Cities are sometimes characterized as homogenous with species assemblages composed of abundant, generalist species having similar ecological functions. Under this assumption, rare species, or species observed infrequently, would have especially high conservation value in cities for their potential to increase functional diversity. Management to increase the number of rare species in cities could be an important conservation strategy in a rapidly urbanizing world. However, most studies of species rarity define rarity in relatively pristine environments where human management and disturbance is minimized. We know little about what species are rare, how many species are rare, and what management practices promote rare species in urban environments. Here, we identified which plants and species of birds and bees that control pests and pollinate crops are rare in urban gardens and assessed how social, biophysical factors, and cross‐taxonomic comparisons influence rare species richness. We found overwhelming numbers of rare species, with more than 50% of plants observed classified as rare. Our results highlight the importance of women, older individuals, and gardeners who live closer to garden sites in increasing the number of rare plants within urban areas. Fewer rare plants were found in older gardens and gardens with more bare soil. There were more rare bird species in larger gardens and more rare bee species for which canopy cover was higher. We also found that in some cases, rarity begets rarity, with positive correlations found between the number of rare plants and bee species and between bee and bird species. Overall, our results suggest that urban gardens include a high number of species existing at low frequency and that social and biophysical factors promoting rare, planned biodiversity can cascade down to promote rare, associated biodiversity.
Understanding the ecological and evolutionary factors that influence species rarity has important theoretical and applied implications, yet the reasons why some species are rare while others are common remain unresolved. As a novel exploration of scientific knowledge, we used network analysis conceptually to visualize the foci of a comprehensive base of >800 studies on plant species rarity within the context of ecology and evolution. In doing so, we highlight existing research strengths that could substantiate novel syntheses and gaps that could inspire new research. Our results reveal strong integrated foci on population dynamics with other ecological concepts. In contrast, despite the potential for ecological and evolutionary processes to interact, few studies explored the interplay of environmental factors and microevolutionary patterns. The cellular and molecular biology, physiology, and plasticity of rare plant species within both ecological and evolutionary contexts similarly provide avenues for impactful future investigations.
more » « less- NSF-PAR ID:
- 10399453
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology and Evolution
- Volume:
- 10
- Issue:
- 17
- ISSN:
- 2045-7758
- Page Range / eLocation ID:
- p. 9037-9047
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Summary Species differ dramatically in their prevalence in the natural world, with many species characterized as rare due to restricted geographic distribution, low local abundance and/or habitat specialization.
We investigated the ecoevolutionary causes and consequences of rarity with phylogenetically controlled metaanalyses of population genetic diversity, fitness and functional traits in rare and common congeneric plant species. Our syntheses included 252 rare species and 267 common congeners reported in 153 peer‐reviewed articles published from 1978 to 2020 and one manuscript in press.
Rare species have reduced population genetic diversity, depressed fitness and smaller reproductive structures than common congeners. Rare species also could suffer from inbreeding depression and reduced fertilization efficiency.
By limiting their capacity to adapt and migrate, these characteristics could influence contemporary patterns of rarity and increase the susceptibility of rare species to rapid environmental change. We recommend that future studies present more nuanced data on the extent of rarity in focal species, expose rare and common species to ecologically relevant treatments, including reciprocal transplants, and conduct quantitative genetic and population genomic analyses across a greater array of systems. This research could elucidate the processes that contribute to rarity and generate robust predictions of extinction risks under global change.
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Abstract Aim Ecological and anthropogenic factors shift the abundances of dominant and rare tree species within local forest communities, thus affecting species composition and ecosystem functioning. To inform forest and conservation management it is important to understand the drivers of dominance and rarity in local tree communities. We answer the following research questions: (1) What are the patterns of dominance and rarity in tree communities? (2) Which ecological and anthropogenic factors predict these patterns? And (3) what is the extinction risk of locally dominant and rare tree species?
Location Global.
Time period 1990–2017.
Major taxa studied Trees.
Methods We used 1.2 million forest plots and quantified local tree dominance as the relative plot basal area of the single most dominant species and local rarity as the percentage of species that contribute together to the least 10% of plot basal area. We mapped global community dominance and rarity using machine learning models and evaluated the ecological and anthropogenic predictors with linear models. Extinction risk, for example threatened status, of geographically widespread dominant and rare species was evaluated.
Results Community dominance and rarity show contrasting latitudinal trends, with boreal forests having high levels of dominance and tropical forests having high levels of rarity. Increasing annual precipitation reduces community dominance, probably because precipitation is related to an increase in tree density and richness. Additionally, stand age is positively related to community dominance, due to stem diameter increase of the most dominant species. Surprisingly, we find that locally dominant and rare species, which are geographically widespread in our data, have an equally high rate of elevated extinction due to declining populations through large‐scale land degradation.
Main conclusions By linking patterns and predictors of community dominance and rarity to extinction risk, our results suggest that also widespread species should be considered in large‐scale management and conservation practices.
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