Following up with my “Theory vs Data” post, I want to share an example of a beautiful theoretical framework to understand the invasion processes and an idea on which can be the perfect study system to validate it.
Mc Dougall et al (2009) have one of the more compelling figures I saw summarising the hypothesis that niche and competitive differences between exotic and native species can explain the outcome of the invasion process. The figure speaks for itself:
While I was in the US I planned to use this framework to understand the effects of Osmia cornifrons (a mason bee) invasion on the native Osmia lignaria, but I had no time to follow-up on this. Anyway, for that end you would need to prove the following:
1) Are their niches overlapping? Both bees are on the same genus, have similar size, phenology, nesting habits, and probably visit similar flowers, you just need to put numbers on those things (e.g. which hole diameter they prefer to nest on). For example, this data is from a preliminary experiments I did on its phenology. Interestingly, the result suggest the invader emerge slightly (but significantly) earlier than the native. So, quantifying all this can be important.
2) Is their fitness different when raised alone? Buying this bees and monitoring its nests is easy. Moreover, measuring offspring (a fairly good proxy of fitness) is a piece of cake compared with other species. Well, at least in theory, because I tried it in 2011 and an April snowstorm killed 80% of both populations. Hence, I have no data here.
3) It’s the native fitness lowered when they are raised together? That’s an important part (especially the effect size), because they may coexists just fine (even if sharing niches).
I am not in the US anymore, so, is impossible for me to do the experiments. If anyone wants to explore this idea further (undergraduates seeking for a project, jump in!), the idea is here, and it’s for free!
MacDougall A.S., Gilbert B. & Levine J.M. (2009). Plant invasions and the niche, Journal of Ecology, 97 (4) 609-615. DOI: 10.1111/j.1365-2745.2009.01514.x
And now, what can occur with this post?
– Worst thing it can happen is that nothing happens.
– Will be pretty cool if someone does this or similar experiments, even if I never know of its existence (well, I hope at least not to miss the article when it gets published!). I would be happy with that because despite I did some thinking on this I assume this ideas are “on the air”, and that’s precisely why I post them here.
– Will be awesome if that someone also contact me and we end up collaborating. (incentive: I have also some ideas on how to analyse it)
– Will be terrific (I am running out of superlatives) if people start reporting they have data on niche and fitness differences for other systems and we end up with a meta-analysis proving (or disproving) that this theory can correctly predict invasion outcome with some generality. For example, where is propagule pressure fitting in this framework? Niche and population growth/species traits hypothesis clearly are captured here, you can even account for lowered native fitness due to disturbance (wow!), but the number of invaders arriving may be a missing piece. Also scaling up to the community level seems a daunting task.
Interesting post and I like the figure. Just two comments:
Phenologies of many organisms, including bees (and flowers) can be highly variable between years. So I’d want to see several years of data to know for sure that one bee species is an earlier emerger than another.
Secondly (more of a question) – how often can we state that “invasive species x is outcompeting native species y” in this fashion? Many invasives are not necessarily having an effect on a single species. Rather they are having a broad community effect by monopolising resources (including space) that would be more generally available. Has anyone done such an analysis? I’m thinking a lot about invasives at the moment having just published a paper in JPE on Nicotiana glauca as an aggressive introduced species.
All the best,
Completely agree on getting data for multiple sites and years.
Regarding competition by resources, is true that is a community proces, but focusing on the most affected native species (likely the one using more similar resources) can be a good start. My gut feeling is that floral resources won’t be limiting for bees in most situations, but nesting sites will be.