OScar GODOY

PhD outcome

I devoted my PhD to answer these questions related to species coexistence and ecosystem functioning under a context of plant invasions. Below, you can find a summary of our main findings. 

1. Functional Traits Determining Invasiveness

Ecophysiological Traits and their Plasticity in Heterogeneous Environments: Two separate bodies of literature have suggested that either specific traits related to resource acquisition, plant competition and stress tolerance, or their plasticity with respect to nutrients, light and water, are major contributors to invasiveness. My research has stressed the necessity of merging trait and trait plasticity because they represent covariant functional strategies of the plant phenotype. Structural equation modeling approaches have shown that specific functional traits are more important than plasticity and integration for the improved performance of invaders in heterogeneous environments. Moreover, I have targeted specific traits and trait plasticity determining invasiveness in Spain. For instance, high carbon acquisition and geographical breath of invaders were related to photosynthetic nitrogen use efficiency  and plasticity in leaf thermal tolerance. 

The Role of Phenology: Phenology determines species’ reproduction success and accordingly there has been much debate about the kinds of phenological differences that favor invasion. One of my earliest research projects documenting flowering phenology patterns for more than 200 invasive-native comparisons between the origin and the introduced region of the invaders in Spain and between three Mediterranean-type regions (California, Spain, and the Cape Region) determined that average invasive-native phenological differences are only a consequence of different histories of human-orchestrated introductions. Flowering phenology tended to show genetic inertia from where invaders evolved, and thus differences in phenology at broad scale reflected whether the majority of invaders were brought from different climatic conditions to those of the invaded region (i.e. different evolutionary histories). More recently, I used an experimental approach to understand mechanistically the consequences for species invasion of these phenological time frames set by human-mediated actions. Coexistence theory revealed that a phenological offset, either earlier or later, creates sufficient niche differences to help European exotic species to establish in native annual serpentine Californian grasslands. However, phenology gave only later invaders enough of a fitness advantage to exclude native species.

Pre-adaptation to invasiveness, Post-evolution or Both: It is important for an effective risk assessment to determine whether exotic species are pre-adapted to be invaders or invasiveness occurs as a response to new evolutionary forces in the introduced region. Research on the Acacia genus native to Australia determined that Acacias evolved under low climatic stress and more useful to humans (e.g. tannins, timber, medicine, food, ornamental) have a greater chance of becoming invasive elsewhere. At the same time, I outlined some mechanism of why Valdivian forests in South America are so resistant to invasion and why invasion dynamics are slower compared to other ecosystems. High phenotypic plasticity pre-adapt exotic species such as Prunella vulgaris to go from open sunny patches along the roadsides to the deep shade of the forest understory. To persist, populations must then adapt to local light conditions. Evolution changes the phenotype and the capacity for exhibiting again a large phenotypic plasticity isolating sun from shade populations, which in turn, slows the invasion spread.

2. Ecosystem Impacts of Biological Invasions

Plant traits are the controller of more than the 50% of green tissue production that is returned to the soil via litter decomposition. Thus, a progressive displacement of native flora by exotic invaders may have important consequences for nutrient cycling if leaf traits between both groups differ. My research found that higher carbon acquisition rates of invasive species translate into much higher lignin content than their native counterparts. This difference combined with low N and P levels of Spanish Mediterranean ecosystems can lead to a slow down in nutrient cycling through slower litter decomposition. By contrast, meta-analytical approaches showed that at a world scale plant invasion augments on average N pools and N fluxes in similar magnitudes, but N fluxes speed up when invasion occurs in most and warn climatic conditions and N pools increase even more when invaders are N-fixing trees and natives are not. Also, islands are more susceptible than continents to changes in N cycling because of their milder conditions.