Functional traits

Question 1

How are functional traits defined? List examples of functional traits and of other characteristics which do not represent functional traits. Explain your decision.

Answer 1

**Functional traits: ** In a broad sense: Any measurable feature at the individual level affecting its fitness directly or indirectly, used to describe, group and rank species according to their functions.
More narrowly: those traits that influence ecosystem functions, e.g. by altering population dynamics.

FT animals: Body size, basal metabolic rate, mode of locomotion, life history traits, trophic level, feeding mode/hunting mode, generalist/specialists
FT terrestrial plants: height, mature plant biomass, specific leaf area, longevity, leaf litter quality, lateral expansion, holding span, stress tolerance
FT phytoplankton: size, shape, N-fixation, phagotrophy, silica demand, motility

Characteristics which are not FT: habitat type, population trend, trophic guild, home range size, conservation status

Question 2

Explain why the different trait values of an organism are not independent of each other. Give examples and explain the respective reason.

Answer 2

Some characteristics influence each other → trade-offs among traits due to energetic or other constraints such as time (e.g. an animal can either search for food or mates on predator-free space).
Values of different traits of an organism are generally not independent from each other (allometry).
➔ Different trade-offs or life history strategies, e.g.
either high max. growth rate (r-strategy) or highly competitive when resource is limited (K-strategy)
either young and small (r-strategy) or old and large (K-strategy) at 1. reproduction etc.
F.e.: shape & motility, building defence mechanism vs. max. growth etc.

Question 3

Explain the advantages and limitations of using trait-based rather than taxonomic approaches.

Answer 3

Advantages:
trait-based approaches are superior for:
-data-poor situations,
-generalisations across systems,
-synthesis,
-to reduce complexity,
-to improve mechanistical understanding & predictability,
- to study constraints of biodiversity by quantifying the maximum possible trait space

functional properties have often a large impact on dynamics, species coexistence and ecosystem functioning

Disadvantages: individuals with same FT/FD sometimes may not belong to one species → i.e. they do not represent one unit to reproduction, selection & evolution

Question 4

Provide a definition of functional diversity. How can it (roughly) be calculated?

Answer 4

Reflects the functional multiplicity within a community: number and relative importance of functional groups, cumulative functional distance between species, trait range/variance of trait distribution
Calculation via PCoA (Principal Coordinate Analysis) – identifies the most influential traits, a n-dimensional trait space is reduced to a 2-dimensional representation

Question 5

Explain for which research questions it is often useful to consider functional diversity alongside/ instead of taxonomic diversity

Answer 5

All studies where the available trait variation is more relevant than the number of populations (i.e. units of reproduction), e.g. for role of diversity for ecosystem functioning, in particular if taxonomical diversity is poorly related to functional diversity since e.g. many taxonomic species have very similar functional traits.

Functional traits provide also a suitable quantitative basis to define functional groups serving e.g. as building blocks for food web studies.