Irene Martín-Forés

Weed abundance is positively correlated with native plant diversity in grasslands of southern Australia

Weeds are commonly considered a threat to biodiversity, yet interactions between native and exotic species in grasslands are poorly understood and reported results vary depending on the spatial scale of study, the factors controlled for and the response variables analysed. We tested whether weed presence and abundance is related to declines in biodiversity in Australian grasslands. We employed existing field data from 241 plots along a disturbance gradient and correlated species richness, cover and Shannon diversity for natives and exotics, controlling for seasonal rainfall, climatic gradients and nutrient status. We found no negative relationships in terms of emergent diversity metrics and occupation of space, indeed, many positive relationships were revealed. When split by land-use, differences were found along the disturbance gradient. In high-moderately disturbed grasslands associated with land-uses such as cropping and modified pastures, positive associations were enhanced. Tolerance and facilitation mechanisms may be involved, such as complementary roles through different life history strategies: the exotic flora was dominated mainly by annual grasses and herbs whereas the native flora represented more diverse growth-forms with a higher proportion of perennials. The positive relationships existing between native and exotic plant species in high-moderately disturbed grasslands of South Australia are most likely due to facilitation through different strategies in occupation of space given that the effect of habitat suitability was controlled for by including environmental and disturbance factors. Consequently, although particular weeds may negatively impact biodiversity, this cannot be generalised and management focusing on general weed eradication in grasslands might be ineffectual.

Ecotypic differentiation and phenotypic plasticity combine to enhance the invasiveness of the most widespread daisy in Chile, Leontodon saxatilis

Dispersal and reproductive traits of successful plant invaders are expected to undergo strong selection during biological invasions. Numerous Asteraceae are invasive and display dimorphic fruits within a single flower head, resulting in differential dispersal pathways - wind-dispersed fruits vs. non-dispersing fruits. We explored ecotypic differentiation and phenotypic plasticity of seed output and fruit dimorphisms in exotic Chilean and native Spanish populations of Leontodon saxatilis subsp. rothii. We collected flower heads from populations in Spain and Chile along a rainfall gradient. Seeds from all populations were planted in reciprocal transplant trials in Spain and Chile to explore their performance in the native and invasive range. We scored plant biomass, reproductive investment and fruit dimorphism. We observed strong plasticity, where plants grown in the invasive range had much greater biomass, flower head size and seed output, with a higher proportion of wind-dispersed fruits, than those grown in the native range. We also observed a significant ecotype effect, where the exotic populations displayed higher proportions of wind-dispersed fruits than native populations. Together, these patterns reflect a combination of phenotypic plasticity and ecotypic differentiation, indicating that Leontodon saxatilis has probably increased propagule pressure and dispersal distances in its invasive range to enhance its invasiveness.

The invasiveness of Hypochaeris glabra (Asteraceae): Responses in morphological and reproductive traits for exotic populations

Scientists have been interested in many topics driven by biological invasions, such as shifts in the area of distribution of plant species and rapid evolution. Invasiveness of exotic plant species depends on variations on morphological and reproductive traits potentially associated with reproductive fitness and dispersal ability, which are expected to undergo changes during the invasion process. Numerous Asteraceae are invasive and display dimorphic fruits, resulting in a bet-hedging dispersal strategy –wind-dispersed fruits versus animal-dispersed fruits–. We explored phenotypic differentiation in seed morphology and reproductive traits of exotic (Chilean) and native (Spanish) populations of Hypochaeris glabra. We collected flower heads from five Spanish and five Chilean populations along rainfall gradients in both countries. We planted seeds from the ten populations in a common garden trial within the exotic range to explore their performance depending on the country of origin (native or exotic) and the environmental conditions at population origin (precipitation and nutrient availability). We scored plant biomass, reproductive traits and fruit dimorphism patterns. We observed a combination of bet-hedging strategy together with phenotypic differentiation. Native populations relied more on bet-hedging while exotic populations always displayed greater proportion of wind-dispersed fruits than native ones. This pattern may reflect a strategy that might entail a more efficient long distance dispersal of H. glabra seeds in the exotic range, which in turn can enhance the invasiveness of this species.

Functional acclimation across microgeographic scales in Dodonaea viscosa

We studied a native Australian shrub—Dodonaea viscosa, or sticky hop bush—in the wild and in a gardening experiment and found that the species can readily adapt to different environments. Our findings are interesting because the plants we used came from sites with quite different environmental conditions, although they were only short distances apart. Our findings indicate that the potential risks associated with moving plants between sites with different environmental conditions are not likely to cause negative outcomes for restoration projects using this species, which is commonly used for restoration in southern Australia.