More Like this

1. Oxygen supply capacity in animals evolves to meet maximum demand at the current oxygen partial pressure regardless of size or temperature

   https://doi.org/10.1101/701417  

   Seibel, B. ( January 2020 , Journal of experimental biology)

   null (Ed.)

   The capacity to extract oxygen from the environment and transport it to respiring tissues in support of metabolic demand reportedly has implications for species’ thermal tolerance, body size, diversity and biogeography. Here, we derived a quantifiable linkage between maximum and basal metabolic rate and their oxygen, temperature and size dependencies. We show that, regardless of size or temperature, the physiological capacity for oxygen supply precisely matches the maximum evolved demand at the highest persistently available oxygen pressure and this is the critical PO2 for the maximum metabolic rate, Pcrit-max. For most terrestrial and shallow-living marine species, Pcrit-max is the current atmospheric pressure, 21 kPa. Any reduction in oxygen partial pressure from current values will result in a calculable decrement in maximum metabolic performance. However, oxygen supply capacity has evolved to match demand across temperatures and body sizes and so does not constrain thermal tolerance or cause the well-known reduction in mass-specific metabolic rate with increasing body mass. The critical oxygen pressure for resting metabolic rate, typically viewed as an indicator of hypoxia tolerance, is, instead, simply a rate-specific reflection of the oxygen supply capacity. A compensatory reduction in maintenance metabolic costs in warm-adapted species constrains factorial aerobic scope and the critical PO2 to a similar range, between ∼2 and 6, across each species’ natural temperature range. The simple new relationship described here redefines many important physiological concepts and alters their ecological interpretation. 

   more » « less
2. Hunters versus hunted: New perspectives on the energetic costs of survival at the top of the food chain

   https://doi.org/10.1111/1365-2435.13649  

   Williams, Terrie M. ; Peter‐Heide Jørgensen, Mads ; Pagano, Anthony M. ; Bryce, Caleb M. ; Crocker, ed., Daniel ( October 2020 , Functional Ecology)

   Global biotic and abiotic threats, particularly from pervasive human activities, are progressively pushing large, apex carnivorous mammals into the functional role of mesopredator. Hunters are now becoming the hunted. Despite marked impacts on these animals and the ecosystems in which they live, little is known about the physiological repercussions of this role downgrading from ultimate to penultimate predator.

   Here we examine how such ecological role reversals alter the physiological processes associated with energy expenditure, and ultimately the cost of survival during peak performance.

   Taxonomic group, preferred habitat and domestication affected the capacity of the oxygen pathway to support high levels of aerobic performance by carnivorous mammals. Fear responses associated with anthropogenic threats also impacted aerobic performance.

   Allometric trends for three energetic metrics [maximum oxygen consumption, field metabolic rates (FMRs) and the cost per stride or stroke], showed distinct trends in aerobic capacity for different evolutionary lineages of mammalian predators. Cursorial canids that chase down prey demonstrated the highest relative maximum oxygen consumption rates (10–25 times resting levels) and FMRs, while ambush predators (i.e. felids) and diving marine mammals had aerobic capacities that were similar to or lower than sedentary domestic mammals of comparable size.

   The maximum energetic cost of performance for apex predators depended on whether the animals were hunters or the hunted. Escape responses were exceptionally costly for marine (narwhalMonodon monoceros) and terrestrial (mountain lionPuma concolor) locomotor specialists, as well as semi‐aquatic (polar bearUrsus maritimus) species; all showed a nearly two‐fold increase in peak energy expenditure when avoiding threats.

   As the duration and frequency of threats to wild species continue to grow, cumulative energetic costs are becoming more apparent. In view of this, attention to the energy demands of apex predators will provide vital predictive power to anticipate mismatches between a species' functional design and human‐induced pressures, and allow for the development of conservation strategies based on how species are built to survive.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

   more » « less
3. Biogeography and depth partitioning in deep‐sea gastropods at the Pacific Costa Rica Margin

   https://doi.org/10.1111/jbi.14722  

   Betters, Melissa ; Stabbins, April ; Keller, Abigail ; Cordes, Erik ( September 2023 , Journal of Biogeography)

   Understanding the global distribution of biodiversity and the factors that influence it are among the central goals of biogeography. How abiotic and biotic factors limit species' ranges has been investigated across a variety of environments and taxonomic groups. However, such investigations across oceanic depths remain underrepresented, particularly for chemosynthetic environments such as hydrocarbon seeps. The depth differentiation (DD) hypothesis suggests that steep environmental gradients in the upper depths of the ocean may limit species' ranges over relatively short vertical distances. The present study aims to investigate the evidence for the DD hypothesis at hydrocarbon seep sites along the Pacific Costa Rica Margin (CRM) by investigating the biogeographic distributions of gastropods sampled there and the factors that influence them.

   Costa Rica.

   Mollusca, Gastropoda, Provannidae, Genus:Provanna(Dall, 1918).

   1813Provannasnails were collected across 1300 metres (m) of depth from Costa Rican hydrocarbon seeps. To test the DD hypothesis, species partitioning across the depth range was investigated. In addition to gradients in oceanographic conditions, such as temperature, oxygen, and salinity, other factors potentially responsible for filtering species were also considered as alternative hypotheses, including the availability of biogenic substrate, the availability of and reliance on chemosynthetic fluids, and specific preferences for certain environmental conditions.

   Three species ofProvannawere identified from the CRM and exhibited partitioning across depth. For the two dominant species (P. laevisandP. goniata), the data suggest that depth‐associated oceanographic conditions are more likely than any other factor investigated to explain their observed partitioning across depth, supporting the DD hypothesis. This study also presents novel evidence that such partitioning may be unilaterally determined, wherein species with narrower depth ranges may limit the local depth ranges of others. This study represents an extension of biogeographic range limit literature into chemosynthetic habitats and across oceanic depths.

    

   more » « less
4. A changing menu in a changing climate: Using experimental and long‐term data to predict invertebrate prey biomass and availability in lakes of arctic Alaska

   https://doi.org/10.1111/fwb.13162  

   Klobucar, Stephen L. ; Gaeta, Jereme W. ; Budy, Phaedra ( August 2018 , Freshwater Biology)

   Changes in seasonality associated with climate warming (e.g. temperature, growing season duration) are likely to alter invertebrate prey biomass and availability in aquatic ecosystems through direct and indirect influences on physiology and phenology, particularly in arctic lakes. However, despite warmer thermal regimes, photoperiod will remain unchanged such that potential shifts resulting from longer and warmer growing seasons could be limited by availability of sunlight, especially at lower trophic levels. Thus, a better understanding of warming effects on invertebrate prey throughout the growing season (e.g. early, peak, late) is important to understand arctic lake food‐web dynamics in a changing climate.

   Here, we use a multifaceted approach to evaluate prey availability to predators in lakes of arctic Alaska. In a laboratory mesocosm experiment, we measured different metrics of abundance for snails (Lymnaea elodes) and zooplankton (Daphnia middendorffiana) across three time periods (early, mid‐ and late growing season) and across three temperature and photoperiod treatments (control, increased temperature and increased temperature × photoperiod). Additionally, we used generalised additive models and generalised additive mixed‐effects models to relate long‐term empirical observations of zooplankton biomass (1983–2015) to observed temperature regimes in an arctic lake. We then simulated zooplankton biomass for the warmest temperature observations across the growing season to inform likely zooplankton biomass regimes under future change.

   We observed variable responses by snails and zooplankton across experiments and treatments. Early in the growing season, snail development was accelerated at multiple life stages (e.g. egg and juvenile). In mid‐season, in accordance with warmer temperatures, we observed significantly increasedDaphniaabundances. However, in the late season,Daphniaappeared to be limited by photoperiod. Confirming our experimental results, our models of zooplankton biomass showed an increase of nearly 20% in warmer years. Further, these model estimates could be conservative as the consumptive demand of fishes may increase in warmer years as well.

   Overall, our results highlight the importance of interactive effects of temperature and seasonality. Based primarily on temperature, we can readily predict the response of fish metabolism in warmer temperatures. However, in this context, we generally require a better understanding of climate‐driven responses of important invertebrate prey resources. Our results suggest invertebrate prey biomass and availability are likely to respond positively with climate change based on temperature and seasonality, as well as proportionally to the metabolic requirements of fish predators. While further research is necessary to understand how other food‐web components will respond climate change, our findings suggest that the fish community at the top of arctic lake food webs will have adequate prey base in a warming climate.

    

   more » « less
5. Microbial diversity and abundance vary along salinity, oxygen, and particle size gradients in the Chesapeake Bay

   https://doi.org/10.1111/1462-2920.16557  

   Cram, Jacob A. ; Hollins, Ashley ; McCarty, Alexandra J. ; Martinez, Grace ; Cui, Minming ; Gomes, Maya L. ; Fuchsman, Clara A. ( January 2024 , Environmental Microbiology)

   Marine snow and other particles are abundant in estuaries, where they drive biogeochemical transformations and elemental transport. Particles range in size, thereby providing a corresponding gradient of habitats for marine microorganisms. We used standard normalized amplicon sequencing, verified with microscopy, to characterize taxon‐specific microbial abundances, (cells per litre of water and per milligrams of particles), across six particle size classes, ranging from 0.2 to 500 μm, along the main stem of the Chesapeake Bay estuary. Microbial communities varied in salinity, oxygen concentrations, and particle size. Many taxonomic groups were most densely packed on large particles (in cells/mg particles), yet were primarily associated with the smallest particle size class, because small particles made up a substantially larger portion of total particle mass. However, organisms potentially involved in methanotrophy, nitrite oxidation, and sulphate reduction were found primarily on intermediately sized (5–180 μm) particles, where species richness was also highest. All abundant ostensibly free‐living organisms, including SAR11 andSynecococcus, appeared on particles, albeit at lower abundance than in the free‐living fraction, suggesting that aggregation processes may incorporate them into particles. Our approach opens the door to a more quantitative understanding of the microscale and macroscale biogeography of marine microorganisms.

    

   more » « less