BS&M Gets Fancy with Metacommunity Ecology

Guest Blogger: Shauhin Alavi

Advertisements

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”

BS&M Does Bears?

A brief follow-up on the Cretan footprints

BS&M returned this past Friday and, alas, I couldn’t attend. Luckily, the discussion centered on the Cretan footprints paper that guest blogger Sarah Hlubik covered in our last post, so you guys aren’t missing out on sweet, sweet new paper coverage.

What apparently went down on Friday was a lot of talk about bears. Were there bears in the area during the Miocene? Yep and yep. Can bears walk upright? Yep! What do bear tracks look like? Like this (according to one site, anyway). Does this mean we need to change our name to Bears, Stones, and Monkeys?

It seems the BS&M crowd is fairly skeptical about the claim of bipedal primate footprints in the Miocene, but loves them some possible bearpedality (thanks for that one, Fred). Personally, I’d love to see the authors find some body fossils of any potential candidate track-maker – and if it’s a primate, even better!

Until next time, I leave you with this (credit to Alex Pritchard):

Sunbear
Exhibit A (left): a sun bear foot. Exhibit B (right): a sun bear after it was recorded saying, “it was ME, it was ME ALL ALONG. Even my family – even my IMMEDIATE family bought it!”

 

Hominin Trackways in the Cretan Miocene?

Guest Blogger: Sarah Hlubik

An in-press paper, available in the Proceedings of the Geologists’ Association on Aug. 31, describes trackways dating to 5.7 mya on Crete (shown in this post’s lead image, from Gierlinski et al. [2017]). This places them just before the Messinian Salinity Crisis, when the Mediterranean dried up, global climates were nice and warm, and the planet really did belong to the apes. A potential hominin trackway (let’s be real, any trackway at all) from this time period is WAY COOL for a couple of reasons:

1. Tracks do not preserve very well. Ever go walking along the beach and look behind you to see your footprints washed away by the next wave? Yeah, me too. Most footprints made in the dirt, sand, or mud, are going to be washed away or destroyed by other individuals, or simply smoothed over because there is so much water in the sediment. For tracks to preserve, they have to dry out a bit, and then be covered pretty quickly by sediment that is a little different in texture or that won’t end up squishing together with the underlying layer. So tracks at all are always really cool, and offer a glimpse into environments and animal communities that we generally don’t see.

2. The Miocene gets called the Planet of the Apes because of the intense radiation of apes that happened during that time period (23-5.3 mya). We know some about the vast array of species that must have occupied the Old World at that time, but there is a lot we don’t know (again, see how to become a fossil), and what we don’t know may have been living on ancient Crete and walking, at least some of the time. Suspensory locomotion evolved sometime during this period (see Pierolapithecus, Dendropithecus, and Dryopithecus), and many later Miocene apes were highly orthograde (which just means they sat upright). Today, suspensory locomotors include gibbons and orangutans, and these (also orthograde) apes are able to walk on two legs over the ground, so it isn’t outside the realm of possibility that a highly orthograde ape had to move across a relatively open, albeit somewhat gooey, landscape and did so on two legs.

Cheezburger animals monkey trees jungle GIF

3. Footprints can tell us a lot about who made them, even if they can’t tell us definitively who made them. Footprints can give us clues about how many toes, or digits, are on a foot, whether the toes had nails, hooves, or claws, and the overall shape of the foot. We can determine the direction individuals were walking, and get a general idea of a minimum number of individuals within a group (to an extent –preserved footprints should represent individuals who are walking over the landscape at roughly the same time, but who can say if they were there together). In this case, the authors claim that the footprints show a foot that resembles ours with all the toes, even the big toe, together, but without claws or a defined arch. Because of this, the authors claim that an original (basal) member of the Hominini clade (our own branch of the family tree) made these tracks, and suggest that whatever it was eventually gave rise to whatever we are now.

I’m not convinced, but I am certainly intrigued. At 5.7 mya, it post-dates early potential basal members of our lineage (Sahelanthropus and Orrorin) residing in Central and Eastern Africa, where current evidence overwhelmingly supports hominin evolution in savannah environments. Crete is a long way from any of these places, even if the Mediterranean Sea wasn’t a factor, and there are no Miocene ape fossils found particularly close to the trackways site. That doesn’t mean these footprints don’t belong to Miocene apes, but it makes it harder to argue that it was definitely an ape and not, say, a bear. Especially given the vast array of apes inhabiting the Planet of the Apes, I don’t have a problem with the possibility that more than one Miocene ape stood up to get across a flat surface, but it would be nice to point to a fossil close by in time and space and say, ‘Hey, it’s probably that guy!’.

Reference
Gierliński, G.D., Niedźwiedzki, G., Lockley, M.G., Athanassiou, A., Fassoulas, C., Dubicka, Z., Boczarowski, A., Bennett, M.R. and Ahlberg, P.E. (2017). Possible hominin footprints from the late Miocene (c. 5.7 Ma) of Crete?. Proceedings of the Geologists’ Association.

Sarah Hlubik is a PhD candidate in the Department of Anthropology at Rutgers University. She works on early hominin control of fire at Koobi Fora, Kenya.