Week 2: Macroecology before Macroecology
Nick Freymueller
Paper for Tuesday – Distribution of the species over the area
Paper for Tuesday – Distribution of the species over the area
Commentary Author: Ethan P. White @ Utah State
Ethan White has been a macroecologist at Utah State since 2007. He received his Ph.D. from UNM in 2005, where his advisor was Jim Brown. His current research has focused on mathematical-based approaches to geographic patterns of species richness and species-time-area relationships (STARs).
Paper Author: Olof Arrhenius
Olof Arrhenius was a Swedish scientist who varied widely in his research from plant growth, metal corrosion, and soil science. His father, Svante Arrhenius, was a Nobel Laureate and is considered the father of physical chemistry. O. Arrhenius is best known for his article on species-area relationships.
Cliff Notes:
1.) “How does the number of species vary with a change in overall area?”
2.) Arrhenius’ approach was to survey islands around Stockholm and meadows in the Swiss alps. The geographic area of both the meadows and the islands varied in size, and were useful to the study because both generally represent geographic isolation. He then tallied the number of species that he observed on each survey to each location and used that to generate a mathematical power function of what the predicted number of species would be in that area given its geographic area and Arrhenius’ observations.
3.) Arrhenius found that his power function reasonably predicts the number of species that one can expect to find in its area given that area’s geographic size. It is also worth noting that difference between xobserved and xpredicted decrease with a greater number of observations.
4.) Arrhenius’ findings have enabled us to look further into how species may be able to inhabit certain areas. It might also offer us the ability to develop predictive models into what will happen if habitat fractionation caused by human urbanization continues to increase.
5.) Since Arrhenius, the field has been expanded into modelling extinctions (McDonald & Brown 1992) and how species immigrate into new areas (MacArthur & Wilson 1963). The math required for calculating these kinds of macroevolutionary patterns has also expanded from the power curve into all sorts of statistical equations (MacArthur & Wilson 1963). (Both papers are cited in Ethan White’s commentary.)
Nice job Nick. A couple of updates. Ethan White moved to Florida State University in Gainesville, where he has really been at the forefront of incorporating modeling/statistics into ecology. He is one of the main folks behind efforts such as 'Data Carpentery' (google it folks!).
ReplyDeleteI'd also challenge you all to think about what influences the slope and intercept of these relationships.
I think that the slope of the regression would do with a multitude of different factors, including how many microhabitats/ habitat diversity is in the areas studied, where more diverse habitats would allow for greater diversification in number of species, the amount of precipitation which corresponds to how much vegetation/ energy is in the base of the trophic systems.
ReplyDeleteThe intercept may be due to convergent evolution where certain niches are filled anywhere there is life on earth, which allows for a 'base' number of species that just seems to always ring true. In an ecosystem, there is almost always the basic primary consumer, alpha predator, detritivores, pollinators. The intercept could show that this number of 'fundamental niches' that end up filled every where is around the same all around the world.
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ReplyDeleteGoodness, the creation of this profile has taken a nearly equivalent length of time as the readings themselves, but I digress. Above is a very nice summary, my compliments. I was, as usual, confused on a few points. I believe I got the gist of the paper - that as the surface area in which an assemblage occurs increases so too do the number of species found there, rapidly at first and then less so until a great increase in area is required to precipitate the smallest increase in diversity. I'm afraid, however, that is the extent of my understanding. The equation given on the first page of Arrhenius' paper (Page 18 in the book) leaves me just as perplexed as the explanation that follows. Arrhenius writes: "The formula y is the area upon which x species are found-" good so far -"and y1 that upon which x1 species are coming," - what now? I have puzzled over this passage a bit and only managed to make myself more confused. Attempts to get the internet to explain it have helped little as well - I've found several other dissimilar equations that deal with the same thing, but the do not illuminate what Arrhenius is talking about. Needless to say, this is a fairly important element of the paper, and I feel my understanding of the relationship diversity has to area, such as it is, is great lacking without an understanding of the mathematical underpinning. I had a similar worry about one of the statements in the next paper, but I'll wait to post that until then. Can someone please explain what is meant by Arrhenius in this bit about the area y1 upon which x1 species are coming?
ReplyDeleteThe intercept of an SAR would be based on what size the species are in the area. (smaller organisms = more per area?) The slope of an SAR would be affected by the "type of area" (ocean vs. land), but I'm not sure how this would affect the slope. I like Mark's idea that slope is affected by habitat diversity; I'm sure this would somehow be affected by the size, or type, of area, so I'm going with that for now.
ReplyDeleteLucius, I appreciate your mentioning of "species are coming," because I didn't really understand that either. Could he be talking about immigration into the area? Could it have something to do with observed vs. calculated? Not sure about this.