Why are woody plants fleshy‐fruited at low elevations? Evidence from a high‐elevation oceanic island

Abstract

Question The composition of fruit types, fleshy vs dry fruits, greatly influences the functioning of plant communities. Literature documenting spatial patterns of fruit types at fine scale is abundant. However, studies at larger geographical scale remain scarce, especially on high‐elevation oceanic islands that provide a great environmental heterogeneity. Here, we investigated how abiotic factors explained the proportion of fleshy‐fruited species (pFF) on Réunion. We asked (a) which abiotic factors were most related to pFF, (b) if fleshy‐fruited canopy species were more sensitive than fleshy‐fruited shrubs to harsh climatic conditions and (c) what are the relationships between pFF, endemism and phylogenetic relatedness. Location Réunion (3,070 m a.s.l), Mascarene archipelago, South‐West Indian Ocean. Methods We used a dataset of 429 vegetation plots and assigned fruit types, growth forms and geographical distribution to 213 native woody species. Phylogenetic trees were constructed for each plot. We used GLMs to measure the relationship between pFF and abiotic factors, controlling for spatial autocorrelation. We then assessed the relationship between pFF, the standardized net relatedness index and the proportion of endemic species. Results The top model explained 78% of the variation in pFF. Elevation was by far the best predictor, with pFF decreasing from 81% at 50 m a.s.l to 0% at 3,000 m a.s.l. At low elevations, pFF was higher on the wet windward (81%) than on the leeward (70%) where phylogenetic clustering was evident. Almost half (48%) of woody plants was fleshy‐fruited trees at low elevations. The proportion of fleshy‐fruited trees declined sharply with elevation and was significantly related to precipitation of the driest month contrary to the proportion of fleshy‐fruited shrubs that showed a hump shaped pattern along elevational gradient and no correlation with precipitation of the driest month. At high elevations, most plant assemblages were phylogenetically clustered and strongly dominated by single‐island endemic dry‐fruited plants. Conclusions The striking relationship between pFF and elevation, the shift among fleshy‐fruited growth forms along climatic gradients and the phylogenetic clustering of assemblages subjected to harsh climatic conditions, suggested that climatic factors were the main drivers of the distribution of fruit types on Réunion. To explain the absence of fleshy‐fruited species at high elevations, we hypothesized that native fleshy‐fruited lineages lacked the evolutionary potential to adapt and fleshy‐fruited cold‐adapted lineages had major difficulties reaching Réunion.

Progress in vegetation science: Trends over the past three decades and new horizons

“…Another runner‐up was the paper co‐authored by Albert, Flores, Rouget, Wilding, and Strasberg (). These authors used a set of vegetation plots from the tropical island of Réunion to describe a pattern of marked decrease in the proportion of fleshy‐fruited trees and shrubs with altitude.…”

Forests Without Frugivores and Frugivores Without Forests – An Investigation Into the Causes of a Paradox in One of the Last Archipelagos Colonized by Humans

“…In particular, we studied the influence of elevation on the proportions of fleshy-fruited plants and large fleshy-fruited plants (i.e., mean fruit diameter >13 mm) within woody plant communities. On Réunion where sampling is substantial, we used spatial statistics for modeling (for more details, see Supplementary Appendix 3; Albert et al, 2018). Such modeling could not be performed on Mauritius because extant forests are too scarce and do not currently display sufficient environmental heterogeneity (Figure 1).…”

Collapse of dispersal trait diversity across a long‐term chronosequence reveals a strong negative impact of frugivore extinctions on forest resilience

“…Our research was made possible because frugivore defaunation in the Mascarene archipelago has been well-documented (Cheke & Hume, 2008;Lougnon, 2005) and because the high volcanic activity on Réunion provides numerous lava flows that constitute a natural experiment acting as a 'time machine'. Forests on old substrata and lava flows that occurred before permanent human settlements are widely dominated by fleshy-fruited species (Albert, Flores, Rouget, Wilding, & Strasberg, 2018). They include LFF plants, that are usually big trees (Diaz et al, 2004;Thompson & Rabinowitz, 1989) with an important structural role in native forests ( Figures S7 and S8).…”