Up, up and away: bird‐mediated ectozoochorous dispersal between aquatic environments

Abstract

SUMMARY1. Aquatic birds can facilitate the dispersal of plants, animals, microbes and fungi. Here, we review existing literature on bird-mediated external (ectozoochorous; synonyms epizoochorous, exozoochorous) dispersal to determine the importance of birds as mobile links between aquatic environments, and to evaluate ectozoochory as a mechanism of dispersal for aquatic organisms and their propagules (collectively referred to as dispersal units). Bird-mediated ectozoochory occurs when dispersal units stick to feathers, feet and bills, become enmeshed within plumage or encapsulated within mud coating the soft parts of vector birds. 2. The importance of waterbird-mediated ectozoochorous dispersal relates to the topical problems of increasing anthropogenic habitat fragmentation, climate change and the associated alterations in species distributions and biological invasions. Nevertheless, some aspects of the bird-mediated ectozoochorous dispersal remain understudied, and poorly understood. 3. This review identifies two areas where further research is required. Firstly, the quantitative contribution of bird-mediated ectozoochory to overall dispersal remains unclear. Secondly, greater consideration of all the requirements necessary for successful waterbird-mediated ectozoochorous dispersal is needed. In particular, the impact of factors which influence attachment and detachment of dispersal units (e.g. dispersal unit densities, preening behaviour and the role of encapsulating mud) needs further examination. Moreover, few investigators have taken the step of examining viability of found dispersal units, and fewer still have examined tolerances of dispersal units to the 'in-flight' conditions experienced during transport, in order to determine probability of survival of external dispersal. 4. Evidence presented in this review indicates that bird-mediated ectozoochorous transport of aquatic dispersal units is a frequent process, at least at a local scale, and therefore needs to be considered in the context of connectivity and gene flow between isolated aquatic environments.

Zoochorous dispersal of freshwater bivalves: an overlooked vector in biological invasions?

“…However, over time, SDD may lead to LDD through multiple SDD events; collectively known as 'stepping-stone' dispersal ( Fig. 1) (Coughlan et al, 2017a(Coughlan et al, , 2017b. Additionally, while Johnson and Carlton (1996) suggest that the rate of attachment of D. polymorpha to waterbirds is low, only scant experimental detail is provided.…”

“…Studies such as Águas et al (2014), Anastácio et al (2014), and Banha et al (2016) have highlighted the importance of aquatic invertebrate densities, water depth and exposure time upon the probability of aquatic invertebrate contact and attachment with waterbirds. Accordingly, the density of waterbirds will also influence the probability of contact with aquatic invertebrates and subsequent bird-mediated ectozoochorous dispersal (Coughlan et al, 2017a). While ectozoochorous dispersal of D. bugensis and C. fluminea has not been examined, these species are likely to adhere to waterbirds in a similar fashion to D. polymorpha.…”

“…In order to develop comprehensive IAS prevention and control measures, species risk assessments must consider not only broad invasion pathway categories, but also specific vectors (Essl et al, 2015). Currently, however, our understanding of the natural dispersal processes operating between hydrologically unconnected water bodies remains limited (Soomers et al, 2013;Incagnone et al, 2015;Coughlan et al, 2017a).…”

“…1) Green, 2016;Coughlan et al, 2017a). Many organisms, particularly propagule stages (e.g., seeds, spores, eggs, ephippia, gemmules, statoblasts, or cysts) can be transported both internally, via the gastrointestinal tract (gut), or upon the exterior surfaces of other animals.…”

“…The association where one organism (or propagule) is externally transported by another organism is categorised under various biological relationships which include, inter alia, ectozoochory, phoresis, commensalism, and fouling. Ectozoochory (synonyms epizoochory, exozoochory), a term originally used to describe the dispersal of plant propagules via external adherence to animal vectors, is now widely employed to refer to external dispersal of a variety of taxa Green, 2016;Coughlan et al, 2017a). Endozoochory, a term originally used to describe seed dispersal, now encompasses the internal dispersal of a variety of taxa.…”