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61.
Miguel A. Ortega-Huerta Enrique Martinez-Meyer Stephen L. Egbert Kevin P. Price A. Townsend Peterson 《国际地球制图》2013,28(3):7-20
Abstract An important methodological and analytical requirement for analyzing spatial relationships between regional habitats and species distributions in Mexico is the development of standard methods for mapping the country's land cover/land use formations. This necessarily involves the use of global data such as that produced by the Advanced Very High Resolution Radiometer (AVHRR). We created a nine‐band time‐series composite image from AVHRR Normalized Difference Vegetation Index (NDVI) bi‐weekly data. Each band represented the maximum NDVI for a particular month of either 1992 or 1993. We carried out a supervised classification approach, using the latest comprehensive land cover/vegetation map created by the Mexican National Institute of Geography (INEGI) as reference data. Training areas for 26 land cover/vegetation types were selected and digitized on the computer's screen by overlaying the INEGI vector coverage on the NDVI image. To obtain specific spectral responses for each vegetation type, as determined by its characteristic phenology and geographic location, the statistics of the spectral signatures were subjected to a cluster analysis. A total of 104 classes distributed among the 26 land cover types were used to perform the classification. Elevation data were used to direct classification output for pine‐oak and coastal vegetation types. The overall correspondence value of the classification proposed in this paper was 54%; however, for main vegetation formations correspondence values were higher (60‐80%). In order to obtain refinements in the proposed classification we recommend further analysis of the signature statistics and adding topographic data into the classification algorithm. 相似文献
62.
Clint C. Muhlfeld J. Joseph Giersch F. Richard Hauer Gregory T. Pederson Gordon Luikart Douglas P. Peterson Christopher C. Downs Daniel B. Fagre 《Climatic change》2011,106(2):337-345
Climate warming in the mid- to high-latitudes and high-elevation mountainous regions is occurring more rapidly than anywhere
else on Earth, causing extensive loss of glaciers and snowpack. However, little is known about the effects of climate change
on alpine stream biota, especially invertebrates. Here, we show a strong linkage between regional climate change and the fundamental
niche of a rare aquatic invertebrate—the meltwater stonefly Lednia tumana—endemic to Waterton-Glacier International Peace Park, Canada and USA. L. tumana has been petitioned for listing under the U.S. Endangered Species Act due to climate-change-induced glacier loss, yet little
is known on specifically how climate impacts may threaten this rare species and many other enigmatic alpine aquatic species
worldwide. During 14 years of research, we documented that L. tumana inhabits a narrow distribution, restricted to short sections (~500 m) of cold, alpine streams directly below glaciers, permanent
snowfields, and springs. Our simulation models suggest that climate change threatens the potential future distribution of
these sensitive habitats and the persistence of L. tumana through the loss of glaciers and snowfields. Mountaintop aquatic invertebrates are ideal early warning indicators of climate
warming in mountain ecosystems. Research on alpine invertebrates is urgently needed to avoid extinctions and ecosystem change. 相似文献
63.
Charles C. Wall Bradley J. Peterson Christopher J. Gobler 《Estuaries and Coasts》2011,34(6):1262-1277
While many coastal ecosystems previously supported high densities of seagrass and abundant bivalves, the impacts of overfishing,
eutrophication, harmful algal blooms, and habitat loss have collectively contributed to the decline of these important resources.
Despite improvements in wastewater treatment in some watersheds and subsequent reduced nutrient loading to neighboring estuaries,
seagrass and bivalve populations in these locations have generally not recovered. We performed three mesocosm experiments
to simultaneously examine the contrasting effects of nutrient loading and historic suspension-feeding bivalve densities on
the growth of eelgrass (Zostera marina), juvenile bivalves (northern quahogs, Mercenaria mercenaria; eastern oysters, Crassostrea virginica; and bay scallops, Argopecten irradians), and juvenile planktivorous fish (sheepshead minnow, Cyprinodon variegatus). High nutrient loading rates led to significantly higher phytoplankton (chlorophyll a) levels in all experiments, significantly increased growth of juvenile bivalves relative to controls with lower nutrient
loading rates in two experiments, and significantly reduced the growth of eelgrass in one experiment. The filtration provided
by adult suspension feeders (M. mercenaria and C. virginica) significantly decreased phytoplankton levels in all experiments, significantly increased light penetration and the growth
of eelgrass in one experiment, and significantly decreased the growth of juvenile bivalves and fish in two experiments, all
relative to controls with no filtration from adult suspension feeders. These results demonstrate that an appropriate level
of nutrient loading can have a positive effect on some estuarine resources and that bivalve filtration can mediate the effects
of nutrient loading to the benefit or detriment of different estuarine resources. Future ecosystem-based approaches will need
to simultaneously account for anthropogenic nutrient loading and bivalve restoration to successfully manage estuarine resources. 相似文献
64.
Marc Laflamme Simon A.F. Darroch Sarah M. Tweedt Kevin J. Peterson Douglas H. Erwin 《Gondwana Research》2013,23(2):558-573
The Ediacaran–Cambrian transition signals a drastic change in both diversity and ecosystem construction. The Ediacara biota (consisting of various metazoan stem lineages in addition to extinct eukaryotic clades) disappears, and is replaced by more familiar Cambrian and Paleozoic metazoan groups. Although metazoans are present in the Ediacaran, their ecological contribution is dwarfed by Ediacaran-type clades of uncertain phylogenetic affinities, while Ediacaran-type morphologies are virtually non-existent in younger assemblages. Three alternative hypotheses have been advanced to explain this dramatic change at, or near, the Ediacaran–Cambrian boundary: 1) mass extinction of most Ediacaran forms; 2) biotic replacement, with early Cambrian organisms eliminating Ediacaran forms; and 3) a Cheshire Cat model, with Ediacaran forms gradually disappearing from the fossil record (but not necessarily going extinct) as a result of the elimination of unique preservational settings, primarily microbial matgrounds, that dominated the Ediacaran. To evaluate these proposed explanations for the biotic changes observed at the Ediacaran–Cambrian transition, environmental drivers leading to global mass extinction are compared to biological factors such as predation and ecosystem engineering. We explore temporal and biogeographic distributions of Ediacaran taxa combined with evaluations of functional guild ranges throughout the Ediacaran. The paucity of temporally-resolved localities with diverse Ediacaran assemblages, combined with difficulties associated with differences in taphonomic regimes before, during, and after the transition hinders this evaluation. Nonetheless, the demonstration of geographic and niche range changes offers a novel means of assessing the downfall of Ediacara-type taxa at the hands of emerging metazoans, which we hypothesize to be most likely due to the indirect ecological impact metazoans had upon the Ediacarans. Ultimately, the combination of studies on ecosystem construction, biostratigraphy, and biogeography showcases the magnitude of the transition at the Ediacaran–Cambrian boundary. 相似文献
65.
Quantifying and relating land-surface and subsurface variability in permafrost environments using LiDAR and surface geophysical datasets 总被引:1,自引:0,他引:1
S. S. Hubbard C. Gangodagamage B. Dafflon H. Wainwright J. Peterson A. Gusmeroli C. Ulrich Y. Wu C. Wilson J. Rowland C. Tweedie S. D. Wullschleger 《Hydrogeology Journal》2013,21(1):149-169
The value of remote sensing and surface geophysical data for characterizing the spatial variability and relationships between land-surface and subsurface properties was explored in an Alaska (USA) coastal plain ecosystem. At this site, a nested suite of measurements was collected within a region where the land surface was dominated by polygons, including: LiDAR data; ground-penetrating radar, electromagnetic, and electrical-resistance tomography data; active-layer depth, soil temperature, soil-moisture content, soil texture, soil carbon and nitrogen content; and pore-fluid cations. LiDAR data were used to extract geomorphic metrics, which potentially indicate drainage potential. Geophysical data were used to characterize active-layer depth, soil-moisture content, and permafrost variability. Cluster analysis of the LiDAR and geophysical attributes revealed the presence of three spatial zones, which had unique distributions of geomorphic, hydrological, thermal, and geochemical properties. The correspondence between the LiDAR-based geomorphic zonation and the geophysics-based active-layer and permafrost zonation highlights the significant linkage between these ecosystem compartments. This study suggests the potential of combining LiDAR and surface geophysical measurements for providing high-resolution information about land-surface and subsurface properties as well as their spatial variations and linkages, all of which are important for quantifying terrestrial-ecosystem evolution and feedbacks to climate. 相似文献
66.
67.
Scaling Ecological Dynamics: Self-Organization, Hierarchical Structure, and Ecological Resilience 总被引:6,自引:0,他引:6
Garry D. Peterson 《Climatic change》2000,44(3):291-309
Assessing impacts of global change is complicated by the problems associated with translating models and data across spatial and temporal scales. One of the major problems of ecological scaling is the dynamic, self-organized nature of ecosystems. Ecological organization emerges from the interaction of structures and processes operating at different scales. The resilience of ecological organization to changes in key cross-scale processes can be used to assess the contexts within which scaling methods function well, need adjustment, and break down. 相似文献
68.
Structural parameters and cation ordering are determined for four compositions in the synthetic MgGa2O4-Mg2GeO4 spinel solid solution (0, 8, 15 and 23 mol% Mg2GeO4; 1400 °C, 1 bar) and for spinelloid β-Mg3Ga2GeO8 (1350 °C, 1 bar), by Rietveld refinement of room-temperature neutron diffraction data. Sample chemistry is determined by
XRF and EPMA. Addition of Mg2GeO4 causes the cation distribution of the MgGa2O4 component to change from a disordered inverse distribution in end member MgGa2O4, [4]Ga = x = 0.88(3), through the random distribution, toward a normal cation distribution, x = 0.37(3), at 23 mol% Mg2GeO4. An increase in ao with increasing Mg2GeO4 component is correlated with an increase in the amount of Mg on the tetrahedral site, through substitution of 2 Ga3+⇄ Mg2++Ge4+. The spinel exhibits high configurational entropy, reaching 20.2 J mol−1 (four oxygen basis) near the compositional upper limit of the solid solution. This stabilizes the spinel in spite of positive
enthalpy of disordering over the solid solution, where ΔH
D
= αx + βx
2, α = 22(3), β = −21(3) kJ mol−1. This model for the cation distribution across the join suggests that the empirically determined limit of the spinel solid
solution is correlated with the limit of tetrahedral ordering of Mg, after which local charge-balanced substitution is no
longer maintained.
Spinelloid β-Mg3Ga2GeO8 has cation distribution M1[Mg0.50(2)Ga0.50(2)] M2[Mg0.96(2)Ga0.04(2)] M3[Mg0.77(2) Ga0.23(2)]2 (Ge0.5Ga0.5)2O8 (tetrahedral site occupancies are assumed). Octahedral site size is correlated to Mg distribution, where site volume, site
distortion, and Mg content follow the relation M1<M3<M2. The disordered cation distribution provides local electrical neutrality
in the structure, and stabilization through increased configurational entropy (27.6 J mol−1; eight oxygen basis). Comparison of the crystal structures of Mg1+
N
Ga2−2
N
Ge
N
O4 spinel, β-Mg3Ga2GeO8, and Mg2GeO4 olivine reveals β-Mg3Ga2GeO8 to be a true structural intermediate. Phase transitions across the pseudobinary are necessary to accommodate an increasing
divergence of cation size and valence, with addition of Mg2GeO4 component. Octahedral volume increases while tetrahedral volume decreases from spinel to β-Mg3Ga2GeO8 to olivine, with addition of Mg and Ge, respectively. Furthermore, M-M distances increase regularly across the join, suggesting
that changes in topology reduce cation-cation repulsion.
Received: 9 November 1998 / Revised, accepted: 3 August 1999 相似文献
69.
Melissa M. Foley Benjamin S. Halpern Fiorenza Micheli Matthew H. Armsby Margaret R. Caldwell Caitlin M. Crain Erin Prahler Nicole Rohr Deborah Sivas Michael W. Beck Mark H. Carr Larry B. Crowder J. Emmett Duffy Sally D. Hacker Karen L. McLeod Stephen R. Palumbi Charles H. Peterson Helen M. Regan Mary H. Ruckelshaus Paul A. Sandifer Robert S. Steneck 《Marine Policy》2010
The declining health of marine ecosystems around the world is evidence that current piecemeal governance is inadequate to successfully support healthy coastal and ocean ecosystems and sustain human uses of the ocean. One proposed solution to this problem is ecosystem-based marine spatial planning (MSP), which is a process that informs the spatial distribution of activities in the ocean so that existing and emerging uses can be maintained, use conflicts reduced, and ecosystem health and services protected and sustained for future generations. Because a key goal of ecosystem-based MSP is to maintain the delivery of ecosystem services that humans want and need, it must be based on ecological principles that articulate the scientifically recognized attributes of healthy, functioning ecosystems. These principles should be incorporated into a decision-making framework with clearly defined targets for these ecological attributes. This paper identifies ecological principles for MSP based on a synthesis of previously suggested and/or operationalized principles, along with recommendations generated by a group of twenty ecologists and marine scientists with diverse backgrounds and perspectives on MSP. The proposed four main ecological principles to guide MSP—maintaining or restoring: native species diversity, habitat diversity and heterogeneity, key species, and connectivity—and two additional guidelines, the need to account for context and uncertainty, must be explicitly taken into account in the planning process. When applied in concert with social, economic, and governance principles, these ecological principles can inform the designation and siting of ocean uses and the management of activities in the ocean to maintain or restore healthy ecosystems, allow delivery of marine ecosystem services, and ensure sustainable economic and social benefits. 相似文献
70.
Michael L. Peterson Joan Fabres Stuart G. Wakeham Cindy Lee Ivn J. Alonso Juan Carlos Miquel 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1547-1557
Further development of the large, surface-tethered sediment trap (NetTrap) employed as part of the MedFlux program is described whereby the large collection capacity of the NetTrap is combined with an Indented Rotating Sphere/Sample Carousel (IRSC) sediment trap (IRSC–NT). This trap is capable of collecting particle flux either in a time series or settling velocity mode; settling velocity mode allows the collection of particles that fall within discrete settling velocity intervals. During short field deployments in the Mediterranean Sea the IRSC–NT configured in the settling velocity mode successfully collected unpoisoned samples for chemical and microbiological experiments. In addition to the development of the IRSC–NT, particle-settling behavior above and below the swimmer-excluding IRS valve was tested during on-deck experiments using a specially constructed water-tight trap. Chemical analyses of settling materials (published elsewhere) suggested that separation of particles by settling velocity was achieved. However, due to the motion of the ship, it was not possible to directly measure particle-settling velocities within the trap. Particle release from the IRS did not bias the apparent settling velocity spectrum. Rotation of the IRS did not engender turbulence at the surface of the sphere or within the skewed funnel below. Tests of different ball designs over the course of the MedFlux program showed that a “ridge and saddle” pattern was optimal for efficiently transferring particles under the IRS seal while still reducing swimmer entrance to the collection funnel. The large size of the IRSC–NT did not prevent it from drifting effectively with the current. Several modifications of the present design are proposed that should improve the accuracy of the settling velocity measurements. 相似文献