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1. Integrating ocean observations across body‐size classes to deliver benthic invertebrate abundance and distribution information

   https://doi.org/10.1002/lol2.10332  

   Ruhl, Henry A. ; Bett, Brian J. ; Ingels, Jeroen ; Martin, Adrian ; Gates, Andrew R. ; Yool, Andrew ; Benoist, Noëlie M. A. ; Appeltans, Ward ; Howell, Kerry L. ; Danovaro, Roberto ( May 2023 , Limnology and Oceanography Letters)

   Invertebrate animals living at the seafloor make up a prominent component of life globally, spanning 10 orders of magnitude in body size over 71% of Earth's surface. However, integrating information across sizes and sampling methodologies has limited our understanding of the influence of natural variation, climate change and human activity. Here, we outline maturing practices that can underpin both the feasibility and impact of establishing Benthic Invertebrate Abundance and Distribution as a Global Ocean Observing System—Essential Ocean Variable, including: (1) quantifying individual body size, (2) identifying the well‐quantified portions of sampled body‐size spectra, (3) taking advantage of (semi‐)automated information processing, (4) application of metadata standards such as Darwin Core, and (5) making data available through internationally recognized access points. These practices enable broader‐scale analysis supporting research and sustainable development, such as assessments of indicator taxa, biodiversity, biomass, and the modeling of carbon stocks and flows that are contiguous over time and space.

    

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2. Body size and temperature affect metabolic and cardiac thermal tolerance in fish

   https://doi.org/10.1038/s41598-023-44574-w  

   Kraskura, Krista ; Hardison, Emily A. ; Eliason, Erika J. ( October 2023 , Scientific Reports)

   Environmental warming is associated with reductions in ectotherm body sizes, suggesting that larger individuals may be more vulnerable to climate change. The mechanisms driving size-specific vulnerability to temperature are unknown but are required to finetune predictions of fisheries productivity and size-structure community responses to climate change. We explored the potential metabolic and cardiac mechanisms underlying these body size vulnerability trends in a eurythermal fish, barred surfperch. We acutely exposed surfperch across a large size range (5–700 g) to four ecologically relevant temperatures (16 °C, 12 °C, 20 °C, and 22 °C) and subsequently, measured their metabolic capacity (absolute and factorial aerobic scopes, maximum and resting metabolic rates; AAS, FAS, MMR, RMR). Additionally, we estimated the fish’s cardiac thermal tolerance by measuring their maximum heart rates (f_Hmax) across acutely increasing temperatures. Barred surfperch had parallel hypoallometric scaling of MMR and RMR (exponent 0.81) and a weaker hypoallometric scaling off_Hmax(exponent − 0.05) across all test temperatures. In contrast to our predictions, the fish’s aerobic capacity was maintained across sizes and acute temperatures, and larger fish had greater cardiac thermal tolerance than smaller fish. These results demonstrate that thermal performance may be limited by different physiological constraints depending on the size of the animal and species of interest.

    

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3. Monitoring muscle over three orders of magnitude: Widespread positive allometry among locomotor and body support musculature in the pectoral girdle of varanid lizards ( Varanidae )

   https://doi.org/10.1111/joa.13273  

   Cieri, Robert L. ; Dick, Taylor J. M. ; Clemente, Christofer J. ( July 2020 , Journal of Anatomy)

   There is a functional trade‐off in the design of skeletal muscle. Muscle strength depends on the number of muscle fibers in parallel, while shortening velocity and operational distance depend on fascicle length, leading to a trade‐off between the maximum force a muscle can produce and its ability to change length and contract rapidly. This trade‐off becomes even more pronounced as animals increase in size because muscle strength scales with area (length²) while body mass scales with volume (length³). In order to understand this muscle trade‐off and how animals deal with the biomechanical consequences of size, we investigated muscle properties in the pectoral girdle of varanid lizards. Varanids are an ideal group to study the scaling of muscle properties because they retain similar body proportions and posture across five orders of magnitude in body mass and are highly active, terrestrially adapted reptiles. We measured muscle mass, physiological cross‐sectional area, fascicle length, proximal and distal tendon lengths, and proximal and distal moment arms for 27 pectoral girdle muscles in 13 individuals across 8 species ranging from 64 g to 40 kg. Standard and phylogenetically informed reduced major axis regression was used to investigate how muscle architecture properties scale with body size. Allometric growth was widespread for muscle mass (scaling exponent >1), physiological cross‐sectional area (scaling exponent >0.66), but not tendon length (scaling exponent >0.33). Positive allometry for muscle mass was universal among muscles responsible for translating the trunk forward and flexing the elbow, and nearly universal among humeral protractors and wrist flexors. Positive allometry for PCSA was also common among trunk translators and humeral protractors, though less so than muscle mass. Positive scaling for fascicle length was not widespread, but common among humeral protractors. A higher proportion of pectoral girdle muscles scaled with positive allometry than our previous work showed for the pelvic girdle, suggesting that the center of mass may move cranially with body size in varanids, or that the pectoral girdle may assume a more dominant role in locomotion in larger species. Scaling exponents for physiological cross‐sectional area among muscles primarily associated with propulsion or with a dual role were generally higher than those associated primarily with support against gravity, suggesting that locomotor demands have at least an equal influence on muscle architecture as body support. Overall, these results suggest that larger varanids compensate for the increased biomechanical demands of locomotion and body support at higher body sizes by developing larger pectoral muscles with higher physiological cross‐sectional areas. The isometric scaling rates for fascicle length among locomotion‐oriented pectoral girdle muscles suggest that larger varanids may be forced to use shorter stride lengths, but this problem may be circumvented by increases in limb excursion afforded by the sliding coracosternal joint.

    

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4. Individual size distributions across North American streams vary with local temperature

   https://doi.org/10.1111/gcb.15862  

   Pomeranz, Justin P. F. ; Junker, James R. ; Wesner, Jeff S. ( September 2021 , Global Change Biology)

   Parameters describing the negative relationship between abundance and body size within ecological communities provide a summary of many important biological processes. While it is considered to be one of the few consistent patterns in ecology, spatiotemporal variation of this relationship across continental scale temperature gradients is unknown. Using a database of stream communities collected across North America (18–68°N latitude, −4 to 25°C mean annual air temperature) over 3 years, we constructed 160 individual size distribution (ISD) relationships (i.e. abundance size spectra). The exponent parameter describing ISD’s decreased (became steeper) with increasing mean annual temperature, with median slopes varying by ~0.2 units across the 29°C temperature gradient. In addition, total community biomass increased with increasing temperatures, contrary with theoretical predictions. Our study suggests conservation of ISD relationships in streams across broad natural environmental gradients. This supports the emerging use of size‐spectra deviations as indicators of fundamental changes to the structure and function of ecological communities.

    

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5. Disentangling the drivers of continental mammalian endemism

   https://doi.org/10.1111/gcb.16628  

   Shipley, Benjamin R. ; McGuire, Jenny L. ( February 2023 , Global Change Biology)

   Endemic species and species with small ranges are ecologically and evolutionarily distinct and are vulnerable to extinction. Determining which abiotic and biotic factors structure patterns of endemism on continents can advance our understanding of global biogeographic processes, but spatial patterns of mammalian endemism have not yet been effectively predicted and reconstructed. Using novel null model techniques, we reconstruct trends in mammalian endemism and describe the isolated and combined effects of physiographic, ecological, and evolutionary factors on endemism. We calculated weighted endemism for global continental ecoregions and compared the spatial distribution of endemism to niche‐based, geographic null models of endemism. These null models distribute species randomly across continents, simulating their range sizes from their degree of climatic specialization. They isolate the effects of physiography (topography and climate) and species richness on endemism. We then ran linear and structural models to determine how topography and historical climate stability influence endemism. The highest rates of mammalian endemism were found in topographically rough, climatically stable ecoregions with many species. The null model that isolated physiography did not closely approximate the observed distribution of endemism (r² = .09), whereas the null model that incorporated both physiography and species richness did (r² = .59). The linear models demonstrate that topography and climatic stability both influenced endemism values, but that average climatic niche breadth was not highly correlated with endemism. Climate stability and topography both influence weighted endemism in mammals, but the spatial distribution of mammalian endemism is driven by a combination of physiography and species richness. Despite its relationship to individual range size, average climate niche breadth has only a weak influence on endemism. The results highlight the importance of historical biogeographic processes (e.g. centers of speciation) and geography in driving endemism patterns, and disentangle the mechanisms structuring species ranges worldwide.

    

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