Week 6, Composition of Biotas
Macroecology: Chapter 5, ‘Composition of Biotas’
Payne, J.L. et al. “Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity.” PNAS 106 (2009): 24-27
The chapter emphasizes the evaluation of species composition over broad taxonomic organizations and distributions over increasing relative scales. These distributions are most often attained through measurements of body size, or mass, relative abundance and energy needs. Size distribution plots uniformly favor small size classes, though not the smallest indicating a lower threshold to size and distribution of species. This relationship was first described by Hutchinson and McAuthor in 1959, showing data that are skewed or non symmetrical to the right, they suggested the environment could be seen as ‘mosaic elements’, where smaller animals require fewer elements than their larger counterparts. The geometric evolution of this hypothesis incorporated fractal properties of self similarity among environments. Both view were limited in explaining the decline of species in the smallest of classes.
Brown incorporates energetics in the reproductive power model to explain this trend. The model is determined by two factors, 1)acquisition of resources and 2)the conversion of resources to reproductive work. In this model the smallest organisms are constrained by the acquisition of resources, while larger are constrained by the conversion of resources to reproductive work. Size class also imposes a limit on abundance and population density, showing limits for both larger and smaller size classes. The influence of energetics is probably the most determinant of composition being most intrinsically related to both biotic and abiotic factors of an ecosystem. These relationships were mainly derived from mammalian data, Brown does suggest further research in varying scales of ecosystems to determine the macroecological trend.
Payne et al. (2009) In the complete interest of macroevolutionary endeavours Payne and colleagues seek to quantify the trend in maximum size of organisms since the initial appearance of life. The data shows two spikes in maximum size, both correlating with increased atmospheric oxygen and respectively with the appearance of eukaryotic cells and multicellular eukaryotes. These data show an increase of size by 16 orders of magnitude over 3.5 billion years. These increases are attributed to biological innovation coupled with environmental opportunity, e.g. multicelluarity and increased atmospheric oxygen.
Payne, J.L. et al. “Two-phase increase in the maximum size of life over 3.5 billion years reflects biological innovation and environmental opportunity.” PNAS 106 (2009): 24-27
The chapter emphasizes the evaluation of species composition over broad taxonomic organizations and distributions over increasing relative scales. These distributions are most often attained through measurements of body size, or mass, relative abundance and energy needs. Size distribution plots uniformly favor small size classes, though not the smallest indicating a lower threshold to size and distribution of species. This relationship was first described by Hutchinson and McAuthor in 1959, showing data that are skewed or non symmetrical to the right, they suggested the environment could be seen as ‘mosaic elements’, where smaller animals require fewer elements than their larger counterparts. The geometric evolution of this hypothesis incorporated fractal properties of self similarity among environments. Both view were limited in explaining the decline of species in the smallest of classes.
Brown incorporates energetics in the reproductive power model to explain this trend. The model is determined by two factors, 1)acquisition of resources and 2)the conversion of resources to reproductive work. In this model the smallest organisms are constrained by the acquisition of resources, while larger are constrained by the conversion of resources to reproductive work. Size class also imposes a limit on abundance and population density, showing limits for both larger and smaller size classes. The influence of energetics is probably the most determinant of composition being most intrinsically related to both biotic and abiotic factors of an ecosystem. These relationships were mainly derived from mammalian data, Brown does suggest further research in varying scales of ecosystems to determine the macroecological trend.
Payne et al. (2009) In the complete interest of macroevolutionary endeavours Payne and colleagues seek to quantify the trend in maximum size of organisms since the initial appearance of life. The data shows two spikes in maximum size, both correlating with increased atmospheric oxygen and respectively with the appearance of eukaryotic cells and multicellular eukaryotes. These data show an increase of size by 16 orders of magnitude over 3.5 billion years. These increases are attributed to biological innovation coupled with environmental opportunity, e.g. multicelluarity and increased atmospheric oxygen.
Hey everyone - Hope the week is going well, for the article I decided to go with something more generalized and not so focused on benthic life. I found the article extremely straight forward and very easy to interpret. The correlations, as with most base macroecological studies, are logical and what would be expected. I do like the implications of biological innovation being a dynamic process limited by environmental contraints, the graphs very much reminded me of returns to scale, for each definable period. I was curious if this pattern would be produced on and ecosystem level, many orders of magnitude less in both spatial and temporal scales.
ReplyDeleteSee you Frinday.
I'm currently looking at figure 2 in the paper. I find it curious that for all non-chordate animals, maximum body size is realized before the end of the Paleozoic. Why are chordates and land plants able to achieve such large body sizes, and what is it about Mollusca and Arthropoda that keeps them at a lower threshold?
ReplyDeleteBoth the paper and chapter this week were interesting as usual! Life is an interesting study, past and present. Anyway, the paper was a good read. I found it to make a lot of sense because as the environment changes, and in earth's case it became more habitable, the organisms evolved to fit their niche. So, as oxygen became present organisms were able to expand if you will. It was awesome to see this graphically and to see it through the fossil record.
ReplyDeleteThe chapter as usual was super intriguing. Couple questions I had: a modal-sized species is an intermediate/middle-ground sized species correct? An then a kind of out there question: wouldn't it make sense that the smaller species (called "specialists") are less plentiful than the larger species ("generalists)? I wonder this because their realized niche is more specific therefore they would be less plentiful because of resource availability? See you guys in class!!!
Mel, I have often wondered the same thing: why do mollusks and arthropods remain small. Granted, not all of them are small; there definitely are large arthropods. I wonder if it goes to what Dr. Brown discussed that the limiting factor for small organisms is acquiring resources.
ReplyDeleteI'm interested in what causes the delay between the development of a new type of structure and the maximum size of that structure being achieved (see the paragraph from the bottom left of page 26.) The authors state that there is a delay without explicitly discussing what causes this evolutionarily.
ReplyDeleteI also thought I'd throw up some pictures of some of these large taxa. Here's Grypania: http://en.wikipedia.org/wiki/File:Grypania_spiralis.JPG
Here's a eurypterid, which I think was the largest arthropod ever: http://commons.wikimedia.org/wiki/File:Mixopterus_kiaeri.JPG
And here's a Parapuzosia seppenradensis (the largest cephalopod ever,) with a guy next to it. http://commons.wikimedia.org/wiki/File:Parapuzosia_seppenradensis_3.jpg
I'm figuring that folks know what a blue whale and giant sequoia look like.
Does it really surprise anyone that increases in body size are seen right after increases in available oxygen? In reading this article I was reminded of the massive arthropods crawling about during the carboniferous. I was always told they were able to reach such massive proportions because the high levels of O2 enabled very efficient respiration, allowing the body to grow larger. Nowadays we have a lower O2 content in the atmosphere and so organims that breath through their skin, or through externial spiracles, must limit their size, because they can only obtain so much oxygen to be passed on through the body.
ReplyDeleteNatalya, when you talk about specialists and generalists are you including single celled organisms? If so, I should think specialists are much more prolific than generalists because they have a relatively huge resource availability. Rather than chasing down a gazelle, or competing for sunlight in a dense forest, they are surrounded by a relative sea of nutrients. Think of a lawn in need of mowing; the larger the lawn mower (consumer), the quicker the lawn (food) is cut.
I found the paper very interesting. It was nice to see the the data in a chart form which helps illustrate the point very well. It's often we talk about the importance of oxygen but the paper really illustrates the potential impact on body size. I would like to know what causes the differences between chordata, mollusca, and arthropoda.
ReplyDelete