comments of Feb 1 version

Hi Cini and all,

here are my comments. Generally, I think it is crucial in agreeing on what we mean by "being or not being different" ...

Regards

Petr

Manuscript outline

Referring to Peter’s (2) - I think we mix two categories – “alien/exotic” (any species that is not native to a region regardless of status) and “invasive” (a subgroup of aliens that are successful, whatever the measure of “success” may be). We need to clarify this before we start. Aliens are a more random subset from source species pool (e.g., species from the same climates worldwide) than invasives, I would predict.

 As Peter, I am also uncomfortable with the statement on dichotomy, as Peter. We should not be prejudicial from the beginning, in one or another direction. I understand we want to come up with something novel and different but …

Section 2

What data EXIST and what data are NEEDED to answer these questions?

What is the appropriate control group? – native vs. introduced genotypes? native and introduced competitors in the same community? invaders vs. abundant natives?

I think for impact, the most appropriate comparison is “invaders vs. abundant natives”. We have done a study comparing features of invading aliens and natives dominating uninvaded communities to see if these differences can be related to impact on species diversity (Hejda et al., Journal of Ecology 97: 393–403, 2009). Martin Hejda, and another PhD student of mine, follow this line in a project looking at impact of invaders vs impact of native dominants in the same communities, but first experiences seem to show that it is not easy to find comparable situation simply because many communities are not dominated by comparably strong dominant species (seems that the circle of reasoning closes here .

If we ask about native vs invaders differences, then comparison of the same species in native and introduced range (do they do the same thing home and away from home?) is not very informative, is it? It can tell you about what is the reason for invasiveness (can be just a new environment), but need not tell anything about being different from native or not

But do these differences systematically alter the ecology or evolution of exotic species? Differences are misperceptions if:

Variation in the abundance and distribution of exotic species is determined by propagule pressure rather than biological differences.

I disagree with point 2 on propagule pressure – ability to create propagule pressure is also a trait. If you have two species, one native and one exotic that are otherwise identical and only differ in propagule pressure, would you say they are NOT different? If such an exotic exerts a greater propagule pressure which leads to more abundant, more widespread, genetically more diverse …. etc. populations, it must differ in at least one trait, ability to disperse propagules. Why none of the natives did not take a chance if they are not different? So I do not think such a difference is misperception.

I am trying to say that ability to disperse is part of “being an alien”, it is also an important trait. Studies tend to focus on differences in traits like growth rate, fecundity, enemy load et., but take as granted that the exotic invader got to the place where it has impact. There maybe a native species that would exert similar effect to that of the invader but it could be that it grows in different habitats and did not make it to the target habitat because of poor dispersal abilities? Does it make and invader that did (make it there) different? I would think yes. For example in Myrica faya example mentioned by Peter – there is no similar nitrogen fixer among native flora (and here we get to evolutionary history), but there was one exotic species with such ability, and it was able to get there.