Ecological consequences of phenotypic plasticity

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Phenotypic plasticity is widespread in nature, and often involves ecologically relevant behavioral, physiological, morphological and life-historical traits. As a result, plasticity alters numerous interactions between organisms and their abiotic and biotic environments. Although much work on plasticity has focused on its patterns of expression and evolution, researchers are increasingly interested in understanding how plasticity can affect ecological patterns and processes at various levels. Here, we highlight an expanding body of work that examines how plasticity can affect all levels of ecological organization through effects on demographic parameters, direct and indirect species interactions, such as competition, predation, and coexistence, and ultimately carbon and nutrient cycles.

Introduction

Phenotypic plasticity can be inclusively defined as the production of multiple phenotypes from a single genotype, depending on environmental conditions 1, 2. It is now clear that a wide diversity of organisms express phenotypic plasticity in response to biotic and abiotic aspects of their environments (reviewed in 3, 4, 5, 6, 7). These plastic responses include changes in behavior, physiology, morphology, growth, life history and demography, and can be expressed either within the lifespan of a single individual [8] or across generations [9]. A fascinating literature has emerged documenting patterns of expression of plasticity and genotype x environment interactions (see Glossary), testing whether responses are adaptive, and modeling how evolution affects plasticity [6]. Here, we focus on an equally important but less well understood aspect of phenotypic plasticity: its ecological impact [10]. We review recent research showing how plasticity alters interactions between individuals and their environments in ways that influence the stability and local biodiversity of populations and communities. We argue that, because plasticity can alter a variety of direct and indirect interactions among individuals and their environments, it should ultimately affect many ecological processes, such as population and community dynamics, and aspects of community and ecosystem functioning.

Some of the general ideas from this body of work are relatively new, whereas others were proposed decades ago but not widely appreciated by researchers working in other disciplines or systems. For instance, there is a long tradition of work on behavioral plasticity in animals and its population- and community-level effects, which has flourished as the distinct area of ‘behavioral ecology’. The general framework for plasticity that we propose will make clear common principles that are relevant to diverse taxa as well as other types of phenotypic plasticity. For example, behavioral plasticity in animals and developmental plasticity in plants can have analogous effects on population stability and trophic interactions. Hence, our goal is to direct attention to the common ecological issues and questions that arise from an awareness of phenotypic plasticity as a general biological phenomenon.

Section snippets

Direct interactions

The recognition that plasticity can be adaptive has stimulated a wealth of studies on how plasticity alters interactions between individual organisms and their environments 3, 4, 5, 6. Although this research program has been motivated largely by evolutionary questions, studies of adaptive plasticity such as inducible defenses and inducible offenses 4, 10, 11 (Box 1) also have clear ecological implications. For example, in East Africa, herbivory by elephants and giraffes induces longer and more

Population stability and species co-existence

The idea that behavioral and physiological plasticity can affect population dynamics was suggested >20 years ago (reviewed in 3, 30). However, there is an increasing interest in the effects of plasticity on population dynamics, and early ideas are being re-discovered or investigated for different types of plasticity. For example, a variety of inducible defenses and offenses can affect the amplitude of population fluctuations, and increase the stability of a population within a community with

Future directions

We have highlighted several ways in which plasticity can alter ecological patterns and processes at the level of individuals, populations and complex communities. However, it remains to be seen whether these higher-level effects of individual plasticity are widespread in natural systems. Several aspects of plasticity deserve attention because they influence the direction and the strength of individual–environment interactions, and are, consequently, likely to alter the ecological impact of

Conclusions

Interest in the ecological consequences of plasticity is increasing. By adopting an inclusive definition for the term ‘phenotypic plasticity’, we hope that researchers will recognize the broad implications of their work for a diversity of taxa and biological disciplines. Studies of plasticity in its ecological context provide a rich opportunity for interdisciplinary collaborations, to reveal not only patterns and mechanisms of environmental response, but also the direct and indirect effects of

Acknowledgements

This article is a product of a symposium at the 2004 annual meeting of the Ecological Society of America. We thank all the symposium participants and co-organizers, and reviewers. This work was funded by a National Science Foundation grant (OCE 0325028) awarded to S.G.M. and B.G.M. and was conducted while D.K.P. was a Sabbatical Fellow at the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (Grant #DEB-0072909), the University of California, and the Santa Barbara

Glossary

Adaptive plasticity:
plasticity maintained by natural selection.
Allee effect:
when the per-capita birth rate increases with density but the per-capita death rate does not [59]. Low population sizes are therefore vulnerable to extinction because the birth rate is less than the death rate.
[59]
Density-mediated indirect interaction (DMII):
when one species affects the density of another species by altering the density of an intermediate species (e.g. keystone predator effects, exploitative competition

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