Interactions among non-native plants and birds

Abstract

Abstract:Humans have introduced many non-native plants into urbanizing landscapes. In numerous cases, the dispersal and establishment of non-native plants are facilitated by birds. We have reviewed documented relationships between birds and non-native plants with specific attention to the urbanizing environment. Birds consume fruits and disperse seeds of non-native plants.They may also increase seed production or plant/seed survival by pollinating non-native plant species or consuming insect predators, respectively. Some avian frugivores facilitate the spread of, and benefit from, non-native plant species. In contrast, some avian nectarivores and insectivores have evolved mutual isms with specific plants and have been negatively influenced by the spread of competing, non-native plants. We enumerate the characteristics of successful, avian-dispersed fruit displays, and then highlight conditions in the urbanizing landscape that influence avian community structure and the spread of non-native plants. Finally, we discuss how these characteristics should influence management decisions and future research directions. INTRODUCTIONHorticultural introductions bring plants across physical barriers to areas of potentially suitable habitat. Having thus overcome geographical barriers to invasion, horticultural plants need only an effective means of dispersal to become naturalized and possibly invasive (Kruger et at. 1986). Birds play an important role in the dispersal of many non-native horticultural plant species from human-altered environments (White and Stiles 1992). 180Chapter 9 movement of diaspores over large distances, and by a high probability that diaspores will be deposited in microenvironments suitable for germination and survival (Proctor 1968, Howe andSmallwood 1982).Some birds enhance non-native plant dispersion and may, in turn, be affected by the resulting plant community depending on their feeding guild and habitat use. Frugivores and omnivores may benefit widely from and, in some cases, facilitate the spread of non-native plant species.Frugivorous and omnivorous birds are often generalists who prove quite able to incorporate new fruit types into their diet (MacDonald 1986). Relationships between granivorous or nectarivorous birds and plants often evolve more closely; thus, non-native plants that rely on avian dispersal of seeds or pollen appear to be less likely to find suitable dispersers in non-native habitat (Stiles 1989). Similarly, non-native plants that displace native vegetation are more likely to negatively affect granivores and nectarivores than frugivorous birds (Breytenbach 1986). There have been notable exceptions, however, in which non-native horticultural plants with showy flowers have been utilized by nectarivorous birds (Waterhouse 1997).Insectivorous birds also can influence the spread of non-native plants through predation on herbivorous insects, but because their effect is mediated by other organisms, the influences of insectivorous birds on plants is usually not as ecologically salient a...

Nest Predation in an Urbanizing Landscape:the Role of Exotic Shrubs

“…Although exotic shrubs in the natural nest study did not appear to negatively impact nest success in rural landscapes, results from the artificial nest experiment indicate that exotic shrubs in rural landscapes can still reduce nest success. Several other studies also have suggested that exotic plants negatively affect avian communities by altering species abundance (Anderson et al 1977, Braithwaite et al 1989, Mills et al 1989, Rottenborn 1997, Germaine et al 1998, Benoit and Askins 1999, species guilds (Hunter et al 1988, Fraser and Crowe 1990, Ellis 1995, brood parasitism rates (Anderson et al 1977, Reichard et al 2001, and nest success (Schmidt andWhelan 1999, Remes 2003). Few of these studies, however, measured other local and landscape variables (e.g., distance from edge and surrounding land uses), potentially confounding their results.…”

“…It is critical that ecologists and land managers understand the interactions among exotic plants and wildlife species, especially as exotic plants become more prevalent (Reichard et al 2001, Zavaleta et al 2001, Byers et al 2002. This study was the first to demonstrate that exotic shrubs can negatively impact avian nest success while explicitly accounting for both distance from edge and the landscape matrix.…”

“…14,No. 6 Exotic plants likely impact songbirds in more ways than just nest success (Braithwaite et al 1989, Fraser and Crowe 1990, Reichard et al 2001, Renne et al 2002 however, not all of these effects are negative. For example, fruit-producing exotic shrubs may be important food resources for migrating and overwintering passerines, especially in areas lacking native fruits (Reichard et al 2001).…”

“…Associations between the landscape matrix and invasion have important implications because exotic shrubs may reduce nesting success and abundance of birds that are already vulnerable due to urbanization and habitat degradation (Mills et al 1989, Germaine et al 1998, Rottenborn 1999, Schmidt and Whelan 1999, Donovan and Flather 2002, Remes 2003. Unfortunately, little empirical data exists to assess how these interactions affect nest success (D'Antonio et al 2001, Reichard et al 2001, Byers et al 2002. Schmidt and Whelan (1999) provided the first evidence that exotic shrubs negatively affect nest success of forest birds in one Chicago area woodlot.…”

Do Highly Modified Landscapes Favour Generalists at the Expense of Specialists? An Example using Woodland Birds

“…Habitat fragmentation may also be more severe than is apparent from the presence of physical gaps alone. Many semi-natural habitats, especially parks and gardens, are dominated by exotic plant species which may support few invertebrates and hence create functional foraging gaps for higher taxa such as birds (Reichard et al, 2001). Exotic plant species may also present birds and other animals with phenological gaps -even if they support significant invertebrate populations, their timing of flowering or leafing may be inappropriate for native species.…”