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Introduction

Last week, I was in the Atacama desert where I've seen many cacti. Some / many of them were seemingly suffering from predation. Most of predation seemed to be on cardón, often restricted (but not only) at the interface between the woody bottom part and the green spiny part. It looks like a big piece (maybe over 300 $\text{cm}^2$) of the flesh was bitten away. Unfortunately, I do not have a picture.

These cacti have very long spines and it was unclear to me what predator could maintain selection for cactus lineages to produce that many large spines.

In the desert, I have seen rabbits, guanacos, small birds, vultures, large black coleoptera and butterflies.

Question

In the Atacama region,

  • What species predate on cacti?
  • Is there a single species that causes most of the predation on cacti?
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  • 1
    $\begingroup$ What does it look like? Are there pieces bitten/picked out, scratches? $\endgroup$ – skymningen Sep 8 '17 at 7:35
  • $\begingroup$ In North America, bighorn sheep are known to eat Ferocactus sp (barrel cactus) by "pawing and butting at the cactus" (according to Warrick and Krausman, 1989). Were there any animals around that could do that? $\endgroup$ – Gaurav Sep 15 '17 at 22:53
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    $\begingroup$ Guanacos probably! I just had a hard time to imagine so few guanacos making so much damage to so many cacti. Also it was surprising to me that guanacos could deal with those spines but I guess that if bighorn sheep can, why guanacos could not! $\endgroup$ – Remi.b Sep 15 '17 at 23:34
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    $\begingroup$ I agree with @Remi.b. I would just also note that I have seen similar damage on candelabra (Browningia sp.) in northern Chile, where an apparently similar-sized wound was effected by perching raptors (scarred by talons). I am pretty sure that one of them was a variable hawk and another a mountain caracara. Also, you likely saw vizcachas, not rabbits! $\endgroup$ – Plantaloons Feb 15 at 16:40
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Short answer

This type of herbivory is probably from feral livestock, especially donkeys.

Long Answer

There is video footage of guanacos eating flowers off of cacti in the Atacama. For example, an image capture of a Getty Images video:

enter image description here

Credit: BBC Natural History

This type of florivory has been documented in related species of cacti as well (e.g., see Gomes et al. (2016)1)

However, I could find little evidence about guanacos eating the trunk of these cacti (especially to the degree you describe).

Actual herbivory of Echinopsis cacti has been reported in multiple publications. For example, Peco et al. (2011)2 cite feral livestock as a major source of herbivory in columnar cacti in South America:

Columnar cacti are an important feature of the arid “cardonal” landscape in South America. The predominant columnar cactus in the southern zone is Echinopsis (=Trichocereus) terscheckii. At some sites, the species suffers considerable trunk damage, attributed in previous studies to feral livestock grazing (donkey and cattle).

In a previous study we found that damage intensity on Echinopsis terscheckii trunks correlated with abundance of livestock dung in their surroundings, but not with the abundance of guanaco dung (Lama guanicoe) (Malo et al., 2011; Novillo and Ojeda, 2008). Futhermore, E. terscheckii was found in summer or winter donkey diet but not in guanaco diet in the study area (Reus pers. comm.). Direct observation of donkeys feeding on columnar cacti suggests that this species is the main cause of stem damage

See this National geographic video explaining how camels and other related animals handle eating spiney cacti. (Specifically, they accomplish eating cacti through the use of hardened papillae guiding the spines down the throat vertically).


Works Cited:

  1. Gomes, V.G.N., Koroiva, R. and Araujo, A.C., 2016. Vertebrate florivory on the short-columnar cactus Echinopsis rhodotricha K. Schum. in the Brazilian Chaco. Plant Ecology, 217(12), pp.1481-1487.

  2. Peco, B., Borghi, C.E., Malo, J.E., Acebes, P., Almirón, M. and Campos, C.M., 2011. Effects of bark damage by feral herbivores on columnar cactus Echinopsis (= Trichocereus) terscheckii reproductive output. Journal of arid environments, 75(11), pp.981-985.

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