Plant survival, on a wing and a prayer…*

As organisms that are mainly fixed in one place, plants have a problem if they are to extend their range and spread to new areas by production of a new generation. This fixedness of plants is also a barrier when it comes to exchanging genetic material between individuals during sexual reproduction and producing that next generation in the first place. Although plants have exploited abiotic factors to overcome some of these obstacles, for millions of years many plant species have relied upon animal intervention – a biotic factor – to help them. Such help has primarily been two-fold, via pollination–transfer services – to facilitate sexual union between otherwise widely dispersed plants, and as seed-dispersers, to help the youngsters establish themselves in new areas away from the parents. Although the animals maybe believe they are getting food-for-free from a source that ‘can’t run away’, I like to think that the plants know that it’s nothing so straightforward. [Ed. – this sentence amended in anticipation of comments regarding the loose use of language – which one now notes have appeared at the bottom of this item (Cheers, David!)! – used in the previous version of this sentence by Mr Cuttings (who does get a little carried away at times…rather like the seeds in the item below).]

This collection celebrates work that extends the catalogue of animal involvement in providing such ‘sexual favours’ for plants. Amongst these items you’ll notice several words that end in the suffix ‘-chory’; chory is the technical term for seed dispersal. The prefix, e.g. icthyo- (meaning ‘fish’), indicates the animal involved in that particular seed dispersing behaviour [for more terms related to seed dispersal, see]. Let’s begin our journey ‘up in the air’ as it were…

Arguably, one of the most intriguing ‘hidden-in-plain-sight’ examples whereby animals help the next generation of plants ‘flee the nest’ – quite literally! – is the phenomenon of caliochory. This is the name that Robert Warren et al. give to the phenomenon whereby plant material – which may contain seeds – is removed from plants and incorporated into nests by birds, some distance from the parent plant – at least 100-200 m (Plant Ecology 218: 1213–1220, 2017; doi: 10.1007/s11258-017-0763-5).

Keeping with an avian theme, Erik Kleyheeg and Casper van Leuwen demonstrate the important role that regurgitation of ingested plant material can have in dispersing seeds some distance away from the parent plant (Aquatic Botany 127: 1–5, 2015; http://dx.doi.org/10.1016/j.aquabot.2015.06.009). In this way waterfowl, such as mallard (Anas platyrhynchos), play an important role in transporting seeds between wetland feeding and resting areas during their daily peregrin–ations (Erik Kleyheeg et al., Journal of Ecology 105: 1279–1289, 2017; doi: 10.1111/1365-2745.12738). This phenomenon – of barfochory? – is in addition to the more traditional method of disseminule dispersal via the faeces, at the other end of the animal’s alimentary tract, so-called endozoochory.

That, comparatively small-scale, local transport of seeds by birds considered by Kleyheeg and van Leuwen, is expanded considerable further afield by Duarte Viana et al. who demonstrate the potential for overseas seed dispersal by migratory birds (Proc. R. Soc. B 283: 20152406; http://dx.doi.org/10.1098/rspb.2015.2406). Indeed, “the constant propagule pressure generated by these LDD [long-distance dispersal] events might, nevertheless, explain the colonization of some islands”. In this way, “migratory birds can mediate rapid range expansion or shifts of many plant taxa and determine their distribution.” Way to go, birds!

From common birds [remember Mr Cuttings lives in the UK…] to much more exotic plumed animals and their role in seed dispersal – and which extends the endozoochory [‘internal seed transport’ by animals] theme introduced by Viana et al. above. Studying seed dispersal by parrots, Guillermo Blanco et al. have attempted to draw attention to what is an otherwise neglected example of mutualism (PeerJ 4:e1688; doi: 10.7717/peerj.1688 **).

Investigating the seed-dispersal activities of 11 parrot species, inhabiting a variety of different bi–omes in Ecuador, Peru, Brazil, Chile and Argentina, Blanco et al. unearthed intact seeds – of seven plant species of five families – from the faeces from four of those parrot species. Although the mean number of seeds of each plant species per dropping ranged between 1 and about 60, they found almost 500 seeds from the cactus Pilosocereus pachycladus  in a single dropping of the endangered Lear’s Macaw (Anodorhynchus leari).

But, and with a note of caution, Blanco et al. conclude their Abstract with: “We encourage the evaluation of seed dispersal and other mutualistic interactions mediated by parrots before their generalized population declines contribute to the collapse of key ecosystem processes”. Animals and plants in some sort of interconnected way? This sounds like ecology … where the actions of one life form influence those of another … and survival of one species is often bound up with, and maybe to, those of another. Who’d’ve thought it? Power – and protection! – to the pulchritudinously-plumed plant-propagating Psitacifformes!

* http://dictionary.cambridge.org/dictionary/english/on-a-wing-and-a-prayer; https://www.phrases.org.uk/meanings/on-a-wing-and-a-prayer.html

** This paper will also introduce readers to the phenomenon of stomatochory, which plant dispersal process is compared to endozoochory in parrots.

[This is part 1 of a multi-part series of short items celebrating the creatively imaginative and enterprising ways in which plants dupe poor unsuspecting animals into doing their sexual bidding…]

Picture credits: Mallards by Richard Bartz; Lear’s Macaw by Edward Lear