We have recently increased the pool of science committee members of COMPADRE & COMADRE by one individual – a very prolific one – who joins the group of researchers that help us make long-term decisions on the sister demographic databases, and obtain funding: Eelke Jongejans.
We have asked him to describe his research and his vision for COM(P)ADRE. This is what he says:
“How much do species differ in survival and reproduction rates? How much do these vital rates vary between populations within species? Can traits like seed mass, brood care and migration behavior explain variation in vital rates within and between species? Or do local environmental conditions have a larger effect than mean trait values? How much does life history variation affect the dynamics of populations of plants and animals? These interesting questions are key to population ecology. Answering them requires information about the life history traits, vital rates and dynamics of multiple populations and species. Bringing together this information for thousands of populations is exactly what the population matrix databases COMADRE and COMPADRE do.
As the goal of this post is to introduce my research, I will give some examples of comparative demography that I have been involved in. Together with various wonderful co-authors I have used data that is now archived in COMPADRE and COMADRE to explore several aspects of life history variation. For instance, we found that for herbs buffering mechanisms (that might have softened the impact of year-to-year climate variation on fluctuations in population size) appeared to be overwhelmed by the effects of positive correlations among vital rates (Jongejans et al. 2010a). Such comparative analyses can be used to explore what could happen in climate scenarios in which not only mean weather parameters change, but also their variability.
Picture: Excursion with students near Nijmegen, The Netherlands, setting up mist nets to survey birds (Photo by M. Lampe)
We also used published matrix population models to study whether there is as much life history variation within the order of Carnivora as within all Mammalia (van de Kerk et al. 2013). Elasticity analyses showed that this was indeed the case, and that Carnivora span a very similar gradient over the slow-fast continuum. However, this study also showed that although there were major differences in e.g. the lifespan between e.g. stoats and grizzly bears, the individual variation within species is often very large and important for population dynamics.
The variability of life histories also becomes apparent in studies in which several populations of the same species are studied at the same time, as already showed by Oostermeijer et al. (1996). Vital rates not only vary considerably between regions of species distributions (e.g. between European countries), but also between localities within regions (Jongejans et al. 2010b). Furthermore, this spatial variation in life history variation appears to be qualitatively different from temporal variation in demography (Jongejans & de Kroon 2005, but see Ramula 2009), making it more difficult to borrow information between spatial and temporal replication for stochastic simulations. It has become clear that life history differences, as quantified by various forms of sensitivity and elasticity analyses do not only depend on species or population characteristics but also on the phase in which the population was during the study period: whether the population was growing, stable or declining.
Given this large life history variability at the individual and population levels, is it still sensible to attempt comparative demography across species? Yes, as long as these other sources of variation are acknowledges or, even better, as soon as novel methods are developed to incorporate these sources in the comparative analyses.
There certainly is a lot to gain from comparative demography, and not just for fundamental ecology. One of the promising applications of large-scale comparative demography is the trait-based interpolation of the life histories and population dynamics of endangered species for which there are none or little demographic data. Comparative demography can thus be used to assist progress towards the dearly needed ‘science- and evidence-based conservation biology’. COMADRE and COMPADRE should therefore also be used to inspire botanists, ornithologists, herpetologists, etc, to embark on the adventure called field demography. By showing what can be learned and achieved from systematic and constant-effort observations, and by providing a complete (!) overview of what species have been studied already (emphasizing the large gaps of demographic knowledge about many other species), these databases and analyses can help both professional and amateur biologists when starting new studies in the field. We wrote a book about how the life cycle of plants can be studied by biologists willing to devote some leisure time to discover the secret life history strategies of a plant species (in Dutch; Bremer et al. 2012) and other such resources and programs exist for plants. However, much can be learned in that respect from field ornithology, which can rely on a large number of volunteer birders to collect data on survival, dispersal and reproduction.”
Department of Animal Ecology and Ecophysiology. Institute for Water and Wetland Research. Radboud University Nijmegen. The Netherlands.
Bremer P, Jongejans E, Oostermeijer G & Willems J (2012) Planten tellen. Over demografisch onderzoek. KNNV 160 pages (Dutch book on plant demography; now also available as digi-book for iPad, tablet or smartphone)
Jongejans E & de Kroon H (2005) Space versus time variation in the population dynamics of three co-occurring perennial herbs. Journal of Ecology 93:681-692
Jongejans E, de Kroon H, Tuljapurkar S & Shea K (2010a) Plant populations track rather than buffer climate fluctuations. Ecology Letters 13:736-743
Jongejans E, Jorritsma-Wienk LD, Becker U, Dostál P, Mildén M & de Kroon H (2010b) Region versus site variation in the population dynamics of three short-lived perennials. Journal of Ecology 98:279-289
Oostermeijer JGB, Brugman ML, de Boer ER & den Nijs HCM (1996) Temporal and spatial variation in the demography of Gentiana pneumonanthe, a rare perennial herb. Journal of Ecology 84:153-166
Ramula S, Dinnétz P, Lehtilä K (2009) Spatial data replacing temporal data in population viability analyses: An empirical investigation for plants. Basic and Applied Ecology 10:401–410. http://dx.doi.org/10.1016/j.baae.2008.10.007
van de Kerk M, de Kroon H, Conde DA & Jongejans E (2013) Carnivora population dynamics are as slow and as fast as those of other mammals: implications for their conservation. PLOS ONE 8:e70354