If we look at the structure of communities it is easy to see why some have more niches than others. Arctic communities have low diversity because much of the structure that supports biodiversity is absent. Where are the trees and bushes and underbrush that are home to so many species? There isn't even any exposed soil! And there are no niches for organisms prone to freezing, which eliminates most terrestrial bugs and reptiles. Biodiversity reflects structure, and more complex structures offer more niches.
Also narrow niches have to be more hospitable than wide ones. Specialised predators have very narrow food niches, but this works OK if there is lots of food available in that niche -- plenty of eucalyptus for koalas and bamboo for pandas. But coyotes in the desert eat whatever comes along, whether prairie dogs, snakes, or insects. Bill Silvert ----- Original Message ----- From: "Charles Welden" <[EMAIL PROTECTED]> To: <ECOLOG-L@LISTSERV.UMD.EDU> Sent: Wednesday, November 21, 2007 9:56 PM Subject: Re: Invasives > Maybe not directly relevant to the discussion, but I wonder about the = > assumption that a more diverse community having more niches than a less = > diverse one. It's also conceivable that it might just have more niche = > overlap. In other words, the presumed correlation between diversity and = > number of niches assumes little or no niche overlap, but there's at least > = > some evidence that niches do overlap within a community. This connects to > = > the equilibrium/disequilibrium discussion of community structure & = > dynamics. > I confess a bias toward looking at things as continua rather than as = > discrete packets. So I'd rather think about niche space (a la Hutchinson, > = > plus) and how you pack species in there. You could pack a lot in if they = > all had small, non-overlapping niches, or if they all had big, overlapping > = > niches, or any combination or intermediate. > ...just random thoughts... > Charles
