Soil Nitrogen Supply Exerts Largest Influence on Leaf Nitrogen in Environments with the Greatest Leaf Nitrogen DemandCheaib, Alissar; Waring, Elizabeth F.; McNellis, Risa; Perkowski, Evan A.; Martina, Jason P.; Seabloom, Eric W.; Borer, Elizabeth T.; Wilfahrt, Peter A.; Dong, Ning; Prentice, Iain Colin; Wright, Ian J.; Power, Sally A.; Hersch‐Green, Erika I.; Risch, Anita C.; Caldeira, Maria C.; Nogueira, Carla; Chen, Qingqing; Smith, Nicholas G.
doi: 10.1111/ele.70015pmid: 39824754
Accurately representing the relationships between nitrogen supply and photosynthesis is crucial for reliably predicting carbon–nitrogen cycle coupling in Earth System Models (ESMs). Most ESMs assume positive correlations amongst soil nitrogen supply, leaf nitrogen content, and photosynthetic capacity. However, leaf photosynthetic nitrogen demand may influence the leaf nitrogen response to soil nitrogen supply; thus, responses to nitrogen supply are expected to be the largest in environments where demand is the greatest. Using a nutrient addition experiment replicated across 26 sites spanning four continents, we demonstrated that climate variables were stronger predictors of leaf nitrogen content than soil nutrient supply. Leaf nitrogen increased more strongly with soil nitrogen supply in regions with the highest theoretical leaf nitrogen demand, increasing more in colder and drier environments than warmer and wetter environments. Thus, leaf nitrogen responses to nitrogen supply are primarily influenced by climatic gradients in photosynthetic nitrogen demand, an insight that could improve ESM predictions.
Foundations and Future Directions for Causal Inference in Ecological ResearchSiegel, Katherine; Dee, Laura E.
doi: 10.1111/ele.70053pmid: 39831541
Ecology often seeks to answer causal questions, and while ecologists have a rich history of experimental approaches, novel observational data streams and the need to apply insights across naturally occurring conditions pose opportunities and challenges. Other fields have developed causal inference approaches that can enhance and expand our ability to answer ecological causal questions using observational or experimental data. However, the lack of comprehensive resources applying causal inference to ecological settings and jargon from multiple disciplines creates barriers. We introduce approaches for causal inference, discussing the main frameworks for counterfactual causal inference, how causal inference differs from other research aims and key challenges; the application of causal inference in experimental and quasi‐experimental study designs; appropriate interpretation of the results of causal inference approaches given their assumptions and biases; foundational papers; and the data requirements and trade‐offs between internal and external validity posed by different designs. We highlight that these designs generally prioritise internal validity over generalisability. Finally, we identify opportunities and considerations for ecologists to further integrate causal inference with synthesis science and meta‐analysis and expand the spatiotemporal scales at which causal inference is possible. We advocate for ecology as a field to collectively define best practices for causal inference.
Non‐Analog Behaviour of Eastern African Herbivore Communities During the Last Glacial PeriodO'Brien, Kaedan; Ashioya, Lilian; Faith, J. Tyler
doi: 10.1111/ele.70041pmid: 39737742
Modern African ungulates navigate seasonal variation in resource availability through diet‐switching (primarily mixed‐feeders) and/or migrating (primarily grass grazers). These ecological generalisations are well‐documented today, but the extent to which they apply to the non‐analog ecosystems of the Pleistocene are unclear. Drawing from serially‐sampled stable isotope measurements from 18 Kenyan large herbivore species from the Last Glacial Period (LGP), we evaluate how diet, diet‐switching, and migration compare to observations from present‐day settings. We find a higher grazing signal in most LGP species and a greater magnitude of diet‐switching than in the present. Additionally, we find that the relationships between grass intake, migration, diet‐switching, and body size during the LGP were unlike those observed today. This establishes a revised paleoecology of LGP herbivore communities and highlights that LGP herbivores were behaviourally non‐analog. Our results imply that ecological observations from present‐day settings offer an incomplete perspective of herbivore‐environment interactions.
High Capacity for Physiological Plasticity Occurs at a Slow Rate in EctothermsBurton, Tim; Einum, Sigurd
doi: 10.1111/ele.70046pmid: 39829299
Phenotypic plasticity enables organisms to express a phenotype that is optimal in their current environment. The ability of organisms to obtain the optimum phenotype is determined by their (i) capacity for plasticity, which facilitates phenotypic adjustment corresponding to the amplitude of environmental change but also their (ii) rate of plasticity, because this determines if the expressed phenotype lags behind changes in the optimum. How the rate of‐ and capacity for plasticity have co‐evolved will thus be critical for the resilience of organisms under different patterns of environmental change. To evaluate the direction of the evolved relationship between plasticity rate and capacity, we reanalysed experiments documenting the time course of thermal tolerance acclimation to temperature change across species of ectothermic animals. We found that the rate and capacity with which thermal tolerance responds plastically to temperature change are negatively correlated, a pattern inconsistent with current theory regarding the evolution of phenotypic plasticity.
A Non‐Equilibrium Species Distribution Model Reveals Unprecedented Depth of Time Lag Responses to Past Environmental Change TrajectoriesLalechère, Etienne; Marrec, Ronan; Lenoir, Jonathan
doi: 10.1111/ele.70040pmid: 39853897
Previous studies have demonstrated legacy effects of current species distributions to past environmental conditions, but the temporal extent of such time lag dynamics remains unknown. Here, we have developed a non‐equilibrium Species Distribution Modelling (SDM) approach quantifying the temporal extent that must be taken into account to capture 95% of the effect that a given time series of past environmental conditions has on the current distribution of a species. We applied this approach on the distribution of 92 European forest birds in response to past trajectories of change in forest cover and climate. We found that non‐equilibrium SDMs outperformed traditional SDMs for 95% of the species. Non‐equilibrium SDMs suggest unprecedented long‐lasting effects of past global changes (average time lag extent ranged from 9 to 231 years). This framework can help to relax the equilibrium hypothesis of traditional SDMs and to improve future predictions of biodiversity redistribution in response to global changes.
A Continuum From Positive to Negative Interactions Drives Plant Species' Performance in a Diverse CommunityBuche, Lisa; Shoemaker, Lauren G.; Hallett, Lauren M.; Bartomeus, Ignasi; Vesk, Peter; Weiss‐Lehman, Christopher; Mayfield, Margaret; Godoy, Oscar
doi: 10.1111/ele.70059pmid: 39836436
With many species interacting in nature, determining which interactions describe community dynamics is nontrivial. By applying a computational modeling approach to an extensive field survey, we assessed the importance of interactions from plants (both inter‐ and intra‐specific), pollinators and insect herbivores on plant performance (i.e., viable seed production). We compared the inclusion of interaction effects as aggregate guild‐level terms versus terms specific to taxonomic groups. We found that a continuum from positive to negative interactions, containing mostly guild‐level effects and a few strong taxonomic‐specific effects, was sufficient to describe plant performance. While interactions with herbivores and intraspecific plants varied from weakly negative to weakly positive, heterospecific plants mainly promoted competition and pollinators facilitated plants. The consistency of these empirical findings over 3 years suggests that including the guild‐level effects and a few taxonomic‐specific groups rather than all pairwise and high‐order interactions, can be sufficient for accurately describing species variation in plant performance across natural communities.
Increasing Aridity May Threaten the Maintenance of a Plant Defence PolymorphismCarley, Lauren N.; Mitchell‐Olds, Tom; Morris, William F.
doi: 10.1111/ele.70039pmid: 39737722
It is unclear how environmental change influences standing genetic variation in wild populations. Here, we characterised environmental conditions that protect versus erode polymorphic chemical defences in Boechera stricta (Brassicaceae), a short‐lived perennial wildflower. By manipulating drought and herbivory in a 4‐year field experiment, we measured the effects of driver variation on vital rates of genotypes varying in defence chemistry and then assessed interacting driver effects on total fitness (estimated as each genotype's lineage growth rate, λ) using demographic models. Drought and herbivory interacted to shape vital rates, but contrasting defence genotypes had equivalent total fitness in many environments. Defence polymorphism thus may persist under a range of conditions; however, ambient field conditions fall close to the boundary of putatively polymorphic environment space, and increasing aridity may drive populations to monomorphism. Consequently, elevated intensity and/or frequency of drought under climate change may erode genetic variation for defence chemistry in B. stricta.
A Natural Disaster Exacerbates and Redistributes Disease Risk Among Free‐Ranging Macaques by Altering Social StructureMotes‐Rodrigo, Alba; Albery, Gregory F.; Negron‐Del Valle, Josue E.; Philips, Daniel; , ; Platt, Michael L.; Brent, Lauren J. N.; Testard, Camille
doi: 10.1111/ele.70000pmid: 39737674
Climate change is intensifying extreme weather events, with severe implications for ecosystem dynamics. A key behavioural mechanism whereby animals may cope with such events is by altering their social structure, which in turn could influence epidemic risk. However, how and to what extent natural disasters affect disease risk via changes in sociality remains unexplored in animal populations. By simulating disease spread in free‐living rhesus macaques (Macaca mulatta) before and after a hurricane, we demonstrate doubled pathogen transmission rates up to 5 years following the disaster, equivalent to an increase in pathogen infectivity from 10% to 20%. Moreover, the hurricane redistributed the risk of infection across the population by exacerbating sex‐related differences. Overall, we demonstrate that natural disasters can amplify and redistribute epidemic risk in animals via changes in sociality. These observations provide unexpected further mechanisms by which extreme weather events can threaten wildlife health, population viability and spillover to humans.