What is functional ecology anyway?

Written by Louise Anderson

Background

Functional ecology has its ‘roots’ in the plant sciences, where researchers started to use the shared characteristics of different species, such as height or leaf size, to tell them things about the plant community structure as a whole, and the ecosystem roles played by different groups. For example, plants in arid environments tend to have small leaves and extensive roots, because these features help them to reduce water loss and make the most of limited resources. These same features make them a moisture source for animals and maintain the integrity of the soil. They are therefore performing an important part in the overall functioning of that community of plants and animals.

In recent decades, this perspective has grown in popularity amongst reef ecologists. From corals to fish and everything in between, scientists are increasingly looking at the functions carried out by different groups on a reef (Fig. 1), and using this understanding to answer all sorts of questions. However, this rapid growth has been accompanied by some ambiguity over important concepts and terminology, which was recently addressed in a review by Bellwood et al., 2019.

Figure 1: A coral reef with different species representing different functions. A large, branching Acropora coral provides shelter for a number of different fish that occupy different trophic groups.  Image credit: Gregory Piper, IYOR 2018 Coral Reef Image Bank

Some key definitions

  • Trait: An inherited characteristic of an organism. A functional trait is one that affects an individual’s fitness (its ability to survive and reproduce in its environment), or to perform ecosystem functions. (Mouillot et al., 2013)

E.g. Fish fecundity or maximum body size.

  • Function: A role carried out by species or groups of species in an ecosystem. There have been recent calls to expand this out to be more about how energy or material is moved through and stored in an ecosystem (Bellwood et al., 2019). This broadened definition makes the concept of functions more applicable across different scales and contexts whilst being very clear about what the term should mean when we talk about ecosystems.

E.g. The lined surgeonfish Acanthurus lineatus (Fig. 2) performs a function by feeding on algal turf (Bellwood et al., 2019), which is in turn underpinned by specific traits which determine what and how this fish eats.

File:Acanthurus lineatus.jpg
Figure 2. Feeding A. lineatus. Image credit: Photo by NFO Photography, distributed under a Creative Commons Attribution 2.0 Generic licence.

Why all the hype?

Applying this perspective to coral reef ecology is exciting for a number of reasons: it is flexible and highly scalable, covering everything from trait variability within a single species to comparisons across different communities and ecoregions. This provides a shared language of sorts to discuss these different types of work. Selecting traits for a study can be highly tailored to specific questions and contexts, such as by focusing on reproductive traits if a question is about the recovery and dispersal of fish communities. Similarly, there are different indices and approaches in a functional ecologist’s toolkit, depending on the research question.

Functional ecology also provides a useful additional perspective to established taxonomic approaches, such as in the context of long term monitoring programs that already capture species diversity and abundance. In some settings this can have useful applications as an ‘early warning’ system, detecting changes in a community before they manifest as species loss by incorporating abundances of different traits rather than just looking at species present (Henriques et al., 2017, Mouillot et al., 2013). Incorporating multiple perspectives in this way is particularly important as we enter an era of rapid global change and are required to make adaptive decisions about management and conservation of vulnerable ecosystems.

What are the weaknesses?

This kind of approach has enormous potential to raise new questions and ways of thinking about coral reefs, but care is needed not to overstate what we currently know. In many cases the link between a trait, and the functions they signify by proxy, are not as clearly established as they are in other disciplines. Additionally, traits being studied might be affected by human-impacts. Fish body size for example can be heavily influenced by size-selective fishing methods, and an awareness of this is important in any conclusions drawn.

What happens when you lose functionality?

Caribbean reefs represent a classic example of what can happen when key functions in a community are lost. Populations of grazing herbivores perform an important job on these reefs by keeping algal growth down, supressing competitive exclusion of corals. This group includes several fish species as well as the sea urchin Diadema antillarum. A combination of factors led to the drastic decline of this group in many areas, which in turn contributed to increased algal growth that out-competed corals, ultimately resulting in a shift to a more algal dominated ecosystem in many parts of the Caribbean (Mumby, 2009).

Take home message

Functional ecology research on reefs is developing quickly. It represents an enormously exciting area of research, particularly in the context of making management and conservation decisions to protect vulnerable and rapidly changing ecosystems. However, there are key areas where research is needed to be able to more confidently draw connections between the traits in a community, the functions that these represent and what that means for protecting the wider ecosystem.

References

BELLWOOD, D. R., STREIT, R. P., BRANDL, S. J. & TEBBETT, S. B. 2019. The meaning of the term ‘function’ in ecology: A coral reef perspective. Functional Ecology.

HENRIQUES, S., GUILHAUMON, F., VILLÉGER, S., AMOROSO, S., FRANÇA, S., PASQUAUD, S., CABRAL, H. N. & VASCONCELOS, R. P. 2017. Biogeographical region and environmental conditions drive functional traits of estuarine fish assemblages worldwide. Fish and Fisheries, 18, 752-771.

MOUILLOT, D., GRAHAM, N. A. J., VILLÉGER, S., MASON, N. W. H. & BELLWOOD, D. R. 2013. A functional approach reveals community responses to disturbances. Trends in Ecology & Evolution, 28, 167-177.

MUMBY, P. J. 2009. Phase shifts and the stability of macroalgal communities on Caribbean coral reefs. Coral Reefs, 28, 761-773.

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