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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. 

A major conceptual gap in taste biology is the lack of a general framework for understanding the evolution of different taste modalities among animal species. We turn to two complementary nutritional frameworks, biological stoichiometry theory and nutritional geometry, to develop hypotheses for the evolution of different taste modalities in animals. We describe how the attractive tastes of Na‐, Ca‐, P‐, N‐, and C‐containing compounds are consistent with principles of both frameworks based on their shared focus on nutritional imbalances and consumer homeostasis. Specifically, we suggest that the evolution of multiple nutritive taste modalities can be predicted by identifying individual elements that are typically more concentrated in the tissues of animals than plants. Additionally, we discuss how consumer homeostasis can inform our understanding of why some taste compounds (i.e., Na, Ca, and P salts) can be either attractive or aversive depending on concentration. We also discuss how these complementary frameworks can help to explain the evolutionary history of different taste modalities and improve our understanding of the mechanisms that lead to loss of taste capabilities in some animal lineages. The ideas presented here will stimulate research that bridges the fields of evolutionary biology, sensory biology, and ecology.

 

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.