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Synopsis Classic debates in community ecology focused on the complexities of considering an ecosystem as a super-organ or organism. New consideration of such perspectives could clarify mechanisms underlying the dynamics of forest carbon dioxide (CO2) uptake and water vapor loss, important for predicting and managing the future of Earth’s ecosystems and climate system. Here, we provide a rubric for considering ecosystem traits as aggregated, systemic, or emergent, i.e., representing the ecosystem as an aggregate of its individuals or as a metaphorical or literal super-organ or organism. We review recent approaches to scaling-up plant water relations (hydraulics) concepts developed for organs and organisms to enable and interpret measurements at ecosystem-level. We focus on three community-scale versions of water relations traits that have potential to provide mechanistic insight into climate change responses of forest CO2 and H2O gas exchange and productivity: leaf water potential (Ψcanopy), pressure volume curves (eco-PV), and hydraulic conductance (Keco). These analyses can reveal additional ecosystem-scale parameters analogous to those typically quantified for leaves or plants (e.g., wilting point and hydraulic vulnerability) that may act as thresholds in forest responses to drought, including growth cessation, mortality, and flammability. We unite these concepts in a novel framework to predict Ψcanopy and its approaching of critical thresholds during drought, using measurements of Keco and eco-PV curves. We thus delineate how the extension of water relations concepts from organ- and organism-scales can reveal the hydraulic constraints on the interaction of vegetation and climate and provide new mechanistic understanding and prediction of forest water use and productivity.

Synopsis Since the late 1800s, anthropogenic activities such as fossil fuel consumption and deforestation have driven up the concentration of atmospheric CO2 around the globe by >45%. Such heightened concentrations of carbon dioxide in the atmosphere are a leading contributor to global climate change, with estimates of a 2–5° increase in global air temperature by the end of the century. While such climatic changes are mostly considered detrimental, a great deal of experimental work has shown that increased atmospheric CO2 will actually increase growth in various plants, which may lead to increased biomass for potential harvesting or CO2 sequestration. However, it is not clear whether this increase in growth or biomass will be beneficial to the plants, as such increases may lead to weaker plant materials. In this review, I examine our current understanding of how elevated atmospheric CO2 caused by anthropogenic effects may influence plant material properties, focusing on potential effects on wood. For the first part of the review, I explore how aspects of wood anatomy and structure influence resistance to bending and breakage. This information is then used to review how changes in CO2 levels may later these aspects of wood anatomy and structure in ways that have mechanical consequences. The major pattern that emerges is that the consequences of elevated CO2 on wood properties are highly dependent on species and environment, with different tree species showing contradictory responses to atmospheric changes. In the end, I describe a couple avenues for future research into better understanding the influence of atmospheric CO2 levels on plant biomaterial mechanics.

SynopsisIntraspecific variation can be as great as variation across species, but the role of intraspecific variation in driving local and large-scale patterns is often overlooked, particularly in the field of thermal biology. In amphibians, which depend on environmental conditions and behavior to regulate body temperature, recognizing intraspecific thermal trait variation is essential to comprehensively understanding how global change impacts populations. Here, we examine the drivers of micro- and macrogeographical intraspecific thermal trait variation in amphibians. At the local scale, intraspecific variation can arise via changes in ontogeny, body size, and between the sexes, and developmental plasticity, acclimation, and maternal effects may modulate predictions of amphibian performance under future climate scenarios. At the macrogeographic scale, local adaptation in thermal traits may occur along latitudinal and elevational gradients, with seasonality and range-edge dynamics likely playing important roles in patterns that may impact future persistence. We also discuss the importance of considering disease as a factor affecting intraspecific variation in thermal traits and population resilience to climate change, given the impact of pathogens on thermal preferences and critical thermal limits of hosts. Finally, we make recommendations for future work in this area. Ultimately, our goal is to demonstrate why it is important for researchers to consider intraspecific variation to determine the resilience of amphibians to global change.

Synopsis Ocean warming is impacting marine systems directly and indirectly via intensifying multiple stressors such as hypoxia, acidification, and kelp forest collapse potentially exacerbating neoextinctions. Abalones are extremely vulnerable to both ocean warming and fishing stressors making them marine “canaries in the coal mine”. The rare flat abalone, Haliotis walallensis, has been subject to a targeted commercial fishery and then exposed to an extreme marine heat wave. We examine the current status of flat abalone before and after a marine heat wave of 2014–2016 and the concomitant collapse of the bull kelp (Nereocystis leutkeana) forest in 2015. We find that flat abalone density (as assessed in surveys) and abundances (inside deployed “abalone modules”) in the core of the range dropped to near-zero after the marine heat wave and have not recovered. Further, we examine the status of flat abalone in southern Oregon after both overfishing and the kelp forest collapse and find dramatic declines, especially in former fishery hot spots. Our results show that flat abalone have experienced a major decline and may be an example of a neoextinction in the making. A standardized and well-funded status review and proactive restoration plan, if not too late, are both critically needed for flat abalone throughout its range.

Synopsis Foundational habitats such as seagrasses and coral reefs are at severe risk globally from climate warming. Infectious disease associated with warming events is both a cause of decline and an indicator of stress in both habitats. Since new approaches are needed to detect refugia and design climate-smart networks of marine protected areas, we test the hypothesis that the health of eelgrass (Zostera marina) in temperate ecosystems can serve as a proxy indicative of higher resilience and help pinpoint refugia. Eelgrass meadows worldwide are at risk from environmental stressors, including climate warming and disease. Disease outbreaks of Labyrinthula zosterae are associated with recent, widespread declines in eelgrass meadows throughout the San Juan Islands, Washington, USA. Machine language learning, drone surveys, and molecular diagnostics reveal climate impacts on seagrass wasting disease prevalence (proportion of infected individuals) and severity (proportion of infected leaf area) from San Diego, California, to Alaska. Given that warmer temperatures favor many pathogens such as L. zosterae, we hypothesize that absent or low disease severity in meadows could indicate eelgrass resilience to climate and pathogenic stressors. Regional surveys showed the San Juan Islands as a hotspot for both high disease prevalence and severity, and surveys throughout the Northeast Pacific indicated higher prevalence and severity in intertidal, rather than subtidal, meadows. Further, among sites with eelgrass declines, losses were more pronounced at sites with shallower eelgrass meadows. We suggest that deeper meadows with the lowest disease severity will be refuges from future warming and pathogenic stressors in the Northeast Pacific. Disease monitoring may be a useful conservation approach for marine foundation species, as low or absent disease severity can pinpoint resilient refugia that should be prioritized for future conservation efforts. Even in declining or at-risk habitats, disease surveys can help identify meadows that may contain especially resilient individuals for future restoration efforts. Our approach of using disease as a pulse point for eelgrass resilience to multiple stressors could be applied to other habitats such as coral reefs to inform conservation and management decisions.

Synopsis Many plant species are known to take up metals from the soil and accumulate them to potentially toxic levels. This may provide tolerance to soils with high metal content or a defensive mechanism against herbivores and pathogens. Accumulators, plants that uptake and store elevated concentrations of metals, can be used in phytoremediation as a means to remove metals from contaminated soils. In this study, the native weed Conyza canadensis was grown in soils contaminated with elevated levels of lead (Pb), barium (Ba), zinc (Zn), copper (Cu), or chromium (Cr). All metals, except for Cr, were accumulated by the plants. Zinc and Cu, both essential elements, accumulated to the highest levels, while Pb and Ba were present at lower levels. All treatments except Cr showed accelerating rates of accumulation over the eight-week experiment. Barium, Cu, and Cr reduced aboveground biomass of the plants, indicating toxicity or a cost to metal accumulation. Lead and Zn promoted early flowering, while plants accumulating Ba, Cr, and Cu flowered in lower numbers. Overall, C. canadensis has promise in the phytoremediation of Pb, Cu, and Zn.

Synopsis Marine organisms have complex life histories. For broadcast spawners, successful continuation of the population requires their small gametes to make contact in the water column for sufficiently long periods for fertilization to occur. Anthropogenic climate change has been shown to impact fertilization success in various marine invertebrates, including sea urchins, which are key grazers in their habitats. Gamete performance of both sexes declined when exposed to elevated temperatures and/or pCO2 levels. Examples of reduced performance included slower sperm swimming speed and thinning egg jelly coat. However, such responses to climate change stress were not uniform between individuals. Such variations could serve as the basis for selection. Fertilization kinetics have long been modeled as a particle collision process. Here, we present a modified fertilization kinetics model that incorporates individual variations in performance in a more environmentally relevant regime, and which the performance of groups with different traits can be separately tracked in a mixture. Numerical simulations highlight that fertilization outcomes are influenced by changes in gamete traits as they age in sea water and the presence of competition groups (multiple dams or sires). These results highlight the importance of considering multiple individuals and at multiple time points during in vivo assays. We also applied our model to show that interspecific variation in climate stress vulnerabilities elevates the risk of hybridization. By making a numerical model open-source, we aim to help us better understand the fate of organisms in the face of climate change by enabling the community to consider the mean and variance of the response to capture adaptive potential.

Synopsis A central question in ecology is to what extent do trophic interactions govern the structure and function of communities? This question is becoming more pressing as trophic interactions shift with rapid climate change. Sea urchins and abalone are key invertebrates in the habitats where they reside. Sea urchins are critical members of exemplar trophic cascades in kelp forests due to their impact on kelp establishment and maintenance; yet their populations are controlled by predators, such as sea otters and sunflower sea stars. Abalone compete with urchins for macroalgal food resources and therefore can help regulate urchin populations in kelp forests. Given that both urchin tests and abalone shells used for predator defense are comprised of calcium carbonate, much research has been conducted on the impacts of ocean acidification (OA) on these calcified structures. A growing body of literature has shown that urchin tests are less calcified and break with less force under OA conditions. Less is known about abalone, but their shells also appear to respond negatively to OA. Using kelp forest communities as exemplar ecosystems, we discuss the morphological, biomechanical, and physiological responses to OA in urchins and abalone and consider how these individual level responses scale to trophic interactions and ultimately whole ecosystem processes. Although the impacts of OA on the calcified structures used for defense have been well studied, calcified mechanisms for food consumption, such as the Aristotle's lantern of urchins, are much less understood. Thus, examining both the feeding and defense sides of trophic interactions would greatly improve our understanding of OA responses across individual to ecosystem scales. More generally, measurements of morphological, biomechanical, and physiological responses to OA can be made in individuals to help predict higher level ecological responses, which would greatly contribute to broader predictions of whole ecosystem responses to OA.