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1. Plasticity in response to plant–plant interactions and water availability

   https://doi.org/10.1002/ecy.3361  

   Wang, Shu ; Callaway, Ragan M. ( May 2021 , Ecology)

   The plastic responses of plants to abiotic and biotic environmental factors have generally been addressed separately; thus we have a poor understanding of how these factors interact. For example, little is known about the effects of plant–plant interactions on the plasticity of plants in response to water availability. Furthermore, few studies have compared the effects of intra‐ and interspecific interactions on plastic responses to abiotic factors. To explore the effects of intraspecific and interspecific plant–plant interactions on plant responses to water availability, we grewLeucanthemumvulgareandPotentillarectawith a conspecific or the other species, and grew pairs of each species as controls in pots with the roots, but not shoots, physically separated. We subjected these competitive arrangements to mesic and dry conditions, and then measured shoot mass, root mass, total mass and root : shoot ratio and calculated plasticity in these traits. The total biomass of both species was highly suppressed by both intra‐ and interspecific interactions in mesic soil conditions. However, in drier soil, intraspecific interactions for both species and the effect ofP. rectaonL. vulgarewere facilitative. For plasticity in response to water supply, when adjusted for total biomass, drought increased shoot mass, and decreased root mass and root : shoot ratios for both species in intraspecific interactions. When grown alone, there were no plastic responses in any trait except total mass, for either species. Our results suggested that plants interacting with other plants often show improved tolerance for drought than those grown alone, perhaps because of neighbor‐induced shifts in plasticity in biomass allocation. Facilitative effects might also be promoted by plasticity to drought in root : shoot ratios.

    

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2. How do lianas and vines influence competitive differences and niche differences among tree species? Concepts and a case study in a tropical forest

   https://doi.org/10.1111/1365-2745.13119  

   Muller‐Landau, Helene C. ; Visser, Marco D. ; Godoy, ed., Oscar ( December 2018 , Journal of Ecology)

   Lianas and other climbing plants are structural parasites of trees, generally reducing host tree survival, growth, and reproduction, yet their influences on the outcome of competition among tree species have remained largely unexplored.

   We propose that there are three distinct components to liana–tree interactions:prevalence, defined as the proportion of infested trees;load, defined as the mean liana cover on infested trees; andtolerance, defined as the effect of a given level of infestation on tree population growth rates. We introduce a new metric that integrates these components, the lianaburden, defined as the total effect of lianas on per capita population growth rates given current prevalence, load, and tolerance. Using these metrics, we quantify variation among 33 co‐occurring tropical tree species in liana–tree interactions and its relation with shade‐tolerance.

   The focal tree species vary strongly in liana prevalence, load, tolerance, and burden. Interspecific variation in tolerance is the largest contributor to interspecific variation in burden. Species rankings of per capita population growth rates under current liana infestation levels differ somewhat from rankings under liana‐free conditions, and differ strongly from rankings under uniformly high liana infestation. Thus, lianas alter competitive hierarchies to benefit tree species that are relatively tolerant of and/or resistant to lianas. Among the focal tree species, shade‐tolerance is positively correlated with liana tolerance and prevalence, but largely unrelated to load and burden, meaning shade‐tolerance does not predict which species are competitively disadvantaged by lianas. We describe a variety of mechanisms by which lianas may potentially increase or decrease niche differences among tree species, including interactions with spatial and temporal environmental niche partitioning, and potential differences among tree species in relative vulnerability to different liana species.

   Synthesis. Lianas, like other natural enemies, can in principle alter competitive hierarchies and niche structure of co‐occurring tree species, and our analyses suggest such influences are substantial in our focal tropical tree community and likely many other tree communities as well. Quantifying these effects requires a more comprehensive approach including analyses and modelling of dynamics of liana–tree interactions and their variation with tree and liana species identities.

    

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3. Range‐wide variations in common milkweed traits and their effect on monarch larvae

   https://doi.org/10.1002/ajb2.1630  

   DeLaMater, David S. ; Couture, John J. ; Puzey, Joshua R. ; Dalgleish, Harmony J. ( March 2021 , American Journal of Botany)

   Leaf economic spectrum (LES) theory has historically been employed to inform vegetation models of ecosystem processes, but largely neglects intraspecific variation and biotic interactions. We attempt to integrate across environment–plant trait–herbivore interactions within a species at a range‐wide scale.

   We measured traits in 53 populations spanning the range of common milkweed (Asclepias syriaca) and used a common garden to determine the role of environment in driving patterns of intraspecific variation. We used a feeding trial to determine the role of plant traits in monarch (Danaus plexippus) larval development.

   Trait–trait relationships largely followed interspecific patterns in LES theory and persisted in a common garden when individual traits change. Common milkweed showed intraspecific variation and biogeographic clines in traits. Clines did not persist in a common garden. Larvae ate more and grew larger when fed plants with more nitrogen. A longitudinal environmental gradient in precipitation corresponded to a resource gradient in plant nitrogen, which produces a gradient in larval performance.

   Biogeographic patterns in common milkweed traits can sometimes be predicted from LES, are largely driven by environmental conditions, and have consequences for monarch larval performance. Changes to nutrient dynamics of landscapes with common milkweed could potentially influence monarch population dynamics. We show how biogeographic trends in intraspecific variation can influence key ecological interactions, especially in common species with large distributions.

    

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4. Climate Change, Ecosystem Processes and Biological Diversity Responses in High Elevation Communities

   https://doi.org/10.3390/cli9050087  

   Seastedt, Timothy ; Oldfather, Meagan ( May 2021 , Climate)

   null (Ed.)

   The populations, species, and communities in high elevation mountainous regions at or above tree line are being impacted by the changing climate. Mountain systems have been recognized as both resilient and extremely threatened by climate change, requiring a more nuanced understanding of potential trajectories of the biotic communities. For high elevation systems in particular, we need to consider how the interactions among climate drivers and topography currently structure the diversity, species composition, and life-history strategies of these communities. Further, predicting biotic responses to changing climate requires knowledge of intra- and inter-specific climate associations within the context of topographically heterogenous landscapes. Changes in temperature, snow, and rain characteristics at regional scales are amplified or attenuated by slope, aspect, and wind patterns occurring at local scales that are often under a hectare or even a meter in extent. Community assemblages are structured by the soil moisture and growing season duration at these local sites, and directional climate change has the potential to alter these two drivers together, independently, or in opposition to one another due to local, intervening variables. Changes threaten species whose water and growing season duration requirements are locally extirpated or species who may be outcompeted by nearby faster-growing, warmer/drier adapted species. However, barring non-analogue climate conditions, species may also be able to more easily track required resource regimes in topographically heterogenous landscapes. New species arrivals composed of competitors, predators and pathogens can further mediate the direct impacts of the changing climate. Plants are moving uphill, demonstrating primary succession with the emergence of new habitats from snow and rock, but these shifts are constrained over the short term by soil limitations and microbes and ultimately by the lack of colonizable terrestrial surfaces. Meanwhile, both subalpine herbaceous and woody species pose threats to more cold-adapted species. Overall, the multiple interacting direct and indirect effects of the changing climate on high elevation systems may lead to multiple potential trajectories for these systems. 

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5. Variability approaching the thermal limits can drive diatom community dynamics

   https://doi.org/10.1002/lno.11430  

   Anderson, Stephanie I. ; Rynearson, Tatiana A. ( March 2020 , Limnology and Oceanography)

   Organismal distributions are largely mediated by temperature, suggesting thermal trait variability plays a key role in defining species' niches. We employed a trait‐based approach to better understand how inter‐ and intraspecific thermal trait variability could explain diatom community dynamics using 24 strains from 5 species in the diatom genusSkeletonema, isolated from Narragansett Bay (NBay), where this genus can comprise up to 99% of the microplankton. Strain‐specific thermal reaction norms were generated using growth rates obtained at temperatures ranging from −2°C to 36°C. Comparison of thermal reaction norms revealed inter‐ and intraspecific similarities in the thermal optima, but significant differences approaching the thermal limits. Cellular elemental composition was determined for two thermally differentiated species and again, the most variation occurred approaching the thermal limits. To determine the potential impact of interspecific variability on community composition, a species succession model was formulated utilizing each species' empirically determined thermal reaction norm and historical temperature data from NBay. Seasonal succession in the modeled community resembled the timing of species occurrence in the field, but not species' relative abundance. The model correctly predicted the timing of the dominant winter–spring species,Skeletonema marinoi, within 0–14 d of its observed peak occurrence in the field. Interspecific variability approaching the thermal limits provides an alternative mechanism for temporal diatom succession, leads to altered cellular elemental composition, and thus has the potential to influence carbon flux and nutrient cycling, suggesting that growth approaching the thermal limits be incorporated into both empirical and modeling efforts in the future.

    

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