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1. Vertebrate Phenological Plasticity: From Molecular Mechanisms to Ecological and Evolutionary Implications

   https://doi.org/10.1093/icb/icac121  

   Aubry, Lise M. ; Williams, Cory T. ( July 2022 , Integrative and Comparative Biology)

   Seasonal variation in the availability of essential resources is one of the most important drivers of natural selection on the phasing and duration of annually recurring life-cycle events. Shifts in seasonal timing are among the most commonly reported responses to climate change and the capacity of organisms to adjust their timing, either through phenotypic plasticity or evolution, is a critical component of resilience. Despite growing interest in documenting and forecasting the impacts of climate change on phenology, our ability to predict how individuals, populations, and species might alter their seasonal timing in response to their changing environments is constrained by limited knowledge regarding the cues animals use to adjust timing, the endogenous genetic and molecular mechanisms that transduce cues into neural and endocrine signals, and the inherent capacity of animals to alter their timing and phasing within annual cycles. Further, the fitness consequences of phenological responses are often due to biotic interactions within and across trophic levels, rather than being simple outcomes of responses to changes in the abiotic environment. Here, we review the current state of knowledge regarding the mechanisms that control seasonal timing in vertebrates, as well as the ecological and evolutionary consequences of individual, population, andmore »species-level variation in phenological responsiveness. Understanding the causes and consequences of climate-driven phenological shifts requires combining ecological, evolutionary, and mechanistic approaches at individual, populational, and community scales. Thus, to make progress in forecasting phenological responses and demographic consequences, we need to further develop interdisciplinary networks focused on climate change science.

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2. Evidence, causes, and consequences of declining nitrogen availability in terrestrial ecosystems

   https://doi.org/10.1126/science.abh3767  

   Mason, Rachel E. ; Craine, Joseph M. ; Lany, Nina K. ; Jonard, Mathieu ; Ollinger, Scott V. ; Groffman, Peter M. ; Fulweiler, Robinson W. ; Angerer, Jay ; Read, Quentin D. ; Reich, Peter B. ; et al ( April 2022 , Science)

   BACKGROUND The availability of nitrogen (N) to plants and microbes has a major influence on the structure and function of ecosystems. Because N is an essential component of plant proteins, low N availability constrains the growth of plants and herbivores. To increase N availability, humans apply large amounts of fertilizer to agricultural systems. Losses from these systems, combined with atmospheric deposition of fossil fuel combustion products, introduce copious quantities of reactive N into ecosystems. The negative consequences of these anthropogenic N inputs—such as ecosystem eutrophication and reductions in terrestrial and aquatic biodiversity—are well documented. Yet although N availability is increasing in many locations, reactive N inputs are not evenly distributed globally. Furthermore, experiments and theory also suggest that global change factors such as elevated atmospheric CO 2 , rising temperatures, and altered precipitation and disturbance regimes can reduce the availability of N to plants and microbes in many terrestrial ecosystems. This can occur through increases in biotic demand for N or reductions in its supply to organisms. Reductions in N availability can be observed via several metrics, including lowered nitrogen concentrations ([N]) and isotope ratios (δ 15 N) in plant tissue, reduced rates of N mineralization, and reduced terrestrial Nmore »export to aquatic systems. However, a comprehensive synthesis of N availability metrics, outside of experimental settings and capable of revealing large-scale trends, has not yet been carried out. ADVANCES A growing body of observations confirms that N availability is declining in many nonagricultural ecosystems worldwide. Studies have demonstrated declining wood δ 15 N in forests across the continental US, declining foliar [N] in European forests, declining foliar [N] and δ 15 N in North American grasslands, and declining [N] in pollen from the US and southern Canada. This evidence is consistent with observed global-scale declines in foliar δ 15 N and [N] since 1980. Long-term monitoring of soil-based N availability indicators in unmanipulated systems is rare. However, forest studies in the northeast US have demonstrated decades-long decreases in soil N cycling and N exports to air and water, even in the face of elevated atmospheric N deposition. Collectively, these studies suggest a sustained decline in N availability across a range of terrestrial ecosystems, dating at least as far back as the early 20th century. Elevated atmospheric CO 2 levels are likely a main driver of declines in N availability. Terrestrial plants are now uniformly exposed to ~50% more of this essential resource than they were just 150 years ago, and experimentally exposing plants to elevated CO 2 often reduces foliar [N] as well as plant-available soil N. In addition, globally-rising temperatures may raise soil N supply in some systems but may also increase N losses and lead to lower foliar [N]. Changes in other ecosystem drivers—such as local climate patterns, N deposition rates, and disturbance regimes—individually affect smaller areas but may have important cumulative effects on global N availability. OUTLOOK Given the importance of N to ecosystem functioning, a decline in available N is likely to have far-reaching consequences. Reduced N availability likely constrains the response of plants to elevated CO 2 and the ability of ecosystems to sequester carbon. Because herbivore growth and reproduction scale with protein intake, declining foliar [N] may be contributing to widely reported declines in insect populations and may be negatively affecting the growth of grazing livestock and herbivorous wild mammals. Spatial and temporal patterns in N availability are not yet fully understood, particularly outside of Europe and North America. Developments in remote sensing, accompanied by additional historical reconstructions of N availability from tree rings, herbarium specimens, and sediments, will show how N availability trajectories vary among ecosystems. Such assessment and monitoring efforts need to be complemented by further experimental and theoretical investigations into the causes of declining N availability, its implications for global carbon sequestration, and how its effects propagate through food webs. Responses will need to involve reducing N demand via lowering atmospheric CO 2 concentrations, and/or increasing N supply. Successfully mitigating and adapting to declining N availability will require a broader understanding that this phenomenon is occurring alongside the more widely recognized issue of anthropogenic eutrophication. Intercalibration of isotopic records from leaves, tree rings, and lake sediments suggests that N availability in many terrestrial ecosystems has steadily declined since the beginning of the industrial era. Reductions in N availability may affect many aspects of ecosystem functioning, including carbon sequestration and herbivore nutrition. Shaded areas indicate 80% prediction intervals; marker size is proportional to the number of measurements in each annual mean. Isotope data: (tree ring) K. K. McLauchlan et al. , Sci. Rep. 7 , 7856 (2017); (lake sediment) G. W. Holtgrieve et al. , Science 334 , 1545–1548 (2011); (foliar) J. M. Craine et al. , Nat. Ecol. Evol. 2 , 1735–1744 (2018)« less
3. Higher-order interactions mitigate direct negative effects on population dynamics of herbaceous plants during succession

   https://doi.org/10.1088/1748-9326/ab8a88  

   Xiao, Junli ; Li, Yuanzhi ; Chu, Chengjin ; Wang, Youshi ; Meiners, Scott J. ; Stouffer, Daniel B. ( June 2020 , Environmental Research Letters)

   Plant succession is regulated by a combination of abiotic and biotic factors. However, previous studies of biotic drivers have focused overwhelmingly on direct pairwise species interactions, ignoring the likely prevalent higher-order interactions (HOIs) in natural systems. Climate also plays a significant role in determining successional dynamics with both direct effects and indirect effects via altered biotic interactions. Here we explored the relative effects of direct species interactions, HOIs, climate, and their interactions on population dynamics of herbaceous plants during 50 years of post-agricultural secondary succession and tested whether the inclusion of HOIs and climate data improved forecasts of population dynamics. Direct intraspecific interactions were competitive and prevalent across the 90 herbaceous plants examined, while direct interspecific interactions only affected populations of 29% species. HOIs, mainly arose from intraspecific HOIs of conspecifics, were mostly positive and thus largely mitigated the competitive effects of direct intraspecific interactions. Species with lower peak cover experienced stronger intraspecific competition and positive intraspecific HOIs of conspecifics. Direct interspecific interactions had neutral or facilitative effects on species with lower peak cover, and tended to have competitive effects on species with higher peak cover. Climate simultaneously influenced population dynamics both directly and indirectly via altered species interactions.more »Forecast performance was significantly improved with the inclusion of HOIs or climate for about half and one-third of species, respectively. Our study emphasizes the importance of HOIs, which largely mitigated direct competitive effects on population dynamics of herbaceous plants during succession. Teasing apart HOIs from direct species interactions substantially refined our understanding of successional dynamics of herbaceous plants and improved the accuracy of forecasting population dynamics during succession in a changing world.

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4. Small spaces, big impacts: contributions of micro-environmental variation to population persistence under climate change

   https://doi.org/10.1093/aobpla/plaa005  

   Denney, Derek A ; Jameel, M Inam ; Bemmels, Jordan B ; Rochford, Mia E ; Anderson, Jill T ( April 2020 , AoB PLANTS)

   Abdelaziz, Mohamed (Ed.)

   Abstract Individuals within natural populations can experience very different abiotic and biotic conditions across small spatial scales owing to microtopography and other micro-environmental gradients. Ecological and evolutionary studies often ignore the effects of micro-environment on plant population and community dynamics. Here, we explore the extent to which fine-grained variation in abiotic and biotic conditions contributes to within-population variation in trait expression and genetic diversity in natural plant populations. Furthermore, we consider whether benign microhabitats could buffer local populations of some plant species from abiotic stresses imposed by rapid anthropogenic climate change. If microrefugia sustain local populations and communities in the short term, other eco-evolutionary processes, such as gene flow and adaptation, could enhance population stability in the longer term. We caution, however, that local populations may still decline in size as they contract into rare microhabitats and microrefugia. We encourage future research that explicitly examines the role of the micro-environment in maintaining genetic variation within local populations, favouring the evolution of phenotypic plasticity at local scales and enhancing population persistence under global change.
5. Detecting climate signals in populations across life histories. Global Change Biology

   https://doi.org/DOI: 10.1111/gcb.16041  

   Jenouvrier S., Long M. ( April 2022 , Global change biology)

   Editorial Board, Editor ; Executive Editor, Rachel Shekar ; Assistant Editor, Rhea Bruno ; Co-Founding Editor Harry Smith FRS, University of ; Reviews Editor Danielle Way, Australian National (Ed.)

   Climate impacts are not always easily discerned in wild populations as detecting climate change signals in populations is challenged by stochastic noise associated with natural climate variability, variability in biotic and abiotic processes, and observation error in demographic rates. Detection of the impact of climate change on populations requires making a formal distinction between signals in the population associated with long-term climate trends from those generated by stochastic noise. The time of emergence (ToE) identifies when the signal of anthropogenic climate change can be quantitatively distinguished from natural climate variability. This concept has been applied extensively in the climate sciences, but has not been explored in the context of population dynamics. Here, we outline an approach to detecting climate-driven signals in populations based on an assessment of when climate change drives population dynamics beyond the envelope characteristic of stochastic variations in an unperturbed state. Specifically, we present a theoretical assessment of the time of emergence of climate-driven signals in population dynamics (urn:x-wiley:13541013:media:gcb16041:gcb16041-math-0001). We identify the dependence of urn:x-wiley:13541013:media:gcb16041:gcb16041-math-0002 on the magnitude of both trends and variability in climate and also explore the effect of intrinsic demographic controls on urn:x-wiley:13541013:media:gcb16041:gcb16041-math-0003. We demonstrate that different life histories (fast species vs. slow species),more »demographic processes (survival, reproduction), and the relationships between climate and demographic rates yield population dynamics that filter climate trends and variability differently. We illustrate empirically how to detect the point in time when anthropogenic signals in populations emerge from stochastic noise for a species threatened by climate change: the emperor penguin. Finally, we propose six testable hypotheses and a road map for future research.« less