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1. Do seed dispersal strategies reflect adaptation to environmental variability?

   https://doi.org/10.1111/1365-2435.14336  

   Van Den Elzen, Courtney L. ; Sigman, Nathan ; Emery, Nancy C. ( April 2023 , Functional Ecology)

   Dispersal is one of the primary mechanisms by which organisms adapt to spatial and temporal variation in the environment. Theory predicts that increasing spatiotemporal variation drives selection for offspring dispersal away from their natal habitat and one another. However, due to inherent difficulties in measuring dispersal in plant systems, there are few empirical tests of the extent to which this hypothesis can explain variation in seed dispersal strategies.

   In this study, we characterized and compared the dispersal patterns of three closely related plant species that segregate across gradients in spatiotemporal variation in seasonal wetlands.

   We tracked individual seeds as they dispersed in their natural habitats to measure seed dispersal distance (the distance travelled from the maternal plant) and inter‐seed spread (distances between dispersed seeds) and to identify the plant traits causing within‐species variation in seed dispersal. We also evaluated the seed traits causing within‐species variation in seed flight distance and terminal velocity in a wind tunnel and a drop tube, respectively.

   We found that average seed dispersal distance was lowest in the species that occupies the most spatiotemporally variable habitat, contradicting our predictions; however, inter‐seed spread was lowest in the species from the least variable habitat, which aligned with our expectations.

   The maternal plant and seed traits explaining intraspecific variation in seed dispersal varied among species as well as the method used to measure dispersal potential. Two traits had non‐intuitive effects on dispersal, including pappus size, which reduced seed flight distance in two of the focal taxa.

   Overall, our results indicate that the differences we detected in seed dispersal among three closely related plant taxa can be only partially explained by current patterns of environmental variability in their respective habitats and that the traits driving within‐species variation in seed dispersal can evolve rapidly and change with the environmental context in which they are measured.

   Read the freePlain Language Summaryfor this article on the Journal blog.

    

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2. Tracking seasonal activity of the western blacklegged tick across California

   https://doi.org/10.1111/1365-2664.13490  

   MacDonald, Andrew J. ; O’Neill, Craig ; Yoshimizu, Melissa H. ; Padgett, Kerry A. ; Larsen, Ashley E. ; Mosher, ed., Brittany ( September 2019 , Journal of Applied Ecology)

   Understanding seasonal patterns of activity, or phenology, of vector species is fundamental to determining seasonality of disease risk and epidemics of vector‐borne disease. Spatiotemporal variation in abiotic conditions can influence variation in phenological patterns and life history events, which can dramatically influence the ecological role and human impact of a species. For arthropod vectors of human diseases such as ticks, these phenological patterns determine human exposure risk, yet how abiotic conditions interact to determine suitable conditions for host‐seeking of vector species is difficult to disentangle.

   Here, we use MaxEnt to model spatial patterns and differences in host‐seeking phenology of the western blacklegged tick (Ixodes pacificus) in California using spatially and temporally refined adult tick occurrence data and similarly refined climate and environmental data. We empirically validate the model using phenological data from field studies conducted at sites across California's latitudinal gradient.

   We find adult tick host‐seeking activity varies substantially throughout the year, as well as across the large latitudinal gradient in the state. Suitable conditions for host‐seeking are found earlier in fall and later in the spring in northern than in southern California. These seasonal patterns are primarily associated with monthly precipitation, minimum winter temperature, and winter precipitation, with maximum monthly temperature possibly playing a more prominent role in limiting host‐seeking activity earlier in the spring in southern than northern California.

   Synthesis and applications. Modelling the seasonal activity of the western blacklegged tick, we find both a longer window for host‐feeding and more protracted risk of human exposure to this vector species in northern than southern California. We further identify key environmental factors associated with these patterns, including precipitation and temperature that are otherwise challenging to elucidate in field and laboratory studies over large spatial scales. Moreover, we illustrate how species distribution models, in combination with temporally refined species occurrence and environmental data, can be used to investigate environmental factors predictive of geographic variation in seasonality or phenology of vector species. This produces not only novel ecological insight, but key information for public health practitioners in managing vector‐borne disease transmission and targeting public outreach and interventions.

    

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3. Soil nutrients and dispersal limitation shape compositional variation in secondary tropical forests across multiple scales

   https://doi.org/10.1111/1365-2745.13126  

   van Breugel, Michiel ; Craven, Dylan ; Lai, Hao Ran ; Baillon, Mario ; Turner, Benjamin L. ; Hall, Jefferson S. ; Chang, ed., Cynthia ( January 2019 , Journal of Ecology)

   Soil resource partitioning and dispersal limitation have been shown to shape the tree community structure of mature tropical forests, but are poorly studied in the context of forest succession. We examined the relative contributions of both ecological processes to the variation in the species composition of young tropical secondary forests at different spatial scales, and if the relative importance of these two ecological processes changed during succession. At the species level, we examined if the association between species abundances and soil fertility differed between early and late successional species and/or changed over the course of succession.

   We used vegetation and soil data from 47 secondary forest sites with two plots each in a tropical agricultural landscape. A distance‐based redundancy analysis and variation partitioning were employed to examine the relative importance of spatial distance (proxy for dispersal limitation) and heterogeneity in soil nutrients (proxy for soil nutrient partitioning) at the landscape scale, and a linear regression to test their effects at the local scale. We examined interspecific variation in species’ responses to successional age and soil nutrients with a joint species distribution model.

   Dispersal limitation and soil niche partitioning drove considerable variation in the composition of plant communities at local and landscape scales. The relative contribution of these two ecological processes changed with scale (local vs. landscape) and topography (lower slope vs. upper slope plots). At the species level, significant abundance–soil fertility associations were mostly positive. Most species became less responsive to soil nutrients over the first few decades of tropical forest succession, probably because light became the main limiting resource in older forests.

   Synthesis.Our key finding is that spatial heterogeneity in soil resources and spatial distance jointly drive compositional variation within and across early successional forests. Our results highlight that a network of forest fragments enhances the resilience of ecological processes and the potential of secondary forests to restore and preserve biodiversity in human‐modified landscapes. To advance our understanding of ecological succession, we need to move beyond single‐factor and local‐scale studies and examine the effects of multiple variables on succession at different spatial scales.

    

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4. Macroimmunology: The drivers and consequences of spatial patterns in wildlife immune defence

   https://doi.org/10.1111/1365-2656.13166  

   Becker, Daniel J. ; Albery, Gregory F. ; Kessler, Maureen K. ; Lunn, Tamika J. ; Falvo, Caylee A. ; Czirják, Gábor Á. ; Martin, Lynn B. ; Plowright, Raina K. ; Fenton, ed., Andy ( January 2020 , Journal of Animal Ecology)

   The prevalence and intensity of parasites in wild hosts varies across space and is a key determinant of infection risk in humans, domestic animals and threatened wildlife. Because the immune system serves as the primary barrier to infection, replication and transmission following exposure, we here consider the environmental drivers of immunity. Spatial variation in parasite pressure, abiotic and biotic conditions, and anthropogenic factors can all shape immunity across spatial scales. Identifying the most important spatial drivers of immunity could help pre‐empt infectious disease risks, especially in the context of how large‐scale factors such as urbanization affect defence by changing environmental conditions.

   We provide a synthesis of how to apply macroecological approaches to the study of ecoimmunology (i.e. macroimmunology). We first review spatial factors that could generate spatial variation in defence, highlighting the need for large‐scale studies that can differentiate competing environmental predictors of immunity and detailing contexts where this approach might be favoured over small‐scale experimental studies. We next conduct a systematic review of the literature to assess the frequency of spatial studies and to classify them according to taxa, immune measures, spatial replication and extent, and statistical methods.

   We review 210 ecoimmunology studies sampling multiple host populations. We show that whereas spatial approaches are relatively common, spatial replication is generally low and unlikely to provide sufficient environmental variation or power to differentiate competing spatial hypotheses. We also highlight statistical biases in macroimmunology, in that few studies characterize and account for spatial dependence statistically, potentially affecting inferences for the relationships between environmental conditions and immune defence.

   We use these findings to describe tools from geostatistics and spatial modelling that can improve inference about the associations between environmental and immunological variation. In particular, we emphasize exploratory tools that can guide spatial sampling and highlight the need for greater use of mixed‐effects models that account for spatial variability while also allowing researchers to account for both individual‐ and habitat‐level covariates.

   We finally discuss future research priorities for macroimmunology, including focusing on latitudinal gradients, range expansions and urbanization as being especially amenable to large‐scale spatial approaches. Methodologically, we highlight critical opportunities posed by assessing spatial variation in host tolerance, using metagenomics to quantify spatial variation in parasite pressure, coupling large‐scale field studies with small‐scale field experiments and longitudinal approaches, and applying statistical tools from macroecology and meta‐analysis to identify generalizable spatial patterns. Such work will facilitate scaling ecoimmunology from individual‐ to habitat‐level insights about the drivers of immune defence and help predict where environmental change may most alter infectious disease risk.

    

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5. Trait sensitivities to seagrass fragmentation across spatial scales shape benthic community structure

   https://doi.org/10.1111/1365-2656.13067  

   Yeager, Lauren A. ; Geyer, Julie K. ; Fodrie, Fredrick Joel ; Rueda, ed., Marta ( August 2019 , Journal of Animal Ecology)

   The structure of local ecological communities is thought to be determined by a series of hierarchical abiotic and biotic filters which select for or against species based on their traits. Many human impacts, like fragmentation, serve to alter environmental conditions across a range of spatial scales and may impact trait–environment interactions.

   We examined the effects of environmental variation associated with habitat fragmentation of seagrass habitat measured from microhabitat to landscape scales in controlling the taxonomic and trait‐based community structure of benthic fauna.

   We measured patterns in species abundance and biomass of seagrass epifauna and infauna sampled using sediment cores from 86 sites (across 21 meadows) in Back Sound, North Carolina, USA. We related local faunal community structure to environmental variation measured at three spatial scales (microhabitat, patch and landscape). Additionally, we tested the value of species traits in predicting species‐specific responses to habitat fragmentation across scales.

   While univariate measures of faunal communities (i.e. total density, biomass and species richness) were positively related to microhabitat‐scale seagrass biomass only, overall community structure was predicted by environmental variation at the microhabitat, patch (i.e. patch size) and landscape (i.e. number of patches, landscape seagrass area) scales. Furthermore, fourth‐corner analysis revealed that species traits explained as much variation in organismal densities as species identity. For example, species with planktonic‐dispersing larvae and deposit‐feeding trophic modes were more abundant in contiguous, high seagrass cover landscapes while suspension feeders favoured more fragmented landscapes.

   We present quantitative evidence supporting hierarchal models of community assembly which predict that interactions between species traits and environmental variation across scales ultimately drive local community composition. Variable responses of individual traits to multiple environmental variables suggest that community assembly processes that act on species via traits related to dispersal, mobility and trophic mode will be altered under habitat fragmentation. Additionally, with increasing global temperatures, the tropical seagrassHalodule wrightiiis predicted to replace the temperateZostera marinaas the dominate seagrass in our study region, therefore potentially favouring species with planktonic‐dispersing larva and weakening the strength of environmental control on community assembly.

    

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