Seed dispersal as an ecosystem service: frugivore loss leads to decline of a socially valued plant, Capsicum frutescens

Abstract

Species interactions, both mutualistic and antagonistic, are widely recognized as providing important ecosystem services. Fruit‐eating animals influence plant recruitment by increasing germination during gut passage and moving seeds away from conspecifics. However, relative to studies focused on the importance of frugivores for plant population maintenance, few studies target frugivores as ecosystem service providers, and frugivores are underappreciated as ecosystem service providers relative to other mutualists such as pollinators. Here, we use an accidental experiment to elucidate the role of seed dispersal by frugivores for maintaining a culturally and economically important plant, the donne’ sali chili (Capsicum frutescens) in the Mariana Islands. One of the islands (Guam) has lost nearly all of its native forest birds due to an invasive snake (Boiga irregularis), whereas nearby islands have relatively intact bird populations. We hypothesized that frugivore loss would influence chili recruitment and abundance, which could have economic and cultural impacts. By using video cameras, we confirmed that birds were the primary seed dispersers. We used captive bird feeding trials to obtain gut‐passed seeds to use in a seedling emergence experiment. The experiment showed that gut‐passed seeds emerged sooner and at a higher proportion than seeds from whole fruits. Consistent with our findings that birds benefit chilies, we observed lower chili abundance on Guam than on islands with birds. In a survey questionnaire of island residents, the majority of residents reported an association between the wild chili and local cultural values and traditions. In addition, we identified a thriving market for chili products, suggesting benefits of wild chilies to people in the Marianas both as consumers and producers. Our study therefore documents seed dispersal as both a cultural and a supporting ecosystem service. We provide a comprehensive case study on how seed‐dispersed plants decline in the absence of their disperser, and how to apply mixed‐methods in ecosystem service assessments. Furthermore, we suggest that scientists and resource managers may utilize fruit–frugivore mutualisms concerning socially valuable plants to gather support for frugivore and forest conservation efforts.

Detecting plant spatial pattern change after disperser loss: A simulation and a case study

“…There is growing evidence, largely from tropical forest ecosystems, that defaunation and the loss of zoochorous seed dispersal services profoundly affects plant populations (Terborgh, ). A number of studies have documented changes in plant spatial pattern (Bagchi et al, ), plant germination and abundance (Egerer, Fricke, & Rogers, ), and altered interaction networks (Fricke, Tewksbury, & Rogers, ) following disperser loss. However, the relationship between disperser decline and seed dispersal can be complex (McConkey & O'Farrill, , ); for example, dispersal services can fail long before the dispersal agent is completely lost, and loss of frugivores may actually increase dispersal in some cases due to shifts in interaction networks (e.g., reduced competition for fruit).…”

A review of regulation ecosystem services and disservices from faunal populations and potential impacts of agriculturalisation on their provision, globally

“…Maas et al 2013, Garratt et al 2016) to a combination of both (e.g. Hougner et al 2006, Egerer et al 2018. Below, we summarise the evidence per service, showing the relevance of animals as FES providers.…”

“…Animal seed dispersal is an essential mechanism in the maintenance of temperate and tropical ecosystems (García and Martínez 2012) and are particularly important for large-seeded plants (Greene and Calogeropoulos 2002, McConkey and Drake 2006, Wenny et al 2016. Approximately one-half of seed plant species are dispersed by animals (Wenny et al 2016, Egerer et al 2018.…”

“…McConkey and Drake (2006) highlighted the relevance of flying foxes to sustain Pacific island forests, since these are the only existing animals capable of dispersing large seeds over long distances in such isolated habitats. Egerer et al (2018) showed that bird dispersal provides a benefit to wild chilli plants in Guam through increased seedling emergence of gut-passed seeds in comparison to depulped seeds and whole fruits.…”

Interspecific competition in germination of bird-dispersed seeds in a habitat with sparse tree vegetation in South Africa

“…Seeds in eshy fruits (i.e., drupe) are dispersed or discarded, often after animals (e.g., birds) have consumed the soft edible portion of the fruit, called the mesocarp, and dispersed the ingested endocarp containing the seeds (Dardick and Callahan, 2014). Seed dispersal is crucial in plant regeneration, since it promotes the maintenance of the genetic structure of many native plant species (Kleyheeg, 2018;Egerer et al, 2018;Castilla et al, 2017;Howe, 2016;Heleno et al, 2011). In addition, many native tree and shrub species require animal-mediated seed dispersal as a longevity strategy in response to environmental change (Howe, 2016).…”