Responding to change : phenotypic plasticity and local adaptation, case studies using native and invasive Erodium species
Creators: name: Davidson, Amy Michelle
Publisher: name: The Australian National University
Year: 2014
Subjects: subject: Erodium Effect of water levels on
subject: Phenotypic plasticity
subject: Plant invasions Water-supply
subject: Invasive plants Ecology

description: Phenotypic plasticity is often postulated to play a role in plant invasions. This thesis explores the role of plasticity in plant invasions with particular emphasis on responses to water availability. The thesis employed two main approaches; the first was a meta-analysis of published literature. The second approach was the use of greenhouse experiments on populations of a congeneric native (Erodium crinitum) - invasive (E. cictuarium ) species pair using seed collected along a natural rainfall gradient. The meta-analysis found that phenotypic plasticity is generally greater in invasive compared to non-invasive species. However this higher plasticity did not always translate to a fitness advantage. In particular, the fitness was partially dependent on whether conditions changed from stressful to average or average to favourable conditions. There were three main greenhouse studies. The first study compared patterns in phenotypic plasticity between wet and dry populations of the native and invasive Erodium species in response to four levels of water availability, ranging from water only at wilting point through to water to saturation daily. Responses in thirty size, growth, leaf morphological, physiological and phenological and fitness traits were measured. Patterns of plasticity in the native and invasive Erodium species were also investigated with respect to responses to water dose applications. Halving the dose at which water was applied had a greater effect on the fitness proxies: seed number and total biomass, than did halving the total amount of water supplied. Consistent with the other greenhouse study, dry site populations of both species displayed higher average seed number across all treatments than did wet site populations. However, the wet site populations maintained superior total biomass. While higher phenotypic plasticity in key traits resulted in higher fitness for seed number, homeostasis in total biomass was associated with lower levels of phenotypic plasticity. The third greenhouse study investigated constraints on plasticity in key traits to water availability and competition. It was expected that constraints would be greater when multiple stresses were present. However, this hypothesis was rejected. Although several constraints to plasticity were detected, such constraints were as common when only one stress was present as when both stresses were imposed. The thesis discusses the findings of these studies in the context of our current knowledge on plant invasions and species adaptation to climate change. Differences between the findings of the meta-analysis in which invasive species were generally more plastic than co-occurring native species, and findings of the greenhouse study, in which little difference was detected between species are also discussed. The results suggest that when range is controlled for invasive species are not inherently more plastic. Both the meta-analysis and the greenhouses studies also suggest that the shorter residency time of invasive species increases the probability that many plastic responses will be maladaptive. Indeed, the greenhouse studies found that species tended to respond more adaptively to situations which were more relevant to their ecological context. For example, dry site populations displayed greater adaptive plasticity than did wet site populations with respect to changes in water availability.