Paper 34: Brown 1981
Two Decades of Homage to Santa Rosalia: Towards a General Theory of Diversity
Blog Author: Lam Le
Blurb Author: Walter Jetz
-Professor of Ecology and Evolutionary Biology and of Forestry and Environmental Studies at Yale University
-” Workin our group addresses the patterns and processes behind the distribution of species and their traits in space and time. We are particularly interested in the scale-dependence of both evidence and mechanism in biodiversity science and how environment, ecological, and macroevolutionary mechanisms combine to determine the co-occurrence of species and the structure of assemblages. We aim to use this as basis for assessing the the fate of biodiversity and its functions under global change. We work with a variety of systems, both animals and plants, but have to date been particularly active addressing birds and terrestrial vertebrates.”
Paper Author: James H. Brown
-University of Chicago paleontologist
-Best known for global compendia of marine animal families and genera, data sets that continue to motivate a tremendous amount of paleobiological research. He identified 3 great Evolutionary Faunas in the marine animal fossil record. Each of his Evolutionary Faunas, the Cambrian, Paleozoic, and Modern Faunas, is composed of Linnean classes of animals that have covarying diversity patterns, characteristic rates of turnover, and broadly similar ecologies. Most importantly, they sequentially replaced one another as dominant groups during the Phanerozoic.
Question: Why are there so many kinds of organisms?
Summary/Main Points:
-Background:
The attempts to provide a general explanation for diversity of living things have been made by Darwin, Wallace, Lotka, Volterra, Grinnell, Gause, Clements, Shelford, Elton, Lack and Lindermann. In 1959, in his seminal paper “Homage to Santa Rosalia”, G. E. Hutchinson asked, why are there so many kinds of living things? The paper provided a general overview of the problem posed by organic diversity and suggested we look for answers.
The Homage: An Emphasis on Genetics:
-The basic message of Hutchinson is that to understand the diversity of life we should investigate how usable energy is acquired by and apportioned among species.
-He develops 5 major themes:
Length and number of food chains
Weblike interrelations among food chains
Effects of productivity and habitable area in limiting diversity
Species can be similar in requirements and still coexist
“Mosaic nature of the environment”
-He concluded that “the reason why there are so many species of animals is at least partly because a complex trophic organization of a community is more stable than a simple one, but that limits are set by the tendency of food chains to shorten or become blurred, by unfavorable physical factors, by space, by the fitness of possible subdivision of niches, and by those characteristics of the environmental mosaic which permit a greater diversity of small than of large allied species.”
Subsequent Community Theory: Energetics Ignored
-Most ideas in “The Homage” have been explored by theoretical ecologists, but the central importance of energetics has been ignored.
-2 schools:
One led by Eugene Odum: concentrate on the flow of energy and matter through the community and emphasized interactions between organisms and the physical environment. Ignore the diversity of the component species and unique role each plays.
One led by Robert MacArthur: concentrate on the ecological and evolutionary interactions between species. Try to expand the competition models of Lotka and Volterra and the models of predation to account for the coexistence of species in complex communities. Ignore energetics as an explicit currency of ecological interaction.
-Evolutionary ecologists have learned a great deal about adaptive strategies of particular species and basic kinds of interspecific interactions, but less successful in determining how these species and their interactions contribute to the structure and functions of communities. 2 reasons:
Failure to appreciate the fundamental role of energetics
Difficulty in trying to understand organization of complex systems by working from the bottom up
-Development of optimal foraging theory was a success for 2 reasons:
Energy as a currency: “eat or be eaten” dominates the lives of many animals, maximize rates of energy intake while minimizing risk of predation
Dissecting foraging behaviors of animals to learn selective and mechanistic processes by which animals make decisions.
Competition Theory: A Disappointment
-Hutchinson developed what he called “the Volterra-Gause principle” to ask how similar 2 species can be in their utilization of limiting resources and still coexist.
-The models and their predictions are highly sensitive to assumptions.
-The models are not empirically operational.
-It is problematic to try to understand complex systems by putting together the basic components in proper relationship to each other.
Island Biogeography Theory: A Heuristic Success
-The theory provides an exceptionally useful conceptual framework for investigating the patterns of species diversity and the underlying mechanisms which produce these patterns.
-3 reasons for success:
Equilibrium model
Confronts the problem of diversity directly
Empirically operational
-MacArthur and Wilson suggested that the influence of area mediated through increasing rates of extinction as island size decreases. Island size decreases, habitat diversity and total productivity decreases.
Prospects for the Future: Ingredients of a General Theory
-Capacity rules: Define physical characteristics which determine their capacity to support life.
The most important is ingredient usable energy. There is a positive causal relationship between productivity and diversity.
The second component must be of variation of the physical environment in time and space. There is problem in measure of harshness, which requires assessment of effects of spatial and temporal heterogeneity on the capacity of environments to maintain populations in the face of extinctions.
-Allocation rules: How available energy is divided among species.
Empirical patterns in characteristics of species which affect their utilization of energy: local abundance, body size, geographic range, and trophic statuses. The most long recognized patterns are in distribution of abundance and body size within local communities.
Conclusion:
-Suggest that we should still be well advised to pursue the ideas Hutchinson advanced.
-Recommend adopting Hutchinson’s emphasis on the role of energetics.
Comments/Questions:
-This paper is written in a language that is easy to understand. Brown is so thorough with each idea. Near the end he seems a bit unsure, giving suggestions but also states that he isnt sure how these suggestions would affect the development of theory. Overal, this is a really interesting paper. I really enjoy reading it.
Species can have similar needs and still occupy the same spaces but I think this is more common with generalists. Which would make more sense since generalists are more common, allowing diversification and the sharing of niches. I think specialists would not overlap as frequently, but then again being a specialist and generalist is a spectrum.
ReplyDeleteI appreciated the holistic view that Brown brought to the concept of species interactions and population dynamics. It was also nice to see some papers that we read or read about earlier in the year incorporated together at the end of the semester.
ReplyDeleteI agree that this was a paper that was easy to read. I liked how he addressed the limitation of mathematical modelling approaches that are too abstract to approach by field observations or measurements. I do think we can get too carried away by designing the perfect mathematical model that could explain a determined process in nature, but if the assumptions of that model can not be corroborated then it seems like the problem was not solved. I liked how he not only criticized the current advances but also made suggestions to approach the subject at hand.
ReplyDeleteThis is an impressive attempt to capture a total picture of identifying and assessing the relationships between species diversity/richness and their effects/impacts to their existence. The author really did a good job of categorizing and capturing these components and assembled these theories to explain the importance of energy in the community organization. I do like this paper and it was easy to follow.
ReplyDeleteI appreciated this quote in the paper: "Since the sizes of geographic ranges vary, particular species must coexist with different combinations of other species to form different communities in different parts of their geographic range". While this is a total "duh" statement, I think some people develop tunnel vision when it comes to communities. Also, as a birder, it's really cool to think about all the different species a migrating bird gets to interact with.
ReplyDeleteIt was interesting he thought the Lotka-Volterra model bad for studying diversity. That’s been taught as part of the interaction gospel in every biology class I’ve ever had, so it was a bit odd to read about how inappropriate it was for other problems.
ReplyDeleteThis was an ideally different read than the others. I enjoy the questions the author brought to light. The paper, however, felt mildly repetitive. I get there are questions that needed to be focused on to get the point across, but still it felt drawn out. Overall, the paper was okay.
ReplyDeleteIt's cool to see ideas for papers we discussed earlier in later papers we explore. Interesting to see the ties between research pieces. I also appreciated his use of mild vernacular, made his points much easier to follow.
ReplyDelete