As the single opportunity for plants to move, seed dispersal has an important impact on plant fitness, species distributions and patterns of biodiversity. However, models that predict dynamics such as risk of extinction, range shifts and biodiversity loss tend to rely on the mean value of parameters and rarely incorporate realistic dispersal mechanisms. By focusing on the mean population value, variation among individuals or variability caused by complex spatial and temporal dynamics is ignored. This calls for increased efforts to understand individual variation in dispersal and integrate it more explicitly into population and community models involving dispersal. However, the sources, magnitude and outcomes of intraspecific variation in dispersal are poorly characterized, limiting our understanding of the role of dispersal in mediating the dynamics of communities and their response to global change. In this manuscript, we synthesize recent research that examines the sources of individual variation in dispersal and emphasize its implications for plant fitness, populations and communities. We argue that this intraspecific variation in seed dispersal does not simply add noise to systems, but, in fact, alters dispersal processes and patterns with consequences for demography, communities, evolution and response to anthropogenic changes. We conclude with recommendations for moving this field of research forward.

As the primary decomposers of organic material in terrestrial ecosystems, fungi are critical agents of the global carbon cycle. Yet our ability to link fungal community composition to ecosystem functioning is constrained by a limited understanding of the factors accounting for different wood decomposition rates among fungi. Here we examine which traits best explain fungal decomposition ability by combining detailed trait-based assays on 34 saprotrophic fungi from across North America in the laboratory with a 5-y field study comprising 1,582 fungi isolated from 74 decomposing logs. Fungal growth rate (hyphal extension rate) was the strongest single predictor of fungal-mediated wood decomposition rate under laboratory conditions, and accounted for up to 27% of the in situ variation in decomposition in the field. At the individual level, decomposition rate was negatively correlated with moisture niche width (an indicator of drought stress tolerance) and with the production of nutrient-mineralizing extracellular enzymes. Together, these results suggest that decomposition rates strongly align with a dominance-tolerance life-history trade-off that was previously identified in these isolates, forming a spectrum from slow-growing, stress-tolerant fungi that are poor decomposers to fast-growing, highly competitive fungi with fast decomposition rates. Our study illustrates how an understanding of fungal trait variation could improve our predictive ability of the early and midstages of wood decay, to which our findings are most applicable. By mapping our results onto the biogeographic distribution of the dominance-tolerance trade-off across North America, we approximate broad-scale patterns in intrinsic fungal-mediated wood decomposition rates.

Although climate warming is expected to make habitat beyond species' current cold range edge suitable for future colonization, this new habitat may present an array of biotic or abiotic conditions not experienced within the current range. Species' ability to shift their range with climate change may therefore depend on how populations evolve in response to such novel environmental conditions. However, due to the recent nature of thus far observed range expansions, the role of rapid adaptation during climate change migration is only beginning to be understood. Here, we evaluated evolution during the recent native range expansion of the annual plant Dittrichia graveolens, which is spreading northward in Europe from the Mediterranean region. We examined genetically based differentiation between core and edge populations in their phenology, a trait that is likely under selection with shorter growing seasons and greater seasonality at northern latitudes. In parallel common garden experiments at range edges in Switzerland and the Netherlands, we grew plants from Dutch, Swiss, and central and southern French populations. Population genetic analysis following RAD-sequencing of these populations supported the hypothesized central France origins of the Swiss and Dutch range edge populations. We found that in both common gardens, northern plants flowered up to 4 weeks earlier than southern plants. This differentiation in phenology extended from the core of the range to the Netherlands, a region only reached from central France over approximately the last 50 years. Fitness decreased as plants flowered later, supporting the hypothesized benefits of earlier flowering at the range edge. Our results suggest that native range expanding populations can rapidly adapt to novel environmental conditions in the expanded range, potentially promoting their ability to spread.

Abstract. Foundation species have a major impact on biotic and abiotic processes and create a stable environment for many other species. Eastern hemlock (Tsuga canadensis), a foundation tree species native to North America, is currently declining due to infestation by an invasive insect, the hemlock woolly adelgid (Adelges tsugae). Loss of hemlock canopies can greatly alter the dark, cool, and damp microclimate of hemlock forests. We studied five years of microclimatic changes following logging or girdling (to simulate physical effects of adelgid) of hemlocks in a multi-hectare-scale experiment in a New England forest. Both logging and girdling of hemlocks caused large changes in light availability, air and soil temperature, and soil moisture. Even though the impact of logging was more rapid than the effect of gradual hemlock mortality after girdling, the microclimatic changes in these two canopy treatments converged over time. The microclimate in hardwood control plots, which represent the predicted forest composition 50 years after hemlock loss, was intermediate between the two canopy treatments and the hemlock control plots. Our fine-scale results were generally consistent with average microclimatic effects observed in comparative studies but revealed additional changes in variance and seasonal rhythms, and the importance of stochastic events such as ice storms. The variance in air temperature, but not in soil temperature, greatly increased after loss of hemlock. We also observed a striking saw-tooth pattern, consisting of a small peak before budbreak in temperature differentials between hemlock control and the two canopy treatments-likely due to the insulating hemlock canopy preventing snow from melting-followed by a larger difference in temperatures after bud-break. We expect the ongoing decline of eastern hemlock-due to both infestation and pre-emptive salvage logging-to greatly impact the microclimate of hemlock forests, as well as the many taxa that are associated with it.