Tracking ecology over geological time: evolution within guilds of vertebrates
Blog author: Sebastian Botero
Dr. Blaire Van Valkenburgh
- Got her Master´s and Ph.D. in vertebrate paleobiology from Johns Hopkins university. After graduating, she did Postdoctoral research in Vertebrate Paleontology, also at Johns Hopkins university.
- Her main research interest is on the evolution of communities through geological time, focusing most of her research on carnivore mammals. For this, she has done several comparative studies of current and past carnivore guilds, using different lines of evidence to infer extinct species ecology. One of her current research projects involves CT scanning of carnivore skulls to describe turbinates (the complex bony scrolls within the nasal chamber, which function to conserve water, warm inspired air during ventilation and smelling). Using this information, air flow can be estimated, which can then be applied to infer fossil animals ecology.
- Teaches at UCLA since 1986.
Background:
Understanding the factors structuring communities is one of the main questions in ecology. From studies on extant faunas, it is known that competition is important (although there is debate around how important compared to other factors). Van Valkenburg argues in the paper that the study of the fossil record can provide a new approach to this question by allowing the study of communities through large time spans that cover significant large-scale environmental changes such as mass extinctions, climatic changes and sea level fluctuations. In this review, the author shows the insights learned about community structure evolution by assessing the fossil record from an ecological perspective in a similar way to Olsen (1966), but at a finer intra-guild scale.
Methods:
- As it is impossible to directly observe ecological attributes of extinct faunas, Van Valkenburg and others cited in the review have used morphometric analyses to infer behavior and ecology. For example, it is shown that in extant carnivores, the relative area of grinding vs. slicing surface of the lower first molar, correlates with the percentage of meat in an animal’s diet.
- Using this morphometric information, researchers can compare species of an assemblage and their distribution in morphospace.
- The study of assemblages through time can provide information on general processes influencing community evolution and structure.
- In this review, the author describes the findings from studying carnivore and scavenging communities from separate time spans as well as the results of a finer scale analysis of community evolution over 12 million years.
Results
- In North American carnivore mammals, it is seen that the distribution of species in the morphological space shows persistent patterns, with species occupying combinations of characters in this space that correspond to generalists, meat eaters, meat-bone eaters and more herbivorous carnivores. The separation of this groups is consistent from the Oligocene to the present, although only in the Pliocene all four groups are present.
- A similar pattern is observed in scavenger birds, with the independent appearance of three feeding types with characteristic beak and cranial morphology in current and paleofaunas. Besides the separation by beak and cranial characters, these species also show a consistent size separation, with three size classes.
- In the analysis of community evolution through 12 my, it was found that although species changed, the distribution in the morphospace continued similar. This analysis also suggest that species are added at the core of the morphospace rather than at the edge.
Discussion
- The appearance and maintenance of the same distribution patterns of species in the morphospace through time and among different regions suggest that competition is an importance force driving community evolution (with no competition, species would be expected to be randomly distributed.
- These results contrast with some ecological studies that have found little evidence of strong interactions in current and fossil communities. This can be due to differences between the analyzed communities (e.g. stronger competition occurring in carnivorous mammals) or by the time scales of analyses that might not include important disturbance events that structured the community through enhaced competition.
- The morphometrical analysis of fossil faunas provide a useful tool to infer extinct species ecology. Future work should account for phylogenetic relations and use null models as well as directly contrast the results with neoecological information to further our understanding of community evolution.
Comments:
- This made me think about the huge impacts humans are having on communities ecology and evolution and how this can be thought of as one of the disturbance events mentioned in the paper. For example, with the extirpation of top predators from vast areas of their ranges, humans are reducing significantly communities morphospace. It is an exciting time to study community evolution.
I really enjoyed this paper. I liked the boxes and figures (especially figure 2, but I'm biased) and thought there were quite a few interesting nuggets of information. After reading it, I am particularly interested in the feeding guilds of marine reptiles, and further exploring the shifts in guild composition over time.
ReplyDeleteThis was a good review paper and I liked that they made suggestions for future studies to further or progress the research. However, I had two thoughts when reading this paper. First, how exactly would you define a stable community? Communities are always changing in response to competition and disturbances so I find it difficult to think there is "stable community". Second, I don't think fossil and present guilds are comparable if they are searching for a rule morphospace and community structure due to different types of disturbance (climatic vs. human)
ReplyDeleteI like reading the part about community evolution. The other paper talks about the importance of the flow of food-derived energy, while this paper talks about how competition plays a role in resource division. Figure 4 is really cool. I also like that at the end they gave some suggestions for further research.
ReplyDeleteThe visuals were great, very clear and well made. Again, liked that the author provided a clear definition of the topic.
ReplyDeleteIt is interesting to read a paper that was at the beginning of the morphospace analytics that has become much more prevalent in paleontology today. While quantitatively comparing limbs or dentary of fossil and modern species has become a norm in paleoecology, it is still relatively modern and many people do those analyses to answer a specific question. Van Valkenburgh does an excellent job explaining the dietary morphospace as it relates to the evolution of a community over time, which has broader impacts to conservation efforts today.
ReplyDeleteI really liked this paper. The information provided in the boxes were of great help to understand the concepts it explained. At some point the author suggested how invertebrates would be a better model to address some of his ideas, so I wonder why he didn't explained that deeper or used those invertebrate records to assess it.
ReplyDeleteI loved reading this paper. I appreciate how the author had defined words that he thought his readers might not understand, and how he had boxes off to the side that went into more depth with its definitions and some of the topics discussed in the paper. That made it way easier to understand the paper.
ReplyDeleteThis paper reminds me of my research on vulture back in Mongolia. I have seen the exact order and patterns of different species of raptors eating freshly died animal. Crow opens up the body, vulture next to rip off the meat, eagles and bone eater the last. It is really cool to see how fast they eat when they are all together and each have their own duty. Very interesting paper and I like it a lot. This is why community assemblage and ecosystem function is important to understand and conserve.
ReplyDeleteI thought it was interesting she says the conflicts between neoecology and paleoecology are unlikely to be resolved soon. The solution she suggests is not possible for every or even most systems. Thinking about my own research, we use modern communities to interpret the paleoecology, yet we recognize it is very nonanalog. A bit of a contradiction, but we’re doing the best we can within our limitations. Overall a neat review.
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