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1. The timing of heat waves has multiyear effects on milkweed and its insect community

   https://doi.org/10.1002/ecy.3988  

   Cope, Olivia L. ; Zehr, Luke N. ; Agrawal, Anurag A. ; Wetzel, William C. ( March 2023 , Ecology)

   Extreme heat events are becoming more frequent and intense as climate variability increases, and these events inherently vary in their timing. We predicted that the timing of a heat wave would determine its consequences for insect communities owing to temporal variation in the susceptibility of host plants to heat stress. We subjected common milkweed (Asclepias syriaca) plants to in‐field experimental heat waves to investigate how the timing of heat waves, both seasonally and relative to a biotic stressor (experimental herbivory), affected their ecological consequences. We found that heat waves had multiyear, timing‐specific effects on plant–insect communities. Early‐season heat waves led to greater and more persistent effects on plants and herbivore communities than late‐season heat waves. Heat waves following experimental herbivory had reduced consequences. Our results show that extreme climate events can have complex, lasting ecological effects beyond the year of the event—and that timing is key to understanding those effects.

    

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2. Developmental timing of extreme temperature events (heat waves) disrupts host–parasitoid interactions

   https://doi.org/10.1002/ece3.8618  

   Moore, Megan Elizabeth ; Hill, Christina A. ; Kingsolver, Joel G. ( March 2022 , Ecology and Evolution)

   When thermal tolerances differ between interacting species, extreme temperature events (heat waves) will alter the ecological outcomes. The parasitoid waspCotesia congregatasuffers high mortality when reared throughout development at temperatures that are nonstressful for its host,Manduca sexta. However, the effects of short‐term heat stress during parasitoid development are unknown in this host–parasitoid system.

   Here, we investigate how duration of exposure, daily maximum temperature, and the developmental timing of heat waves impact the performance ofC.congregataand its host¸M.sexta. We find that the developmental timing of short‐term heat waves strongly determines parasitoid and host outcomes.

   Heat waves during parasitoid embryonic development resulted in complete wasp mortality and the production of giant, long‐lived hosts. Heat waves during the 1st‐instar had little effect on wasp success, whereas heat waves during the parasitoid's nutritionally and hormonally critical 2nd instar greatly reduced wasp emergence and eclosion. The temperature and duration of heat waves experienced early in development determined what proportion of hosts had complete parasitoid mortality and abnormal phenotypes.

   Our results suggest that the timing of extreme temperature events will be crucial to determining the ecological impacts on this host–parasitoid system. Discrepancies in thermal tolerance between interacting species and across development will have important ramifications on ecosystem responses to climate change.

    

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3. Seed type and origin‐dependent seedling emergence patterns in Danthonia californica , a species commonly used in grassland restoration

   https://doi.org/10.1002/pei3.10105  

   Jones, S. Holden ; Reed, Paul B. ; Roy, Bitty A. ; Morris, William F. ; DeMarche, Megan L. ( April 2023 , Plant-Environment Interactions)

   Danthonia californicaBolander (Poaceae)is a native perennial bunchgrass commonly used in the restoration of prairie ecosystems in the western United States. Plants of this species simultaneously produce both chasmogamous (potentially outcrossed) and cleistogamous (obligately self‐fertilized) seeds. Restoration practitioners almost exclusively use chasmogamous seeds for outplanting, which are predicted to perform better in novel environments due to their greater genetic diversity. Meanwhile, cleistogamous seeds may exhibit greater local adaptation to the conditions in which the maternal plant exists. We performed a common garden experiment at two sites in the Willamette Valley, Oregon, to assess the influence of seed type and source population (eight populations from a latitudinal gradient) on seedling emergence and found no evidence of local adaptation for either seed type. Cleistogamous seeds outperformed chasmogamous seeds, regardless of whether seeds were sourced directly from the common gardens (local seeds) or other populations (nonlocal seeds). Furthermore, average seed weight had a strong positive effect on seedling emergence, despite the fact that chasmogamous seeds had significantly greater mass than cleistogamous seeds. At one common garden, we observed that seeds of both types sourced from north of our planting site performed significantly better than local or southern‐sourced seeds. We also found a significant seed type and distance‐dependent interaction, with cleistogamous seedling emergence peaking approximately 125 km from the garden. These results suggest that cleistogamous seeds should be considered for greater use inD. californicarestoration.

    

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4. Data from: Plant-soil microbe feedbacks depend on distance and ploidy in a mixed cytotype population of Larrea tridentata

   https://doi.org/10.5061/dryad.bk3j9kdk7  

   Gerstner, Benjamin ; Laport, Robert ; Rudgers, Jennifer ; Whitney, Kenneth ( January 2023 , Dryad)

   Premise of the study Theory predicts that mixed ploidy populations should be short-lived due to strong fitness disadvantages for the rare ploidy. However, mixed ploidy populations are common, suggesting that the fitness costs for rare ploidies are counterbalanced by ecological benefits that emerge when rare. We investigated whether differences in ecological interactions with soil microbes help to maintain a tetraploid-hexaploid population of Larrea tridentata (creosote bush) in the Sonoran Desert, California, USA, where prior work documented ploidy-specific root-associated microbes. Methods We used a plant-soil feedback (PSF) experiment to test whether host-specific soil microbes can alter the outcomes of intra-ploidy vs. inter-ploidy competition. Host-specific soil microbes can build up over time; thus, distance from a host plant can affect the fitness of nearby plants. Key results Seedlings grown in soils from near plants of a different ploidy produced greater biomass relative to seedlings grown in soils from near plants of the same ploidy. Moreover, seedlings grown in soils from near plants of a different ploidy produced greater biomass than those grown in soils from further away from plants of a different ploidy. This suggests the ecological consequences of PSF may facilitate the persistence of mixed ploidy populations. Conclusions This is the first evidence, to our knowledge, consistent with plant-soil microbe feedback as a viable mechanism to maintain the coexistence of multiple ploidy levels in a single population. 

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5. Seedling survival declines with increasing conspecific density in a common temperate tree

   https://doi.org/10.1002/ecs2.3292  

   Jevon, Fiona V. ; Record, Sydne ; Grady, John ; Lang, Ashley K. ; Orwig, David A. ; Ayres, Matthew P. ; Matthes, Jaclyn Hatala ( November 2020 , Ecosphere)

   Feedbacks between plants and their soil microbial communities often drive negative density dependence in rare, tropical tree species, but their importance to common, temperate trees remains unclear. Additionally, whether negative density dependence is driven by natural enemies (e.g., soil pathogens) or by high densities of seedlings has rarely been assessed. Density dependence may also depend on seedling size, as smaller and/or younger seedlings may be more susceptible to mortality agents. We monitored seedlings ofQuercus rubra, a common, canopy‐dominant temperate tree, to investigate how the density of neighboring adults and seedlings influenced their survival over two years. We assessed how the soil microbial community influenced seedling survival by growing seedlings in a glasshouse inoculated with soil collected from beneath conspecific and heterospecific mature trees. In the field, seedling survival was lower in areas with high densities of mature conspecifics but was unrelated to either conspecific or heterospecific seedling density. Smaller seedlings were also more sensitive than larger seedlings to neighboring adult conspecifics. In the glasshouse, seedlings grown with soil from beneath a conspecific adult had a higher mortality rate than seedlings grown with soil from beneath heterospecific adults or sterilized soil, suggesting that soil microbial communities drive the patterns of mortality in the field. These results illustrate the importance of negative density‐dependent feedbacks resulting from the soil microbial community in a common and ecologically important temperate tree species.

    

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