Sunday, 30 January 2011

Conserving weeds


A couple of weeks ago I wrote about Angela Moles' work on twining plants. Today Angela is featured in the Sun-Herald for her work on rapidly evolving weeds.

Nicky Phillips reports that Angela and others have been comparing the vital statistics - height of plant, leaf size - of weeds stored in our preserved plant collections held in 'herbaria'. (This highlights yet again the importance of herbarium collections.)

Since 1948, plants such as clover have adapted to their low-nutrient, low-rainfall home in Australia.

Clover back in the UK hasn't changed as much. Nor have a bunch of native Australian grasses they tested. Dr Angela Mole concludes the changes in these weedy species are due to the new environment.

Which makes sense. It's changes in environment that select for different characteristics and historically lead to speciation - that is, new species evolving. Still, it's nice to evolution in action.

Angela asks whether if they evolve enough to become new species (i.e. they are obviously different from the original species and find it difficult to breed with the UK plants) we should treasure them as rare new species or still try to eradicate them.

The whole weed questions is a tricky one, particularly if you think of humans as just one more vector for the spreading of plants (along with birds, wind and so on). I'd suggest that if an 'introduced' species (whether still looking like the one that came in or better adapted to the environment) is displacing local species and dramatically changing the structure and function of the local ecosystem then let's get rid of it, if we can.

Some environments are very 'weedy' already. In UK for example it can be difficult to determine what is a human-induced landscape v. a 'natural' landscape, and whether this really matters. In Australia we do have these lovely areas with a flora and fauna evolved over millions of years and little impacted by us, so why not hold on to them if we can.

So I think clover, old or new species, can be carefully weeded out...

As a little aside, Darwin used clover to help explain this theory of evolution by natural selection in Origin of Species. His argument went a like this:
  • The tubes at the base of a clover flower vary in length, and hold nectar.
  • The hive-bee can get nectar from the Incarnate Clover (Trifolium incarnatum) but not the Red Clover (Trifolium pratense).
  • The humble-bee, however, has a ‘proboscis’ long enough to reach into the tube of the Red Clover to get the nectar.
  • Hive-bees like the Red Clover nectar, and in autumn they will bite holes in the base of the tube to get at it!
  • The difference in tube length is very small – in fact, anecdotally, if the Red Clover is mown, the second crop sometimes has slightly smaller flowers and the nectar in these flowers can be reached by the hive-bees…
  • Red clover is very common in England and it would seem to be a great advantage for the hive-bee to have a longer, or different shaped, proboscis, to get at its nectar.
  • From the plant’s perspective, it depends upon bees for fertilisation so if humble-bees became rare, those individual plants with shorter tubes allowing the hive-bee to get the nectar, would be more likely to reproduce and be ‘favoured’
  • Darwin notes that he could understand how such a system could adapt and change over time.
Image: Red Clover from www.panoramio.com/photo/10625768  (www.panoramio.com/photo/10625768

2 comments:

Jim said...

My garden is a Weed Heritage Area. Several PhDs and a Nobel Prize or two lurk within.

Barbie from office plants said...

Wow, nice post ! Explanatory and very easy to understand because of all the images you took.

Good job I really appreciate your effort.