.
We explored variation in infection outcomes and processes explaining that variation in multiple taxa of Daphnia exposed to the pathogen, Australozyma monospora (formerly Metschnikowia bicuspidata). Three laboratory assays were conducted to explore (1) variation in likelihood of infection and pathogen load, (2) host encounter and defense traits, and the influence of host maturity on these traits, and (3) the fitness costs of preventing infection. We found considerable among-taxon variation in susceptibility as well as the pathogen’s ability to reproduce following successful infection. Notably, in both the most susceptible (D. dentifera) and least susceptible (D. pulicaria) host species, we discovered that host barriers and immune responses, but not encounter rates, play an important role in shaping infection outcomes. Although differences in body size could underlie variation in barriers and immune responses between the two taxa, they could not explain infection differences across the broader set of host taxa. Finally, we found that the least susceptible taxon did not exhibit a cost of resistance, whereas the most susceptible taxon-suffered fitness declines when preventing infection. These results underscore the complexity of taxon-level differences in host–pathogen interactions and provide a framework for understanding how variation among and within taxa can shape disease outbreaks.
Understanding forest carbon sequestration is crucial for predicting and managing the carbon cycle, yet we lack evidence for whether, when and how the carbon sink in tropical forests recovering from land use change is nutrient limited. Here we show how the tropical forest recovery rate responds to experimental nutrient manipulation over a secondary succession gradient in a naturally recovering Central American landscape. Nutrient limitation of aboveground biomass accumulation shifts from strong nitrogen limitation in young forests to no evidence of nitrogen or phosphorus limitation in older secondary or mature forests. Nitrogen addition increases aboveground biomass accumulation by 95% in recently abandoned pasture and 48% in 10-year-old forests. Conversely, we observe no influence of nitrogen on older forests and no evidence of phosphorus limitation at any stage. If our findings of nitrogen limitation extend to young tropical forests globally, nitrogen could prevent the sequestration of 0.69 (0.47-0.84) Gt CO2 each year.
Wood density is central for estimating vegetation carbon storage and a plant functional trait of great ecological and evolutionary importance. However, the global extent of wood density variation is unclear, especially at the intraspecific level. We assembled the most comprehensive wood density collection to date, including 109 626 records from 16 829 plant species across woody life forms and biomes (GWDD v.2, available here: doi: 10.5281/zenodo.16919509). Using the GWDD v.2, we explored the sources of wood density variation within individuals, within species and across environmental gradients. Intraspecific variation accounted for c. 15% of overall wood density variation (SD = 0.068 g cm-3). Variance was 50% smaller in sapwood than heartwood, and 30% smaller in branchwood than trunkwood. Individuals in extreme environments (dry, hot and acidic soils) had higher wood density than conspecifics elsewhere (+0.02 g cm-3, c. 4% of the mean). Intraspecific environmental effects strongly tracked interspecific patterns (r = 0.83) but were 70-80% smaller and varied considerably among taxa. Individual plant wood density was difficult to predict (root mean square error > 0.08 g cm-3; single-measurement R2 = 0.59). We recommend: (1) systematic sampling of multiple individuals and tissues for local applications; and (2) expanded taxonomic coverage combined with integrative models for robust estimates across ecological scales.
Pulsed resources, including mast production by forest trees, often have knock-on effects on consumer populations and their prey, predators, parasites and mutualists. Response by small rodents to fluctuating acorn production in temperate forests is a widespread example. Long-term research in Maine, USA, recently suggested combined effects of a warming climate and forest maturation on acorn production by red oak trees, leading to directional increases in average population density and body mass of white-footed mice. To foster reproducibility in long-term ecological research, we analysed data from our long-term study in southeastern New York, USA, which used similar field methods. Such a comparison allowed us to assess impacts of climate warming and forest growth on the same pulsed resource and responses by the same consumer species over time and at different latitudes. Despite a clear directional increase in mean minimum temperature and considerable growth in the average size and total basal area of trees during our 33-year study, neither acorn production by red oak trees nor abundance of white-footed mice showed directional increases. Similarly, average body mass of the mice did not change through time. Abundance of mice in mid-summer increased with increasing red oak acorn production the prior autumn. Mouse abundance also was higher in warmer years, although the effect of acorn abundance on mice was stronger. We found no evidence that temperature modified the acorn-driven population responses by mice. Long-term studies are notoriously hard to maintain and even harder to replicate between sites. The direct comparison of similar studies between Maine and New York provides an opportunity to assess the generality of mechanistic models linking climate change, mast seeding and consumer responses.
