Urban yards have a large potential for providing habitat, and important considerations when studying these spaces are the tritrophic interactions between plant species, herbivores, and predators. Dr. Marion Dresner, Professor at Portland State University, has spent years studying these interactions in backyard habitats and is particularly interested in understanding how the management of backyards provides food for birds. In her 2019 IUWC talk, she synthesized her past studies that have examined these relationships.
Dr. Dresner mentioned that most Pacific Northwest birds feed their young arthropods, and due to this the presence of shrubs is important in yards because these plants provide both structural concealment and food for arthropods. Her lab has performed both malaise trapping and branch beating to investigate arthropod abundance and diversity in Portland gardens.
Malaise trapping proved to be the most effective method to investigate what arthropods are found in these urban gardens. She discovered that some shrubs were better for native caterpillars and that there was no difference between the presence of native vs. ornamental shrubs – many species of both were productive for arthropods. Dr. Dresner did note that many of the sampled arthropods are non-native species, so co-evolution between native plants and native arthropods may not have played a large roll in these systems. Finally, spider abundance was found to decrease with distance from green space, highlighting the roll geography plays in urban species distribution.
A recent study investigated asked homeowners to record bird sightings in their yard twice a week, recording bird behavior (behavior signaling nesting or residency received a higher score than transient behavior), as this is a better way to assess an area’s ecological value to birds than simply sampling arthropods.
Dr. Dresner has found that arthropod and bird abundance and richness are both correlated, and that tree cover significantly explains bird species richness in urban yards. Similar results have been found by her colleague, Dr. Andy Gibbs, who found a strong relationship between trees and birds. Dr. Dresner’s research gives urban ecologists and land managers insights on the drivers of arthropod and bird abundance in urban backyards and highlights the importance of providing shrubs and tree cover as habitat in our growing cities.
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