Habitat Structure Affects Reproductive Success of the Rare Endemic Tree Syzygium mamillatum (Myrtaceae) in Restored and Unrestored Sites in Mauritius

Abstract

Invasive alien plants affect the functioning of ecosystems by altering plant–animal interactions, such as pollination, which may impede natural regeneration of native plant species. In Mauritius, we studied the reproductive traits and pollination ecology of the rare endemic cauliflorous tree Syzygium mamillatum in a restored forest (all alien plant species removed) and an adjacent unrestored area (degraded by alien plants). Flowers of S. mamillatum were only visited by generalist bird species. Although the initial number of flower buds per tree in the restored forest tended to be higher than that of trees in the unrestored area, final fruit set and the number of seeds per fruit were lower in the restored forest. This corresponded with lower bird visitation rates in the restored area. Additionally, during budding stage, most trees were severely attacked by lepidopteran larvae, and bud loss through herbivory was higher in the restored forest. Thus, the difference in reproductive performance of S. mamillatum between the two localities was caused by contrasting herbivore attack and bird visitation behavior in restored and unrestored areas. Our findings illustrate the importance of restoration efforts in mimicking the original physical structure of habitats and interaction structure of interspecific relationships, and the difficulty of doing so given the imperfect knowledge and the reality that many native species have become locally extinct and replaced by exotic species.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…Shifts in behaviour (e.g. flower visitation rates) may also occur among individuals of the same species of pollinator, leading to differences in fruit and seed set among habitats (Kaiser et al, 2008). Additionally, the roles of species in an ecological network (e.g.…”

Invasive Alien Plants Elicit Reduced Production of Flowers and Fruits in Various Native Forest Species on the Tropical Island of Mauritius (Mascarenes, Indian Ocean)

“…Our findings thus suggest a possible mechanism for the greater density and species richness of native seedlings, saplings and adults trees found in weeded Mauritian lowland wet forest [14,17]. However, the greater number of flowers produced in the weeded areas does not always translate into more seeds being produced, due to other post-flower bud interactions like herbivory or pollination, as shown for Syzygium mamillatum Bosser & Guého (Myrtaceae) in Mauritius [35]. In our study, no signs of herbivory were found on flower buds/flowers of the selected species except in G. psychotrioides, which suffered light losses of flower buds that were chewed, suggesting herbivory of flower buds and flowers may not be very widespread.…”

“…The relative importance of post-flower bud processes in fostering or hindering population and community recovery thus remains to be quantified. It would be dauntingly difficult, if not impossible, to study the factors affecting each species with the level of detail found for example in Kaiser et al [35] or the studies of Hansen and Müller [57][58], who showed that the critically threatened endemic plant Roussea simplex is pollinated and dispersed by endemic arboreal geckos and that alien ants can disrupt these mutualisms. Such detailed studies should, from a conservation standpoint, be undertaken on the most threatened species.…”

Bird Pollinator Visitation is Equivalent in Island and Plantation Planting Designs in Tropical Forest Restoration Sites

“…While a focus on particular species may be warranted in some cases [17], restoring ecological processes will often be a more constructive and attainable goal. This work indicates that pollination in the early years following planting may not be as affected by characteristics of restoration design as other ecological processes like seed dispersal and vertebrate consumption of herbivorous arthropods e.g., [10,11].…”

“…Animal pollination is particularly important in the tropics; 94% of tropical plant species are pollinated by animals [15] with birds being a particularly important group of pollinators [16]. Inadequate pollinator visitation rates may impede plant reproductive success with consequences for restoration [17].…”