Plant demography and ecological interactions

Plant-herbivore-mutualist interactions

Most plant species interact with a diverse suite of antagonists (herbivores, competitors) and mutualists (pollinators, defenders, symbiotic microbes).

Yet, we know surprisingly little about the role of these biotic interactions in shaping patterns of plant distribution and abundance. Evaluating the impacts of interacting species on plant fitness and population dynamics requires a demographic approach that integrates interactions over potentially long and complex life cycles. We are using demographic approaches to quantify the roles of multiple consumer guilds in the

population dynamics of cacti (Opuntia spp.) in the Chihuahuan desert of New Mexico and along the Gulf coast of Texas. Cacti are an important component of many arid and semi-arid ecosystems, and are threatened by an invasive cactus-feeding moth (Cactoblastis cactorum) that is currently spreading westward through the Gulf coast region. Our work is quantifying the potential impacts of this invasive herbivore on cactus population dynamics and evaluating the effects of biotic defense provided by cactus-tending ant mutualists. (related papers: Miller 2007 Oikos, Miller et al. 2009 Ecol. Monographs, Miller et al. 2010 Biol.Invasions)

Host-symbiont interactions.

I am collaborating with Jenn Rudgers on demographic studies of symbiosis between grasses and vertically transmitted fungal endophytes.

The population dynamics of grass-endophyte systems (and all symbioses for that matter) are driven by a complex balance of benefits to hosts organisms, costs to host organisms, and efficiency of transmission. We are developing models and conducting experiments to explore how factors such as host life history, demographic structure, and density dependence can modify host and symbiont population dynamics. (Related papers: Rudgers et al. (in press) Ecology, Yule et al. (in review))

 

Competition among plant consumers.

I am collaborating with Charlotte Lee and Brian Inouye on studies of competitive interactions that occur between consumers (including herbivores and mutualists) that share host plants but consume the plant (or parts of it) at different  life stages or influence its demography in different ways. For example, some herbivores specialize on vegetative plant stages while other attack only reproductive stages. These herbivores may never encounter each other on the same plant, but they are dynamically linked to each other via their effects on the demographic rates of their shared resource. Situations like this, which are common in nature, fall outside the bounds of traditional competition theory, which doesn’t pay much attention to resource demography. We are building theoretical models to investigate coexistence criteria for consumers of stage-structured resources, and tying the models to plant-herbivore and plant-mutualist systems in the field. (Related papers: Miller and Rudolf 2011 TREE, Lee et al. (in press) Am Nat)