Passive directed dispersal of plants by animals

Abstract

Conceptual gaps and imprecise terms and definitions may obscure the breadth of plant-animal dispersal relationships involved in directed dispersal. The term 'directed' indicates predictable delivery to favourable microsites. However, directed dispersal was initially considered uncommon in diffuse mutualisms (i.e. those involving many species), partly because plants rarely influence post-removal propagule fate without specialized adaptations. This rationale implies that donor plants play an active role in directed dispersal by manipulating vector behaviour after propagule removal. However, even in most classic examples of directed dispersal, participating plants do not influence animal behaviour after propagule removal. Instead, such plants may take advantage of vector attraction to favourable plant microsites, indicating a need to expand upon current interpretations of directed dispersal. We contend that directed dispersal can emerge whenever propagules are disproportionately delivered to favourable microsites as a result of predictably skewed vector behaviour. Thus, we propose distinguishing active and passive forms of directed dispersal. In active directed dispersal, the donor plant achieves disproportionate arrival to favourable microsites by influencing vector behaviour after propagule removal. By contrast, passive directed dispersal occurs when the donor plant takes advantage of vector behaviour to arrive at favourable microsites. Whereas predictable post-removal vector behaviour is dictated by characteristics of the donor plant in active directed dispersal, characteristics of the destination dictate predictable post-removal vector behaviour in passive directed dispersal. Importantly, this passive form of directed dispersal may emerge in more plant-animal dispersal relationships because specialized adaptations in donor plants that influence post-removal vector behaviour are not required. We explore the occurrence and consequences of passive directed dispersal using the unifying generalized gravity model of dispersal. This model successfully describes vectored dispersal by incorporating the influence of the environment (i.e. attractiveness of microsites) on vector movement. When applying gravity models to dispersal, the three components of Newton's gravity equation (i.e. gravitational force, object mass, and distance between centres of mass) become analogous to propagules moving towards a location based on characteristics of the donor plant, the destination, and relocation processes. The generalized gravity model predicts passive directed dispersal in plant-animal dispersal relationships when (i) animal vectors are predictably attracted to specific destinations, (ii) animal vectors disproportionately disperse propagules to those destinations, and (iii) those destinations are also favourable microsites for the dispersed plants. Our literature search produced evidence for these three conditions broadly, and we identified 13 distinct scenarios where passive directed dispersal likely occurs because vector behavio...

Food resource richness increases seed disperser visitations and seed rain richness

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“…As a result, resource tracking may result in a positive relationship between the richness of resources and seed rain. Depending on subsequent post‐dispersal interactions and microsite quality associated with such disperser‐preferred resources, this relationship could result in positive feedback that supports diversity in diffuse mutualisms (Gleditsch et al., 2017 ; Herrera, 1985 ; Kissling et al., 2007 ; Mason et al., 2022 ; Morán‐López et al., 2018 ; Salazar et al., 2013 ; Spiegel & Nathan, 2010 ). Conversely, shifting food resources as a result of climate change, plant invasions, land cover alteration, harvesting, and shifting disturbance regimes (Boyle et al., 2012 ; Damschen et al., 2019 ; Fricke & Svenning, 2020 ; Gleditsch & Carlo, 2011 ; McConkey & O'Farrill, 2016 ; McKinney & Lockwood, 1999 ; Moegenburg & Levey, 2003 ; Mollot et al., 2017 ; Rojas et al., 2019 ) could diminish food resource richness and may influence resource tracking and thus seed dispersal (McConkey & O'Farrill, 2016 ).…”

Multifunctionality of angiosperm floral bracts: a review

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“…The transport of seeds may occur by abiotic (e.g., wind) or biotic (animals) vectors. Surprisingly, despite the large body of research on animal seed dispersal in ecology (Mason et al., 2022), we still know relatively little regarding the relative importance of animals in postfire vegetation restoration (Cavallero et al., 2013; Dafni et al., 2013). By allowing new plants to germinate and recruit far away from their parent plants, seed dispersal is a key regulating ecosystem service with direct implications for the long‐term vegetation dynamics (Traveset et al., 2014).…”