BS&M Gets Fancy with Metacommunity Ecology

Guest Blogger: Shauhin Alavi


Last week, I instigated my fellow BS&Mers into veering a little off the beaten path, and convinced everyone to discuss a recent Ecography paper that took a metacommunity approach to studying shape variation in rodents. Metacommunities are sets of communities linked by the dispersal of more than one species. Community scale studies are largely lacking across evolutionary anthropology, and given that many extant primates (and probably fossil hominins) fit nicely in the metacommunity framework, this seemed like a good opportunity to explore the potential applications of this approach to anthropological questions.

The paper was met with mixed reviews within our group. Part of the problem was that not everyone was familiar with some of the metrics and analyses (and jargon) utilized in the metacommunity framework. Namely, community weighted means (CWM), principal coordinates of neighborhood matrices (PCNM), principal coordinates of phylogenetic structure (PCPS), and redundancy analysis (RDA). Admittedly, the paper was not written in the most accessible way. For anyone that might be interested in reading this paper, see the table at the end of this post for my best attempts at explaining these (at least for our group) commonly unfamiliar concepts.

One talking point amongst the BS&Mers was whether we actually learn anything new by zooming out to the metacommunity level. A few people (mostly from the B&S contingent of our group) argued that we don’t necessarily need the added complexity of communities to study how environment influences shape variation, and that this is easily done at the species level. I personally believe that looking at variation in community level indices (like CWM) allows us to look at very large scale evolutionary relationships that we might miss at the species level. By scaling up to metacommunities, we are acknowledging (after accounting for phylogeny) that all members of the ecological community are subject to the same environmental variables, and therefore the same selection pressures. Understanding how the mean trait value for the entire community varies with the environment gives us a starting point when trying to understand function.

Another interesting talking point amongst the BS&M crowd was whether or not the paper should have been rooted in some hypotheses. Some of us expressed dissatisfaction at how function was implied throughout the paper, yet there were no hypotheses given for how shape should vary with respect to environmental variables. I actually think that in this case, not having explicit expectations was a bit refreshing. I certainly wouldn’t have considered some of the traits that the authors found to vary significantly with environment.

One thought I was left with after reading this paper was that I wish the authors had included community weighted variance (CWV) in their analysis. Having a measure of variance would at least tell us if a particular trait is worth considering in the first place. It would have also been nice to have incorporated a model averaged phylogeny (sensu 10ktrees).

BS&M ended with a very productive brainstorming session about how to extend this framework to primatological and anthropological questions. I think it would be interesting to use remotely sensed measures of canopy structure to see how morphology varies across primate metacommunities. I also think it would be important to use this framework to uncover how neutral and niche processes shape primate communities. Others proposed extending this framework to studying how various measures of social organization may affect primate trait evolution at the metacommunity level. And of course, we couldn’t resist discussing how we might extend this framework to studying trait evolution across fossil hominin communities. A fair bit of the hominin discussion was how to surmount the palimpsest nature of the hominin record.

Overall the BS&M crew seemed receptive to the approach presented in the paper and acknowledged the importance of the complexity inherent at the metacommunity level.

Click through for the table of jargon and references!  Continue reading “BS&M Gets Fancy with Metacommunity Ecology”

Anthro News


So, the big fossil news that the Leakey Foundation was teasing when last I posted? It was this:

Alesi_anterior view
Anterior view of the cranium of Nyanzapithecus alesi (Nengo et al. 2017)

BS&M Blog readers, meet Nyanzapithecus alesi, a new 13 million-year-old Miocene ape from Kenya. HOW COOL IS THAT?!

I will tell you how cool. VERY COOL. I’m biased (as always – because I pick the things I want to write about for the blog, which are things that I think are very cool), but seriously. There are a bunch of reasons this discovery is awesome, like:

1) You don’t often find complete crania (the skull minus the jaw) of fossil apes. Typically, the bones at the back of the skull (the ones that form the brain case) break sometime before a fossil is found (if it’s found at all, which is a whole different issue). If you want to become a primate fossil, it takes specific circumstances and a lot of luck.

2) You really don’t find fossil ape crania in Africa dated to between 10-14 million years old. Alesi is it. Other fossil ape partial crania are known from this time period in Europe (Pliobates cataloniae at 11.6 mya and Pierolapithecus catalaunicus at 12.5-13 mya from Spain, and Rudapithecus hungaricus at 10 mya from Hungary, to name a few) and Asia (Sivapithecus indicus at 12.3 from Pakistan), which might say something about where fossil apes originated or it might either be the result of less digging having happened in Africa resulting in a deficient fossil record or the difficulty in identifying the earliest apes.

Pliobates (Alba et al. 2015), Pierolapithecus (Moya-Sola et al. 2004), and Rudapithecus (Begun et al. 2012). (Left to right)

3) You also rarely find infant material in the primate fossil record. (Yes, I know, the Taung Child is an exception to this rule, too.) Infant bones are smaller and more fragile than those of adults, which makes them even less likely to fossilize and be recovered later.

Alesi is also awesome, simply by virtue of being a Miocene ape (my Miocene bias is definitely showing). The Miocene (23-5.3 mya) often gets called a “planet of the apes” because there was a huge diversity of hominoids (the fancy taxonomic group name for apes, including us, is Hominoidea) that lived through Europe, Africa, and Asia at that time. Which is SUPER AWESOME because they were “experimenting” with different types of locomotion at that time (which is totally my jam), but also makes it really hard to tell our potential ancestors from our side-branch cousins. A classic problem for people who work on Miocene apes is that they have ape faces and monkey bodies, and the field disagrees about which is more important (the face or the body) for figuring out who is related to who. Hopefully one of the authors of the Alesi paper (shout out to Kelsey Pugh!) will be able to work some of these relationships out with her dissertation research.

My final thought/question (for now) on Alesi is: the authors suggest that gibbon-like features evolved in parallel several times in different branches of the hominoid lineage – why couldn’t these features be ancestral, rather than derived? If that was the case, it would just require that a different set of facial features evolved in parallel instead. So why the gibbon-like ones and not the other ones?

That’s all for now! Hopefully BS&M will be back on September 8th – catch you then!

Alba, D.M., Almécija, S., DeMiguel, D., Fortuny, J., de los Ríos, M.P., Pina, M., Robles, J.M. and Moyà-Solà, S. (2015). Miocene small-bodied ape from Eurasia sheds light on hominoid evolution. Science350(6260), aab2625.

Begun, D. R., Nargolwalla, M. C., & Kordos, L. (2012). European Miocene hominids and the origin of the African ape and human clade. Evolutionary Anthropology: Issues, News, and Reviews21(1), 10-23.

Moyà-Solà, S., Köhler, M., Alba, D. M., Casanovas-Vilar, I., & Galindo, J. (2004). Pierolapithecus catalaunicus, a new Middle Miocene great ape from Spain. Science306(5700), 1339-1344.

Nengo, I., Tafforeau, P., Gilbert, C.C., Fleagle, J.G., Miller, E.R., Feibel, C., Fox, D.L., Feinberg, J., Pugh, K.D., Berruyer, C. and Mana, S. (2017). New infant cranium from the African Miocene sheds light on ape evolution. Nature548(7666), 169.

A Plethora of Pelvis Papers

Part 1 – The Ilium

The pelvis is the coolest skeletal element. I might be slightly biased, given that I wrote my dissertation on it. But probably not – it is, objectively, the coolest.

Why is the pelvis so cool? Because it can tell us a lot about how a primate walks around and gives birth, while simultaneously being super complicated to try to figure out.

Recently, two special issues of the scientific journal The Anatomical Record were published focusing exclusively on the pelvis. It was like your gift-receiving holiday of choice for pelvis nerds like me. (And, really, there can never be a true plethora of pelvis papers; the more pelvis papers, the better!) I’m finally getting around to reading them, so I figured I’d do a short series of posts on some of the ones that particularly interested me, starting with one on the ilium.

But first, a quick primer on the pelvis:

The pelvis is made up of two innominates (hipbones) and the sacrum/coccyx (tailbone). The two hipbones are themselves made up of three bones each (the ilium, ischium, and pubis) that fuse within the socket of the hip joint (called the acetabulum, which is Latin for “little vinegar cup”) around ages 16-18.

male pelvis
A complete male pelvis (Gray 1918)

Anthropologists really dig the pelvis because ours is highly modified for walking on two feet (bipedalism), so it looks very different from the pelvis of our closest living relative, the chimpanzee.

schultz primate torsos
The trunk skeletons of a macaque, gibbon, chimpanzee, and human (left to right) (Schultz 1950).

The trend in paleoanthropology recently has been to think of our last common ancestor (LCA) with chimpanzees as being more chimp-like than human-like (though there are some who have argued against this, like the team that discovered Ardipithecus ramidus). So what might this mean for the anatomy of the pelvis of the LCA? Was it more chimp-like or more human-like, and how can we test this?

Hammond and Almecija set out to answer these questions in their contribution to the May special issue (“Lower Ilium Evolution in Apes and Hominins”). They focused on the lower ilium because it varies in length between primate species and the variation has been suggested to be related to differences in how different species move around. They used a combination of measurements, statistics, and tree-building programs to look at variation in lower ilium height within and between species, tried to reconstruct the pelvic anatomy of progressively older LCAs (including the chimp-human LCA and the LCA of all of the living apes), and then compared those reconstructions to some of the predictions that the Ardipithecus team made about the evolution of the pelvis when they published that fossil.

What they found (based on a really large sample of pelvic measurements from 58 humans, 112 great apes, 61 gibbons/siamangs, 95 Old World monkeys, 33 New World monkeys, and 8 fossils), was that the variation they saw in lower ilium height was not purely size-related, which suggests that there might be functional or evolutionary reasons behind it. They also found that gorillas have ilia that might resemble the primitive condition for all hominoids (apes + hominins) and that the chimp-human LCA probably had a shorter lower ilium than living chimpanzees, as had been suggested by the Ardipithecus team. What this means is that living chimpanzees and orangutans may have both independently evolved long lower ilia, which complicates our use of parsimony when building evolutionary trees; sometimes shared features don’t come from a common ancestor, but evolve (via similar pathways, from similar structures) in two related taxa due to similar pressures.

So what’s the take-home message? Well, a lot of people have suggested that there is a characteristic “ape-like” long lower ilium that is somehow functionally related to their locomotion, but that doesn’t seem to actually be the case. The innominate is a complicated bone and it’s not just how a primate gets around that influences it.

Also worth taking home: the pelvis is super cool and so are fossil apes.

If you dig the pelvis, stay tuned! This is the first post in what will be a short series on the pelvis. (Maybe short. Maybe not. Much like the evolutionary history of the lower ilium.)

Disclaimer: I have met/know the authors of this paper. And I’d be just as excited about it even if I didn’t because the lower ilium needs all the love it can get.

Hammond, A.S. and Almécija, S. (2017). Lower ilium evolution in apes and hominins. The Anatomical Record, 300(5), 828-844.