[APWG] Invaders

[Philip Thomas (www.HEAR.org)]

NATIVE species richness in an area might be a more interesting "index of 
diversity"...

pt at hear.org

Daniel Gluesenkamp wrote:
> 
> Of course, we care whether species are going extinct.  But we also care if
> they are going 99.9% extinct.  150 years ago, California hills and valleys
> were amazing tapestries of color, covered by sweet-scented native
> wildflowers and buzzing with native bees.  Today those hills are brown with
> just a few species of European grass.  The wildflowers are not extinct, but
> instead of millions of flowers a grassland may contain just a handful.
> However, we still care about the dramatic changes that these invasive
> grasses have caused.
> 
> Species richness is one index of diversity, often favored by modelers and
> theoreticians because it is simple and easily pulled out of grey literature
> and incomplete data sets.  But there are other indices of diversity, which
> include relative abundance and better capture dramatic changes in community
> structure.  To right brain it: I prefer an uninvaded park which contains
> it's historic evolved community, versus a weed lot with a whole lot of
> species.  
> 
> -dan
> 
> 
>      ____________________________________________
>       Daniel Gluesenkamp, Ph.D.
>       Director, Habitat Protection and Restoration
>       Audubon Canyon Ranch
>       415-939-6681 mobile
>   
> 
> 
> -----Original Message-----
> From: apwg-bounces at lists.plantconservation.org
> [mailto:apwg-bounces at lists.plantconservation.org] On Behalf Of maryann
> whitman
> Sent: Friday, September 12, 2008 8:49 AM
> To: 'Bob Beyfuss'; 'Michael Schenk'; apwg at lists.plantconservation.org
> Subject: Re: [APWG] Invaders
> 
> Here is a comment on the NYT article from another list. The last couple of
> paragraphs are particularly relevant to this conversation.-Maryann
> 
>  
> 
> [Authors] point out that the invasion has not led to a mass extinction of
> native plants. The number of documented extinctions of native New Zealand
> plant species is a grand total of three
> 
> The key word here is documented - that is the plants that were discovered
> and known about before they dissapeared.  The Department of Conservation's
> NZ Threat Classification List lists six plants that are known to be extinct
> 
> Lepidium obtusatum Kirk
> Brassicaceae      
> Logania depressa Hook.f.
> Loganiaceae 
> Myosotis traversii var. cinerascens (Petrie) L.B.Moore      Boraginaceae
> None
> Known
> Pseudognaphalium (a) (CHR 365358; Zoo)
> Stellaria elatinoides Hook.f.
> Caryophyllaceae   
> Trilepidea adamsii (Cheeseman) Tiegham                      Loranthaceae
> Adams
> mistletoe
> 
> Descriptions for 5 of these species can be found on www.nzpcn.org.nz All but
> the last are small herbs, that were found once or on a very small number of
> occasions, indicating that they were probably not common.  Most were in very
> restricted and specialised habitats.  The last is a reasonably large
> mistletoe species and Historic records indicate that this species was never
> common.
> 
> Many more species may have gone extinct without anybody noticing -
> especially in unpleasant habitats (e.g. seabird roosts, swamps) or in very
> small and unusual habitats.  
> 
> Furthermore extinction generally depends on the European observation of
> plants.  It is not know how many plant species dissapeared when the Maori
> (and Moriori) settled in New Zealand with their range of introduced species
> (principally the Pacific rat or kiore Rattus exulans and dog, kuri Canis
> familiaris)and their habit of burning vegetation.  Nor do we know how many
> plant species dissapeared when pigs and goats were liberated by Europeans on
> islands to act as food for potential cast aways.  Species may have
> dissapeared before Europeans botanised an area, because Europeans were even
> better at burning vegetation.
> 
> We suspect that invasive species are the cause of extinction for some
> species (e.g. all large leaved New Zealand mistletoes seem to be favourite
> food of the introduced Australian brush tail possum - Trichosurus vulpecula)
> and that could certainly account for the dissapearnce of Trilepidea adamsii
> on mainland NZ.  But Trilepidea adamsii was also found on Great Barrier
> Island (NZ not Aus) and possums were never released there.
> 
> It is also difficult to definitifly say that invasive species caused the
> demise of some of these plant species, unless you include humans as an
> invasive species.  Some extinctions are more likely to have been caused by
> habitat loss or modification.  Others may be caused indirectly through
> invasive species, for instance guana loving plant species are highly
> threatened because many mainland seabird colonies have been decimated by
> introduced predators, the predators don't however eat these plant species as
> far as we know.
> 
> So in a nutshell - I don't agree with the statement that there were only
> three plant species known to have become extinct due to invasive species.
> We don't know how many have gone extinct, and in many cases extinction is
> more likely to have been through habitat destruction or modification by
> humans rather than invasive species.
> 
> The case for extinction of animal species by invasive species is much
> clearer, especially when you can find rodent or mustelid teeth marks on the
> bones, or find piles of bones in human made ovens.
> 
> Astrid van Meeuwen-Dijkgraaf (PhD)
> 
> 
> 
> 
> 
> 
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Hawaiian Ecosystems at Risk project (HEAR) - http://www.hear.org
P.O. Box 1272
Puunene (Maui), Hawaii  96784  USA

Philip A. Thomas - pt at hear.org

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