How specialised must natural enemies be to facilitate coexistence among plants?

The Janzen‐Connell hypothesis proposes that plant interactions with host‐specific antagonists can impair the fitness of locally abundant species and thereby facilitate coexistence. However, insects and pathogens that associate with multiple hosts may mediate exclusion rather than coexistence. We employ a simulation model to examine the effect of enemy host breadth on plant species richness and defence community structure, and to assess expected diversity maintenance in example systems. Only models in which plant enemy similarity declines rapidly with defence similarity support greater species richness than models of neutral drift. In contrast, a wide range of enemy host breadths result in spatial dispersion of defence traits, at both landscape and local scales, indicating that enemy‐mediated competition may increase defence‐trait diversity without enhancing species richness. Nevertheless, insect and pathogen host associations in Panama and Papua New Guinea demonstrate a potential to enhance plant species richness and defence‐trait diversity comparable to strictly specialised enemies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99082/1/ele12130.pd

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

International audienceThe relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential

Limits to reproduction and seed size-number tradeoffs that shape forest dominance and future recovery

The relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential

783 Effects of dispersal, shrubs, and densitydependent

mortality on seed and seedling distributions in temperate forest

When ‘Higher’ means ‘Hungrier’: Climate and population trait differences drive increased insect herbivory with elevation in a perennial subalpine wildflower

Because short growing seasons severely constrain plant growth and biomass accumulation in high elevation habitats, herbivory can profoundly impact both individual fitness and community dynamics in these settings. All else being equal, climate change is expected to increase the activity of insect herbivores as their metabolic rates rise with temperature. However, montane species may have more complex responses than those in agricultural or lowland ecosystems, since many factors that shape plant-insect interactions, including temperature, shift with elevation. From 2016 to 2018 we conducted field observations of grasshopper herbivory on subalpine lupines in Mt. Rainier National Park and combined these with multiple leaf trait analyses and a set of manipulative feeding trials to explore how insect herbivory varies along a climatic gradient, and whether differences in plant or insect herbivore phenotypes that are influenced by a population's climatic history can explain these patterns. We found a significant increase in herbivory with elevation that was related to both abiotic drivers, particularly snowmelt timing, and population traits, particularly leaf nutrition and grasshopper feeding rates. Our results suggest that some high-elevation plants may already be experiencing ecologically meaningful levels of insect herbivory that could intensify with climate warming. They also highlight the complexity of predicting how species interactions will change with warming in alpine and subalpine ecosystems, where environmental plasticity or local adaptation driven by elevational differences in climate may lend tremendous complexity to ecological dynamics.ISSN:2666-900

forestexplorR: an R package for the exploration and analysis of stem-mapped forest stand data

Stem-mapped forest stands offer important opportunities for investigating the fine-scale spatial processes occurring in forest ecosystems. These stands are areas of the forest where the precise locations and repeated size measurements of each tree are recorded, thereby enabling the calculation of spatially-explicit metrics of individual growth rates and of the entire tree community. The most common use of these datasets is to investigate the drivers of variation in forest processes by modeling tree growth rate or mortality as a function of these neighborhood metrics. However, neighborhood metrics could also serve as important covariates of many other spatially variable forest processes, including seedling recruitment, herbivory and soil microbial community composition. Widespread use of stem-mapped forest stand datasets is currently hampered by the lack of standardized, efficient and easy-to-use tools to calculate tree dynamics (e.g. growth, mortality) and the neighborhood metrics that impact them. We present the forestexplorR package that facilitates the munging, exploration, visualization and analysis of stem-mapped forest stands. By providing flexible, user-friendly functions that calculate neighborhood metrics and implement a recently-developed rapid-fitting tree growth and mortality model, forestexplorR broadens the accessibility of stem-mapped forest stand data. We demonstrate the functionality of forestexplorR by using it to investigate how the species identity of neighboring trees influences the growth rates of three common tree species in Mt Rainier National Park, WA, USA. forestexplorR is designed to facilitate researchers to incorporate spatially-explicit descriptions of tree communities in their studies and we expect this increased diversity of contributors to develop exciting new ways of using stem-mapped forest stand data.ISSN:0906-7590ISSN:1600-058

Species-specific differences in bumblebee worker body size between different elevations: Implications for pollinator community structure under climate change

Pollinator populations face growing threats from global climate change, particularly in alpine environments with rapidly rising temperatures. Understanding how bumblebees, critical alpine pollinators, respond to these temperature changes is therefore an important goal. Predicting species’ responses to climate change requires several different approaches, one of which is to compare processes at different elevations, which experience different temperature regimes. Bumblebee body size is linked to fitness through its influence on nutritional requirements and foraging capacity. It is also a highly plastic trait that depends on ecological factors such as temperature. Thus, understanding how body size varies at different elevations may help predict bumblebee fitness under climate change. We collected bumblebee workers from five species in a single growing season, at two distinct elevations in the Swiss Alps. Our study aimed to examine whether body size responses differed among species and across functional traits related to foraging and nesting. Larger body size is thought to confer an advantage under cold conditions; we therefore expected greater body size with elevation, but with species-specific relationships. Contrary to our expectation, not all species were larger at high elevations. Specifically, while two species were significantly larger at high elevation, one (Bombus terrestris) was significantly smaller at high elevation, and two showed no size differences with elevation. Additionally, interspecific variation in body size was greater at low elevations. This suggests a divergence of body size with warming, although local factors may also play a role in shaping functional traits

Code and data suppporting "Theobald, Breckheimer, and HilleRisLambers. 2017. Climate drives phenological reassembly of a mountain wildflower meadow community. In Press. Ecology

Identical to v1.0, but a new release is required for Zenodo archiving and DOI assignment