Post by cjm on Dec 12, 2016 4:29:27 GMT
Plants defending themselves by varying palatability
There are instances of plant colonies being sought after food by animals, while the same species of plant in different locations being poisonous or less palatable.
The suggestion I have, is that colonies being grazed (or overgrazed) or suffering stress, may enter defense mode and change taste. I am not talking here about plants which are mildly toxic and where there is a gradual build-up of toxins in the body of the grazer. This also constitutes a defense mechanism against overgrazing, but is not what I have in mind here.
The thesis (if one may call it that) is but a shot in the dark as the differences between plants may be climate, soil and cultivation (to name but a few).
For the purposes of illustration I unearthed three examples in Vlok’s Plants of the Klein Karoo (Umdaus, 2010).
1. The Common Melkbos (Euphorbia mauritanica; a similar species is Euphorbia burmanii).
Euphorbia (p378)
...
This group requires further scientific study as authors disagree
about species concepts (there are often several names for
variable species). Plants are generally considered to be
toxic, but small game species often browse fresh growth
of plants that grow on ’heuweltjies’ and porcupines
are very fond of the rootstocks of certain species.
The milky sap of some species was used to poison
fish and served as an arrow poison. Many species
are pollinated by wasps when they collect oil from
the large nectarines (that resemble petals).
...
Euphorbia mauritanica (p380)
Melkbos, Geelmelkbos
...
This widespread species occurs throughout South Africa.
lt varies much in palatability, with some plants
sometimes heavily browsed and others close-by
remaining untouched.
2. Spekboom (Portulacaria afra)
Portulacaria (p474)
One of the three species [ie Portulacaria afra -Spekboom]
occurs in the Klein Karoo.
This well-known succulent is often used to create
hedges and is a popular pot plant overseas. It is an
important fodder plant for game and stock, but not
all plants are equally palatable. Some plants contain
high levels of tannin and are rarely browsed. It is
currently being restored in many sites where plants
were removed through grazing by stock, in part also
to contribute towards reducing carbon levels (C02)
in the air.
...
3. Ankerkaroo (Pentzia incana)
Pentzia incana (p296)
Ankerkaroo
...
This widespread species occurs from Namaqualand
to the Eastern Cape It is usually a valuable fodder
plant to stock, but some populations are less
palatable than others. The strongly scented leaves
contribute much to the Characteristic taste of karoo
lamb, it is a useful species to restore disturbed
lowland sites with clayey soils.
A final musing about defensive plant reactions is what the effect of harvesting is on crops. Some crops, such as lucerne, might not be too happy about being grazed. Grapes (and other fruit) might welcome its consumption (as consumption aids in the distribution of the seed). Damage to trees/vines might be another issue though.
There are instances of plant colonies being sought after food by animals, while the same species of plant in different locations being poisonous or less palatable.
The suggestion I have, is that colonies being grazed (or overgrazed) or suffering stress, may enter defense mode and change taste. I am not talking here about plants which are mildly toxic and where there is a gradual build-up of toxins in the body of the grazer. This also constitutes a defense mechanism against overgrazing, but is not what I have in mind here.
The thesis (if one may call it that) is but a shot in the dark as the differences between plants may be climate, soil and cultivation (to name but a few).
For the purposes of illustration I unearthed three examples in Vlok’s Plants of the Klein Karoo (Umdaus, 2010).
1. The Common Melkbos (Euphorbia mauritanica; a similar species is Euphorbia burmanii).
Euphorbia (p378)
...
This group requires further scientific study as authors disagree
about species concepts (there are often several names for
variable species). Plants are generally considered to be
toxic, but small game species often browse fresh growth
of plants that grow on ’heuweltjies’ and porcupines
are very fond of the rootstocks of certain species.
The milky sap of some species was used to poison
fish and served as an arrow poison. Many species
are pollinated by wasps when they collect oil from
the large nectarines (that resemble petals).
...
Euphorbia mauritanica (p380)
Melkbos, Geelmelkbos
...
This widespread species occurs throughout South Africa.
lt varies much in palatability, with some plants
sometimes heavily browsed and others close-by
remaining untouched.
2. Spekboom (Portulacaria afra)
Portulacaria (p474)
One of the three species [ie Portulacaria afra -Spekboom]
occurs in the Klein Karoo.
This well-known succulent is often used to create
hedges and is a popular pot plant overseas. It is an
important fodder plant for game and stock, but not
all plants are equally palatable. Some plants contain
high levels of tannin and are rarely browsed. It is
currently being restored in many sites where plants
were removed through grazing by stock, in part also
to contribute towards reducing carbon levels (C02)
in the air.
...
3. Ankerkaroo (Pentzia incana)
Pentzia incana (p296)
Ankerkaroo
...
This widespread species occurs from Namaqualand
to the Eastern Cape It is usually a valuable fodder
plant to stock, but some populations are less
palatable than others. The strongly scented leaves
contribute much to the Characteristic taste of karoo
lamb, it is a useful species to restore disturbed
lowland sites with clayey soils.
A final musing about defensive plant reactions is what the effect of harvesting is on crops. Some crops, such as lucerne, might not be too happy about being grazed. Grapes (and other fruit) might welcome its consumption (as consumption aids in the distribution of the seed). Damage to trees/vines might be another issue though.