Invasions!

Exotic taxa less related to native species are more invasive. Strauss, et al. PNAS 2006

Species invasions and extinction: The future of biodiversity on islands. Sax amd Gaines. PNAS 2008

So, it's been a while since I posted! I've been reading quite a bit, just keep forgetting to post on it. Which is unfortunate, I think this'll be a good resource later, when I remember reading something but don't remember where....

First off, the species invasions and extinctions paper was a fun read, although a little dissatisfying in terms of their conclusions. Also, it contradicts the work I did in Hawaii. They claim that, so far, native plant species richness has not really declined on islands, whereas vertebrate richness has. Vertebrate richness decline is pretty well known, I think they would have been better served just focusing on plants. In Hawaii, however, many plants are being driven to extinction by invasives. Their inclusion of New Zealand might have potentially skewed their results- NZ is so large, from a plant’s perspective, that it would provide numerous refugia and sub-optimal habitat in which, potentially, a plant species could persist. Most other islands, however, are much smaller, not providing such respite from the invasion. I realize it was a large scaled study, and so included lots of variation, but the predictions would be different for smaller islands with less topographical variation (and less area in general). At least in Hawaii, competition with invaders is a major cause of native species going extinct. But, perhaps it’s a special case- I doubt it, I think it’s more related to island size. I also believe their case would have been strengthened had they included functionally extinct species in the “extinct” column (and they imply that they think so too), but they only included actual extinctions. The other paper was quite cool, and directly addressed one of my questions earlier in the semester. Basically, the more unrelated an introduced species is to the native flora, the more likely it is to be a pest species, supporting the enemy release hypothesis and Darwin’s naturalization hypothesis (in that species more closely related often succeed, but don’t become pests because of in-common predators). It makes me wonder a few things- would a dramatic change in disturbance regimes cause native species to become pests, or would natural controls ramp up fast enough? Are globally distributed pest species (like the verbena family) more phylogenetically isolated as a whole? Is there also a phylogenetic relationship with the most impacted species from an invasion (seems less likely, in that the most impacted species is probably more a function of morphological traits and life histories)?