■ Abstract The literature on effects of habitat fragmentation on biodiversity is huge. It is also very diverse, with different authors measuring fragmentation in different ways and, as a consequence, drawing different conclusions regarding both the magnitude and direction of its effects. Habitat fragmentation is usually defined as a landscape-scale process involving both habitat loss and the breaking apart of habitat. Results of empirical studies of habitat fragmentation are often difficult to interpret because (a) many researchers measure fragmentation at the patch scale, not the landscape scale and (b) most researchers measure fragmentation in ways that do not distinguish between habitat loss and habitat fragmentation per se, i.e., the breaking apart of habitat after controlling for habitat loss. Empirical studies to date suggest that habitat loss has large, consistently negative effects on biodiversity. Habitat fragmentation per se has much weaker effects on biodiversity that are at least as likely to be positive as negative. Therefore, to correctly interpret the influence of habitat fragmentation on biodiversity, the effects of these two components of fragmentation must be measured independently. More studies of the independent effects of habitat loss and fragmentation per se are needed to determine the factors that lead to positive versus negative effects of fragmentation per se. I suggest that the term “fragmentation” should be reserved for the breaking apart of habitat, independent of habitat loss.

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Effects of Habitat Fragmentation on Biodiversity

Urban areas are hot spots that drive environmental change at multiple scales. Material demands of production and human consumption alter land use and cover, biodiversity, and hydrosystems locally to regionally, and urban waste discharge affects local to global biogeochemical cycles and climate. For urbanites, however, global environmental changes are swamped by dramatic changes in the local environment. Urban ecology integrates natural and social sciences to study these radically altered local environments and their regional and global effects. Cities themselves present both the problems and solutions to sustainability challenges of an increasingly urbanized world.

http://leml.asu.edu/jingle/web_pages/wu_pubs/pdf_files/grimm_etal-2008-gc+ecology of cities.pdf

Global Change and the Ecology of Cities

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

Climate Change 2007: The Physical Science Basis.

▶ Addresses a wide range of timely environment, economic and energy topics ▶ A forum to review, analyze and stimulate the development, testing and implementation of mitigation and adaptation strategies at regional, national and global scales ▶ Contributes to real-time policy analysis and development as national and international policies and agreements are discussed and promulgated ▶ 94% of authors who answered a survey reported that they would definitely publish or probably publish in the journal again

Mitigation and Adaptation Strategies for Global Change

Landscape modification and habitat fragmentation are key drivers of global species loss. Their effects may be understood by focusing on: (1) individual species and the processes threatening them, and (2) human-perceived landscape patterns and their correlation with species and assemblages. Individual species may decline as a result of interacting exogenous and endogenous threats, including habitat loss, habitat degradation, habitat isolation, changes in the biology, behaviour, and interactions of species, as well as additional, stochastic threats. Human-perceived landscape patterns that are frequently correlated with species assemblages include the amount and structure of native vegetation, the prevalence of anthropogenic edges, the degree of landscape connectivity, and the structure and heterogeneity of modified areas. Extinction cascades are particularly likely to occur in landscapes with low native vegetation cover, low landscape connectivity, degraded native vegetation and intensive land use in modified areas, especially if keystone species or entire functional groups of species are lost. This review (1) demonstrates that species-oriented and pattern-oriented approaches to understanding the ecology of modified landscapes are highly complementary, (2) clarifies the links between a wide range of interconnected themes, and (3) provides clear and consistent terminology. Tangible research and management priorities are outlined that are likely to benefit the conservation of native species in modified landscapes around the world.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1466-8238.2007.00287.x

Landscape modification and habitat fragmentation: a synthesis

Forest fragmentation, the disruption in the continuity of forest habitat, is hypothesized to be a major cause of population decline for some species of forest birds because fragmentation reduces nesting (reproductive) success Nest predation and parasitism by cowbirds increased with forest fragmentation in nine midwestern (United States) landscapes that varied from 6 to 95 percent forest cover within a 10-kilometer radius of the study areas Observed reproductive rates were low enough for some species in the most fragmented landscapes to suggest that their populations are sinks that depend for perpetuation on immigration from reproductive source populations in landscapes with more extensive forest cover Conservation strategies should consider preservation and restoration of large, unfragmented "core" areas in each region

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Regional Forest Fragmentation and the Nesting Success of Migratory Birds

Ecological processes neat" habitat edges often differ from processes away fromedges. Yet, the generality of "edge effects" has been hotly debated because results vary tremendously. To understand the factors responsible for this variation, we described nest predation and cowbird distribution patterns in forest edge and forest core habitats on 36 randomly selected plots in three states in the midwestern United States. We tested four hypotheses that may explain the variation and mechanisms responsible for edge effects - among the 36 plots: (1) the landscape context, (2) the local predator community, (3) the local bird (host-prey) community, and (4) the nest site microhabitat structure. We used artificial nests baited with quail and clay eggs to determine nest predation patterns and " predators and used point count surveys to determine cowbird and host abundance in forest edge and forest core habitats. Raccoons, Opossums, canids, and birds accounted for most predation of artificial nests. Neither local host abundance nor mean nest concealment of artificial nests significantly •influenced nest predation rates in habitat edge or in habitat core. Nest predation was sig- nificantly greater in highly fragmented landscapes than in unfragmented landscapes and was significantly higher in edge habitats than in core habitats. However, detection of edge effects varied, depending upon landscape type. Higher predation rates in edge habitats were detected in highly and moderately fragmented landscapes, but not in unfragmented land- , , s.capes. Both mammalian and avian predator groups contributed to higher predation rates along edges in highly and moderately fragmented landscapes. ,Cowbird abundance was significantly related to host abundance, but the effect of hosts varied depending upon habitat type. In edge habitats, cowbird abundance was negatively associated with host abundance in all three landscapes studied. By contrast, cowbird abun- dance was positively associated with host abundance in core habitats. Once the effects of host abundance were removed, cowbird abundance in core habitat was greater in highly fragmented landscapes than in moderately and unfragmented landscapes, but did not differ between the latter two. In edge habitat, cowbird abundance did not differ between land- scapes, but abundance in edges tended to be highest in the highly fragmented landscape and lowest in the unfragmented landscape. Cowbird abundance did not vary between edge and core habitat in any of the landscapes studied. We suggest that the first approximation to predicting the impact of agricultural or permanently managed edges on forest songbird reproductive success is to assess habitat characteristics at the landscape scale. Given geographic location, local factors such as host abundance and predator composition should be assessed.

https://www.nrs.fs.fed.us/pubs/jrnl/1997/nc_1997_Donovan_001.pdf

Variation in Local-Scale Edge Effects: Mechanisms and landscape Context

Population declines of many avian species are often attributed to increased rates of nest predation in fragmented landscapes, yet mechanisms underlying these effects have rarely been examined. We reviewed the literature to determine the extent to which hypotheses about nest predators and fragmentation have been invoked and compared this to the number of direct tests of predators with respect to habitat edge, patch size, or landscape type. We also conducted a meta-analysis of tested predator effects to evaluate whether predator responses—numerical, functional, or species richness—to fragmentation depend on spatial scale (edge, patch, or landscape), landscape type, geographic region, or predator taxa. We found 120 papers containing hypoth- eses about nest predators and fragmentation, but only 31 with hypothesis tests. Most tests were of a single predator species or guild, whereas most cited hypotheses generalized across broader taxonomic groups. Re- sults of predator tests were variable, but some general patterns were evident. Predator effects, including in- creased abundance, activity, or species richness in edges, small patches, or certain landscapes, were more prevalent (1) in tests conducted at the landscape scale than at the local scale, (2) in agricultural landscapes than in predominantly forested landscapes, (3) in certain biogeographic regions, and (4) for avian predators than for mammalian predators. Local-scale (edge and patch) effects were most common when the land sur- rounding patches was agricultural and when tests were conducted within agricultural landscapes. The re- sponse of nest predators to fragmentation is complex, taxon-specific, and context-dependent. Conservation ef- forts for declining avian species may therefore need to be customized according to the nest-predator species primarily responsible for local nest mortality and the nature of the landscape mosaic.

/pdf/nest-predators-and-fragmentation-a-review-and-meta-analysis-2bqkkp6yph.pdf

Nest Predators and Fragmentation: a Review and Meta-Analysis

Fragmentation of breeding habitat in North America has been implicated in the decline of forest-nesting, Neotropical migrant birds. We used a comparative approach to examine the effects of fragmentation on three forest-nesting migrants: Ovenbird (Seiurus aurocapillus), Red-eyed Vireo (Vireo ofivaceus), and Wood Thrush (Hylocichla mustelina). We surveyed birds and monitored reproductive success on 28 study plots in fragmented and contiguous forests in two midwestern regions. Distribution of individuals between fragmented and contiguous forests appeared to vary among species and regions, but total nest failure was significantly higher in fragments than contiguous forests in both regions for all species (p = 0.053). We attributed greater nest failure to increased nest predation (p = O. 093) and increased brood parasitism by the Brownheaded Cowbird (Molothrus ater, p = 0. 009). In addition to greater total nest failure, partial nest failure due to cowbird parasitism led to a reduction in the number of host fledglings. Although the causes of nest mortality appeared to be species specific, total nest failure and partial nest failure acted in concert to reduce the number of offspring per adult for all three species on fragments. We used simple population growth models to assess the viabaity of the three species in fragmented and contiguous habitats in both regions. In general, populations on fragments appeared to be population sinks and populations on continguous forests appeared to be population sources. Assuming constant mortality during winter, projected growth indicated that without immigration Ovenbird and Red-eyed Vireo populations should become extinct on fragments in both regions and Wood Thrush populations should be maintained or slightly decline on fragments. Populations of all three species should increase in contiguous habitats in both regions without emigration. We suggest that habitat fragmentation reduces local reproduction and may have ramifications for the entire population. A clear understanding of population demography depends on examination of demographic dynamics within and among sources and sinks. We emphasize that the long-term viability of these species depends on maintaining large tracts of forest throughout the breeding range until the spatial scale at which source and sink populations interact can be determined.

https://www.nrs.fs.fed.us/pubs/jrnl/1995/nc_1995_Donovan_001.pdf

Reproductive Success of Migratory Birds in Habitat Sources and Sinks

▪ Abstract Natural ecological disturbance creates habitats that are used by diverse groups of birds. In North America, these habitats or ecosystems include grasslands or prairies, shrublands, savannas, early successional forests, and floodplains. Whereas the extent of all natural habitats has diminished significantly owing to outright loss from agriculture and development, the suppression of disturbance by agents such as fire and flooding has led to further losses. Accordingly, the abundances of many bird species adapted to disturbance-mediated habitats have declined as well. In North America, these declines have been more severe and common than those of species associated with less frequently disturbed habitats such as mature or closed-canopy forests. Field studies consistently reveal the direct role of disturbance and successional processes in structuring avian habitats and communities. Conservation strategies involving the management of disturbance through some combination of flooding, application of f...

https://www.jstor.org/stable/info/2678641

Frank R. Thompson

Papers

Regional Forest Fragmentation and the Nesting Success of Migratory Birds

Variation in Local-Scale Edge Effects: Mechanisms and landscape Context

Nest Predators and Fragmentation: a Review and Meta-Analysis

Reproductive Success of Migratory Birds in Habitat Sources and Sinks

The role of disturbance in the ecology and conservation of birds