Consumer resource matching in urbanizing landscapes: are synanthropic species over-matching?

Population responses of synanthropic species to urbanization may be explained by the resource-matching rule, which postulates that individuals should distribute themselves according to resource availability. According to the resource-matching rule, urban habitats will contain greater densities if they provide better resources than rural habitats. However, because resource availability is density dependent, individuals in urban areas would ultimately achieve fitness levels comparable to, but no better than, individuals in less urban areas. Some ecologists suggest that synanthropic birds may not conform to the resource-matching rule and may instead overmatch (i.e., overexploit) in urban habitats, ultimately leading to lower fitness despite greater resource levels. Using the Northern Cardinal (Cardinalis cardinalis) as a focal species, we evaluated if Cardinal populations in urban and rural habitats were consistent with predictions of consumer resource matching. During 2003-2006 we documented population density, adult body condition, apparent survival, and annual reproductive productivity of Cardinals in riparian forest stands within urban (n = 8 stands) and rural (n = 6 stands) landscapes in Ohio, USA. Density of Cardinals in urban forests was four times that found in more rural forests. Mark-resight data from 147 males and 125 females over four years indicated that apparent survival rates were similar between urban and rural landscapes (phi = 0.64, SE = 0.039 for males and phi = 0.57, SE = 0.04 for females). Similarly, body condition indices of 168 males, 142 females, and 118 nestlings did not differ significantly between landscapes. Annual reproductive productivity (mean number of fledglings per pair over breeding season) of 294 pairs was comparable for urban (2.4 +/- 0.18 [mean +/- SE] and rural (2.1 +/- 0.18) young birds. Thus, contrary to recent suggestions, we find that high densities of certain synanthropic species in urban landscapes are consistent with expectations of consumer resource matching.     

Dynamic selective environments and evolutionary traps in human-dominated landscapes

Human activities can alter selective environments in ways that can reduce the usefulness of certain ornamental traits as honest signals of individual quality and, in some cases, may create evolutionary traps, where rapid changes in selective environments result in maladaptive behavioral decisions. Using the sexually dichromatic, socially monogamous Northern Cardinal (Cardinalis cardinalis) as a model, we hypothesized that urbanization would erode the relationship between plumage coloration and reproductive success. Because the exotic Amur honeysuckle (Lonicera maackii) provides carotenoids, is a preferred habitat attribute, and increases vulnerability to nest predation, we predicted the presence of an evolutionary trap, whereby the brightest males would achieve the lowest reproductive success. Working at 14 forests in Ohio, USA, 2006-2008, we measured plumage color, monitored reproduction, and quantified habitat within territories. In rural landscapes, the brightest males bred earliest in the season and secured more preferred territories; however, annual reproduction declined with plumage brightness. Coloration of urban males was not associated with territory attributes or reproduction. Female redness across all landscapes was negatively related to reproduction. Poor reproductive performance of otherwise higher-quality males probably resulted from preferences for honeysuckle, which reduces annual reproduction when used as a nesting substrate early in the season. In this way, exotic shrubs prompted an evolutionary trap that was avoided in urban forests where anthropogenic resources disassociated male color and reproductive phenology and success. Our study illustrates how modified selective environments in human-dominated landscapes might shape microevolutionary processes in wild bird populations.