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1. Mayfly emergence production and body length response to hydrology in a tropical lowland stream

   https://doi.org/10.7717/peerj.9883  

   Gutiérrez-Fonseca, Pablo E.; Ramírez, Alonso (January 2020, PeerJ)

   null (Ed.)

   Background Hydrological impacts on aquatic biota have been assessed in numerous empirical studies. Aquatic insects are severely affected by population declines and consequent diversity loss. However, many uncertainties remain regarding the effects of hydrology on insect production and the consequences of energy transfer to the terrestrial ecosystem. Likewise, sublethal effects on insect morphology remain poorly quantified in highly variable environments. Here, we characterized monthly fluctuation in benthic and emerged biomass of Ephemeroptera in a tropical lowland stream. We quantified the proportion of mayfly production that emerges into the riparian forest. We also examined the potential morphological changes in Farrodes caribbianus (the most abundant mayfly in our samples) due to environmental stress. Methods We collected mayflies (nymphs and adults) in a first-order stream in Costa Rica. We compared benthic and adult biomass from two years’ worth of samples, collected with a core sampler (0.006 m 2 ) and a 2 m 2 -emergence trap. The relationship between emergence and annual secondary production (E/P) was used to estimate the Ephemeroptera production that emerged as adults. A model selection approach was used to determine the relationship between environmental variables that were collected monthly and the emergent biomass. To determine potential departures from perfect bilateral symmetry, we evaluated the symmetry of two morphological traits (forceps and forewing) of F. caribbianus adults. We used Spearman’s rank correlation coefficients (ρ) to examine potential changes in adult body length as a possible response to environmental stress. Results Benthic biomass was variable, with peaks throughout the study period. However, peaks in benthic biomass did not lead to increases in mayfly emergence, which remained stable over time. Relatively constant mayfly emergence suggests that they were aseasonal in tropical lowland streams. Our E/P estimate indicated that approximately 39% and 20% (for 2002 and 2003, respectively) of the nymph production emerged as adults. Our estimated proportion of mayfly production transferred to terrestrial ecosystems was high relative to reports from temperate regions. We observed a strong negative response of F . caribbianus body length to increased hydrology (Spearman: ρ = −0.51, p < 0.001), while slight departures from perfect symmetry were observed in all traits. Conclusion Our two years study demonstrates that there was large temporal variability in mayfly biomass that was unrelated to hydrological fluctuations, but potentially related to trophic interactions (e.g., fish predation). Body length was a good indicator of environmental stress, which could have severe associated costs for mayfly fitness in ecosystems with high temporal variation. Our results highlight the complex ecological and evolutionary dynamics of tropical aquatic insects, and the intricate connection between aquatic and terrestrial ecosystems. 

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2. A global assessment of environmental and climate influences on wetland macroinvertebrate community structure and function

   https://doi.org/10.1111/gcb.17173  

   Epele, Luis B.; Williams‐Subiza, Emilio A.; Bird, Matthew S.; Boissezon, Aurelie; Boix, Dani; Demierre, Eliane; Fair, Conor G.; García, Patricia E.; Gascón, Stephanie; Grech, Marta G.; et al (February 2024, Global Change Biology)

   Abstract Estimating organisms' responses to environmental variables and taxon associations across broad spatial scales is vital for predicting their responses to climate change. Macroinvertebrates play a major role in wetland processes, but studies simultaneously exploring both community structure and community trait responses to environmental gradients are still lacking. We compiled a global dataset (six continents) from 756 depressional wetlands, including the occurrence of 96 macroinvertebrate families, their phylogenetic tree, and 19 biological traits. Using Bayesian hierarchical joint species distribution models (JSDMs), we estimated macroinvertebrate associations and compared the influences of local and climatic predictors on both individual macroinvertebrate families and their traits. While macroinvertebrate families were mainly related to broad‐scale factors (maximum temperature and precipitation seasonality), macroinvertebrate traits were strongly related to local wetland hydroperiod. Interestingly, macroinvertebrate families and traits both showed positive and negative associations to the same environmental variables. As expected, many macroinvertebrate family occurrences were positively associated with temperature, but a few showed the opposite pattern and were found in cooler or montane regions. We also found that wetland macroinvertebrate communities would likely be affected by changing climates through alterations in traits related to precipitation seasonality, temperature seasonality, and wetland area. Temperature increases may negatively affect collector and shredder functional groups. A decrease in precipitation could lead to reductions in wetland area benefiting drought‐tolerant macroinvertebrates, but it may negatively affect macroinvertebrates lacking those adaptations. Wetland processes may be compromised through broad‐scale environmental changes altering macroinvertebrate family distributions and local hydroperiod shifts altering organism traits. Our complementary family‐based and trait‐based approaches elucidate the complex effects that climate change may produce on wetland ecosystems. 

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3. Thermal traits of freshwater macroinvertebrates vary with feeding group and phylogeny

   https://doi.org/10.1111/fwb.13992  

   Tomczyk, Nathan J.; Rosemond, Amy D.; Rogers, Phoenix A.; Cummins, Carolyn S. (November 2022, Freshwater Biology)

   Abstract Functional traits of organisms, especially feeding traits, influence how organisms mediate ecosystem processes. As climate change, landscape modification and industrial waste heat release continue to increase water temperatures, shifts in the composition of feeding traits within aquatic macroinvertebrate communities may alter ecosystem processes. However, it is unclear whether thermal traits of macroinvertebrates vary systematically across functional feeding groups (FFGs; i.e., categories based on feeding ecology such as herbivores, shredders, predators, etc.) or phylogeny. We used previously published datasets on hundreds of macroinvertebrate taxa to evaluate how thermal traits differed across FFGs. We also examined the strength of phylogenetic signal in both FFG and thermal traits, using a new phylogeny of insect taxa. Then, we tested whether phylogenetic patterns offered a plausible explanation for differences in thermal traits among FFGs by comparing phylogenetic and non‐phylogenetic regressions. Shredders tended to have lower temperature preferences, optima and maxima (three of five of the thermal traits evaluated) than other FFGs. Patterns for other FFGs differed by thermal trait, but predators, collector‐gatherers and filterers had some of the highest thermal trait values. FFG explained 40% of the variation in critical thermal maximum, but <12% of the variation in the four other thermal traits. Phylogeny explained 26%–88% of the variation in thermal and feeding traits. For the subset of taxa and trait data that were available, phylogeny explained more than double the variation in thermal traits relative to FFG, but comparison of phylogenetic and non‐phylogenetic regressions highlighted that FFG explained variation in thermal traits that was independent of phylogeny. Our results highlight phylogeny and FFG as predictors of thermal traits in aquatic macroinvertebrates. Our results suggest that warmer water temperatures could favour predators, filterers and collector‐gatherers over shredders. Furthermore, our results confirm that certain orders of macroinvertebrates, such as Diptera, may be better suited to warmer temperatures than other orders, such as Plecoptera. 

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4. Plant sex influences on riparian communities and ecosystems

   https://doi.org/10.1002/ece3.10308  

   Scheuerell, River P.; LeRoy, Carri J. (July 2023, Ecology and Evolution)

   Abstract Over the past several decades, we have increased our understanding of the influences of plant genetics on associated communities and ecosystem functions. These influences have been shown at both broad spatial scales and across many plant families, creating an active subdiscipline of ecology research focused on genes‐to‐ecosystems connections. One complex aspect of plant genetics is the distinction between males and females in dioecious plants. The genetic determinants of plant sex are poorly understood for most plants, but the influences of plant sex on morphological, physiological, and chemical plant traits are well‐studied. We argue that these plant traits, controlled by plant sex, may have wide‐reaching influences on both terrestrial and aquatic communities and ecosystem processes, particularly for riparian plants. Here we systematically review the influences of plant sex on plant traits, influences of plant traits on terrestrial community members, and how interactions between plant traits and terrestrial community members can influence terrestrial ecosystem functions in riparian forests. We then extend these influences into adjacent aquatic ecosystem functions and aquatic communities to explore how plant sex might influence linked terrestrial‐aquatic systems as well as the physical structure of riparian systems. This review highlights data gaps in empirical studies exploring the direct influences of plant sex on communities and ecosystems but draws inference from community and ecosystem genetics. Overall, this review highlights how variation by plant sex has implications for climate change adaptations in riparian habitats, the evolution and range shifts of riparian species and the methods used for conserving and restoring riparian systems. 

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5. Soil microbes weaken the positive effect of an aquatic–terrestrial subsidy on plant performance

   https://doi.org/10.1093/jpe/rtaa079  

   Garcia, Alejandra B; Locke, Hannah; Crawford, Kerri M (February 2021, Journal of Plant Ecology)

   Hu, Shuijin (Ed.)

   Abstract Aims Linkages formed through aquatic–terrestrial subsidies can play an important role in structuring communities and mediating ecosystem functions. Aquatic–terrestrial subsidies may be especially important in nutrient-poor ecosystems, such as the freshwater sand dunes surrounding Lake Michigan. Adult midges emerge from Lake Michigan in the spring, swarm to mate and die. Their carcasses form mounds at the base of plants, where they may increase plant productivity through their nutrient inputs. However, the effect of aquatic–terrestrial subsidies on plant productivity could depend on other biotic interactions. In particular, soil microbes might play a key role in facilitating the conversion of nutrients to plant-available forms or competing for the nutrients with plants. Methods In a greenhouse experiment, we tested how carcasses from lake emergent midges (Chironomidae) and soil microbes independently and interactively influenced the performance of a common dune grass, Calamovilfa longifolia. To determine whether midges influenced abiotic soil properties, we measured how midge additions influenced soil nutrients and soil moisture. Important Findings Midges greatly increased plant biomass, while soil microbes influenced the magnitude of this effect. In the absence of soil microbes plant biomass was seven times greater with midges than without midges. However, in the presence of soil microbes, plant biomass was only three times greater. The effect of midges might be driven by their nutrient inputs into the soil, as midges contained 100 times more N, 10 times more P and 150 times more K than dune soils did. Our results suggest that soil microbes may be competing with plants for these nutrients. In sum, we found that midges can be an important aquatic–terrestrial subsidy that produces strong, positive effects on plant productivity along the shorelines of Lake Michigan, but that the impact of aquatic–terrestrial subsidies must be considered within the context of the complex interactions that take place within ecological communities. 

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