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1. Rare species do not disproportionately contribute to phylogenetic diversity in a subalpine plant community

   https://doi.org/10.1002/ajb2.70061  

   Veldhuisen, Leah N; Zepeda, Verónica; Enquist, Brian J; Dlugosch, Katrina M (June 2025, American Journal of Botany)

   Abstract PremiseWithin plant communities, few species are abundant, and most are locally rare. Worldwide, 36% of plant species are exceedingly rare and often face high extinction risk. However, the community phylogenetic impact of the loss of rare plants is largely unknown in many systems. We address this gap by investigating how rare species contribute to phylogenetic diversity, considering multiple metrics of rarity and multiple elevations in a subalpine plant community. MethodsWe collected abundance data at three sites near the Rocky Mountain Biological Laboratory (Colorado, USA). We calculated each species' range size from public occurrence data. We calculated phylogenetic signal for abundance and range size, compared community phylogenetic metrics weighted by range size and abundance to unweighted metrics, and quantified the change in phylogenetic diversity when removing single species and groups of species ranked by rarity. ResultsWe found phylogenetic signal for abundance, but not range size. There was no difference between rarity‐weighted and ‐unweighted phylogenetic diversity metrics. Finally, phylogenetic diversity did not decline more when we removed single rare species or groups of rare species than when we removed single common species and groups of common species. ConclusionsWe found that rare species, whether at low abundance or with a small range, do not disproportionately contribute to phylogenetic diversity in our subalpine plant community. These results were consistent across elevations. Instead, rare species might provide phylogenetic redundancy with common species. Deeper understanding of functional differentiation is needed to understand contributions of rare species to this system. 

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2. Traits of dominant plant species drive normalized difference vegetation index in grasslands globally

   https://doi.org/10.1111/geb.13644  

   Engel, Thore; Bruelheide, Helge; Hoss, Daniela; Sabatini, Francesco M; Altman, Jan; Arfin‐Khan, Mohammed_A S; Bergmeier, Erwin; Černý, Tomáš; Chytrý, Milan; Dainese, Matteo; et al (May 2023, Global Ecology and Biogeography)

   Abstract AimTheoretical, experimental and observational studies have shown that biodiversity–ecosystem functioning (BEF) relationships are influenced by functional community structure through two mutually non‐exclusive mechanisms: (1) the dominance effect (which relates to the traits of the dominant species); and (2) the niche partitioning effect [which relates to functional diversity (FD)]. Although both mechanisms have been studied in plant communities and experiments at small spatial extents, it remains unclear whether evidence from small‐extent case studies translates into a generalizable macroecological pattern. Here, we evaluate dominance and niche partitioning effects simultaneously in grassland systems world‐wide. LocationTwo thousand nine hundred and forty‐one grassland plots globally. Time period2000–2014. Major taxa studiedVascular plants. MethodsWe obtained plot‐based data on functional community structure from the global vegetation plot database “sPlot”, which combines species composition with plant trait data from the “TRY” database. We used data on the community‐weighted mean (CWM) and FD for 18 ecologically relevant plant traits. As an indicator of primary productivity, we extracted the satellite‐derived normalized difference vegetation index (NDVI) from MODIS. Using generalized additive models and deviation partitioning, we estimated the contributions of trait CWM and FD to the variation in annual maximum NDVI, while controlling for climatic variables and spatial structure. ResultsGrassland communities dominated by relatively tall species with acquisitive traits had higher NDVI values, suggesting the prevalence of dominance effects for BEF relationships. We found no support for niche partitioning for the functional traits analysed, because NDVI remained unaffected by FD. Most of the predictive power of traits was shared by climatic predictors and spatial coordinates. This highlights the importance of community assembly processes for BEF relationships in natural communities. Main conclusionsOur analysis provides empirical evidence that plant functional community structure and global patterns in primary productivity are linked through the resource economics and size traits of the dominant species. This is an important test of the hypotheses underlying BEF relationships at the global scale. 

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3. Pawpaws prevent predictability: A locally dominant tree alters understory beta‐diversity and community assembly

   https://doi.org/10.1002/ecs2.70115  

   Wassel, Anna C; Myers, Jonathan A (January 2025, Ecosphere)

   Abstract While dominant species are known to be important in ecosystem functioning and community assembly, biodiversity responses to the presence of dominant species can be highly variable. Dominant species can increase the importance of deterministic community assembly by competitively excluding species in a consistent way across local communities, resulting in low site‐to‐site variation in community composition (beta‐diversity) and nonrandom community structure. In contrast, dominant species could increase the importance of stochastic community assembly by reducing the total number of individuals in local communities (community size), resulting in high beta‐diversity and more random community structure. We tested these hypotheses in a large, temperate oak‐hickory forest plot containing a locally dominant tree species, pawpaw (Asimina triloba; Annonaceae), an understory tree species that occurs in dense, clonal patches in forests throughout the east‐central United States. We determined how the presence of pawpaw influences local species diversity, community size, and beta‐diversity by measuring the abundance of all vascular plant species in 1 × 1‐m plots both inside and outside pawpaw patches. To test whether the presence of pawpaw influences local assembly processes, we compared observed patterns of beta‐diversity inside and outside patches to a null model in which communities were assembled at random with respect to species identity. We found lower local species diversity, lower community size, and higher observed beta‐diversity inside pawpaw patches than outside pawpaw patches. Moreover, standardized effect sizes of beta‐diversity from the null model were lower inside pawpaw patches than outside pawpaw patches, indicating more random species composition inside pawpaw patches. Together these results suggest that pawpaw increases the importance of stochastic relative to deterministic community assembly at local scales, likely by decreasing overall numbers of individuals and increasing random local extinctions inside patches. Our findings provide insights into the ecological processes by which locally dominant tree species shape the assembly and diversity of understory plant communities at different spatial scales. 

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4. Multiple co‐occurring bioeconomic drivers of overexploitation can accelerate rare species extinction risk

   https://doi.org/10.1111/1365-2664.14376  

   Almeida, Ryan J.; Bonachela, Juan A.; Lockwood, Julie L. (May 2023, Journal of Applied Ecology)

   Abstract The unsustainable harvest of species for the global wildlife trade is a major cause of vertebrate extinction. Through the anthropogenic Allee effect (AAE), overexploitation to extinction can occur when a species' rarity drives up its market price, enabling profitable harvest of all remaining individuals. Even in the absence of rarity value, however, the harvest of other species can subsidize the overexploitation of a rare species to the point of extinction, a phenomenon termed opportunistic exploitation. These two pathways to extinction have been considered independently, but many traded species experience them simultaneously.In this study, we develop a simple model that incorporates these mechanisms simultaneously and demonstrate that including multiple harvest strategies with market‐based feedbacks fundamentally alters rare species extinction risk and the rate at which overexploitation occurs. As a pertinent case study, we consider the harvest of ground pangolinsSmutsia temminckii.Our results show that pangolin extinction was generally associated with high rarity value, the use of multiple harvest strategies and the simultaneous harvest of a common species that has a fast life history. Pangolin population depletion and short‐term extinction risk were greatest when harvesters used a combination of pursuit and opportunistic (i.e. multi‐species) harvest strategies.Policy implications.Our results suggest that feedbacks between multiple financial incentives to overharvest can exacerbate the risk of extinction of rare species. As a result, continuing to address AAE and opportunistic exploitation as separate extinction pathways may insufficiently capture extinction risk for many exploited species. Criteria for assessing extinction risk or harvest sustainability of exploited species should incorporate multiple drivers of harvest pressure, with an expanded focus on including species with high rarity value that are exploited in multi‐species harvest regimes. 

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5. Demographic trade-offs and functional shifts in a hurricane-impacted tropical forest

   https://doi.org/10.1093/aob/mcad004  

   Umaña, María Natalia; Needham, Jessica; Forero-Montaña, Jimena; Nytch, Christopher J; Swenson, Nathan G; Thompson, Jill; Uriarte, María; Zimmerman, Jess K (January 2023, Annals of Botany)

   Abstract Background and AimsUnderstanding shifts in the demographic and functional composition of forests after major natural disturbances has become increasingly relevant given the accelerating rates of climate change and elevated frequency of natural disturbances. Although plant demographic strategies are often described across a slow–fast continuum, severe and frequent disturbance events influencing demographic processes may alter the demographic trade-offs and the functional composition of forests. We examined demographic trade-offs and the shifts in functional traits in a hurricane-disturbed forest using long-term data from the Luquillo Forest Dynamics Plot (LFPD) in Puerto Rico. MethodsWe analysed information on growth, survival, seed rain and seedling recruitment for 30 woody species in the LFDP. In addition, we compiled data on leaf, seed and wood functional traits that capture the main ecological strategies for plants. We used this information to identify the main axes of demographic variation for this forest community and evaluate shifts in community-weighted means for traits from 2000 to 2016. Key ResultsThe previously identified growth–survival trade-off was not observed. Instead, we identified a fecundity–growth trade-off and an axis representing seedling-to-adult survival. Both axes formed dimensions independent of resprouting ability. Also, changes in tree species composition during the post-hurricane period reflected a directional shift from seedling and tree communities dominated by acquisitive towards conservative leaf economics traits and large seed mass. Wood specific gravity, however, did not show significant directional changes over time. ConclusionsOur study demonstrates that tree demographic strategies coping with frequent storms and hurricane disturbances deviate from strategies typically observed in undisturbed forests, yet the shifts in functional composition still conform to the expected changes from acquisitive to conservative resource-uptake strategies expected over succession. In the face of increased rates of natural and anthropogenic disturbance in tropical regions, our results anticipate shifts in species demographic trade-offs and different functional dimensions. 

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