Julian Schrader, Dylan Craven, Cornelia Sattler, Rodrigo Cámara Leret, Soetjipto Moeljono, & Holger Kreft
In review in Journal of Ecology
Sampling design:
We established transects of 2 x 10 m comprised of five 2 x 2 m plots. The number of transects on an island was roughly proportional to the island area and ranged from one to six transects. For islands < 10 m2 we placed as many plots as possible on the island at the longest extension. This was the case for the ten smallest islands. Larger islands had two transects oriented towards the island centre on the opposite of the island. The interior was covered with a varying number of transects (depending on the island size) of perpendicular orientation ranging from one to four transects. Distance between transects on each island with multiple transects was held constant but was related to the longest extension of an island, and hence varied among islands. Following this method, we ensured to sample the island edge as well as the interior. Soil depth was recorded in all plots at five spots with equal distance to each other (33 cm) and spaced along the central axis of the transect.
Figure D 1 Study region and study design. a) Location of 40 islands studied (largest sampled islands highlighted in dark grey) in Gam Bay (Raja Ampat Archipelago, Indonesia). b) Species richness and stem numbers were recorded in plots (2 m x 2 m) and transects (10 m x 2 m). Number of transects placed on an island depended on island area, whereas larger islands received more transects. On islands smaller than the area of a single transect, we placed as many plots as possible on each island. c) Gam Bay with some of the islands studied (Photo credit: JS).
Table D 1 Island properties of the 40 islands studied. Stem numbers were extrapolated to the whole island from the stem numbers recorded in the transects. FDis: functional dispersion, calculated from eleven traits using the R-package FD (Laliberté and Legendre 2010). FDisinc: FDis calculated based on incidence data.
FDisabun: FDis calculated based on abundance data. Soil depth sd: standard deviation of soil depth recorded in plots on each island.
Table D 1 continued
Table D 2 Species-trait matrix of 57 species sampled on 40 islands in the study area. Seed mass refers to the dry mass of an average seed. Height indicated the maximal tree height for each species sampled. LMA: leaf mass per area; Chlorophyll values from Chlorophyll-meter (Konica Minolta, SPAD – 502DI Plus) were transformed using the equation from Coste et al. (2010). WD: wood density. LA: Leaf area. Ch: Chlorophyll.
Species Fruit
J.R.Forst. &
T.Durand ex
Trait values in bold were derived from trait imputation using R-package ‘mice’ (Buuren and Groothuis-Oudshoorn 2011).
Figure D 2 Skewness values of functional dispersion (FDis) for incidence and abundance data for all traits and trait syndromes with island area of the 1,000 randomisations (null models were used that maintained sampled species richness). Linear regression indicate that data was left-skewed (positive values) and differed significantly with island area. 95% confidence intervals are indicated by grey bands. Significant responses (p
< 0.05) are indicated by solid black lines.
Figure D 3 Scaling of the effect size (ES) of functional dispersion (FDis) of observed communities and randomly created communities of all traits and four trait syndromes with tree basal area for incidence (left panels) and abundance (right panels) data of trees on islands. Positive ES indicate that the observed functional dispersion on the island is greater than expected and negative ES indicate that the observed FDis is lower than expected. FDis was calculated as partial residuals of tree basal area corrected for island area.
95% confidence intervals are indicated by grey bands. Regression lines are calculated by applying generalised additive mixed effects models. Significant smoothed fixed effects (p < 0.05) are indicated by solid black lines and not significant smoothed fixed effects are indicated by dashed lines. Grouping of traits into life history dimensions are shown in Table 5.1 in the main document.
Figure D 4 Scaling of functional dispersion (FDis) and species richness for incidence (left panels) and abundance (right panels) data of trees on islands. 95% confidence intervals are indicated by grey bands.
Regression lines are calculated by applying generalised additive mixed effects models. Significant smoothed fixed effects (p < 0.05) are indicated by solid black lines.
Figure D 5 Scaling of species richness and functional richness with island area in log-log space. a) The Power model is used to fit the relationship of species richness and island area. The Power model is most the most commonly used species-area model and normally provides the best fit to island species-area relationships (Matthews et al. 2016). b) Functional richness is a commonly used measure to describe functional diversity on islands (e.g. Ding et al. 2013; Whittaker et al. 2014) and we provide the fit of functional richness with island area to make our results comparable to other literature on functional diversity-area relationships. Regression line for the functional richness-area relationship was calculated by applying generalised additive mixed effects models. Significant smoothed fixed effects (p < 0.05) are indicated by solid black lines.
Figure D 6 Spatial scaling of rarefied functional dispersion (FDis) in its a) incidence and b) abundance form of trees on islands. Rarefied FDis increased for both incidence and abundance data indicating that other effects but area, such as habitat and niche diversity, lead to an increase in FDis with island area. Rarefied functional diversity was calculated from the mean FDis of 20 randomly drawn individuals repeated 1000 times for each island. Note that only on 23 islands more than 20 individuals were sampled, which was the threshold for islands being included in this analyses. Regression lines indicate partial fits of island area after accounting for tree basal area. 95% confidence intervals are displayed by grey bands. Regression lines are calculated by applying generalised additive mixed effects models. Significant smoothed fixed effects (p<0.05) are indicated by solid black lines and non-significant smoothed fixed effects are indicated by dashed lines.
Table D 3 Pearson correlation between effect size of functional dispersion (for all traits and four trait syndromes) of observed communities and communities derived from 1,000 randomisations of two different null models for incidence and abundance data. Null models were calculated within the R-package picante (Kembel et al. 2010) using the command randomizeMatrix. One null model maintained sampled species richness for each island (richness) and one null model maintaining species occurrence frequency and sampled species richness (independentswap).
Data type All traits
Dispersal Fast-slow dimension
Light acquisition
Nutrient acquisition
Incidence 0.99 0.98 0.98 0.98 0.94
Abundance 0.66 0.70 0.80 0.46 0.65