailwater food web, but not in complex downstream food webs. Recognizing that species traits, species interactions, and disturbance mediate contaminant exposure can improve risk management of linked aquatic-terrestrial ecosystems. 

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3. Variation in food web reliance on green and brown energy pathways across ecosystem gradients

   https://doi.org/10.1371/journal.pone.0336521  

   Sturges, James W; James, W Ryan; Rezek, Ryan J; Santos, Rolando O; White, Mack; Badlowski, Gina A; Trabelsi, Shakira; Massie, Jordan; Lesser, Justin S; Trexler, Joel C; et al (February 2026, PLOS One)

   Prasath, Barathan Balaji (Ed.)

   Aquatic food webs typically include highly coupled fast, ‘green’ energy pathways driven by algae or phytoplankton and slower, ‘brown’ energy channels driven by detritus and terrestrial plants. Quantifying how much energy biological communities obtain from each of these pathways is essential, particularly across multiple interconnected food webs over large areas, because energy dynamics are known to influence ecosystem structure and function. Despite their importance, few studies track variance in energy channel contributions to food webs across interconnected habitats during distinct hydrologic seasons. In this study, we used tri-isotope Bayesian mixing models to quantify seasonal contributions of energy pathways to consumers in nine aquatic food webs across two river drainages in the Florida coastal Everglades. Sites span an ecosystem gradient from freshwater marshes to estuarine riverine mangroves and marine seagrass habitats. We found that green energy channels were the dominant pathway for consumers in 12 of 18 seasonal food webs, with the remaining 6 being more reliant on detrital energy channels. There were contrasting spatiotemporal trends between river networks. Shark River Slough food webs showed a clearer pattern of greener marsh food webs upstream switching to browner food webs more heavily reliant on mangrove detritus downstream. In contrast, Taylor Slough food webs showed the opposite pattern of browner marsh food webs upstream switching to greener food webs downriver and in marine seagrass habitats. Seasonal switching of the dominant energy channel was less common than expected, with 2 of 9 food webs shifting from green to brown dominance between the dry and wet season. Seasonal shifts disrupted spatial gradients in energy channel use, but the seasonal dynamics quantified in this single year study require further contextualization. Our findings provide a short but dynamic view of energy pathways in aquatic communities across the Everglades, but continued research will allow us to better predict how species, food webs, and ecological networks may respond to environmental drivers under future global change. 

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4. Analysis of population size of Pterygoplichthys multiradiatus and its intake of microplastics in streams with different land uses

   https://doi.org/10.1088/2752-664X/ad0cfe  

   Lozada-Gómez, Edgar J; Pérez-Reyes, Omar (December 2023, Environmental Research: Ecology)

   Abstract Most freshwater habitats have been substantially affected by anthropogenic factors such as fish introductions, plastic pollution, and river regulation. Urban rivers are highly vulnerable to impacts associated with land use changes resulting from increasing urbanization, including altering habitat and establishing aquatic biological communities in these areas. In turn, the introduction of exotic species into sensitive and threatened ecosystems such as tropical urban streams and their rapid establishment, such asPterygoplichthys multiradiatus, was used as an ecological model to determine the relative population size of the species. Also, the species was used to evaluate the presence of microplastics (MPs) in the gastrointestinal tract (GIT) of fish in rivers with different land use history. Our results showed significant differences in pleco abundance between areas with high and low urban (LU) development in the watersheds. The study demonstrated that abiotic environmental factors directly influence the relative abundance of plecos at the range and watershed scales. In a total of 42 fish examined, only 85.7% showed MPs retained in the GIT, with fibers and fragments being the most common. A total of 22 pieces of microplastic were identified with Nile Red staining by slide analysis. A significant difference was found between the abundance of microplastic ingested per total fish length between streams with high and LU development reaches. Therefore, in relatively small amounts, microplastic ingestion appears to be common inP. multiradiatusspecies, regardless of the habitat in which they are found and the diet present. 

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5. Amazonian birds in more dynamic habitats have less population genetic structure and higher gene flow

   https://doi.org/10.1111/mec.16886  

   Johnson, Oscar; Ribas, Camila C; Aleixo, Alexandre; Naka, Luciano N; Harvey, Michael G; Brumfield, Robb T (May 2023, Molecular Ecology)

   Abstract Understanding the factors that govern variation in genetic structure across species is key to the study of speciation and population genetics. Genetic structure has been linked to several aspects of life history, such as foraging strategy, habitat association, migration distance, and dispersal ability, all of which might influence dispersal and gene flow. Comparative studies of population genetic data from species with differing life histories provide opportunities to tease apart the role of dispersal in shaping gene flow and population genetic structure. Here, we examine population genetic data from sets of bird species specialized on a series of Amazonian habitat types hypothesized to filter for species with dramatically different dispersal abilities: stable upland forest, dynamic floodplain forest, and highly dynamic riverine islands. Using genome‐wide markers, we show that habitat type has a significant effect on population genetic structure, with species in upland forest, floodplain forest, and riverine islands exhibiting progressively lower levels of structure. Although morphological traits used as proxies for individual‐level dispersal ability did not explain this pattern, population genetic measures of gene flow are elevated in species from more dynamic riverine habitats. Our results suggest that the habitat in which a species occurs drives the degree of population genetic structuring via its impact on long‐term fluctuations in levels of gene flow, with species in highly dynamic habitats having particularly elevated gene flow. These differences in genetic variation across taxa specialized in distinct habitats may lead to disparate responses to environmental change or habitat‐specific diversification dynamics over evolutionary time scales. 

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