Species In Urban Environments Research Articles

From patterns to emerging processes in mechanistic urban ecology

Rapid urbanization has become an area of crucial concern in conservation owing to the radical changes in habitat structure and loss of species engendered by urban and suburban development. Here, we draw on recent mechanistic ecological studies to argue that, in addition to altered habitat structure, three major processes contribute to the patterns of reduced species diversity and elevated abundance of many species in urban environments. These activities, in turn, lead to changes in animal behavior, morphology and genetics, as well as in selection pressures on animals and plants. Thus, the key to understanding urban patterns is to balance studying processes at the individual level with an integrated examination of environmental forces at the ecosystem scale.

Colonizing potential of Drosophilidae (Insecta, Diptera) in environments with different grades of urbanization

Modern environmental destruction through human action has had a big impact on biological diversity. In the Brazilian Cerrado, the second largest South American biome, more than 60% of the native vegetation has been devastated mainly due to anthropic activities. One of the consequences of these activities is the distinct dispersion patterns of endemic and colonizer species in urban environments. In this report we assess the colonizing potential of drosophilids in environments with different grades of urbanization, defined according to the vegetation cover, edifications and demographic density. We performed 12 monthly collections in the city of Brasilia, the capital of Brazil, which is located in the core region of the Cerrado. Although we identified 16 species, 90% of the 22,509 captured specimens were Zaprionus indianus, a species recently introduced in Brazil, and the cosmopolitan D. simulans. We captured all the exotic species that occur in the Biome, with the exception of D. kikkawai, but only 8 from the 25 endemic species that occur in natural sites around Brasilia. The abundance of four endemic species (D. nebulosa, D. sturtevanti, D. cardini and D. prosaltans) decreased as the grade of urbanization increased. D. immigrans, an exotic species, showed the opposite pattern. We concluded that most endemic species of Drosophilidae are not able to colonize the new environment represented by the city, and that some species of this family may detect not only environmental alteration, by their presence or absence, but also the grade of environmental disturbance, by their relative abundance.

Land use, scale, and bird distributions in the Phoenix metropolitan area

Most urban areas have land use maps, but these maps have not been used to explore whether land use categories affect bird distributions. We explored how land use, at 10 different scales, affected the distribution of bird species surveyed in the Phoenix metropolitan area during the breeding season. Based on vegetation cover and built structure, we randomly established 30, 1 km transects located in older residential neighborhoods, younger residential neighborhoods, remnant desert areas, and golf courses. Each transect was divided into five 200 m segments, and we surveyed transects between 1 May and 31 July 1998. From Maricopa Associations of Governments (MAG) land use data, we measured the amount of different land uses surrounding each segment from a small circular buffer, 100 m radius, to a large circular buffer, 2500 m radius. For each buffer area and species, we conducted multiple regressions between average bird counts and percent area represented by each land use category. Across all scales, results demonstrated that only 4 of 26 species had a significant coefficient of multiple determination >0.5 between average bird counts and land use. For most species, these results indicate that land use, as defined by MAG, has limited predictability on the number of birds found in an area. We hypothesize that the structural design of given area (e.g. quantity and types of trees planted) probably plays a primary role in affecting the distribution of most bird species in urban environments. Thus, regardless of land use designation, landscape design and management of an urban area may strongly influence whether an area is attractive to a given bird species.

Predation on artificial bird nests along an urban gradient: predatory risk or relaxation in urban environments?

Urbanization - the anthropogenic conversion of natural ecosystems into human-dominated ecosystems - has occurred on global scales. The human-dominated landscape presents particular challenges to researchers because the effects of urbanization on ecological processes are not well understood. We investigated the influence of urbanization on predation by conducting an artificial nest experiment along an urban gradient of six sites ranging from natural to urbanized ecosystems. Previous hypotheses suggest that predation pressures in urban environments will either 1) increase because of the high abundance of exotic species which act as predators or 2) decrease due to the lack of natural predators. To determine relative predation pressures among sites along the urban gradient, we monitored the fates of 16 artificial avian nests at each of the six sites for a total of 96 nests in each year (1996, 1997). We analyzed the dependency of nest fate (depredated or undisturbed) on intensity of urbanization (sites along the urban gradient), nest height (ground, above-ground), and year using loglinear models. The frequency of nest predation was strongly dependent on site along the urban gradient, indicating that urbanization intensity was an important determinant of nest fate. Predation pressure exhibited an overall decline from natural to urban sites in both years, suggesting that urban environments have low predation pressures relative to natural areas. The predatory relaxation in urban environments may partially explain the greater abundance of some species in urban environments, particularly urban exploiters such as european starlings Sturnis vulgaris. house sparrows Passer domesticus. and rock doves Columba livia.

Rare and endangered plants at Gateway National Recreation Area: a case for protection of urban natural areas

The diversity of native plant species in urban environments is usually overlooked when biodiversity levels are considered. Inventories of native plants reveal many to be rare species surviving the harsh conditions encountered in urban ecosystems. Knowledge of their existence and an inventory of their distribution will assist in maintaining these populations. Protection strategies for rare plant species are outlined for urban National Parks.

Observational learning in great, blue and marsh tits

Great tits ( Parus major L.), blue tits ( P. caeruleus) and marsh tits ( P. palustris) were compared with respect to their ability to learn food finding from other individuals. The great tits were more successful than the other two species. This seems to be related to difference in adaptability in the wild, where the great tit is the most successful of the three species in urban environments.