Diet of Macropus in Banksia woodland, with special reference to foliar spinescence

(writing in progress)
 
The following is information relevant to the relationship between Macropus and foliar-spinescent plants: https://www.rswa.org.au/publications/Journal/80(2)/80(2)wann.pdf.
 
The following shows that Macropus irma and Macropus fuliginosus, in Banksia woodland on the Swan coastal plain, eat mainly graminoid, herbaceous and non leaf-spinescent plants.
 
The graminoids eaten include the restio Alexgeorgia, the tussock-grass Danthonia, the cosmopolitan lawn grass Cynodon, and the introduced annual grass Ehrharta.
 
The herbaceous or relatively soft plants eaten include introduced Carpobrotus, Corynotheca, Dampiera, and Tricoryne.
 
So far, no surprises because I expected Macropus to concentrate on herbaceous plants, particularly graminoids.
 
Now things get a bit more interesting.
 
The diets include several shrubs of the nutrient-poor, ‘kwongan’ type, such as Adenanthos and Beaufortia. However, these are not particularly sclerophyllous and are not leaf-spinescent. In the case of Adenanthos, the leaves are not even sclerophyllous. These leaves are extremely nutrient-poor, but I can undersand why they are sometimes eaten, because at least they seem poorly defended.
 
Also eaten is the small shrub Oxylobium. The species concerned is non-sclerophyllous. Here again, I can understand why this species is eaten: it is an N-fixer and relatively poorly defended.
 
So far, we have complications to the idea that Macropus eats mainly graminoid and other herbaceous plants, but no real surprises w.r.t. sclerophylly and leaf-spinescence, not so?
 
Several species of typical ‘epacrids’ are eaten. The species concerned of Conostephium and Leucopogon are typical ‘epacrids’ in having small, sclerophyllous, leaf-spinescent leaves. The sclerophylly of these shrubs is noteworthy despite the leaves being far smaller than typical sclerophyllous leaves of e.g. proteas, and their (modest) leaf-spinescence is also noteworthy. These ‘epacrids’ do indeed indicate some degree of ‘tolerance’ of Macropus for the ‘kwongan syndrome’ of sclerophylly combined with leaf-spinescence. Furthermore, there is little ‘excuse’ in terms of these plants having particularly attractive nutritional modes such as N-fixation or hemiparasitism. But in the final analysis the ‘epacrids’ are still not in the same ballpark as grossly leaf-spinescent, large-leafed shrubs such as hakeas, not so?
 
By far the most sclerophyllous and leaf-spinescent plant eaten here is Macrozamia. I do indeed find it surprising that Macropus, including the smaller species M. irma, eats this genus. However, what makes this a bit more understandable is the fact that Macrozamia is a N-fixer.
 
The final genus eaten, in this summary, is the hemiparasite Nuytsia. This makes sense because the foliage of this plant is not particularly sclerophyllous, is not leaf-spinescent, and by virtue of nutrient-parasitism may perhaps concentrate trace elements deficient in the rest of the diets.
 
As I see it, these results are ambivalent w.r.t. kwongan on a broader front, which does not seem to have been studied for the diets of Macropus. It does indeed remain possible that Macropus is a significant browser of leaf-spinescent plants.
 
I can summarise these results as follows:

• the diets of Macropus in Banksia woodland consist mainly of graminoid, herbaceous, and relatively non-sclerophyllous plants;
• there is a significant attraction to introduced taxa (most notably Carpobrotus, which had no counterpart in the native flora of this vegetation);
• there is a significant attraction to ‘nutrient-supplementing’ plants including N-fixers and hemiparasites; and
• there is a significant, if minor, incidence of sclerophyllous, leaf-spinescent plants.

This study shows that one cannot simply generalise that Macropus is mainly a grazing genus. This genus certainly does ‘browse’ shrubs significantly, and this is remarkable considering how little Megaleia browses the more fleshy shrubs of the semi-arid interior, particularly Amaranthaceae.

The inference is that Macropus treats certain oligotrophic taxa as ‘honorary grass’, i.e. extremely fibrous but acceptable plants not to be confused with the sort of ‘nutritious browse’ associated with ruminant browsers elsewhere on Earth.
 
The bottom line seems to be that it does indeed remain possible that leaf-spinescence is an adaptation, at least in part, to browsing by large marsupials.

(writing in progress)

Publicado el julio 30, 2022 06:34 TARDE por milewski