I’ve got a new paper out today, in Nature*! Working with a large group of researchers as part of the Smithsonian ETE Community Assembly and Disassembly Through Time working group, we pulled together fossil and modern datasets spanning plants and animals, from many hundreds of millions of years ago, to thousands of years ago, to a hundred years ago and today. We show that across most dataset, the non-random species pairs tend to be aggregated. That is, most taxa are randomly associated across the landscape, but some are significantly aggregated (occur at the same sites more often than expected) or significantly segregated (occur at different sites more often than expected). But starting around 6,000 years ago, something starts to change, and we see more and more segregated pairs. Today, most significantly associated species-pairs are segregated across the landscape! So after being relatively stable for 300 million years, something has changed over roughly the past 10,000 years.
In our working group meetings over the past several years, we wracked our brain trying to figure out what might cause this change. We first went to all the usual suspects that paleobiologists think are important. We know that taphonomy is important- that is, there are processes involved in forming fossil deposits that may obscure our inferences of ecological or evolutionary processes. So we asked: Was something different about the spatial resolution of fossil vs modern data? Was the difference in time- averaging across datasets responsible for the change? Were there systematic differences in the taxonomic resolution of our datasets that might be causing this apparent switch in community assembly processes? But after collating and analyzing a dataset of all these different potential confounding variables, none of those appeared to be causing the switch from aggregated to segregated pairs. We also considered whether there was something about climatic variability within the time spans of the fossil deposits that may be causing the pairs to appear aggregated. Again, no. So we still don’t know WHAT is causing the switch from aggregated to segregated pairs, but by process of elimination we’ve settled on human activity as the most likely explanation.
Human-related activity really ramps up over the past 10,000 years-increases in human population sizes, beginning of agriculture in North America, cultivation and domestication of species, changes in land use, habitat fragmentation, and increasing predation and hunting pressure (over and above the human impacts on megafaunal populations prior to 10,000 years ago). It’s likely that not one single thing was impacting ecological communities- all of the above combined to impact them. So while there is a lot of work still to be done to nail down the exact mechanisms, our data”suggest that the rules governing the assembly of communities have recently been changed by human activity”.
Here are links to some of the press about the paper:
*If you’re unable to access the paper through your institution, email me and I’ll send you a copy: jblois(at)ucmerced(dot)edu.
After almost three years at UC Merced, with two postdocs, four graduate students, and many undergraduate students doing exciting work in the lab, our research descriptions were a bit outdated. A major fall project for me and the lab has been to update the descriptions of what we do, and it’s finally (mostly) done! This was also a good chance for me to reflect on the research going on in my lab- and realize, again, how exciting it all is! We are working on paleo-modeling projects, community assembly and range shift projects, traits, genetic diversity and phylogeography, and basic natural history. I can’t think of a more ideal set of intellectually exciting topics to work on. And, I have been fortunate to have attracted an absolutely fantastic set of people to work with me at UC Merced, in addition to wonderful collaborators at UCM and elsewhere. So check out our new research descriptions!
Kaitlin Maguire will be leaving the Blois lab at the end of this week! Kaitlin got a job as an Ecologist and Statistician for the USGS in Boise, Idaho. She will be joining the Forest and Rangeland Ecosystem Science Center and primarily working on a project modeling the effects of fire and other ecosystem disturbances on communities. We will greatly miss Kaitlin’s presence in the lab, but wish her the best of luck in her new job!