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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.

 

In many lentic ecosystems, hydroperiod, or the duration of inundation, controls animal community composition and biomass. Although hydroperiod-imposed differences in wetland animal communities could cause differences in animal-driven nutrient supply, hydroperiod has not been considered as a template for investigating patterns of animal-driven nutrient cycling. Here, we use nutrient excretion rates (NH4-N and SRP) and biomasses of pelagic and benthic invertebrates and salamanders and nutrient uptake rates in a simulation model to estimate animal-driven nutrient supply and pond-level demand along a hydroperiod gradient of 12 subalpine ponds in the U.S. Rocky Mountains that are vulnerable to climate change. We found that animal biomass increased with hydroperiod duration and biomass predicted animal-driven supply contributions among hydroperiod classifications (temporary-permanent). Consequently, community-wide supply was greatest in permanent ponds. Animal-driven N supply exceeded demand in permanent and semi-permanent ponds, whereas P supply equaled demand in both. Conversely, temporary ponds had large deficits in N and P supply due to lower community biomass and hydroperiod-induced constraints on dominant suppliers (oligochaetes and chironomids). The distribution of taxon-specific supply also differed among hydroperiods, with supply dominated by a few taxa in permanent ponds and supply more evenly distributed among temporary pond taxa. The absence or lower biomass of dominant suppliers in temporary ponds creates nutrient deficits and possible limitation of productivity. Thus, as climate warming causes hydroperiods to become increasingly temporary and indirectly prompts biomass declines and compositional shifts, animal-driven nutrient supply will decrease and strong nutrient limitation may arise due to loss of animal-driven supply. 

Small ponds account for a disproportionately high percentage of carbon dioxide emissions relative to their small surface area. It is therefore crucial to understand carbon flow in these ponds to refine the current global carbon budget, especially because climate change is affecting pond hydrology. High elevation ponds in the Elk Mountains of western Colorado are drying more frequently as the timing of snowmelt advances. We compared CO2 concentrations and fluxes among ponds of different hydroperiods over diel sampling periods during the course of the 2017 open-water period. CO2 concentrations were significantly negatively correlated with pond depth and averaged 77.6 ± 24.5 μmol L−1 (mean ± S.E.) across all ponds and sampling events. Ponds were up to twenty times supersaturated in CO2 with respect to the atmosphere. Flux was highly variable within individual ponds but correlated with time of sampling and was highest at night. Flux averaged 19.7 ± 18.8 mg CO2 m−2 h−1 across all ponds and sampling events. We also compared flux values obtained using modeled and empirical methods and found that widely-applied models of gas exchange rates using wind-based gas exchange (K) values yielded estimates of CO2 flux that were significantly higher than those obtained using the floating chamber approach, but estimates of CO2 flux using globally averaged convection-based K values were lower than those obtained using the floating chambers. Lastly, we integrated soil vs. water efflux measurements with long-term patterns in hydrology to predict how total season-long efflux might change under the more rapid drying regimes and longer seasons that are already occurring in these systems. Because soil CO2 efflux averaged 277.0 ± 49.0 mg CO2 m−2 h−1, temporary ponds emitted 674.1 ± 99.4 kg CO2 m−2 over the course of the 2017 season from ice-out to refreezing, which was over twice as much as permanent and semi-permanent ponds. Our results emphasize that contributions of CO2 from small ponds to the global carbon budget estimates will vary with pond hydroperiod and sampling methodology, which have been overlooked given that most previous estimates were collected from limited sampling periods and from pond waters alone. Furthermore, pond CO2 contributions are predicted to increase over time as pond areas transition from efflux from water to efflux from soil. 

While many species distributions are shifting poleward or up in elevation in response to a changing climate, others are shifting their habitats along localized gradients in environmental conditions as abiotic conditions become more stressful. Whether species are moving across regional or local environmental gradients in response to climate change, range‐shifting species become embedded in established communities of competitors and predators. The consequences of these shifts for both resident and shifting species are often unknown, as it can be difficult to isolate the effects of multiple species interactions.

Using a model system of insects in high‐elevation ponds in the Rocky Mountains of Colorado, we sought to disentangle the effects of predation and intraguild interactions on the survival and development of a semi‐permanent pond resident caddisflyLimnephilus externusand the habitat‐shifting caddisAsynarchus nigriculusthat is being forced into semi‐permanent ponds as temporary ponds dry too quickly to complete development.

We conducted a manipulative in‐situ pond cage experiment in whichL. externusandA. nigriculuscaddisfly larvae in single‐species treatments and together were exposed to the presence/absence of predatoryDytiscusdiving beetle larvae. This approach allowed us to isolate the effects of intraguild interactions and predation on the survival and development of both the resident and habitat‐shifting species.

We found that intraguild interactions had strong negative effects on the resident and habitat‐shifting species. Intraguild interactions reduced the survival of the residentL. externusand increased the variation in survival of the shiftingA. nigriculus. However,Dytiscuspredators reduced these negative effects, stabilizing the community by increasingL. externussurvival and reducing variation inA. nigriculussurvival. We also found that intraguild interactions reducedL. externusbiomass but resulted in increasedA. nigriculusdevelopment.A. nigriculusdevelopment was also increased by predation.

Our results show that strong intraguild interactions between resident and shifting species are likely to have negative consequences for both species. However, the presence of predators reduces these negative consequences of the habitat shift on both the resident and the shifting.

 

While inundated, small ponds (< 1000 m²area) account for disproportionately large contributions of CO₂efflux to the global carbon budget and also store carbon in anoxic sediments. However, pond hydrology is shifting toward increasingly dry conditions in alpine and temperate zones, which might lead to increased exposure of shallow pond sediments. We analyzed sediment CO₂efflux rates in dried sediments of multiple ponds of varying hydrology and sediment characteristics at montane and subalpine elevations near the Rocky Mountain Biological Laboratory in Colorado. Average CO₂efflux rates from exposed sediments, 331.5 ± 11.5 mmol m⁻²d⁻¹at the montane sites and 142.8 ± 45.1 mmol m⁻²d⁻¹at the subalpine sites, were 10 times higher than average CO₂efflux rates from pond water. Principal components analysis to reduce dimensionality of sediment characteristics revealed that random inter‐pond differences rather than exposure timing or hydroperiod drove variation among sediments. In linear mixed effects models of CO₂flux rates, significant predictors included sediment moisture and temperature, pH, total organic carbon, and organic matter content at all pond hydroperiod classifications and sites. However, the sediment characteristics explaining the most variance differed among sites and hydroperiods and included nitrate concentrations, pH, bulk density, and temperature. We conclude that pond sediments are heterogeneous both within and among ponds in close proximity, and drivers of relatively high CO₂efflux rates differ among pond hydroperiods and elevations. This work emphasizes that local differences can impact predictions of CO₂flux from lentic sediments which are becoming increasingly exposed.

 

Species’ geographic range shifts toward higher latitudes and elevations are among the most frequently reported consequences of climate change. However, the role of species interactions in setting range margins remains poorly understood. We used cage experiments in ponds to test competing hypotheses about the role of abiotic and biotic mechanisms for structuring range boundaries of an upslope range‐shifting caddisflyLimnephilus picturatus. We found that competition with a ubiquitous speciesLimnephilus externussignificantly decreasedL. picturatussurvival and emergence at subalpine elevations supporting the notion that species interactions play a critical role in determining upslope range limits. However, without competitors,L. picturatussurvival was greater at high‐elevation than low‐elevation sites. This was contrary to decreases in body mass (a proxy for fecundity) with elevation regardless of the presence of competitors. We ultimately show that species interactions can be important for setting upslope range margins. Yet, our results also highlight the complications in defining what may be abiotically stressful for this species and the importance of considering multiple demographic variables. Understanding how species ranges will respond in a changing climate will require quantifying species interactions and how they are influenced by the abiotic context in which they play out.