Thorny questions (my guess)

[Panza, Robin]

>>>>>
1)  Why are thorny plants more abundant in savannas and areas like the
Black Belt than elsewhere?
2)  If thorns were an adaptation against Pleistocene and earlier browsers,
what kept these browsers from going into habitats where plants were less
thorny?  Why wouldn't other plants outside savannas develop thorniness as a
defense against these browsers.
<<<<<

My *guess* would be that it has to do with the competition (grass).  Grass
is not a great source of animal nutrition, relative to the effort.  Any
dicots in a sea of grass would seem to be pretty prime food.  By definition,
there are relatively few dicots in a grassland, so there are few plants
"sharing the load" of vertebrate predation, so to speak.  That's pretty
strong selection for anti-predator tactics.

One dicot species surrounded by other dicots (in a woodland, say) has much
lower risk of debilitation or death from predation, so there's less
selective advantage to using its resources for strong woody projections.

just the 2 cents of a zoologist,
Robin

Robin K Panza                         panzar at carnegiemuseums.org
Collection Manager, Section of Birds          ph:  412-622-3255
Carnegie Museum of Natural History       fax: 412-622-8837
4400 Forbes Ave.
Pittsburgh  PA  15213-4008  USA