Food values of sundry plants in East Africa

Most recent: Calculation of silica content in diet of ostrich

See

https://www.jstor.org/stable/1940401

https://pubmed.ncbi.nlm.nih.gov/16578767/ and https://europepmc.org/article/med/16578767

https://www.researchgate.net/publication/355163451_Forage_quality_in_tundra_grasslands_under_herbivory_Silicon-based_defences_nutrients_and_their_ratios_in_grasses

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7317429/

https://eprints.nwisrl.ars.usda.gov/id/eprint/510/1/673.pdf

https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00438/full

https://www.researchgate.net/publication/267292612_Silica_as_a_plant_defense_against_herbivorous_insects

https://api.research-repository.uwa.edu.au/ws/portalfiles/portal/106649226/AAM_A_shift_from_phenol_to_silica_based.pdf

https://www.researchgate.net/publication/6432754_Herbivore_specific_induction_of_silica-based_plant_defences

https://esajournals.onlinelibrary.wiley.com/doi/am-pdf/10.1002/ecy.3250

In each case, the first value is % of diet, and the second value is silica %

Asteraceae 15.6% 8.0% 124.8
Malvaceae 18.6% 4.0% 74.4
Commelinaceae 12.8% 8.5% 108.8
Fabaceae 8.1% 0.7% 5.67
Balanitaceae 5.4% 0.2% 1.08
Solanaceae 5.4% 0.1% 0.54
Acanthaceae 0.8% 7.0% 5.6
Convolvulaceae trace 3.0% 0.03
Poaceae 18.0% 4.8% 86.4
seed capsules 4.0% 0.3% 1.2
inflorescences 3.5% 0.2% 0.7
pods of legumes 2.0% 0.3% 0.6
succulents 1.5% 0.4% 0.6
fib st 0.8% 0.2% 0.16
faeces 1.0% 4.0% 4
fleshy fruits 0.5% 0.2% 0.1
invertebrates trace 0% 0
other 2.0% 1.0% 2.0

Total = 416.68
Mean = 4.2% silica content

Solanum fruits rival grass leaves in crude fibre: 30% (Field 1975)

Ratios of condensed tannins to crude protein:
Vachellja drepanolobium 5.9/21=0.28
Vachellia seyal 1.7/15.5=0.11
Vachellia xanthophloea (Wrangham and Waterman 1981 and Altman et al.) about 0.09
Aspilia mossambicensis 0.7/15= 0.046
Hibiscus flavifolius 0.8/15= 0.053
So, ratios of condensed tannins to crude protein in Vachellia spp. (about 0.1-0.3) seem double those of staples in the diet of the ostrich, viz. Aspilia and Hibiscus.

Look up Dougall and Sheldrick (1964), who record Melhania ovata crude protein in stem and leaf 11.8%

Wilson and Bredon (1963) record crude protein of Pavonia patens as 19.1%

Ratios of silica to crude fibre
Dougall (1963a):
grasses 4.11/30.28=0.135
herbaceous legumes 1.18/21.9=0.054
leguminous browse (woody plants) 0.59/30.32=0.019
non-leguminous browse 1.6/28.78=0.056
Bredon and Wilson:
whole plants of grasses in Zone I, Karamoja:
6.29/27.74=0.23
6.48/31.49=0.21
7.33/33.02=0.22
8.75/34.88=0.25
7.77/35.86=0.22
13.66/27.63=0.49
9.19/32=0.29
7.45/34.04=0.22
5.47/34.86=0.16
6.57/30.91=0.21
Mean = 0.25

Dougall (1963a) found that, in general,

• grasses have ratios of silica to crude fibre 7-fold those of leguminous browse plants such as Vachellia,
• herbaceous legumes showed intermediate ratios, and
• ratios in leguminous browse are less than half those in herbaceous legumes.

From Wilson and Bredon (1963), New nutrient analyses to feed into my calculations:
Commelina cp 7.1-14.4% cf 19.8-28.3% si 5.3-15.3% with mean 9.65%, making a new overall mean of 8.5%
Justicia exigua si 5.99% (!!!)
Heliotropium rather calcium-rich si 5.3% (!)
Ipomoea spp. si range 0.74-5.13 mean 2.96
Crossandra cp 10.9% cf 24.3% si 11.5% (!!!)
Hibiscus 8-14.7%
Monechma cp 18.2% cf 26.5% si 1.6%
Pavonia cp 19.1% cf 16.3% si 11.9% (!!!)

CHEMICAL DEFENCES

There is a definite link between woodiness and tannin content. Acacias are particularly rich in tannins, the leaves varying with age in tannin content.

Acanthaceae

• are bitter-tasting, rather than spicy
• contain flavonoids
• are poor in tannins
• contain compounds of nitrogen; in some cases fairly toxic with alkaloids (not as much as in Solanum), including iridoids, quiniline alkaloids, and quinaziline alkaloids

Capparidaceae (Boscia and Capparis are well-known, Maerua is not)

• usually spicy (amides or glucosinolates)
• Boscia known to have glucosinolates (mustard)
• some (probably excluding Maerua) have cyanogenic glycosides
• Maerua contains small pepperidine alkaloids, as in Salvadora; tastes spicy like pepper; Maerua and Salvadora probably contain less tannin than do acacias
• condensed tannin content unknown

Salvadoraceae

• contain calcium oxalate and potassium salts, but not potassium oxalate
• silica-rich (evergreen rough leaves in Dobera)
• Salvadora persica contains small nitrogenous molecules and is stringy, and perhaps antibacterial substances (mildly antiseptic)

Grass leaves do sometimes contain oxalates (typically associated with succulents). Birds may be preadapted to deal with oxalates.

Euphorbia (including forbs)

• nasty latex
• diterpenes in foliage and fruit
• heterochroma

Celtis leaves silica-rich, according to Waterman

Balanites

• seed largely non-toxic, containing oil and simple, common triterpenes
• fleshy fruit-pulp is very palatable
• probably poor in tannins

Zygophyllaceae

• peculiar chemically
• leaves of Tribulus relatively innocuous
• seeds contain alkaloids

Cucumis

• well-known for bitter principles
• few alkaloids, as in Cucurbitaceae generally
• cucurbitacins
• not phenolic
• triterpenes (containing no nitrogen, which is true also for diterpenes)

Achyranthes, Achyropsis

• seem fairly innocuous
• poorly-known

Boraginaceae, particularly Heliotropium

• tend to be rather toxic
• alkaloids of quinilidine type, as in Senecio
• no tannins

Echium and Echinops

• various defences, including small alkaloids

Similarities among Salvadora, Maerua, and Acanthaceae:

• small, non-aromatic nitrogenous compounds (e.g. azomin, carpane)
• 2-methylpepperidines, which taste peppery but lack antimicrobial activity

Posted on May 15, 2024 09:37 AM by milewski