Abstract:  Managed landscapes in which non‐native ornamental plants are favored over native vegetation now dominate the United States, particularly east of the Mississippi River. We measured how landscaping with native plants affects the avian and lepidopteran communities on 6 pairs of suburban properties in southeastern Pennsylvania. One property in each pair was landscaped entirely with native plants and the other exhibited a more conventional suburban mixture of plants—a native canopy with non‐native groundcover and shrubs. Vegetation sampling confirmed that total plant cover and plant diversity did not differ between treatments, but non‐native plant cover was greater on the conventional sites and native plant cover was greater on the native sites. Several avian (abundance, species richness, biomass, and breeding‐bird abundance) and larval lepidopteran (abundance and species richness) community parameters were measured from June 2006 to August 2006. Native properties supported significantly more caterpillars and caterpillar species and significantly greater bird abundance, diversity, species richness, biomass, and breeding pairs of native species. Of particular importance is that bird species of regional conservation concern were 8 times more abundant and significantly more diverse on native properties. In our study area, native landscaping positively influenced the avian and lepidopteran carrying capacity of suburbia and provided a mechanism for reducing biodiversity losses in human‐dominated landscapes.

Summary: The pattern of a few abundant species and many rarer species is a defining characteristic of communities worldwide. These abundant species are often referred to as dominant species. Yet, despite their importance, the term dominant species is poorly defined and often used to convey different information by different authors. Based on a review of historical and contemporary definitions we develop a synthetic definition of dominant species. This definition incorporates the relative local abundance of a species, its ubiquity across the landscape, and its impact on community and ecosystem properties. A meta‐analysis of removal studies shows that the loss of species identified as dominant by authors can significantly impact ecosystem functioning and community structure. We recommend two metrics that can be used jointly to identify dominant species in a given community and provide a roadmap for future avenues of research on dominant species. In our review, we make the case that the identity and effects of dominant species on their environments are key to linking patterns of diversity to ecosystem function, including predicting impacts of species loss and other aspects of global change on ecosystems.

The impact of non‐native plant invasions on ecosystems has been controversial because obvious local effects have not yet led to the global extinction of any native plant species on continents and large islands. We suggest that extinction is not the appropriate measure of impact on ecosystem function and present evidence that non‐native plant invasions or the replacement of native plants with non‐native ornamentals results in significant bottom‐up reductions of energy available for local food webs. Using replicated common gardens we compared Lepidoptera species richness and abundance on native plants, non‐native congeners of those natives, and non‐native species with no close relatives in the study area. Non‐native plants supported significantly fewer caterpillars of significantly fewer specialist and generalist species even when the non‐natives were close relatives of native host plants. However, the effect size was smaller in the latter category indicating phylogenetic similarity to local natives may positively impact herbivory. Cluster analysis revealed that a non‐native plant congener often supports a lepidopteran community that is a subset of the similar, but more diverse community found on its native congener. The proportion of the Lepidoptera community consisting of specialist species was about five times larger across native species within sites compared to non‐native plant species. In addition, species accumulation trajectories suggested that in a fully sampled community the differences between the Lepidoptera supported by native and non‐native plants may be even greater than presented here.

Humans promote and inhibit other species on the urban landscape, shaping biodiversity patterns. Institutional racism may underlie the distribution of urban species by creating disproportionate resources in space and time. Here, we examine whether present‐day street tree occupancy, diversity, and composition in Baltimore, MD, USA, neighborhoods reflect their 1937 classification into grades of loan risk—from most desirable (A = green) to least desirable (D = “redlined”)—using racially discriminatory criteria. We find that neighborhoods that were redlined have consistently lower street tree α‐diversity and are nine times less likely to have large (old) trees occupying a viable planting site. Simultaneously, redlined neighborhoods were locations of recent tree planting activities, with a high occupancy rate of small (young) trees. However, the community composition of these young trees exhibited lower species turnover and reordering across neighborhoods compared to those in higher grades, due to heavy reliance on a single tree species. Overall, while the negative effects of redlining remain detectable in present‐day street tree communities, there are clear signs of recent investment. A strategy of planting diverse tree cohorts paired with investments in site rehabilitation and maintenance may be necessary if cities wish to overcome ecological feedbacks associated with legacies of environmental injustice.