Browsing by Subject "Pot experiment"

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Native and alien species suffer from late arrival, while negative effects of multiple alien species on natives vary
(2021) Ferenc, Viktoria; Merkert, Christian; Zilles, Frederik; Sheppard, Christine S.
Ongoing globalisation and climate change are causing plant species to invade new habitats and thereby alter biodiversity and ecosystem functioning. Since numbers of plant invasions continue to increase globally, it is crucial to investigate the effects of multiple co-occurring alien species on native communities. Furthermore, priority effects due to the earlier emergence of certain species affecting fitness of later arriving species can shape community structure and affect native species performance. We investigate in a common garden pot experiment the interactions among five alien-native species pairs. First we focus on the effect of growing with either one or two alien neighbour species on a native plant, second we alter the arrival time of the alien or native neighbour by 3 weeks. Generally, native species performance decreased when surrounded by two alien species compared to only one, although the magnitude of this effect varied depending on species, with one species even performing better with alien neighbours than in monoculture. Species performance greatly decreased when arriving second in the pot, for both native and alien species. In contrast, alien species tended to benefit more from arriving early. Given that we studied annual ruderal species, their potentially lower competitive ability might explain why we detected negative effects of late arrival. We highlight the need to further elucidate underlying mechanisms of small-scale invasion dynamics to achieve generalisations concerning the response of multiple alien and native plants given their species-specific differences in response to neighbour species and arrival time.
The performance of and interactions between multiple co-occurring alien and native plant species
(2023) Ferenc, Viktoria; Sheppard, Christine
This thesis focuses on investigating species interactions in the context of alien species establishment, which poses severe threats to species, communities, and ecosystems due to climate change and globalization. The study emphasizes the need to understand the effects of multiple co-occurring alien species and their potential explanations, such as niche or fitness differences. The outcome of competition can also be influenced by priority effects, where earlier emerging species affect later emerging species in a given environment. Positive interactions, like facilitation, are often overlooked but play a significant role in species interactions. Legumes, known for their ability to fix atmospheric nitrogen, can facilitate alien species, leading to both severe negative effects on natives and reduced resource competition. The research conducted three common garden pot experiments to address various aspects of alien species interactions. The first experiment examined pairwise combinations of 20 alien annual plant species in Germany to identify the mechanisms driving these interactions. It tested the prevalence of competition versus facilitation and assessed the effectiveness of individual traits, hierarchical or absolute trait distances, multivariate trait or phylogenetic distance, and trait plasticity in explaining plant performance. Results indicated that while interspecific competition was more common, interspecific facilitation occurred in 24% of cases. Hierarchical trait distances provided better explanations for interactions than phylogenetic or multivariate trait distances. Accounting for trait plasticity did not necessarily improve plant performance predictions. Notably, taller individuals with lower specific leaf area than their alien neighbours exhibited increased biomass and seed production when growing together. The second experiment focused on interactions between five pairs of alien and native species. It evaluated the impact of growing with one or two alien neighbour species on native plants and manipulated the arrival time of alien or native neighbours. Generally, native species performed worse when surrounded by two alien species compared to one, although the effect varied among species. Both native and alien species experienced significant performance decreases when arriving second in the pot, while alien species tended to benefit more from early arrival. However, further studies are required to generalize these findings across multiple alien and native plants regarding neighbour species and arrival time responses. The third experiment delved into legume facilitation in more detail. It involved growing 30 annual Asteraceae species (neophytes, archaeophytes, and natives) in communities with or without legume presence. The study measured functional traits, fitness, and nitrogen characteristics to understand how legume presence affected Asteraceae fitness and the relationship between traits, nitrogen concentration, and fitness. Using the δ15N natural abundance method, the research explored whether facilitation mechanisms differed among native phytometer, neophyte, and archaeophyte Asteraceae. Specific leaf area negatively affected aboveground biomass and seed production, with a stronger effect in the absence of legumes. Nitrogen concentration was positively correlated with biomass but did not significantly increase seed production. The results suggested direct legume facilitation for the native grass phytometer Festuca rupicola when growing alongside archaeophytes but not neophytes. This indicated varied mechanisms of competition for nitrogen between natives and alien species of different residence times and deepened understanding of altered facilitative leguminous effects in the presence of alien species. Overall, this research demonstrates the application of community ecology concepts and theories to investigate alien species interactions, particularly when multiple co-occurring alien species are involved. As the rate of alien species arrival in new habitats continues to increase, understanding their combined impact on native species, communities, and ecosystems becomes increasingly crucial.