Trends in Ecology & Evolution
ReviewFunctional Rarity: The Ecology of Outliers
Section snippets
The Multiple Facets of Rarity
Rarity has fascinated ecologists and evolutionary biologists [1], and has become the cornerstone of many research fields, and especially of conservation biology 2, 3, 4. Why do species become rare? Why are there so many rare species on Earth? Many studies have examined the biological characteristics of species with a view to explaining the reasons for their rarity (e.g., 5, 6, 7, 8, 9) and the potential consequences of their extirpation 3, 4. Rare species perform different functions in
On the Importance of Functional Rarity
The maintenance of scarce and unique phenotypes in communities is a well-known phenomenon because lower frequency and greater distinctiveness limit both intra- and interspecific competition (negative frequency-dependence) [32]. It has also been described as a ‘strategy' for a species to expand its niche width via a release of intraspecific competition or the exploitation of alternative resources [33]. In addition, both microbial experiments and theoretical studies have emphasized the positive
Functional Rarity: A Conceptual Framework
The definition of functional rarity is the most crucial conceptual point before making significant progress in this new ecology of outliers.
For decades ecological rarity has been estimated at the species level using three main characteristics ultimately related to extinction risk [41]: geographical range, habitat specificity, and local abundance. The combination of these three characteristics defines seven forms of species rarity [21], with the rarest species having small range, a high level of
Measuring Functional Rarity
For over three decades a myriad of metrics have been developed to quantify many facets of biodiversity 57, 58, 59, 60, 61, 62, 63. However, this prolific field has poorly integrated the measurement of functional rarity versus commonness.
To combine the different facets of rarity (Table 1 and Box 1) into a single index, we propose an ‘integrated' view of functional rarity that accounts for both the functional distinctiveness/uniqueness of a species (based on traits, Box 2) and its taxonomic
Functional Rarity and Ecosystem Functioning
Assessing the importance of functional rarity in BEF will require appropriate design to disentangle the effects of species functional distinctiveness and species scarcity. To this end, we propose hypothetical scenarios wherein the influence of biodiversity loss on the shape of BEF relationships (Figure 1) depends on species functional rarity according to the four categories identified at local scale in Figure I. Indeed, if ecosystem functions such as productivity are expected to decrease with
Functional Rarity Across the Tree of Life
An evolutionary perspective on functional rarity can shed light on the processes that are at the origin of functional rarity across the tree of life and allow its maintenance. Although no work has been done so far following our suggested framework, there is a long tradition in evolutionary biology to investigate how ecological specializations evolves (e.g., 71, 72). Pioneering work by Futuyma and Moreno [73] has focused on specialization for resource in terms of diet and feeding behavior.
Concluding Remarks
Our framework for measuring functional rarity paves the way for an ecology of outliers, which allows a deeper understanding of the role of individuals, genotypes, or species bearing distinct trait values within populations, ecosystems, or biomes. A conservation strategy for ecological outliers can also emerge beyond the identification of areas where functional and evolutionary distinctiveness tend to aggregate [79]. For instance, the effectiveness of protected areas for ecological outliers is
Acknowledgments
This research is supported by the French Foundation for Research on Biodiversity (FRB; www.fondationbiodiversite.fr) in the context of the CESAB project ‘Causes and consequences of functional rarity from local to global scales’ (FREE). CV is supported by the European Research Council (ERC) Starting Grant Project ‘Ecophysiological and biophysical constraints on domestication in crop plants’ (Grant ERC-StG-2014-639706-CONSTRAINTS). WT acknowledges support from the European Research Council
Glossary
- Ecology of outliers
- a research area that studies how and why species (or organisms) are outliers given their local or regional abundances and trait distinctiveness, and the consequences of the persistence of those outliers for the structure and dynamics of communities and ecosystems.
- Functional distinctiveness (or trait distinctiveness)
- local-scale characteristics of a species (or an organism) having traits dissimilar from those of other species (organisms) in the community. A metric of functional
References (100)
- et al.
The biology of rarity: patterns, causes, and consequences
Trends Ecol. Evol.
(1993) Fifteens forms of biodiversity trend in the Anthropocene
Trends Ecol. Evol.
(2015)Rebuilding community ecology from functional traits
Trends Ecol. Evol.
(2006)The return of the variance: intraspecific variability in community ecology
Trends Ecol. Evol.
(2012)Phylogenetic diversity and nature conservation: where are we?
Trends Ecol. Evol.
(2013)Distribution and conservation of global evolutionary distinctness in birds
Curr. Biol.
(2014)Vegetation ecology meets ecosystem science: permanent grasslands as a functional biogeography case study
Sci. Tot. Env.
(2015)Emergent neutrality
Trends Ecol. Evol.
(2006)Conservation Biology: the Science of Scarcity and Diversity
(1986)Rarity
(1994)
The Biology of Rarity: Causes and Consequences of Rare-Common Differences
What do we really know about extinction?
How plant life-history and ecological traits relate to species rarity and commonness at varying spatial scales
Ecology
Do rock endemic and widespread plant species differ under the leaf-height-seed plant ecology strategy scheme?
Ecol. Lett.
Rarity and body size: generality is important
Conserv. Biol.
The value of structuring rarity: the seven types and links to reproductive ecology
Biol. Conserv.
The importance of rare species: a trait-based assessment of rare species contributions to functional diversity and possible ecosystem function in tall-grass prairies
Ecol. Evol.
Plant attribute diversity, resilience and ecosystem function: the nature and significance of dominant and minor species
Ecosystems
Realistic losses of rare species disproportionately impact higher trophic levels
Ecol. Lett.
Rare species and ecosystem functioning
Conserv. Biol.
An inordinate foundness of rarity
PLoS Biol.
Loss of rare fish species from tropical floodplain food webs affects community structure and ecosystem multifunctionality in a mesocosm experiment
PLoS One
Dissociating several forms of commonness in birds sheds new light on biotic homogenization
Global Ecol. Biogeogr.
Measuring and explaining large-scale distribution of functional and phylogenetic diversity in birds: separating ecological drivers from methodological choices
Global Ecol. Biogeogr.
The functions of biological diversity in an age of extinction
Science
Essential biodiversity variables
Science
Seven forms of rarity
From Plant Traits to Vegetation Structure. Chance and Selection in the Assembly of Ecological Communities
The emergence and promise of functional biogeography
Proc. Natl Acad. Sci. U.S.A.
Applying trait-based models to achieve functional targets for theory-driven ecological restoration
Ecol. Lett.
Predicting communities from functional traits
Trends Ecol. Evol.
Effects of biodiversity on ecosystem functioning: a consensus of current knowledge
Ecol. Monogr.
Functional diversity – at the crossroads between ecosystem functioning and environmental filters
Beyond species: functional diversity and the maintenance of ecological processes and services
J. Appl. Ecol.
Challenges in the quest for keystones
BioScience
The biodiversity-dependent ecosystem service debt
Ecol. Lett.
The importance of niches for the maintenance of species diversity
Nature
Evolution of niche width
Am. Nat.
Biodiversity as spatial insurance in heterogeneous landscapes
Proc. Natl Acad. Sci. U.S.A.
Community rescue in experimental metacommunities
Proc. Natl Acad. Sci. U.S.A.
Extinction and ecosystem function in the marine benthos
Science
Benefits of plant diversity to ecosystems: immediate, filter and founder effects
J. Ecol.
Extinction rates of North American freshwater fauna
Conserv. Biol.
Rapid worldwide depletion of predatory fish communities
Nature
Rare species support vulnerable functions in high-diversity ecosystems
PLoS Biol.
Long-term differences in extinction risk among the seven forms of rarity
Proc. R. Soc. B
Plant ecological strategies: some leading dimensions of variation between species
Annu. Rev. Ecol. Evol. Syst.
A novel framework for linking functional diversity of plants with other trophic levels for the quantification of ecosystem services
J. Veg. Sci.
Predicting changes in community composition and ecosystem functioning from plant traits: revisiting the Holy Grail
Funct. Ecol.
Let the concept of trait be functional!
Oikos
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