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1. Evaluating the influences of floral traits and pollinator generalism on α and β diversity of heterospecific pollen on stigmas

   https://doi.org/10.1111/1365-2435.14465  

   Ashman, Tia‐Lynn ; Wei, Na ( November 2023 , Functional Ecology)

   Pollinator sharing often leads to receipt of heterospecific pollen (HP) along with conspecific pollen. As a result, flowering plants can accumulate diverse communities of HP on stigmas. While variation in HP diversity is an important selective force contributing to flowering plant fitness, evolution and community assembly, our understanding of the extent and drivers of heterogeneity of HP diversity is limited.

   In this study, we examined the species compositions and abundances of ~1000 HP communities across 59 co‐flowering plant species in three serpentine seep communities in California, USA. We evaluated the variation in HP diversity (γ diversity) across plant species in each seep and asked whether the variation in HP γ diversity was caused by variation in HP diversity within stigmas (α diversity) or HP compositional variation among stigmas (β diversity) due to the replacement of HP species (turnover) or their loss (nestedness) from one stigma to another. We further evaluated the potential drivers of variation in HP α and β diversity using phylogenetic structural equation models.

   We found that variation in HP γ diversity across plant species was driven strongly by differences among species in HP α diversity and to a lesser extent by HP β diversity. HP community turnover contributed more to HP β diversity than nestedness consistently across plant species and seeps, suggesting a general pattern of HP compositional heterogeneity from stigma to stigma. The phylogenetic structural equation models further revealed that floral traits (e.g., stigma area, stigma‐anther distance, stigma exposure) and floral abundance were key in determining HP α diversity by influencing HP abundance (load size), while floral traits and abundance showed variable impact on HP β diversity (turnover and nestedness). Pollination generalism contributed relatively less to HP‐α and β diversity.

   These findings disentangle the heterogeneity in HP diversity at different levels, which is essential for understanding the process underlying patterns of HP receipt in plant communities. That floral traits drive the heterogeneity in HP diversity points to additional avenues by which HP receipt may contribute to plant evolution.

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

    

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2. Differential organization of taxonomic and functional diversity in an urban woody plant metacommunity

   https://doi.org/10.1111/avsc.12266  

   Swan, Christopher M. ; Johnson, Anna ; Nowak, David J. ; Acosta, ed., Alicia ( October 2016 , Applied Vegetation Science)

   Urban ecosystems present an opportunity to study ecological communities in the context of unprecedented environmental change. In the face of urban land conversion, ecologists observe new patterns of species composition, dominance, behaviour and dispersal. We propose a hypothetical socioeconomic template that describes a gradient in human investment in community composition to aid in organizing the human role in shaping urban biodiversity. We asked: (1) what is the relative magnitude of taxonomic and functional turnover of urban woody plant communities across different land‐use types; and (2) do land uses exhibiting higher intensity of human management of biodiversity support higher turnover over those with less human influence?

   Baltimore,MD,USA(39°17′ N, 76°38′ W).

   We examined patterns in woody plant biodiversity across 209 plots of different urban land uses. Six land‐use types were arranged along a gradient in the intensity through which humans are hypothesized to manage species composition at the plot scale. We calculated local, or α‐diversity, and compositional turnover, or β‐diversity, of taxonomic and functional diversity across plots within each land‐use type. We compared the magnitude of these biodiversity measures between land uses to test our conceptual template for how the intensity of human management can predict urban woody plant biodiversity.

   We observed high taxonomic turnover in residential and commercial plots compared with vacant or open space land‐use areas. This was associated with a weaker, but similar, pattern in functional diversity. This was associated with low total abundance in residential and commercial plots. Furthermore, the number of unique species was extremely high in the same land‐use types.

   Our observations help explain why turnover can be high in heavily managed plots relative to vacant land. In patches without heavy human management, we found low levels of turnover. This highlights the importance of assessing diversity both locally and at the level of turnover between patches. Management and policy can benefit from the perspective embodied in the conceptual approach tested here.

    

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3. Tracking the assembly of nested parasite communities: using β-diversity to understand variation in parasite richness and composition over time and scale

   Moss*, W. E. ( January 2020 , Journal of animal ecology)

   Community composition is driven by a few key assembly processes: ecological selection, drift and dispersal. Nested parasite communities represent a powerful study system for understanding the relative importance of these processes and their relationship with biological scale. Quantifying β‐diversity across scales and over time additionally offers mechanistic insights into the ecological processes shaping the distributions of parasites and therefore infectious disease. To examine factors driving parasite community composition, we quantified the parasite communities of 959 amphibian hosts representing two species (the Pacific chorus frog, Pseudacris regilla and the California newt, Taricha torosa) sampled over 3 months from 10 ponds in California. Using additive partitioning, we estimated how much of regional parasite richness (γ‐diversity) was composed of within‐host parasite richness (α‐diversity) and turnover (β‐diversity) at three biological scales: across host individuals, across species and across habitat patches (ponds). We also examined how β‐diversity varied across time at each biological scale. Differences among ponds comprised the majority (40%) of regional parasite diversity, followed by differences among host species (23%) and among host individuals (12%). Host species supported parasite communities that were less similar than expected by null models, consistent with ecological selection, although these differences lessened through time, likely due to high dispersal rates of infectious stages. Host individuals within the same population supported more similar parasite communities than expected, suggesting that host heterogeneity did not strongly impact parasite community composition and that dispersal was high at the individual host-level. Despite the small population sizes of within‐host parasite communities, drift appeared to play a minimal role in structuring community composition. Dispersal and ecological selection appear to jointly drive parasite community assembly, particularly at larger biological scales. The dispersal ability of aquatic parasites with complex life cycles differs strongly across scales, meaning that parasite communities may predictably converge at small scales where dispersal is high, but may be more stochastic and unpredictable at larger scales. Insights into assembly mechanisms within multi‐host, multi‐parasite systems provide opportunities for understanding how to mitigate the spread of infectious diseases within human and wildlife hosts. 

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4. Tracking the assembly of nested parasite communities: Using β ‐diversity to understand variation in parasite richness and composition over time and scale

   https://doi.org/10.1111/1365-2656.13204  

   Moss, Wynne E. ; McDevitt‐Galles, Travis ; Calhoun, Dana M. ; Johnson, Pieter T. J. ; Cattadori, ed., Isabella ( March 2020 , Journal of Animal Ecology)

   Community composition is driven by a few key assembly processes: ecological selection, drift and dispersal. Nested parasite communities represent a powerful study system for understanding the relative importance of these processes and their relationship with biological scale. Quantifyingβ‐diversity across scales and over time additionally offers mechanistic insights into the ecological processes shaping the distributions of parasites and therefore infectious disease.

   To examine factors driving parasite community composition, we quantified the parasite communities of 959 amphibian hosts representing two species (the Pacific chorus frog,Pseudacris regillaand the California newt,Taricha torosa) sampled over 3 months from 10 ponds in California. Using additive partitioning, we estimated how much of regional parasite richness (γ‐diversity) was composed of within‐host parasite richness (α‐diversity) and turnover (β‐diversity) at three biological scales: across host individuals, across species and across habitat patches (ponds). We also examined howβ‐diversity varied across time at each biological scale.

   Differences among ponds comprised the majority (40%) of regional parasite diversity, followed by differences among host species (23%) and among host individuals (12%). Host species supported parasite communities that were less similar than expected by null models, consistent with ecological selection, although these differences lessened through time, likely due to high dispersal rates of infectious stages. Host individuals within the same population supported more similar parasite communities than expected, suggesting that host heterogeneity did not strongly impact parasite community composition and that dispersal was high at the individual host-level. Despite the small population sizes of within‐host parasite communities, drift appeared to play a minimal role in structuring community composition.

   Dispersal and ecological selection appear to jointly drive parasite community assembly, particularly at larger biological scales. The dispersal ability of aquatic parasites with complex life cycles differs strongly across scales, meaning that parasite communities may predictably converge at small scales where dispersal is high, but may be more stochastic and unpredictable at larger scales. Insights into assembly mechanisms within multi‐host, multi‐parasite systems provide opportunities for understanding how to mitigate the spread of infectious diseases within human and wildlife hosts.

    

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5. Compositional variation in grassland plant communities

   https://doi.org/10.1002/ecs2.4542  

   Bakker, Jonathan D. ; Price, Jodi N. ; Henning, Jeremiah A. ; Batzer, Evan E. ; Ohlert, Timothy J. ; Wainwright, Claire E. ; Adler, Peter B. ; Alberti, Juan ; Arnillas, Carlos Alberto ; Biederman, Lori A. ; et al ( June 2023 , Ecosphere)

   Human activities are altering ecological communities around the globe. Understanding the implications of these changes requires that we consider the composition of those communities. However, composition can be summarized by many metrics which in turn are influenced by different ecological processes. For example, incidence‐based metrics strongly reflect species gains or losses, while abundance‐based metrics are minimally affected by changes in the abundance of small or uncommon species. Furthermore, metrics might be correlated with different predictors. We used a globally distributed experiment to examine variation in species composition within 60 grasslands on six continents. Each site had an identical experimental and sampling design: 24 plots × 4 years. We expressed compositional variation within each site—not across sites—using abundance‐ and incidence‐based metrics of the magnitude of dissimilarity (Bray–Curtis and Sorensen, respectively), abundance‐ and incidence‐based measures of the relative importance of replacement (balanced variation and species turnover, respectively), and species richness at two scales (per plot‐year [alpha] and per site [gamma]). Average compositional variation among all plot‐years at a site was high and similar to spatial variation among plots in the pretreatment year, but lower among years in untreated plots. For both types of metrics, most variation was due to replacement rather than nestedness. Differences among sites in overall within‐site compositional variation were related to several predictors. Environmental heterogeneity (expressed as the CV of total aboveground plant biomass in unfertilized plots of the site) was an important predictor for most metrics. Biomass production was a predictor of species turnover and of alpha diversity but not of other metrics. Continentality (measured as annual temperature range) was a strong predictor of Sorensen dissimilarity. Metrics of compositional variation are moderately correlated: knowing the magnitude of dissimilarity at a site provides little insight into whether the variation is driven by replacement processes. Overall, our understanding of compositional variation at a site is enhanced by considering multiple metrics simultaneously. Monitoring programs that explicitly incorporate these implications, both when designing sampling strategies and analyzing data, will have a stronger ability to understand the compositional variation of systems and to quantify the impacts of human activities.

    

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