Trends in Ecology & Evolution
Volume 35, Issue 11, November 2020, Pages 1037-1047
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Review
The Net Effect of Functional Traits on Fitness

https://doi.org/10.1016/j.tree.2020.07.010Get rights and content

Highlights

  • Community ecology seeks to generalize the effects of traits on performance across species, which may be possible if traits explain variation in population fitness.

  • Linking traits to a specific demographic rate, such as survival or reproduction, is an important step but can be misleading because trade-offs among demographic rates obscure the net effect on fitness.

  • Integrating demographic rates (survival, growth, and reproduction) and computing low density population growth rates incorporates these trade-offs into measures of fitness.

  • Several approaches can be used to quantify the net effect of traits on fitness, and these approaches span a trade-off of empirical rigor and logistical ease.

  • The adaptive value of traits is evident when intrinsic growth rates are explained by trait–environment interactions across multiple coexisting species spanning an environmental gradient.

Generalizing the effect of traits on performance across species may be achievable if traits explain variation in population fitness. However, testing relationships between traits and vital rates to infer effects on fitness can be misleading. Demographic trade-offs can generate variation in vital rates that yield equal population growth rates, thereby obscuring the net effect of traits on fitness. To address this problem, we describe a diversity of approaches to quantify intrinsic growth rates of plant populations, including experiments beyond range boundaries, density-dependent population models built from long-term demographic data, theoretical models, and methods that leverage widely available monitoring data. Linking plant traits directly to intrinsic growth rates is a fundamental step toward rigorous predictions of population dynamics and community assembly.

Section snippets

Demographic Trade-offs and Population Fitness

The alluring prospect that functional traits (see Glossary) can explain variation in species performance has invigorated comparative functional ecology, yet identifying the traits that determine fitness remains an important empirical challenge [1., 2., 3., 4., 5., 6.]. Inspired by classic evolutionary theory that linked morphology to performance and fitness [7], ecologists have recently intensified their search for relationships between functional traits and vital rates, but have avoided the

Vital Rates Can Be Misleading Proxies for Fitness

Individual vital rates can be misleading proxies for fitness without considering demographic trade-offs. For example, species with fast individual growth rates may exhibit low rates of survival. If the growth–survival trade-off can generate covariation in individual growth rates and survival rates that yield equal fitness, all else being equal (e.g., equal reproduction rates), then individual growth rates tell us little about fitness [32,33] (Figure 1). Similarly, populations with high survival

Quantify Intrinsic Growth Rates

Theory predicts that species are sorted along environmental gradients because species only occur in sites (i) to which they can disperse, (ii) where their traits are adapted to the local conditions, and (iii) where they maintain competitive advantage in multispecies communities [26]. We are focused on the second step in this review, and so our emphasis is on the difficult task of quantifying the fundamental niche. Many statistical approaches test if traits predict species occurrences and

Identify the Traits That Drive Intrinsic Growth Rates

The next step is to model fitness as a function of trait-by-environment interactions [12,55,91]. This tests the dynamic adaptive landscape model to determine how the effects of traits on population fitness across species depends on the environment [92]. The question is not whether population fitness among species varies along environmental gradients; this has been known for centuries (Figure 3A). The question is whether traits explain variation in population fitness (or occurrence) among

Concluding Remarks

Predicting fates of populations and communities using traits has often been called the ‘holy grail’ of ecology [1,102], yet we often lack clear evidence that functional traits live up to the hype [24]. To advance this important research agenda, we encourage studies that link traits directly to intrinsic growth rates to test the generality of traits for predicting species performance. The complexity of population dynamics may have hindered an earlier integration of population demography into

Acknowledgments

This work was funded by a grant to the authors from the National Science Foundation (DEB-1906243).

Glossary

Community assembly
process by which species arrive, establish, persist, increase, or decrease in abundance over time, and go extinct within and across environmental gradients.
Components of fitness
measures of individual performance including survival, growth, and reproduction; also referred to as vital rates. The integration of fitness components yields an estimate of total fitness and integration of vital rates yields an estimate of population growth rate.
Demographic trade-offs
negative

References (104)

  • J.L. Funk

    Revisiting the Holy Grail: using plant functional traits to understand ecological processes

    Biol. Rev.

    (2017)
  • R. Salguero-Gómez

    Delivering the promises of trait-based approaches to the needs of demographic approaches, and vice versa

    Funct. Ecol.

    (2018)
  • B. Shipley

    Reinforcing loose foundation stones in trait-based plant ecology

    Oecologia

    (2016)
  • N. Pistón

    Multidimensional ecological analyses demonstrate how interactions between functional traits shape fitness and life history strategies

    J. Ecol.

    (2019)
  • J.T. Anderson

    Plant fitness in a rapidly changing world

    New Phytol.

    (2016)
  • O. Cotto

    Maladaptive shifts in life history in a changing environment

    Am. Nat.

    (2019)
  • S.J. Arnold

    Morphology, performance and fitness

    Am. Zool.

    (1983)
  • P.B. Adler

    Functional traits explain variation in plant life history strategies

    Proc. Natl. Acad. Sci. U. S. A.

    (2014)
  • A. Ordonez

    Functional differences between native and alien species: a global-scale comparison

    Funct. Ecol.

    (2010)
  • L. Poorter et al.

    Leaf traits are good predictors of plant performance across 53 rain forest species

    Ecology

    (2006)
  • M.D. Visser

    Functional traits as predictors of vital rates across the life cycle of tropical trees

    Funct. Ecol.

    (2016)
  • D.C. Laughlin

    Survival rates indicate that correlations between community-weighted mean traits and environments can be unreliable estimates of the adaptive value of traits

    Ecol. Lett.

    (2018)
  • B. Blonder

    Microenvironment and functional-trait context dependence predict alpine plant community dynamics

    J. Ecol.

    (2018)
  • S.J. Worthy

    Alternative designs and tropical tree seedling growth performance landscapes

    Ecology

    (2020)
  • G. Kunstler

    Plant functional traits have globally consistent effects on competition

    Nature

    (2016)
  • M. Franco et al.

    A comparative demography of plants based upon elasticities of vital rates

    Ecology

    (2004)
  • J. Silvertown

    Comparative plant demography—relative importance of life-cycle components to the finite rate of increase in woody and herbaceous perennials

    J. Ecol.

    (1993)
  • J. Villellas

    Demographic compensation among populations: what is it, how does it arise and what are its implications?

    Ecol. Lett.

    (2015)
  • P. Chesson

    Mechanisms of maintenance of species diversity

    Annu. Rev. Ecol. Syst.

    (2000)
  • C. Violle

    Let the concept of trait be functional!

    Oikos

    (2007)
  • J.B. McGraw et al.

    Estimation of individual fitness from life-history data

    Am. Nat.

    (1996)
  • M.A. Geber et al.

    Inheritance and natural selection on functional traits

    Int. J. Plant Sci.

    (2003)
  • D.D. Ackerly

    The evolution of plant ecophysiological traits: recent advances and future directions

    Bioscience

    (2000)
  • N.G. Swenson

    A reframing of trait–demographic rate analyses for ecology and evolutionary biology

    Int. J. Plant Sci.

    (2020)
  • P.A. Keddy

    Assembly and response rules: two goals for predictive community ecology

    J. Veg. Sci.

    (1992)
  • N.J.B. Kraft

    Community assembly, coexistence and the environmental filtering metaphor

    Funct. Ecol.

    (2015)
  • R.E. Snyder et al.

    Pluck or luck: does trait variation or chance drive variation in lifetime reproductive success?

    Am. Nat.

    (2018)
  • S.P. Brady

    Understanding maladaptation by uniting ecological and evolutionary perspectives

    Am. Nat.

    (2019)
  • J.M. Diez

    Probabilistic and spatially variable niches inferred from demography

    J. Ecol.

    (2014)
  • T. Bohner et al.

    Extensive mismatches between species distributions and performance and their relationship to functional traits

    Ecol. Lett.

    (2020)
  • M. Mangel et al.

    Trade-offs between growth and mortality and the maintenance of individual variation in growth

    Evol. Ecol. Res.

    (2001)
  • U.K. Steiner et al.

    Neutral theory for life histories and individual variability in fitness components

    Proc. Natl. Acad. Sci. U. S. A.

    (2012)
  • S.N. Sheth et al.

    Demographic compensation does not rescue populations at a trailing range edge

    Proc. Natl. Acad. Sci. U. S. A.

    (2018)
  • C. Metcalf

    Growth–survival trade-offs and allometries in rosette-forming perennials

    Funct. Ecol.

    (2006)
  • S.C. Stearns

    The Evolution of Life Histories

    (1992)
  • N. Rüger

    Beyond the fast–slow continuum: demographic dimensions structuring a tropical tree community

    Ecol. Lett.

    (2018)
  • S.J. Wright

    Functional traits and the growth–mortality trade-off in tropical trees

    Ecology

    (2010)
  • S. Kimball

    Fitness and physiology in a variable environment

    Oecologia

    (2012)
  • N.J.B. Kraft

    Plant functional traits and the multidimensional nature of species coexistence

    Proc. Natl. Acad. Sci. U. S. A.

    (2015)
  • A.L. Angert

    Phenotypic plasticity and precipitation response in Sonoran Desert winter annuals

    Am. J. Bot.

    (2010)
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