Pielou, E.C. 1977. Latitudinal spans of seaweed species and their patterns of overlap. Journal of Biogeography 4:299-311
Blog author: Lam Le
Christy M. McCain:
-PhD at University of Kansas, 2003
-Associate professor & CU Museum Curator of Vertebrates
-” Iam interested in the mechanisms producing and maintaining patterns of species distribution, abundance, and diversity”
Evelyn Chrystalla “E.C” Pielou
-Canadian statistical ecologist
-Canadian statistical ecologist
-Born in 1924 in United Kingdom, died in 2016 in Canada
-Professor of Biology at Queen’s University, Kingston, Ontario, and at Dalhousie University in Halifax, Nova Scotia, and Oil Sands Environmental Research Professor at University of Lethbridge, Alberta
-Contribute significantly to the development of mathematical ecology, the mathematical modeling of natural systems, and wrote 6 academic books on the subjects.
Paper Summary
1. Main question:
-Background: Quantitative studies have not attempted to analyze the overlapping of geographic ranges because ranges extend to two dimensions rather than one. This paper describes a method of analyzing map and apply this to discuss latitudinal span of shoreline species across north-south trending coast
-Main question: Are the range limits of species from the same genus independently located? Or are the ranges themselves independently located?
2. Methods:
-Data: based on northern and southern limits where they found 684 species of benthic marine algae. The main factor controlling alga is water temperature, with gradient goes from north to south.
-Methods: analyze map and apply it to look at the geographic ranges of algae, take measurements of the overlap, derive different equations for each hypothesis to find expected overlap of a sheaf of s-species spans
3. Results:
-Under hypothesis I, distribution of overlapping is symmetrical. After testing on 3 algal classes, hypothesis is rejected. Species from the same genus overlap one another more than they would when location of boundaries are independent.
-Under hypothesis II, distribution of overlapping is not symmetrical, so this hypothesis cannot be tested the same way as the first one. However, there is no reason to reject hypothesis II. Species spans are located independently and are not affected by interspecies competition.
-Distribution of species span in 3 algal classes show the same pattern: shorter spans are most numerous.
4. Conclusion:
-Congeneric species overlap much more in range limits than predicted by competitive exclusion.
-New species must have had time to adapt to conditions of location without competition.
-Separated species will be mixed together and be confined to restricted environmental conditions.
-More barriers to dispersal, less developed seaweed zonation.
5. Questions:
-How would you apply the findings in this paper to conservation?
-Do you like how this paper doesn’t go on and on about math?
I thought it was very elegant how they derived their equations using lines to represent species' ranges. While this technique is surely a bit conservative, it made their analysis very clear and easy to follow. I wonder if anyone has applied this to other taxa, perhaps using circles instead of lines to denote ranges. I feel like it wouldn't be much harder to derive equations for overlaps in circular ranges, but I'm not a mathematician so I could be wrong.
ReplyDeleteYes, I think the same approach can be applied to two-dimensional distribution data. I know of a paper in which this is done with palearctic mammals. Here they measured range overlap of sister species using published distribution maps and compared it to expectations from hypothesis regarding the effect of competition and niche conservatism in habitat requirement.
DeleteLetcher et al., 1994. Patterns of overlap in the geographic ranges of Palearetic and British mammals
This is a difficult argument to find any conclusion too, which is why I love it! There is a lot to consider and I believe this paper is a little too black and white on the subject, which is my issue with many ecological theories and studies. First, I think it is important to consider why speciation occurred that allowed the diversification. Pielou only mentions geographic isolation which I don't agree is the only possibility. I also think it depends on what resources are overlapping (are their alternatives?) and what traits separate them. I think you can find congeneric species overlap and competition, it just depends where and what you are looking at.
ReplyDeletePielou´s study system seems very appropriate to tackle these kind of questions at the time (without GIS and other advances). for the seaweeds you can calculate geographic overlap in just one dimension, as well as, fine scale habitat segregation on the intertidal and depth gradient can be assessed. I would like to know if both geographical and habitat overlap were simultaneously assessed in further papers.
ReplyDeleteAlong Lam's comment, I appreciate that there wasn't as much math in this piece as the previous, though I was lost in some of the verbiage. Can you extrapolate these results to non-seaweed species? Are there other papers that explore other species?
ReplyDeleteLike Maria, I thought the system designed was very elegant. Since they spent so much time explaining the system with lines, I wonder if they tried to Convert all of their data into a sheaf of spans like in figure 1. That would be a very large a messy illustration, but if they plotted it according to latitude, would it visually Confirm the latitudinal gradient? If I were a seaweed person, I might be interested to see what seaweed had the longest ranges and what their climatic preferences might say about them.
ReplyDeleteI also think this was a fine study done with the resources she had at that time. And I also wonder if there are more recent papers analyzing if this approach is still robust, considering the GIS related tools available nowadays, and also considering other organisms.
ReplyDeleteI agree with Alex too: there could be several other ways explaining how those ranges came to be, both geographically and locally, even if she just analyses one possible way, that of course is related to her main question. But I think it is good to have in mind that there might be other causes for those patterns.
The research idea was the pioneering part here. Yes, I agree this is a little to black and white model that tries to fit everything towards the model. But the main idea can be used in the conservation by expecting and prioritizing certain habitat when we study biodiversity and their preferred systems. However, we need more data on each species case at a different time. I keep wondering the biological evolution was always carried by the geological evolution. I wonder what the fossil records would tell us in gradient species patterns. Cool concept! I bet this was a challenge to collect all these data (literature only). Also, it is algae.
ReplyDeleteI appreciate how the author told us exactly what we were supposed to get from the paper in the introduction along with where we should find the information. That made reading this paper much easier and I think all writers should follow her footsteps. I feel like the author was a head of her time judging by how well the paper was written and how the system was designed.
ReplyDeleteI agree with the comments about the cleanliness of her approach and the impressiveness of this paper without the use of GIS or other modern mapping and analytics. However, I do wonder how much of this paper should be extrapolated to species that can move freely. This research is performed on algae in the ocean, and therefore most or any movement is due to the current flow, which is in fact controlling the temperature gradients throughout the oceans.
ReplyDelete