Urbanization-driven changes in web building and body size in an orb web spider

Area of Science:

• Ecology and Evolutionary Biology
• Animal Behavior
• Urban Ecology

Background:

• Environmental changes, such as urbanization, pose challenges to animal populations.
• Behavioral responses are crucial for population persistence, but can be constrained by traits like body size.
• The interplay between body size, behavior, and urbanization is not well understood.

Purpose of the Study:

• To investigate how urbanization influences the body size and web-building behavior of the garden spider, Araneus diadematus.
• To determine if behavioral responses to urbanization are constrained by body size.
• To explore the roles of plasticity and genetic selection in spider adaptation to urban environments.

Main Methods:

• Studied 63 populations of Araneus diadematus across varying urbanization intensities at local and landscape scales.
• Quantified web-building behavior (web surface, mesh width) and spider body size.
• Employed multivariate mixed modeling to analyze relationships between urbanization, body size, and web traits.

Main Results:

• Spiders were smaller in highly urbanized sites; web surface and mesh width decreased with local urbanization.
• Web surface increased with landscape-scale urbanization, potentially compensating for reduced prey availability.
• Behavioral responses (web traits) were not constrained by body size, showing independence across populations and scales.

Conclusions:

• Behavioral responses in size-dependent traits can be decoupled from body size changes, enabling adaptation to novel urban environments.
• Responses suggest a combination of genetic adaptation (web investment) and plasticity (mesh width) across spatial scales.
• Despite reduced fecundity, stable spider abundance indicates overall successful population-level adaptation to urbanization.