Demography to infinity and beyond!

One of my favourite manuscripts provides a detailed account as to why evolutionary biologists should be demographers (Metcalf & Pavard 2007). The authors argue that, because the propagation of genes into future generations depends on the st/age-specific vital rates of survival, fecundity and migration of individuals within and between populations, and such rates are precisely at the core business of demography, a formal link exists between both disciplines… but that this link has not been explored to its full potential. Based on the strong belief that the ramifications of demography are indeed much broader than “just” the population, and that they reach out to evolutionary biology, and also to genetics, physiology, conservation biology, and community and landscape ecology, we (below) organised the symposium “Demography beyond the Population”, which took place two weeks ago (March 24-26 2015) in Sheffield, UK. This symposium was supported by the British Ecological Society, and brought together ca. 100 delegates from all four corners of the world (e.g. UK, USA, Russia, French Guiana, Brazil, Australia, Mexico).

In case you were not able come to Sheffield or follow us on Twitter (Alden Griffith (@alden_griffith) and myself (@DRobcito) tweeted frequently using #BeyondDemog), allow me to virtually walk you through some of the highlights of the symposium. This demographic extravaganza actually started on Monday March 23rd with five workshops on integral projection models (Metcalf et al. 2013, Merow et al. 2014), age-by-stage matrix population model decompositions (Caswell 2012; Caswell & Salguero-Gomez 2013), continuous physiological models (de Roos 2008) and Bayesian survival analyses (Colchero et al. 2012). These four workshops showcased the vast richness of analytical approaches to analyze individual-level demographic records, even in the presence of uncertainty (BaSTA). To me, however, the greatest highlight of that day was a mini-workshop ran over lunch by Marco Visser on the importance of programming efficiently for demographic analyses. Marco and his colleagues recently published a manuscript with great tips for ecologists and evolutionary biologists (Visser et al. 2015), resulting from a working group organized at the Max Planck Institute for Demographic Research in 2012. Marco’s presentation, based on this publication, emphasized the need to think very carefully how to expedite calculations: when should you get a more powerful computer?, when to bother with parallel core processing?, or simply how does one track which lines of code are taking most RAM (and how to make them faster)? I have learned a lot from the useful advice from Marco, and I have already started to apply it to my own programming. Certainly Marco is an early career ecologist to keep in the radar due to his already important scientific and computational contributions to the field (https://github.com/MarcoDVisser).

The official start day of the symposium, Tuesday, and the rest of it, took place at Cutler’s Hall. To say that I’ve never been to a conference venue like would be quite an understatement… I’ve never been to a wedding venue like this one either! Great corridors, a broad, red-carpeted stair with a large painting of the queen welcoming us at the end, and then the English grandeur of the conference room.

The symposium covered a wide range of topics at the forefront of demography and its application. The invited speakers included Yvonne Buckley, Johan Ehrlén, Hal Caswell, Steve Ellner, Elizabeth Crone, Jordan Golubov, Dave Hodgson, Eelke Jongejans, Frank Schurr, Maria del Carmen Mandujano, Shripad Tuljapurkar, Mark Rees and María Uriarte. Collectively, they highlighted the importance of including major axes of variation in demography (variation through space, through ecological time, through evolutionary time, and through disciplines) to better understand the context in which demographic processes operate and how far one can project in time before projections become too uncertain. I was particularly excited to see Elizabeth Crone’s presentation about how to model the variation in vital rates as a function of time, space and plant’s “personalities”. The latter, personalities, is a term commonly used in human demography (Chen et al. 2006) whose analyses are finally making their way into non-human ecology and evolution. Maria del Carmen Mandujano & Jordan Golubov gave a combo-presentation drawing from phylogenetic analyses and demographic field data in the Cactaceae to evaluate the role of seedbanks (one of the big unknowns in plant demography), and a novel approach to incorporate genetic structure into matrix population models in an Opuntia species.

One of the main premises in demography is that individuals contribute to the population differently as a function of their age, stage or size. Honouring this fundament of demography, and having admittedly only briefly covered above some contributions by more senior scientist contributed to the symposium, I have the full intent to focus what follows in early career folks exclusively. Demography has in the last years experienced a rather prominent recruitment event (yep, pun intended!), whereby a sizable number of early career ecologists and evolutionary biologists are making very important, dynamic contributions. As a result of their oral presentations and accompanied posters, three students were recognized with awards sponsored by Journal of Ecology and the British Ecological Society. The two runner-ups were Julia Barthold and Maria Paniw. Julia and Maria presented respective state-of-the-art research lines on the estimation of unobserved demographic processes such as mortality rates in migrant male lions (Barthold), and seedbank rates of another carnivorous (plant) creature: Drosophylum lusitanicum (Paniw). The winner of the student award was Edgar Gonzalez, based on his work on the “inverse demographic problem”. This challenge consists on the determination of individual-level vital rates based on the observation of population structures, and it is one of the long-standing unresolved questions in our field. Interestingly, and perhaps not by coincidence, Edgar, Julia and Maria’s approaches were based on Bayesian statistics, further supporting my thought that we will all soon be talking priors and posteriors. If you haven’t taking at least an intro course in Bayesian statistics… you might soon become rusty in population studies!

Other very interesting presentations included the decomposition of individual heterogeneity effects onto whole-population dynamics by Merel Jansen, based on a publication in Journal of Ecology (Jansen et al. 2012), bee demography using integral projection models (IPMs) by Natalie Kerr, the examination of which climate variables affect most the demography of a rare orchid also using IPMs by Sascha van der Meer, or the decomposition of plant-animal interactions on a plant population using (you guessed it!) IPMs by Zdenek Janovsky. Matrix Population Models (MPMs; Caswell 2001) and IPMs (Easterling et al. 2000, Metcalf et al. 2013, Merow et al. 2014) were indeed a recurrent tool throughout the symposium, as it was the recently launched COMPADRE Plant Matrix Database , published this year in Journal of Ecology (Salguero-Gómez et al. 2015), and used by Dave Hodgson, Shaun Coutts, Anna Csergo, Yvonne Buckley and myself on separate talks to explore questions as broad as the structuring factors of transient dynamics, the role of phylogenies and geographic proximity on population dynamics, or the connection between traits and life history strategies.

An important advancement in the field of plant population ecology is underway. I already commented in an earlier blog on the need to replicate plots through space more extensively to really encompass the range of demographic responses and underlying mechanisms that (plant) species may display. Suzzane Lommen has been conducting a European-wide project in the last years coordinating data collection of the invasive ragweed by researchers. Maria Begoña García shared with us her valuable experiences in organizing and engaging with the general public to collect demographic information on various endangered plant species in NE Spain. Last by not least, Yvonne Buckley ran a break-out group discussion on the recently launched PlantPopNet, a globally replicated demographic census of the cosmopolitan Plantago lanceolata with the ultimate goals of trying to understand the local, regional and global determinants of population dynamics in the wild (http://plantago.plantpopnet.com/).

But of course most science developed not in the main hall, but away from oral presentations. We, the organizers, made sure to have ample and frequent coffee breaks and to work with our local co-organizer, Dylan Childs, to give the symposium participants a true Sheffield experience. Furthermore, some social events were planned throughout the symposium, which included an informal networking event at a local pub sponsored by the BES journals and a brewery tour on the Wednesday night. I have since heard great things about the tour of the brewery!

Ultimately, I hope that this symposium will have been thought-provoking to all its participants and that we will all go back to our home institutions with a better understanding of what the big questions are, and what directions we should push next to take “demography beyond the population”. And now that we have almost recovered from this symposium, all co-organizers are working with five BES journals (Journal of Ecology, Journal of Animal Ecology, Journal of Functional Ecology, Journal of Applied Ecology and Methods in Ecology & Evolution) to put together the first-ever cross-BES-journals special feature… stay tuned!

I must also express my greatest gratitude to Lauren Sandhu, Andrea Baier, Amelia Simpson, Amy Everard, Richard English and the rest of the fantastic BES staff team for the excellent support prior to and during the symposium. It has been a pleasure working with the BES. I can’t wait for the 13-16 December BES annual meeting!

Rob Salguero-Gómez

Associate Editor, Journal of Ecology

Information about the symposium organizers:

Here is a picture that Amelia took of all the symposium organizers at the end of the symposium.

(L-R)
Rob Salguero-Gómez (Associate Editor Journal of Ecology)
The University of Queensland (Australia)
Max Planck Institute for Demographic Research (Germany)
Cory Merow
Fish & Wildlife Service (USA)
University of Connecticut (USA)
Alden Griffith
Wellesley College (USA)
Dylan Childs (AE Journal of Animal Ecology)
Sheffield University (UK)
Jess Metcalf (AE Methods in Ecology & Evolution)
Princeton University (USA)
Sean McMahon (AE Methods in Ecology & Evolution)
Smithsonian Environmental Research Center (USA)

References:

H Caswell (2012) Matrix models and sensitivity analysis of populations classified by age and stage: a vec-permutation matrix approach. Theoretical Ecology
5: 403–417.

H Caswell & R Salguero-Gómez (2013) Age, stage and senescence in plants. Journal of Ecology 101: 585-595.

Y-F Chen, C-M Wang & H-J Lin (2006) Explore the relationships among demography, personality traits and self-directed learning. The Journal of Human Resource and Adult Learning Nov: 141-150

F Colchero, OR Jones & M Rebke (2012) BaSTA: an R package for Bayesian estimation of age-specific survival from incomplete mark-recapture/recovery data with covariates. Methods in Ecology and Evolution 3: 466–470.

MR Easterling, SP Ellner & PM Dixon (2000) Size-specific sensitivity: applying a new structured population model. Ecology 81: 694-708.

M Jansen, PA Zuidema, NPR Anten & M Martinez-Ramos (2012) Strong persistent growth differences govern individual performance and population dynamcis in a tropical forest understory palm. Journal of Ecology 100: 1224-1232

C. Merow, JP Dahlgren, CJE Metcalf, DZ Childs, MEK Evans, E Jongejans, S Record, M Rees, R Salguero-Gómez, SM McMahon (2014) Advancing population ecology with integral projection models: a practical guide. Methods in Ecology and Evolution 5: 99-110.

CJE Metcalf & S Pavard (2007) Why evolutionary biologists should be demographers. TRENDS in Ecology and Evolution

CJE Metcalf, SM McMahon, R Salguero-Gómez & E Jongejans (2013) IPMpack: an R package for integral projection models. Methods in Ecology and Evolution 4: 195-200.

AM de Roos (2008) Demographic analysis of continuous-time life-history models. Ecology Letters 11: 1-15.

R Salguero-Gómez, OR Jones, CR Archer, YM Buckley YM, J Che-Castaldo, H Caswell, A Scheuerlein, DA Conde, A Baudisch, E Brinks, H de Buhr, C Farack, F Gottschalk, A Hartmann, A Henning, G Hoppe, G Römer, J Runge, T Ruoff, J Wille, S Zeh, D Vieregg, R Altwegg, F Colchero, M Dong, D Hodgson, H de Kroon, J-D Lebreton, CJE Metcalf, M Neel, I Parker, T Takad, T Valverde, LA Vélez-Espino, GM Wardle, M Franco & JW Vaupel (2015) The COMPADRE Plant Matrix Database: an online repository for plant population dynamics. Journal of Ecology 103: 202-218.

MD Visser, SM McMahon, C Merow, PM Dixon, S Record & E Jongejans (2015) Speeding up ecological and evolutionary computations in R; Essentials of high performance computing for biologists. PLOS Computational Biology DOI:10.1371/journal.pcbi.1004140