Reproductive trait differences drive offspring production in urban cavity-nesting bees and wasps
Marco Moretti1, Simone Fontana1,2, Kelly A Carscadden3
1Biodiversity and Conservation Biology Swiss Federal Research Institute WSL Birmensdorf Switzerland.
Ecology and Evolution
|August 9, 2021
Summary
Urban biodiversity requires understanding reproductive success. This study found that evenness in reproductive traits, not environmental factors, best predicts offspring production in bees and wasps, suggesting diverse strategies reduce competition.
Area of Science:
- Urban ecology
- Insect reproductive biology
- Biodiversity science
Background:
- Urbanization causes complex biodiversity changes, necessitating mechanistic understanding of community assembly.
- Organismal reproductive success is crucial for population persistence and biodiversity maintenance in urban environments.
- Individual-level reproductive traits offer insights into environmental drivers, offspring production, and urban biodiversity.
Purpose of the Study:
- To investigate how reproductive traits, trait diversity, and offspring production respond to urban environmental variables.
- To determine if reproductive trait variation explains offspring production by reflecting trade-offs between resource acquisition and parasite exposure.
- To link individual reproductive strategies to broader patterns of urban biodiversity.
Main Methods:
- Studied cavity-nesting solitary bees and wasps over three years in four urban green space types in Toronto, Canada.
- Measured nest reproductive traits: total brood cells, parasite-free cells, and parasite-free non-emerged brood cells.
- Analyzed responses of reproductive traits and offspring production to environmental variables and trait variation.
Main Results:
- Environmental variables poorly predicted mean reproductive traits, trait diversity, and offspring production.
- Offspring production strongly correlated positively with reproductive trait evenness and negatively with trait richness and divergence.
- Reproductive trait variation showed insensitivity to urbanization gradients, diverging from typical biodiversity patterns.
Conclusions:
- A narrow range of reproductive traits appears optimal for reproduction, with even distribution of traits potentially reducing competition.
- Selection may favor diverse reproductive strategies to enhance resilience and reduce inter-species competition in urban settings.
- The disconnect between reproductive trait variation and urbanization gradients questions the role of habitat mosaics and biodiversity metric consistency in cities.
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