Oxygen isotopic compositions of asteroidal materials returned from Itokawa by the Hayabusa mission     

Yurimoto H  Abe K  Abe M  Ebihara M  Fujimura A  Hashiguchi M  Hashizume K  Ireland TR  Itoh S  Katayama J  Kato C  Kawaguchi J  Kawasaki N  Kitajima F  Kobayashi S  Meike T  Mukai T  Nagao K  Nakamura T  Naraoka H  Noguchi T  Okazaki R  Park C  Sakamoto N  Seto Y  Takei M  Tsuchiyama A  Uesugi M  Wakaki S  Yada T  Yamamoto K  Yoshikawa M  Zolensky ME 《Science (New York, N.Y.)》2011,333(6046):1116-1119

Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.  相似文献   

The historic influence of dams on diadromous fish habitat with a focus on river herring and hydrologic longitudinal connectivity     

Carolyn J. Hall  Adrian Jordaan  Michael G. Frisk 《Landscape Ecology》2011,26(1):95-107

The erection of dams alters habitat and longitudinal stream connectivity for migratory diadromous and potamodromous fish species and interrupts much of organismal exchange between freshwater and marine ecosystems. In the US, this disruption began with colonial settlement in the seventeenth century but little quantitative assessment of historical impact on accessible habitat and population size has been conducted. We used published surveys, GIS layers and historical documents to create a database of 1356 dams, which was then analyzed to determine the historical timeline of construction, use and resultant fragmentation of watersheds in Maine, US. Historical information on the anadromous river herring was used to determine natural upstream boundaries to migration and establish total potential alewife spawning habitat in nine watersheds with historic populations. Dams in Maine were constructed beginning in 1634 and by 1850 had reduced accessible lake area to less than 5% of the virgin 892 km² habitat and 20% of virgin stream habitat. There is a near total loss of accessible habitat by 1860 that followed a west-east pattern of European migration and settlement. Understanding historic trends allows current restoration targets to be assessed and prioritized within an ecosystem-based perspective and may inform expectations for future management of oceanic and freshwater living resources.  相似文献   

Weak effect of edges on avian nesting success in fragmented and forested landscapes in Ontario,Canada     

Karla J. Falk  Erica Nol  Dawn M. Burke 《Landscape Ecology》2011,26(2):239-251

We studied the effects of anthropogenic edges on predation and parasitism of forest bird nests in an agriculturally fragmented landscape and a continuously forested landscape in Ontario, Canada. Nesting data were collected at 1937 nests across 10 species in the fragmented landscape from 2002–2008, and 464 nests across 4 species in the continuously forested landscape from 2006–2008. Brood parasitism only occurred in the fragmented landscape, and was positively related to the proportion of rural grassland and row crop habitats within 500-m of nests. Daily nest survival was negatively related to the density of roads within 500-m of nests in the fragmented landscape, but was not influenced by distance to anthropogenic edge in either landscape. Predation rates were higher in the fragmented landscape for Ovenbird and Rose-breasted Grosbeak nests, but did not differ between landscapes for Veery and American Redstart nests. Uniformly high predation in the fragmented landscape may be a result of (1) matrix predators that penetrate deep (>300 m) into the forest interior, or (2) the additive effect of forest-dependent and matrix-associated predators that results in high predation pressure in both edge and interior habitats. Further research focused on the identification of nest predators, their population dynamics, and habitat use is required to understand the underlying mechanisms leading to uniformly high nest predation in fragmented landscapes.  相似文献   

Population genetic structure and landscape connectivity of the Eastern Yellowbelly Racer (<Emphasis Type="Italic">Coluber constrictor flaviventris</Emphasis>) in the contiguous tallgrass prairie of northeastern Kansas,USA     

Page E. Klug  Samantha M. Wisely  Kimberly A. With 《Landscape Ecology》2011,26(2):281-294

The tallgrass prairie of North America has undergone widespread habitat loss and fragmentation (<4% remains). The Flint Hills region of Kansas and Oklahoma is the largest tallgrass prairie remaining and therefore provides an opportunity to study the population genetic structure of grassland species in a relatively contiguous landscape and set a baseline for evaluating changes when the habitat is fragmented. We adopted a landscape genetics approach to identify how landscape structure affected dispersal, population genetic structure, and landscape connectivity of the Eastern Yellowbelly Racer (Coluber constrictor flaviventris) across a 13,500-km² landscape in northeastern Kansas, USA. The racer population had high allelic diversity, high heterozygosity, and was maintaining migration-drift equilibrium. Autocorrelation between genetic and geographic distance revealed that racers exhibited restricted dispersal within 3 km, and isolation-by-distance. Significant isolation-by-distance occurred at broad regional scales (>100 km), but because of sufficient gene flow between locations, we were unable to define discrete subpopulations using Bayesian clustering analyses. Resistance distance, which considers the permeability of habitats, did not explain significant variation in genetic distance beyond Euclidean distance alone, suggesting that racers are not currently influenced by landscape composition. In northeastern Kansas, racers appear to be an abundant and continuously distributed snake that perceives the landscape as well connected with no cover type currently impeding snake dispersal or gene flow.  相似文献   

Relative importance of management vs. design for implementation of large-scale ecological networks   总被引：1，自引：0，他引：1  

Corinna S. Bazelet  Michael J. Samways 《Landscape Ecology》2011,26(3):341-353

Ecological networks (ENs) are used to mitigate landscape-scale habitat loss, and are managed and designed to conserve regional biodiversity. In our study region in southern Africa, ENs of isolated grassland remnants are specifically set aside and managed for conservation, and are complemented by corridor-like power line servitudes which are maintained by regular mowing. Using grasshoppers, a sensitive and reliable bioindicator taxon, we determine whether ENs effectively conserve biodiversity. We used cluster analysis and variation partitioning to select the best subset of environmental variables which explained the patterns of species composition. We then compared the relative importance of environmental variables grouped by the scale of their influence: local-scale variables affected by management practices vs. landscape-scale variables affected by design of ENs. Management was consistently and significantly 2–5 times more influential than design in determining grasshopper assemblages within ENs and servitudes. Servitudes had a higher proportion of bare ground, lower proportion of tall grasses and higher abundance of grasshoppers relative to ENs. Three grasshopper species were strongly associated with servitudes and exhibited traits consistent with early colonizers. As management actions are primarily responsible for vegetation succession, the use of ENs for conservation efforts should first focus on appropriate management strategies, such as fire regime and grass height management before altering the landscape structure (e.g. increasing connectivity or enlarging patches). The conservation implications of these results are that, if ENs are managed and designed for heterogeneity and to simulate multiple successional stages, they may be beneficial for biodiversity conservation.  相似文献   

Desertification and power laws     

Salvador Pueyo 《Landscape Ecology》2011,26(3):305-309

There is an ongoing controversy on the use of the patch-size distribution as an early warning signal for abrupt shifts to a desertified state in Mediterranean arid landscapes. This controversy started with Kéfi et al.’s suggestion that, when approaching the transition point to widespread desertification, vegetation patches would switch from a power-law (PL) to a truncated power-law (TPL) distribution. Here I show that, for fundamental reasons, no untruncated power law can be found in this context, irrespective of the level of degradation. This result does not deny the importance of the findings by Kéfi et al., but means that these have to be reinterpreted by moving from the PL/TPL dichotomy to other categorizations of the patch-size distribution. Physical constraints on patch-size distributions have general interest for landscape ecology.  相似文献   

A GIS-based method for the reconstruction of the late eighteenth century forest vegetation in the Prignitz region (NE Germany)   总被引：1，自引：0，他引：1  

Monika Wulf  Hendrik Rujner 《Landscape Ecology》2011,26(2):153-168

Our goal was to reconstruct the late eighteenth century forest vegetation of the Prignitz region (NE Germany) at a scale of 1:50,000. We also wanted to relate the historical forest vegetation to the actual and potential natural vegetation. For these purposes, we selected 15 woody species and transferred relevant data found in historical records from various sources together with the recent localities of (very) old individuals belonging to these woody species into ArcView GIS. Following multi-step data processing including the generation of a point density layer using a moving window with kernel estimation and derivation of vegetation units applying Boolean algebra rules together with information on site conditions, we derived 17 forest communities corresponding to the potential natural vegetation. We were able to reconstruct the historical forest vegetation for 90% of the forest area ca. 1780. Only two of the 17 forest communities covered large parts of the forested area. The oak forest with Agrostis capillaris covered about 44% of the total forest area, and alder forests on fenland made up about 37%. Oak-hornbeam forests with Stellaria holostea comprised slightly less than 6% of the forest area, while all other forest communities comprised less than 1%. The historical forest vegetation is more similar to the potential forest vegetation and quite different from the actual forest vegetation because coniferous tree species currently cover approximately two-thirds of the actual forest area. The most beneficial result of this study is the map of high-resolution historical vegetation units that may serve as the basis for various further studies, e.g., modelling long-term changes in biodiversity at the landscape scale.  相似文献   

A global perspective on reforesting landscapes     

Brian C. McCarthy 《Landscape Ecology》2011,26(4):601-602

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Modelling dynamics of ecosystem services basket in Mediterranean landscapes: a tool for rational management   总被引：1，自引：1，他引：0  

Gili Koniak  Imanuel Noy-Meir  Avi Perevolotsky 《Landscape Ecology》2011,26(1):109-124

Natural ecosystems are life-supporting systems providing diverse ecosystem services (ESs) and benefits to human societies: e.g., food and clean water, recreation opportunities or climate regulation. The contribution of natural and semi-natural ecosystems to the provision of such services depends to a large extent on vegetation structure and composition, which, in turn, change as a result of interactions between human decisions about land management, and spontaneous biological and environmental processes. Rational management of these dynamic ecosystems requires an ability to predict short- and long-term effects of management decisions on the desired ESs. The vegetation then contributes to, and modifies, the products and services obtained from the land. We applied mathematical modeling to study these complex relationships. We developed a model for a Mediterranean ecosystem which predicts the dynamics of multiple services in response to management scenarios, mediated by vegetation changes. Six representative ESs representing different groups were selected, based on available scientific information, for a detailed study: (1) density of geophytes, (2) potential contribution to honey production, (3) energy density of fleshy fruits foraged by birds, (4) forage for goats, (5) forage for cattle, and (6) carbon retention in woody plants. Mean contributions to each service by different vegetation cover types were estimated, and the overall service provided by the site was calculated as a weighted mean of these contributions. Services were measured in their appropriate units and subsequently standardized to a percentage of the maximum value observed in the study area. We attempted to combine all studied ESs, despite their different nature, into one “ESs basket”. This paper presents the dynamics of simulated vegetation composition and values of services in response to management scenarios involving grazing, fire and their combinations. Our approach can help land managers to evaluate alternative management scenarios by presenting the “services basket” obtained from the entire managed area.  相似文献   

Analyzing the effect of stepping stones on target patch colonisation in structured landscapes for Eurasian lynx     

Stephanie Kramer-Schadt  Tobias S. Kaiser  Karin Frank  Thorsten Wiegand 《Landscape Ecology》2011,26(4):501-513

With habitat loss and fragmentation having become two of the major threats to the viability of species, the question of how to manage landscapes for species conservation has attracted much attention. In this context, the planning of stepping stones has been proposed to increase connectivity in fragmented landscapes. We present a simulation study with a neutral landscape approach to assess the effects of stepping stones on colonization success. To that end, we used a spatially explicit, calibrated population model of the European lynx (Lynx lynx) coupled with structured landscapes, in which we could control the landscape parameters of dispersal habitat coverage and contagion, as well as the number and size of stepping stones available for breeding. In general, we found that colonization success increased with increasing habitat coverage but decreased with increasing habitat contagion, while the introduction of stepping stones had significant effects in critical situations. Especially at low to medium dispersal habitat coverage and high disperser mortality, stepping stones had a positive effect on colonization success when they were large enough to produce new dispersers, but negative effects when they were small and located in a way that dispersers would be distracted from more suitable breeding habitat patches. The latter clearly constituted a shading effect and argues for a thorough consideration of the trade-offs related to stepping stone size and location when implementing stepping stones as a conservation measure, especially when the number of individuals of conservation concern is low.  相似文献