Intraspecific variation shapes community‐level behavioral responses to urbanization in spiders

Abstract

Urban areas are an extreme example of human-changed environments, exposing organisms to multiple and strong selection pressures. Adaptive behavioral responses are thought to play a major role in animals' success or failure in such new environments. Approaches based on functional traits have proven especially valuable to understand how species communities respond to environmental gradients. Until recently, they have, however, often ignored the potential consequences of intraspecific trait variation (ITV). When ITV is prevalent, it may highly impact ecological processes and resilience against stressors. This may be especially relevant in animals, in which behavioral traits can be altered very flexibly at the individual level to track environmental changes. We investigated how species turnover and ITV influenced community-level behavioral responses in a set of 62 sites of varying levels of urbanization, using orb web spiders and their webs as models of foraging behavior. ITV alone explained around one-third of the total trait variation observed among communities. Spider web structure changed according to urbanization, in ways that increase the capture efficiency of webs in a context of smaller urban prey. These trait shifts were partly mediated by species turnover, but ITV increased their magnitude, potentially helping to buffer the effects of environmental changes on communities. The importance of ITV varied depending on traits and on the spatial scale at which urbanization was considered. Despite being neglected from community-level analyses in animals, our results highlight the importance of accounting for intraspecific trait variation to fully understand trait responses to (human-induced) environmental changes and their impact on ecosystem functioning.

Where Have All the Spiders Gone? Observations of a Dramatic Population Density Decline in the Once Very Abundant Garden Spider, Araneus diadematus (Araneae: Araneidae), in the Swiss Midland

“…observations). Interestingly, while other orb-weaver species-especially the larger ones-showed dramatic declines in both abundance and species richness along an urbanization gradient [59,60], A. diadematus was found to reach similar low densities across this land-use gradient. In other words, local densities at spatial scales of approx.…”

Where have all the spiders gone? Observations of a dramatic population density decline in the once very abundant garden spider,Araneus diadematus(Araneae: Araneidae), in the Swiss midland

“…Interestingly, while other orb-weaver speciesespecially the larger onesshowed dramatic declines in both abundance and species richness along an urbanisation gradient [53,54], A. diadematus was found to reach similar low densities across this land-use gradient. Or put conversely, local densities at spatial scales of approximately 100 km were alarmingly low in both the more natural and human impacted regions, demonstrating regional declines beyond the scale of local land-use.…”

Guiding lights: Foraging responses of juvenile nocturnal orb‐web spiders to the presence of artificial light at night

“…Orb‐web spiders may shift web decorating behaviours and web width in response to ambient illumination containing UV wavelengths (Elgar et al, ), although behavioural responses to LED lights, which lack UV light, are untested. Dahirel, Dierick, Cock, and Bonte () found that spiders alter their web architecture to increase prey capture rates in response to shifts in the types of prey available in urban areas. However, they did not investigate such shifts in relation to artificial lights, which alter insect community composition (Davies, Bennie, & Gaston, ), and hence prey availability.…”