In the southern Benguela upwelling ecosystem off the west coast of South Africa, seabird populations are decreasing dramatically because of reduced availability of pelagic fish. We tested the hypothesis that the west coast fishing industry is competing for the remaining stocks of anchovy and sardine with the largest colony of Vulnerable Cape Gannets (Morus capensis) along the Atlantic coast. Using GPS-tracking of the birds, echo-sounding of pelagic fish, and vessel log books, we located overlap areas between bird foraging ranges, pelagic fish distribution, and fishing activities. We then compared fish catches by gannets and vessels within their joint foraging zones. In October 2007, purse-seine fishing grounds and gannet foraging areas overlapped by only 13%. However, for a 1-month period, the amount of fish removed from this area by purse-seine boats amounted to 41% of the food requirements of the 72,000 gannets breeding on Malgas Island (25% of the world population). The fishery’s catch in this area is significant in terms of its potential impact on gannets, but comprises only 3.6% of total fishery catch. Based on this finding, the rapidly decreasing size of the gannet colony and the stated objectives of South Africa’s Marine Living Resources Act of 1998, the case for considering and experimenting with at-sea ‘no-take’ areas for the purse-seine fishery is strong. Efforts to establish whether ‘no-take’ fishing zones increase food availability for top predators is an important next step in conservation of the southern Benguela Ecosystem. 相似文献
Transferring ecological information across scale often involves spatial aggregation, which alters information content and
may bias estimates if the scaling process is nonlinear. Here, a potential solution, the preservation of the information content
of fine-scale measurements, is highlighted using modeled net ecosystem exchange (NEE) of an Arctic tundra landscape as an
example. The variance of aggregated normalized difference vegetation index (NDVI), measured from an airborne platform, decreased
linearly with log(scale), resulting in a linear relationship between log(scale) and the scale-wise modeled NEE estimate. Preserving
three units of information, the mean, variance and skewness of fine-scale NDVI observations, resulted in upscaled NEE estimates
that deviated less than 4% from the fine-scale estimate. Preserving only the mean and variance resulted in nearly 23% NEE
bias, and preserving only the mean resulted in larger error and a change in sign from CO2 sink to source. Compressing NDVI maps by 70–75% using wavelet thresholding with the Haar and Coiflet basis functions resulted
in 13% NEE bias across the study domain. Applying unique scale-dependent transfer functions between NDVI and leaf area index
(LAI) decreased, but did not remove, bias in modeled flux in a smaller expanse using handheld NDVI observations. Quantifying
the parameters of statistical distributions to preserve ecological information reduces bias when upscaling and makes possible
spatial data assimilation to further reduce errors in estimates of ecological processes across scale. 相似文献
Chitosan has been widely accepted as a wall material for preparing microcapsules of various purposes in human medicine. The possibility of using chitosan as a wall material for microencapsulating nutrients and drugs for aquaculture purposes, specifically to Macrobrachium rosenbergii larvae was evaluated in this study. Two types of chitosan-coated microcapsules were prepared using either acetone (MEC-A) or NaOH (MEC-N) as the cross-linking agents. They were compared with a microbound diet relative to total leaching of nutrients and free amino acids (FAA). Among the microcapsules, MEC-N showed the lowest level of total leaching of nutrients (23.3%) during 5 h of immersion in seawater and released 65% FAA after 60 min. During laboratory trials, 75% larvae had accepted the MEC-N capsule. The results of the study suggest that chitosan can be used as a wall material for preparing microcapsules to deliver drugs and nutrients to M. rosenbergii larvae. 相似文献
The boreal forest is globally important for its influence on Earth’s energy balance, and its sensitivity to climate change. Ecosystem functioning in boreal forests is shaped by fire activity, so anticipating the impacts of climate change requires understanding the precedence for, and consequences of, climatically induced changes in fire regimes. Long-term records of climate, fire, and vegetation are critical for gaining this understanding.
Objectives
We investigated the relative importance of climate and landscape flammability as drivers of fire activity in boreal forests by developing high-resolution records of fire history, and characterizing their centennial-scale relationships to temperature and vegetation dynamics.
Methods
We reconstructed the timing of fire activity in interior Alaska, USA, using seven lake-sediment charcoal records spanning CE 1550–2015. We developed individual and composite records of fire activity, and used correlations and qualitative comparisons to assess relationships with existing records of vegetation and climate.
Results
Our records document a dynamic relationship between climate and fire. Fire activity and temperature showed stronger coupling after ca. 1900 than in the preceding 350 yr. Biomass burning and temperatures increased concurrently during the second half of the twentieth century, to their highest point in the record. Fire activity followed pulses in black spruce establishment.
Conclusions
Fire activity was facilitated by warm temperatures and landscape-scale dominance of highly flammable mature black spruce, with a notable increase in temperature and fire activity during the twenty-first century. The results suggest that widespread burning at landscape scales is controlled by a combination of climate and vegetation dynamics that together drive flammability.
Regional economic resilience can be defined as an economy’s ability to withstand and recover quickly from shocks. The ability to measure resilience is necessary to developing our understanding of what influences resilience. In this paper, we develop a new, two‐dimensional quantitative measure of resilience using observed differences between expected and actual employment in a region following a shock and distinguish the response to the shock from random variation. We demonstrate one application of this metric to US county‐level employment data to compare county responses to the 2007–2009 national recession and discuss how different regions of the United States responded to the shock of the Great Recession in terms of resilience. 相似文献