Urban Environments Aid Invasion of Brown Widows (Theridiidae: Latrodectus geometricus) in North America, Constraining Regions of Overlap and Mitigating Potential Impact on Native Widows

Abstract

Urbanization is a major cause of biotic homogenization and habitat fragmentation for native communities. However, the role of urbanization on the success of biological invasions on a continental scale has yet to be explored. Urbanization may facilitate the establishment success of invasive species by minimizing niche differentiation between native and invaded ranges. In such cases, we might expect anthropogenic variables to have stronger influence on the geographic distribution of invasive compared to native populations. In this study, we use ecological niche modeling to define the distribution of non-native brown widow spider (Latrodectus geometricus) and three native black widows (L. hespersus, L. mactans, L. variolus) in North America and gauge the importance of urbanization on the geographic ranges of widows at a continental scale. We also quantify the geographic overlap of L. geometricus with each native widow to assess potential species and regions at risk of ecological impact. Consistent with our hypothesis, we find that the distribution of L. geometricus is strongly constrained to urban environments, while native widow distributions are more strongly driven by climatic factors. These results show that urbanization plays a significant role in facilitating the success of invasion, weakening the significance of climate on the realized niche in its invaded range.

Climatic niche overlap models reveal niche partitioning among black widow spiders and potential ecological impacts of invasive brown widows in North America

“…We have previously demonstrated that human population density was an important predictor of the North American distribution of brown widows, but not as strong a predictor for native widows (Sadir and Marske 2021), concurring with previous studies that have shown a preference for human-associated habitats in brown widows (Muller 1993, Vetter et al 2012a. Where diet and habit niche partitioning do not occur, differences in climatic niche may facilitate geographic partitioning among species.…”

“…A previous study found that L. geometricus favors subtropical climates, and its global climatic niche is best predicted by mean annual temperature and precipitation (Taucare-Rios et al 2016), which most closely matches the climate L. mactans occupies in North America. We also previously found that L. geometricus geographically overlaps with L. hesperus and L. mactans across North America (Sadir and Marske 2021), suggesting the potential for competitive interactions with brown widows to impact native populations in these areas. Although geographic overlap is a useful measurement of co-occurrence, we did not measure climatic niche overlap.…”

“…We found that these two species do not overlap climatically either, making the risk of ecological impact on L. variolus minimal. On the other hand, we found that L. geometricus' climatic niche strongly overlaps with those of L. mactans and L. hesperus, two species that share significant parts of its current distribution (Sadir & Marske 2021). Interestingly, the most important variables for predicting niche overlap between species were similar between invasive/ native and native/native species interactions (Table 1).…”

“…However, L. geometricus' preference for urban habitats may limit potential impact on non-urban widow populations: differences in diet or microhabitats, such as an apparent preference for human-made structures as web-building sites (Vetter et al 2016), might allow L. geometricus to co-occur with L. hesperus and L. mactans despite climatic niche overlap. Our previous work has also shown that L. geometricus prefers urban environments over non-urban environments, in contrast to their native congeners (Sadir and Marske 2021). Given the dietary plasticity L. mactans displays in urban and agricultural populations, where it feeds on invasive fire ants (Nyffeler et al 1988), this species may also be less impacted by L. geometricus than predicted by geographic and niche overlap.…”

An expert-curated global database of online newspaper articles on spiders and spider bites

“…Also, recent niche modelling studies have shown that internet-derived distribution data can be useful for mapping the predicted distribution of spiders (reviewed in ref. 53 ), especially species that are easily identified in the field or by photos 54 – 57 . For some of the most abundant species in our database (e.g., Loxosceles spp.…”