Discussion Questions:
- What do you think about Connell’s conclusions about the roles of intraspecific versus interspecific competition among the barnacle species? Do you think these results are robust/repeatable/reliable?
- Were there any factors of Connell’s experimental design or the study organisms (two barnacles and a predatory snail – Chthamalus, Balanus, and Thais) that you felt may have adversely affected/biased his results over the course of the study?
- Wauters et al. argue that the two plausible explanations for sociability expression seen in the red squirrels (which could both be happening) are: 1) interspecific competition drives natural selection by favoring certain personality phenotypes, and 2) observed differences in red squirrels are the result of context-dependent behavioral plasticity. Based on the study and your own research/knowledge, are you more convinced by one of these mechanisms as the explanation for their results, or perhaps an alternative? Why/why not?
I liked both papers and (like the moth paper) have heard a lot about this barnacle one (though this was my first time reading it). In response to the first question, I thought the methods and their conclusions seemed pretty valid and repeatable. The experimental set up appeared pretty straight forward and simple. As for the second question, I think it would be interesting to see the effect of climate on this competition (as another variable other than the predatory snails).
ReplyDeleteIn terms of the Wauters et al. paper, I am not sure how one determines the line between behavioural plasticity and natural selection. Ecologically speaking, I am not sure how one determines one is happening versus another unless large spans of time are involved.
I likes the older paper. I found it interesting that until this was written, little direct evidence in nature existed to show that interspecific competition was important in determining species populations and distribution. It seems so widely excepted today. I thought his choice of organism allowed him to have a clean experimental design.
ReplyDeleteI didn't really buy the second paper. I'm skeptical of the personality test and its significance to survival and competition.
-Miranda
I have used Connell's barnacle study as an example for teaching interspecific competition and realized niches, but I had not realized that predation was a factor included in the original study. After seeing Connell’s conclusion that the predator snail had very little effect on Chthamalus, it is understandable to see why predation is omitted from the classroom example. I don’t have much experience in ecological studies, but is it considered a sampling bias that Connell picked the first eight suitable sites that he found?
ReplyDeleteThe authors of the companion paper indicated that many behaviors have a heritable and a flexible component. I don’t know how much of the “sociability” behavior is heritable between generations of squirrels, so I would need further evidence about the heritability of sociability before attributing the change in red squirrel behavior strictly to natural selection.
I have read Connell's barnacle study before and think that it's a great study showing interspecific competition. He had a good choice of study organisms selected for this experiment, and made strong conclusions that supported an experimental, in-nature case of interspecific competition occurring and was able to show his contemporary scientists that there was direct evidence of this ecological interaction occurring. I also found the figures he used useful in "painting a picture" of what was going on in his system and with his data.
ReplyDeleteThe newer paper was an interesting follow-up looking at a very different system of animals. I am uncertain just how rigorous the personality testing is, as this is a very different sort of study from my background.
- Elizabeth
The Connell paper was fascinating. Like Crystal, I had heard the barnacle story before, but had no idea it was so complex. It's a great work of classic ecology, combining natural history with theory. The Wauters paper was interesting because it made me think about the language we use in science. It uses pretty standard behavioral ecology terms, but I've been reading mostly population ecology papers lately, so I sort of re-noticed that some behavioral ecology terminology (e.g., "personality") is kind of different from other scientific language. It made me think about all the discussions we've had about language from the past this semester, and to wonder whether our modern language would be interpretable to a scientist from the early or even mid 20th century.
ReplyDeleteI enjoyed reading the Connell paper. Like others, I have heard this example multiple times in high school and undergrad biology classes. Because of this, it was neat to read the original paper and really dig into this paper. Like Crystal, I didn't realize predation played a role in the study until reading the paper.
ReplyDeleteThe newer paper was unique and an interesting read. I haven't considered before that traits such as personality might change in response to other species.
The Connell paper effectively connected the natural history of the study organisms to the competitive process. His experiment was very well set up, though I wondered why he used an elaborate system of glass panes instead of just marking areas and photographing them, especially because they made a paper map and never used the glass again. That part baffled me a bit, even though it seemed effective enough. The community dynamics with inter- and intraspecific competition and predation, spatial distribution, and consideration of density-independent factors such as temperature and seasonality made this an amazing comprehensive study.
ReplyDeleteI was disappointed with the squirrel study. They made very bold claims and conclusions considering there was no evidence for any of their hypotheses. I am also fairly certain they are not grasping the terminology correctly for assessing trait variance.. they talk about increased functional diversity because of the higher variance in sociable personality traits, but were not clear about which functional niche axis they were referring to.
I’m unaware of attempts to replicate the findings in Connell, but it seems like the study could be replicated and I would be surprised if the results were drastically different. Overall, I thought the Connell paper was great and didn’t notice any aspects of the experimental design that would have biased the findings. One thing I thought was strange is that even though he claimed that the cages didn’t impact mortality, he found that uncaged Chthamulus had higher survival than caged Chthamulus in the highest zone.
ReplyDeleteI don’t know too much about behavioral ecology or evolution so it’s tough for me to evaluate the hypotheses put forth in the Wauters et al. paper about the mechanism behind personality differences between red only and red-grey sites. As Crystal mentioned, it is important to know how heritable these personalities are before we can say much about plasticity or natural selection. Miranda has a good point about whether the personality tests can link behavioral differences to fitness differences.
Another possible source of confounding is that there are systematic differences between red only vs red-grey sites. They mentioned that red only are in conifer dominated forests while red-grey sites are in mixed deciduous-conifer forests that are oak dominated. These differences may result in different resource availabilities which could confound comparisons in survival and reproduction between red only and red-grey populations. Furthermore, there is active management of grey (i.e., culling) in red-grey sites. Is there also supplemental feeding or higher human presence in these areas? If so, human activity could be another factor that could explain differences in personality between red only and red-grey locations.
- David