An official website of the United States government
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.
more »
« less
Using Plant Invasions to Compare Occurrence‐ and Abundance‐Based Calculations of Biotic Homogenisation: Are Results Complementary or Contradictory?
ABSTRACT AimBeta diversity quantifies the similarity of ecological assemblages. Its increase, known as biotic homogenisation, can be a consequence of biological invasions. However, species occurrence (presence/absence) and abundance‐based analyses can produce contradictory assessments of the magnitude and direction of changes in beta diversity. Previous work indicates these contradictions should be less frequent in nature than in theory, but a growing number of empirical studies report discrepancies between occurrence‐ and abundance‐based approaches. Understanding if these discrepancies represent a few isolated cases or are systematic across a diversity of ecosystems would allow us to better understand the general patterns, mechanisms and impacts of biotic homogenisation. LocationUnited States. Time Period1963–2020. Major Taxa StudiedVascular plants. MethodsWe used a dataset of more than 70,000 vegetation survey plots to assess differences in biotic homogenisation with and without invasion using both occurrence‐ and abundance‐based metrics of beta diversity. We estimated taxonomic biotic homogenisation by comparing beta diversity of invaded and uninvaded plots with both classes of metrics and investigated the characteristics of the non‐native species pool that influenced the likelihood that these metrics disagree. ResultsIn 78% of plot comparisons, occurrence‐ and abundance‐based calculations agreed in direction, and the two metrics were generally well correlated. Our empirical results are consistent with previous theory. Discrepancies between the metrics were more likely when the same non‐native species was at high cover at both plots compared for beta diversity, and when these plots were spatially distant. Main ConclusionsIn about 20% of cases, our calculations revealed differences in direction (homogenisation vs. differentiation) when comparing occurrence‐ and abundance‐based metrics, indicating that the metrics are not interchangeable, especially when distances between plots are high and invader diversity is low. When data permit, combining the two approaches can offer insights into the role of invasions and extirpations in driving biotic homogenisation/differentiation.
more »
« less
- Award ID(s):
- 2217817
- PAR ID:
- 10586147
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Global Ecology and Biogeography
- Volume:
- 34
- Issue:
- 3
- ISSN:
- 1466-822X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT Scale‐Dependency of Native StatusClassifying populations as native or nonnative requires well‐defined range boundaries for species. While many studies define native status according to large biogeographic realms, natural dispersal barriers often limit species distributions at regional or smaller spatial extents. As such, native/nonnative definitions are inherently scale‐dependent and estimates of community invadedness thus depend on the spatial resolution at which native status is defined. For example, nonnative species can be introduced among realms, among regions within realms, and among ecological provinces within regions (hereafter, simply “provinces”). By explicitly considering the scale‐dependency of native/nonnative status definitions, we can more effectively compare results across studies, more comprehensively evaluate the degree of invasion levels, and more objectively communicate the native status of a species. Location30,034 stream segments, conterminous United States. Time Period2000–2023. Major Taxa StudiedFreshwater fishes. Quantifying Fish Community Invadedness Across<styled-content style='fixed-case'>US</styled-content>StreamsWe illustrate the importance of scale‐dependent native status definitions by quantifying nonnative species richness and relative abundance in stream fish communities across the United States, finding that provincially nonnative species are nearly four times as prevalent as extra‐realm nonnative species, and represented approximately 10% of all individuals in average community surveys. ImplicationsUnrealistically broad native status definitions underestimate community invadedness. Dismissing regionally and provincially nonnative species can have severe ecological consequences, including displacement and hybridisation with native species and the loss of unique communities through biotic homogenisation. These consequences may undermine efforts to maintain and protect distinct local biodiversity and conserve endemic species.more » « less
-
None (Ed.)Abstract AimEvaluate the temporal changes in species diversity, composition, and structure of ephemeral plant communities and the seed bank in response to long‐term herbivore exclusion over 11 years in plots with and without herbivores. LocationNorth‐central Chile. MethodsWe obtained information on ephemeral vegetation cover in August and September using the intercept point method and recorded seed abundance in April. The Bosque Fray Jorge National Park Long‐Term Socio‐Ecological Research (LTSER) provided these records covering 11 years (2009–2019). From the original experiment of 20 plots, we used eight plots divided into two treatments: four plots allowed free access to all herbivores (with herbivores), while the other four plots excluded herbivores (without herbivores). ResultsWe found that Hill–Shannon diversity increased in plant communities with herbivores and a temporal increase in the cover of the dominant species,Plantago hispidula, under herbivore exclusion. In wet years, species richness and temporal turnover of plant communities increased independently of treatment. Although seed abundance differed among treatments and years, population structure remained constant over time and among treatments, suggesting that the seed bank acts as a buffer against shocks that modify plant community dynamics. Structural equation modeling revealed that precipitation, via its positive effects onPlantago hispidula, increases native plant richness to a greater extent than herbivores. However, in the absence of herbivores, precipitation directly affects native species richness. Moreover, we found that precipitation also influences the native species richness of the seed bank, both directly and indirectly, although its impacts exhibit a time lag. ConclusionsOur study demonstrates that the temporal dynamics of ephemeral plant communities and seed banks in semi‐arid ecosystems are strongly coupled to climate variability, highlighting the vulnerability of these communities to biodiversity loss and climate change.more » « less
-
ABSTRACT AimNon‐native plants have the potential to harm ecosystems. Harm is classically related to their distribution and abundance, but this geographical information is often unknown. Here, we assess geographical commonness as a potential indicator of invasive status for non‐native flora in the United States. Geographical commonness could inform invasion risk assessments across species and ecoregions. LocationConterminous United States. Time PeriodThrough 2022. Major Taxa StudiedPlants. MethodsWe compiled and standardised occurrence and abundance data from 14 spatial datasets and used this information to categorise non‐native species as uncommon or common based on three dimensions of commonness: area of occupancy, habitat breadth and local abundance. To assess consistency in existing categorizations, we compared commonness to invasive status in the United States. We identified species with higher‐than‐expected abundance relative to their occupancy, habitat breadth or residence time. We calculated non‐native plant richness within United States ecoregions and estimated unreported species based on rarefaction/extrapolation curves. ResultsThis comprehensive database identified 1874 non‐native plant species recorded in 4,844,963 locations. Of these, 1221 species were locally abundant (> 10% cover) in 797,759 unique locations. One thousand one hundred one non‐native species (59%) achieved at least one dimension of commonness, including 565 species that achieved all three. Species with longer residence times tended to meet more dimensions of commonness. We identified 132 species with higher‐than‐expected abundance. Ecoregions in the central United States have the largest estimated numbers of unreported, abundant non‐native plants. Main ConclusionsA high proportion of non‐native species have become common in the United States. However, existing categorizations of invasive species are not always consistent with species' abundance and distribution, even after considering residence time. Considering geographical commonness and higher‐than‐expected abundance revealed in this new dataset could support more consistent and proactive identification of invasive plants and lead to more efficient management practices.more » « less
-
Estimating biodiversity change across the planet in the context of widespread human modification is a critical challenge. Here, we review how biodiversity has changed in recent decades across scales and taxonomic groups, focusing on four diversity metrics: species richness, temporal turnover, spatial beta-diversity and abundance. At local scales, change across all metrics includes many examples of both increases and declines and tends to be centred around zero, but with higher prevalence of declining trends in beta-diversity (increasing similarity in composition across space or biotic homogenization) and abundance. The exception to this pattern is temporal turnover, with changes in species composition through time observed in most local assemblages. Less is known about change at regional scales, although several studies suggest that increases in richness are more prevalent than declines. Change at the global scale is the hardest to estimate accurately, but most studies suggest extinction rates are probably outpacing speciation rates, although both are elevated. Recognizing this variability is essential to accurately portray how biodiversity change is unfolding, and highlights how much remains unknown about the magnitude and direction of multiple biodiversity metrics at different scales. Reducing these blind spots is essential to allow appropriate management actions to be deployed. This article is part of the theme issue ‘Detecting and attributing the causes of biodiversity change: needs, gaps and solutions’.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/geb.70022
