Examining the effects of urbanization on arthropods communities within urban gardens and pocket prairies in Grand Rapids, Michigan (USA)

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Garrett Maher, Graham Johnson and Justin D. Burdine, Kinesiology and Science, Cornerstone University, Grand Rapids, MI

Background/Question/Methods
Arthropod populations are declining globally, and human-modification of natural habitat is a primary driver of these declines. However, there is growing evidence that cities may provide refugia to arthropod populations thus maintaining diverse communities. We investigated the abundance, diversity, and evenness of arthropod communities within 16 urban greenspaces across metropolitan Grand Rapids, Michigan (USA) in 2020. Our research aimed to understand how urbanization impacts particular arthropod orders. We focused our efforts on urban gardens and pocket prairies and measured a vast array of predictor variables at each site (impervious surface, distance to city center, site area, site perimeter, temperature, humidity, total flower abundance, yellow flower abundance, purple flower abundance). The sample collection was performed using colored bowls (blue, yellow, white) of multiple sizes (175mL and 350mL). Twelve bowls of each size were placed across the site for collection, and each site was sampled in June and July 2020. Data were analyzed using permanova and generalized linear mixed-effects models in R.
Results/Conclusions
We collected 5,657 arthropods that span 13 taxonomic orders. Two variables were associated with the structure of arthropod community composition: impervious surface (F₁,₇ = 5.39, p < 0.01, at α = 0.05) and yellow flower abundance (F₁,₇ = 3.09, p = 0.04, at α = 0.05). Additionally, arthropod diversity was negatively associated with impervious surface (F₁,₅ = 3.43, p = 0.01, at α .05). These results suggest that expanding greenspace availability within cities may benefit arthropod communities by reducing the negative impacts of impervious surface. Furthermore, supplementing floral resources (particularly yellow flowers) may benefit arthropods that perform critical ecosystem services. Overall, understanding the impacts urbanization has on arthropod communities can inform development decisions in growing urban centers that resemble Grand Rapids, Michigan (USA).