The power of comparative demography: booms and busts

Jenni McDonald’s work on transient dynamics using COMPADRE was recently recognized with the Postdoctoral Excellence Award of the Plant Population Ecology of the Ecological Society of America. Congrats Jenni! Here we leave you with a short summary of her work.

 

The natural world is not static and populations don’t exist in a vacuum. Environmental variation is inevitable for wild populations. Consequently, the vital rates, stage structures and dynamics of every wild population will change through time. Earlier this year our paper linking stochastic dynamics into contributions from transient dynamics (driven by non-stable stage structures) and asymptotic dynamics (caused by changes in vital rates) was published in Journal of Ecology.

The idea of transients being important within stochastic environments was not a new one. However, we built on previous work by exploring absolute dynamics, which accounts for the strength of opposing asymptotic and transient effects. We also used a large-scale comparative database to test this hypothesis, using data from 277 plant populations across 132 species from the COMPADRE Plant Matrix Database. This comparative framework opened up exploration of evolutionary and ecological patterns. Our key result was that transients are ubiquitous in plant populations, contributing to half the dynamics in stochastic environments.

Understanding transients is vital for management of both pest species and those of conservation concern. Perturbations in the environment, such as fire, harvesting, disease epidemics and weather changes, will mean that populations are rarely at stable stage structure. Given the contribution of transients to population growth, ignoring non-stable population structure will have implications for management as population growth will be different from that predicted by the long term population growth rate. Consequently, an understanding of transient boom (accelerated population growth) and bust (reduced population growth) could be exploited by managers and conservationists to maintain persistence (or cause extinction) of wild populations. Transients may also provide an explanation as to how some species thrive in a variable landscape, whereas others suffer population declines, for example endangered species potentially may be those who respond poorly to demographic disturbance. Harnessing the power of comparative analysis enabled us to explore evolutionary and ecological patterns and start to shed light on these possibilities.

The COMPADRE Plant Matrix Database provides open access to thousands of plant population projection matrices parameterised from empirical data previously dispersed throughout peer-reviewed and grey literature. COMPADRE is the ideal resource to explore transients across populations varying in evolutionary history, growth form and life stage complexity. We found that both transient contributions and asymptotic contributions are influenced heavily by the number of life stages modelled. This could mean that species with complex life histories are able to bounce back from demographic disturbances; alternatively, this observation may be an artefact of modelling design. We found no phylogenetic signal in the contribution of transients to stochastic growth, nor clear patterns related to growth form. Plant populations have a tendency to boom rather than bust in response to variable environments. This raises the future question; have populations evolved to bounce back from disturbance?

Our research also highlights the value of large-scale databases. The power of comparative demography allowed us to ask questions regarding the impact of non-equilibrium stage structure on stochastic population dynamics and reveal patterns that would not have been deduced from other means. Empirical data on the life histories of living organisms stored in COMPADRE can contribute to a diverse spectrum of research areas and is of relevance to scientists working in the fields of conservation, ecology and evolution. In addition to the ability to ask new questions, the free and instant access of the database removes any logistical obstacles that many researchers may face in terms of field work and laboratory studies. Such a resource has the potential to inspire new scientific insights, while also embracing the diversity of work life patterns of scientists – undoubtedly a powerful resource.

Jenni McDonald

Postdoctoral researcher at Exeter University

 

Advertisements

New COMPADRE & COMADRE versions are out!

Yesterday, coinciding with the symposium “Landscape demography: Population dynamics across spatial scales” at the 2016 Ecological Society of America annual meeting, where we gave the talk “Global plant and animal demography: tearing the curtain and filling up the gap“, we released the new two versions of the sister databases: COMPADRE version 4.0.0 and COMADRE version 2.0.0. These can be downloaded fully open-access at www.compadre-db.org.

Screen Shot 2016-08-11 at 10.32.41.png

Our goals, at COMPADRE & COMADRE: to digitise and standardise matrix population models published and communicated to us by population ecologists, to error-check, fix and complement the information with metadata (e.g. taxonomy, phylogeny, biogeography), and to make it open access. In other words: to bring the field demographic data to your computer.

What’s new in them? More matrix population models, more species, more metadata! The COMPADRE Plant Matrix Database now contains 695 unique taxonomically accepted plant species from 819 published or personally communicated studies, adding up to a total of over 7,000 population matrix models. Similarly, the COMADRE Animal Matrix Database now contains 405 taxonomically accepted animal species outsourced from 508 studies, with a total of 1,927 matrix models.

Screen Shot 2016-08-11 at 10.33.40.png

Summary statistics of the new versions of COMPADRE and COMADRE: more species, more matrix population models, and more metadata.

The increase in species and number matrices adds up to an unprecedented geographic cover. Clearly, however, geographic and taxonomic biases do exist in the databases, and we encourage users to carry out demographic research using matrix population models in under-explored areas (e.g. Belgium, Ireland, Italy, Greece, Russia, Morocco, Ecuador, Philippines, etc)

Screen Shot 2016-08-11 at 10.33.17.png

Geographic location of the studies where GPS information was provided in the publications, showing the global coverage of COMPADRE and COMADRE (Salguero-Gómez et al. in prep.)

In addition to the new species and matrix models, we have also archived new variables. For instance, the latitudes and longitudes are no longer provided as separate degrees, minutes and seconds, but rather provided as two vectors (Lat and Lon), which is a more manageable format. For instance, try the following in your R console, after you have downloaded the Rdata objects and loaded them onto R:

load("~/WhereverYouSaveYourStuff/COMPADRE_v.4.0.0.RData")
map("world",col="white",fill=T,bg="white",xlim=c(-175,176),ylim=c(-60,85),border="gray",mar=rep(0,4))
points(compadre$metadata[,c("Lon","Lat")])

We’ve also renamed some other variables to unify the organization of plants and animals, for instance:

load("~/WhereverYouSaveYourStuff/COMADRE_v.2.0.0.RData")
table(comadre$metadata$OrganismType)

load("~/WhereverYouSaveYourStuff/COMPADRE_v.4.0.0.RData")
table(compadre$metadata$OrganismType)

 

More information about the databases, their organisation, the way we digitise, complement, error-check and release information, and some useful workshop materials and R functions (incoming R package… stay tuned!) can be found here.

Happy COM(P)ADRE-ing!

The COMPADRE & COMADRE core committee

     Rob Salguero-Gomez – The University of Sheffield & Max Planck Institute for Demographic Research (MPIDR)

     Owen Jones – Southern Denmark University (SDU), MaxO

     Ruth Archer – Exeter University

     Yvonne Buckley – Trinity College Dublin

     Judy Che-Castaldo – Lincoln Zoo

     Hal Caswell – University of Amsterdam

     Tom Ezard – University of Southampton

     Dave Hodgson – Exeter University

     Alex Scheuerlein – MPIDR

     Jim Vaupel – MPIDR & SDU, MaxO