Functional Traits and Niche-based tree community assembly in an Amazonian Forest

Kraft et al. 2008

Co-existence Theories1) Niche Differentiation

Soil 1

Soil 2

Co-existence Theories1) Niche Differentiation

Soil 1

Soil 2

Co-existence Theories1) Niche Differentiation (anti-theory)• Environmental filtering

Regional SpeciesPool

Local Community

Soil 1

Soil 2

Co-existence Theories1) Niche Differentiation (anti-theory)• Environmental filtering

Co-existence Theories2) Neutral Theory• Random events (dispersal / stochastic events)

Predictions

• Niche Differentiation -> all the plants in the sample rainforest have unique trait sets

• Neutral theory -> all the plant traits in the sample area have the same set of traits

Trait Choices?

Trait Choices?

Key TraitsProductivity - Leaf traits

• SLA – Specific leaf area

• Nitrogen - fixation

• Size - dimensions

Key Traits• Fitness – seed mass

Key TraitsPlant strategies – Life form

• Wood Density – growth vs strength/pathogen resistance

• Maximum dbh – light capture and avoidance of browsing

Experiment

• Location – Yasuni Forest, Ecuador

• Area – 25 ha plot with > 150,000 mapped trees

• Measure – six key plants traits

• Statistics – compare neutral theory (no differences) to observed plant traits.

Results• Analyses found strong evidence for niche-based

processes.

• Mean traits values varied significantly compared to null model.

Random effects• Adults in each quadrat exhibited stronger non-

random patterns than saplings.

Trait DifferentiationWhat encourages niche differentiation:

• Direct competition

• Density-dependent process

Conclusions

• Using a functional trait approach, we have found evidence for niche-based processes having a stabilizing effect on biodiversity.

• Supports a niche-based view of tropical forest dynamics in which subtle but pervasive habitat specialization/differentiation contribute to species coexistence.

• Niche differentiation among species contributes to maintenance of diversity in one of the worlds most diverse tropical forests.