Current work: plant population responses to climate
My research is mostly focused on the response of plant populations to climate change. The biggest project I am involved in is the sApropos working group, led by Rob Salguero-Gómez and Tiffany Knight. Most of research activity is now linked to the main objectives of this working group, which are:
- Testing new statistical approaches to link plant demographic rates to climatic drivers.
- Finding life-history or biome predictors linked to plant population responses to climate
- Forecasting the effects of climate change on short term plant population dynamics.
Comparing alternative methods linking climate drivers to demographic rates
I am estimating which months of the year have the best power predicting plant demographic rates. We compared three separate hierarchical Bayesian approaches to simple regressions using annual (rather than monthly) anomalies using data from the COMPADRE database (forthcoming).
My PhD student, Sanne Evers, has recently applied the sliding window methodology to four long term demographic datasets. Surprisingly, she found that plant vital rates often correlate with dormant season climate and “lagged” climate variables (in review). These results challenge the widely held assumption that plant population growth rates are affected by the climate during the growing season.
Can life history and biome predict plant population responses to climate?
In a synthesis study using plant population projection models, I found that the larger the generation time, the smaller the response of plants to climate (in review). However, site climatic conditions, such as average water availability index, had a non-significant predictive power. This relationship has an ecologically substantial magnitude, but it is non-significant because of its large uncertainty.
Forecasting
Under the supervision of Tiffany Knight, and in collaboration with Eleanor Pardini, I have recently completed a forecasting study on an endangered Lupine species endemic to the Californian coast. We found surprisingly strong negative correlations between temperature and the demographic rates of this plant. Our forecast suggests that without management actions, climate change will very likely push this plant towards extinction (forthcoming).
In a global analysis, Maria Paniw showed that the vital rates of the vital rates of animals (e.g. survival and reproduction) tend to respond in contrasting ways to the same climatic drivers (in review).
PAST WORK
Database development
Under the supervision of Tom E. X. Miller, I have developed the Popler database and its associated R package, in order to provide structured, long-term population data to test how climatic variability affects population dynamics. Climatic variability is generally assumed to have negative effects on long-term population growth. In theory, however, variability in climate could also have neutral and positive effects on long-term population growth. We are currently using this data to test whether climatic variability has negative, neutral, or positive effects on the long-term population growth rates of ecological populations in the field (forthcoming).
I am also an active contributor to the COMPADRE Plant Matrix database, and the forthcoming PADRINO database on integral projection models. The work on these databases is led by Rob Salguero-Gómez and Sam Levin, respectively.
I am also an active contributor to the COMPADRE Plant Matrix database, and the forthcoming PADRINO database on integral projection models. The work on these databases is led by Rob Salguero-Gómez and Sam Levin, respectively.
Two-sex population dynamicS
Population models of sexually reproducing species generally ignore males. This is a good modeling assumption when the relative number of males in a population does not limit reproduction. However, mate limitation is common in nature, generally because unequal demographic rates between the sexes skew population sex ratios. In collaboration with Tom E. X. Miller, we carried out field and greenhouse experiments to quantify mate limitation, and sex-specific demographic rates in the native grass Texas Bluegrass (Poa arachnifera).
In a field experiment, we quantified the effect of sex ratio and absolute density on mating and sex-specific vital rates. We set up an experiment that varies both the relative frequency and absolute density of Texas bluegrass males and females. I found out that the negative effect of pollen limitation on seed viability is amplified by low absolute population density.
Second, we have set up a common garden experiment across Texas bluegrass’ native range, with sites encompassing a large gradient in mean annual precipitation. According to field observations, we hypothesized that i) sex-specific vital rates responses to precipitation would result in female biased sex ratios at high mean annual precipitation, thereby ii) substantially decreasing population growth rate. As hypothesized, we found sex-specific responses to mean annual precipitation would result in female biased populations at high precipitation. However, this sex ratio bias was not extreme enough to have substantial effects on population growth rate (manuscript in preparation).
In a field experiment, we quantified the effect of sex ratio and absolute density on mating and sex-specific vital rates. We set up an experiment that varies both the relative frequency and absolute density of Texas bluegrass males and females. I found out that the negative effect of pollen limitation on seed viability is amplified by low absolute population density.
Second, we have set up a common garden experiment across Texas bluegrass’ native range, with sites encompassing a large gradient in mean annual precipitation. According to field observations, we hypothesized that i) sex-specific vital rates responses to precipitation would result in female biased sex ratios at high mean annual precipitation, thereby ii) substantially decreasing population growth rate. As hypothesized, we found sex-specific responses to mean annual precipitation would result in female biased populations at high precipitation. However, this sex ratio bias was not extreme enough to have substantial effects on population growth rate (manuscript in preparation).
Climate change and Cheatgrass (bromus tectorum)
Global climate change demands ecological forecasts, but the science that links the demographic performance of field populations to climatic drivers is in its infancy. I tackled this problem in my Ph.D., by carrying out two field experiments designed to quantify the effect of increased temperature and snowmelt on the invasive annual grass cheatgrass (Bromus tectorum). I found that increased temperature boosts cheatgrass population growth, especially if coupled with sufficient precipitation. Moreover, this positive effect of temperature and precipitation is further increased if precipitation shifts from rain to snow.