Seed dispersal, the Ecuadorian dimension…

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Rather belatedly in our look at animals and seed dispersal, we have our Darwin connection (after all, what biological item would be complete without mention of that venerable Victorian vegephile, Charles Darwin?). If your habitat is devoid of elephants or chimpanzees (see parts 2 and 3 of this series), what other animals could the intrepid plant press into service? Well, if it’s the Galápagos Islands, then it’s already established that the Galápagos tortoise (Chelonoidis nigra) is an effective dispersers of seeds (Stephen Blake et al., Journal of Biogeography 39: 1961–1972, 2012; doi: 10.1111/j.1365-2699.2011.02672.x).

Less well-known – apart from anecdotes, which are not sufficiently, scientifically substantial as evidence – was any contribution that the islands’ land iguana (Conolophus subcristatus) might make in this regard. It’s now been established by Anna Traveset et al. – or, rather their “results strongly suggest” – that the land iguana “plays an important role as a seed disperser of not only of native species but also some introduced plants in the Galápagos Islands” (Integrative Zoology 11: 207–213, 2016; doi: 10.1111/1749-4877.12187). This phenomenon of internal seed dispersal by lizards is named sauroendozoochory [from the prefix sauro- (which means lizard), and –endozoochory meaning seed dispersal via ingestion by vertebrate animals]. In that latter regard iguanas are like the archipelago’s giant tortoises that are also effective dispersers of introduced, invasive, alien plant species (guava (Psidium guajava) and passion fruit (Passiflora edulis) (Diego Ellis-Soto et al., PLoS ONE 12(7): e0181333. https://doi.org/10.1371/journal.pone.0181333).

For completeness, other regular seed dispersers in these islands are non-iguanan lizards, medium-sized passerine birds, small non-finch passerine birds, and finches (Manuel Nogales et al., Ecology 98: 2049–2058, 2017; doi: 10.1002/ecy.1816). And for those who’ve not yet had their fill of Galápagoan frugivory [the consumption of fruits, which often leads to seed dispersal – e.g. Richard Corlett, Global Ecology and Conservation 11: 1-22, 2017; https://doi.org/10.1016/j.gecco.2017.04.007], numerous fruit-eating relationships on the islands have been reviewed by Ruben Heleno et al. (Integrative Zoology 6: 110-129, 2011; doi: 10.1111/j.1749-4877.2011.00236.x).

And by way of illustrating the companion process to endozoochory, here’s another creature feature (which also underlines the fact that iguanas are not just a Galápagos life-form). Eloisa Lasso and Lucas Barrientos present what they believed to be the first evidence of reptile epizoochory involving seeds of Melocactus curvispinus and the common green iguana (Iguana iguana) in the dry forests of Colombia (Colombia Forestal 18(1): 151-159, 2015; http://dx.doi.org/10.14483/udistrital.jour.colomb.for.2015.1.a09).

Although the plant’s seeds were consumed and voided in the iguana’s faeces, such endozoochorously translocated seeds suffered in terms of viability during their digestive transit. By contrast, those seeds transported externally [via the process of ectozoochory], attached to the lizard’s snout, germinated faster and in higher numbers. As the authors reasonably conclude “our data suggest that we may have overlooked an alternative means of seed dispersal by lizards that do not comprise a passage through their digestive tract, and that deserves further attention for the understanding of dry forest ecology.”

[This is part 4 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…]

Image credits: Galápagos land iguana from Jimrules42 at en.wikipedia; Green (if a little reddish of hue) iguana from Cary Bass


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