Seed dispersal of fleshy‐fruited invasive plants by birds: contributing factors and management options

Abstract

The ecology of seed dispersal by vertebrates has been investigated extensively over recent decades, yet only limited research has been conducted on how suites of invasive plants and frugivorous birds interact. In this review, we examine how plant fruit traits (morphology, colour and display, nutritional quality, accessibility and phenology), avian traits (fruit handling techniques, gut passage time and effect, bird movements and social behaviour and dietary composition) and landscape structure (fruit neighbourhood, habitat loss and fragmentation and perch tree effects) affect frugivory and seed dispersal in invasive plants. This functional approach could be used to develop generic models of seed dispersal distributions for suites of invasive plant species and improve management efficiencies. Four broad research approaches are described that could direct management of bird‐dispersed invasive plants at the landscape scale, by manipulating dispersal. First, research is needed to quantify the effect of biological control agents on dispersal, particularly how changes in fruit production and/or quality affect fruit choice by frugivores, dispersal distributions of seed and post‐dispersal processes. Second, we explore how seed dispersal could be directed, such as by manipulating perch structures and/or vegetation density to attract frugivorous birds after they have been foraging on invasive plant fruits. Third, the major sources of seed spread could be identified and removed (i.e. targeting core or satellite infestations, particular habitats and creating barrier zones). Fourth, alternative food resources could be provided for frugivores, to replace fruits of invasive plants, and their use quantified.

Implications of newly-formed seed-dispersal mutualisms between birds and introduced plants in northern California, USA

“…A number of factors may influence bird visitation to fruiting plants. Small fruits and seeds appear to be removed and dispersed more effectively than large fruits (Gosper et al 2005;Rey et al 1997). Birddispersed seeds are often contained in fruits that are bright or bicolored (Wheelwright and Janson 1985;Whelan and Willson 1994).…”

“…Furthermore, such mutualisms are generally diffuse, with many mutualist species interacting with each plant species (Aslan and Rejmánek 2010;Bascompte and Jordano 2007;Jordano 1987b). For this reason, many introduced plants with fleshy fruits are able to develop effective dispersal interactions with resident fauna (e.g., Bartuszevige and Gorchov 2006;Drummond 2005;Gosper et al 2005;Panetta and McKee 1997;Renne et al 2002). Plant species unable to form novel dispersal mutualisms with new partners in their region of introduction may have greatly reduced potential for invasive spread (Gosper et al 2005).…”

“…For this reason, many introduced plants with fleshy fruits are able to develop effective dispersal interactions with resident fauna (e.g., Bartuszevige and Gorchov 2006;Drummond 2005;Gosper et al 2005;Panetta and McKee 1997;Renne et al 2002). Plant species unable to form novel dispersal mutualisms with new partners in their region of introduction may have greatly reduced potential for invasive spread (Gosper et al 2005). Bird-mediated dispersal is therefore a trait that many rubrics associate with plant invasiveness (Pheloung et al 1999;Pyšek and Richardson 2007;Rejmánek 2000;Rejmánek et al 2005).…”

“…Long-distance dispersal events may greatly increase the overall spread rate of a dispersed species (Nathan 2006). Seeds passing through bird guts receive mechanical and chemical treatments that sometimes promote germination (Gosper et al 2005;Traveset 1998). Additionally, because their dispersal is assisted, fleshy-fruited seeds can often be larger than wind-dispersed seeds, enabling them to carry energy stores that enhance survival over a variety of environmental conditions (Leishman et al 2000).…”

“…Bird-mediated dispersal removes seeds from the immediate neighborhood of the parent tree, possibly separating seeds and seedlings from natural enemies and often depositing them in suitable recruitment sites (Connell 1971;Gosper et al 2005;Janzen 1970;Wenny 2001). Long-distance dispersal events may greatly increase the overall spread rate of a dispersed species (Nathan 2006).…”