Abstract
The Earth’s biodiversity underlies functional ecosystems and is intimately linked to human well-being through the variety of services ecosystems provide. Human influences can impinge biodiversity thereby disrupting ecosystem services. Increased global trade, travel and tourism are linked to biodiversity change by inadvertently increasing biotic exchange of species between regions, countries and continents. Biotic exchange is considered negative when introduced species cause negative impacts on ecosystems, or cause economic or human detriment, i.e. biological invasions. Biological invasions are recognized as a major threat to global biodiversity.
The harlequin ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) was introduced to North America from Asia in the early 20th century as a biocontrol agent. In the late 20th century the beetle became invasive and has since spread to many countries on 4 continents, including Denmark. Evidence shows native European predatory insect species are negatively impinged by H. axyridis and there is concern that decline of native predatory insect populations may alter the regulating ecosystem service provided by these natural enemies.
This PhD thesis addressed both direct and indirect trophic interactions (i.e. predation and interspecific competition) between H. axyridis and Anthocoris nemoralis (Heteroptera: Anthocoridae), a European flower bug which shares habitat and prey with invasive H. axyridis in urban habitats. Laboratory assays illuminated the relative strengths of direct predation and interspecific competition, and possible effects thereof on predators. A field-based study using DNA gut-content analysis tested whether trophic interactions between co-occurring predators in urban arboreal habitats reflected findings from laboratory assays. In addition, infection of H. axyridis by naturally occurring entomopathogenic fungi and distribution of fungi in arboreal habitats was assessed. Finally, a laboratory study compared insect behaviour relevant to invasions between native/invasive H. axyridis populations.
Laboratory assays revealed a sublethal effect on A. nemoralis weight gain suggesting interspecific competition with H. axyridis is a stronger interaction for A. nemoralis than direct predation by H. axyridis. In urban arboreal habitats, DNA gut-content analysis revealed little direct predation by H. axyridis, but a high level of prey overlap between predators, thereby confirming the relative strengths of interspecific interactions among wild populations. Coupled with high temporal and spatial niche overlap of predators findings demonstrate that interspecific competition for prey by H. axyridis has the potential to affect local populations of native predatory insects whose habitat is invaded by H. axyridis. Five species of naturally occurring entomopathogenic fungi from three genera were distributed in arboreal habitats, however two of these genera were responsible for most fungi prevalence in H. axyridis. This suggests trees are a source of infection and entomopathogenic fungi may contribute to regulation of H. axyridis populations in invaded urban habitats. Finally, comparison of behaviours revealed that an invasive eastern North American and native Chinese population displayed greater dispersal activity than three other populations. Although an invasive/native dichotomy was not established, results suggest that trait differences may reflect population-level adaptions.
This PhD thesis contributes novel insights into interspecific interactions involving the harlequin ladybird which have implications for species coexistence in invaded urban ecosystems. Findings highlight the importance of assessing indirect interspecific trophic interactions as they potentially affect a wider range of taxa than direct interspecific interactions.
The harlequin ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) was introduced to North America from Asia in the early 20th century as a biocontrol agent. In the late 20th century the beetle became invasive and has since spread to many countries on 4 continents, including Denmark. Evidence shows native European predatory insect species are negatively impinged by H. axyridis and there is concern that decline of native predatory insect populations may alter the regulating ecosystem service provided by these natural enemies.
This PhD thesis addressed both direct and indirect trophic interactions (i.e. predation and interspecific competition) between H. axyridis and Anthocoris nemoralis (Heteroptera: Anthocoridae), a European flower bug which shares habitat and prey with invasive H. axyridis in urban habitats. Laboratory assays illuminated the relative strengths of direct predation and interspecific competition, and possible effects thereof on predators. A field-based study using DNA gut-content analysis tested whether trophic interactions between co-occurring predators in urban arboreal habitats reflected findings from laboratory assays. In addition, infection of H. axyridis by naturally occurring entomopathogenic fungi and distribution of fungi in arboreal habitats was assessed. Finally, a laboratory study compared insect behaviour relevant to invasions between native/invasive H. axyridis populations.
Laboratory assays revealed a sublethal effect on A. nemoralis weight gain suggesting interspecific competition with H. axyridis is a stronger interaction for A. nemoralis than direct predation by H. axyridis. In urban arboreal habitats, DNA gut-content analysis revealed little direct predation by H. axyridis, but a high level of prey overlap between predators, thereby confirming the relative strengths of interspecific interactions among wild populations. Coupled with high temporal and spatial niche overlap of predators findings demonstrate that interspecific competition for prey by H. axyridis has the potential to affect local populations of native predatory insects whose habitat is invaded by H. axyridis. Five species of naturally occurring entomopathogenic fungi from three genera were distributed in arboreal habitats, however two of these genera were responsible for most fungi prevalence in H. axyridis. This suggests trees are a source of infection and entomopathogenic fungi may contribute to regulation of H. axyridis populations in invaded urban habitats. Finally, comparison of behaviours revealed that an invasive eastern North American and native Chinese population displayed greater dispersal activity than three other populations. Although an invasive/native dichotomy was not established, results suggest that trait differences may reflect population-level adaptions.
This PhD thesis contributes novel insights into interspecific interactions involving the harlequin ladybird which have implications for species coexistence in invaded urban ecosystems. Findings highlight the importance of assessing indirect interspecific trophic interactions as they potentially affect a wider range of taxa than direct interspecific interactions.
| Originalsprog | Engelsk |
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| Forlag | Department of Geosciences and Natural Resource Management, Faculty of Science, University of Copenhagen |
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| Status | Udgivet - 2014 |
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