permaculture

["Scott Pittman" <scott@permaculture.org>]

So what is the bio-feedback loop that informs the plant that wind dispersed
seed is not germinating??  While the conclusion seems right in line with
Darwinian evolutionary principals, it is still a very mysterious process.

The simple answer is that Crepis sancta trys multiple methods of seed
dispersal and the method that is most successful in a given environment is
the one that endures but.. 

the answer may lie in the writings of Stephen Buhner, particularly "The Lost
Language of Plants".  I would not be farfetched if the mycelia of some
specialized fungi carried the chemical message back to the parent plant if
it was a perennial but I'm not sure how annual's feedback loops work - since
the germination would take place the following growing season.  Perhaps
there is a "morphogenetic field" of all Crepis sancta and the strength of
that field is a measurement of the success of germination - I'll have to
talk with Rupert Sheldrake on that.

Pardon the musings .... 

Scott Pittman
Director
Permaculture Institute
www.permaculture.org

-----Original Message-----

Plant seeds 'adapt to city life'
By Mark Kinver
Science and nature reporter, BBC News

Weed non-dispersing (top) and dispersing (bottom) seed (Image: Eric Imbert)
Heavier seeds had a better chance of germinating in urban areas
A species of plant found in cities has evolved rapidly in order to adapt to
the challenges of surviving in the concrete 
jungle, a study suggests.

Crepis sancta growing in urban areas produces heavy seeds that fall to the
ground rather than lighter seeds that are 
dispersed by the wind.

Wind-blown seeds are less likely to germinate because most end up on
concrete surfaces, scientists say.

The findings appear in Proceedings of the National Academy of Sciences.

Researchers from the Centre d'Ecologie Fonctionelle et Evolutive (CEFE),
based in Montpellier, estimate that the change 
in the way the plant disperses its seeds has taken place in as little as
five to 12 generations (five to 12 years).

Co-author Pierre-Oliver Cheptou said the team was surprised by the speed of
the change.

"Logic would assume that this sort of evolutionary trait would develop more
slowly, which is probably the case in less 
fragmented situations," he told BBC News.

"However, at the same time, it is consistent with the estimation we had for
the trait in a fragmented urban situation."

Risky business

The team collected seed samples from the weed, which grows on wasteland or
next to roadside trees, from various 
locations around the French city.

        
Crepis sancta (Image: Gilles Przetak)
In fragmented situations, the evolution towards lower dispersal leads to
more isolated populations; increasing the risk 
of extinction
Dr Pierre-Olivier Cheptou,
Report co-author

They then grew them in a greenhouse to see what fraction of the resulting
plants' seeds were of the light, 
wind-dispersible variety.

Compared with specimens taken from the countryside, the urban samples
produced far fewer of these seeds.

The researchers said "dispersing" seeds had a 55% lower chance of
germinating because the majority ended up on concrete 
surfaces.

The heavier seeds were at an evolutionary advantage because they would fall
down into the patch of soil that had 
supported the previous generation of the plant.

They added that their findings supported "cost of dispersal" theories.

"When dispersal is passive (wind or water transport) and habitat choice is
random, the probability of settling in a 
suitable site is positively dependent upon the frequency of suitable sites
in the landscape," they wrote.

"Many empirical studies have reported a reduction in dispersal structures in
organisms that live on islands, such as 
plants or insects."

Dr Cheptou said that their study showed the same also applied to plants in
urban areas, where suitable soil was widely 
fragmented by buildings, pavements and roads.

He explained that such a strategy, while increasing the odds of survival for
the next generation, could have drawbacks.

"We can hypothesise that in fragmented situations, the evolution towards
lower dispersal leads to more isolated 
populations, increasing the risk of extinction."
                
SEE ALSO
Take cover by saving urban trees
04 Mar 08 |  Science/Nature
Arctic ice no barrier for plants
15 Jun 07 |  Science/Nature



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