Dendrochronology-based fire history of mixed-conifer forests in the San Jacinto Mountains,California

The growing public awareness of the increasing number of large wildfires across forested landscapes, coupled with needs of resource base management has accelerated research into forest reference conditions and the historical role of fire in coniferous ecosystems. This work investigates historical fire regimes of mixed-conifer forests in the San Jacinto Mountains of southern California using fire-scar dendrochronology. As such this is the first reconstruction of fire history in the mixed-conifer forests of southern California using landscape-scale systematic-based fire-scar dendrochronology. The pre-historical fire size, seasonality, and frequency within these forests are reconstructed and demonstrated graphically, employing systematic sampling and Geographical Information System (GIS) reconstruction. A 250 m grid system was overlaid upon a 270 ha sample location, and fire-scar samples were collected from each of the grid intersection points. Fire-scar dendrochronology resulted in a 653 years long chronology, indicating a point mean fire return interval of 5.2 years, and an area wide grand mean fire interval of 32.2 years. The majority of fires occurred within latewood or at the ring boundary. Graphic modelling of fire events indicate three-quarters of all fires sampled were less than 6.25 ha in size, but burned over 50% of the area sampled during the period; only a small portion of fires were larger than 18 ha within the sample area. Use of systematic sampling is an important step in modeling long-term frequency and effects of fire on a landscape level, and is invaluable to the long-term management planning.     

兔解偶联蛋白1基因第2外显子基因多态性研究

为了解兔肉质性状特征,给兔的品种选种选育提供理论依据。本试验选取新西兰兔和加利福尼亚兔分别构建各自的DNA池,对解偶联蛋白1(uncouplingprotein 1,UCP1)基因的第2外显子及第1内含子部分序列进行扩增,扩增产物进行双向测序,利用BLAST和DNAStar分析并确定其SNP。结果分析,在新西兰兔中发现6个SNPs:T135C、C232T、T332C、C360T、T550C和A560G,其中T135C和C232T为同义突变,T332C、C360T、T550C、A560G 4个突变位点位于内含子区。利用RNA在线预测软件预测UCP1基因RNA二级结构最小自由能由-917.51 kJ/mol变为-866.10 kJ/mol,说明SNPs对UCP1基因的RNA二级结构产生影响。     

Spatial patterning of habitat for Oncorhynchus mykiss in a system of intermittent and perennial streams

Abstract –  The salmonid Oncorhynchus mykiss tends to inhabit forested or snow-fed streams having cold reliable flows, but in the California chaparral they inhabit rain-fed stream networks with extensive areas of intermittent flow. We hypothesised that hydrological mechanisms in such watersheds tend to spatially segregate spawning and over-summering habitats, and tested the hypothesis using observations from a series of tributaries in a pristine watershed. Consistent with the hypothesis, reaches with suitably sized spawning gravels tended to occur in intermittent tributaries, and also the perennial mainstem (which was too warm for over-summering). In early summer, juvenile O. mykiss (<10 cm) occurred at similar densities in the intermittent and perennial tributaries, but larger fish had greater densities in perennial tributaries. Large wood debris would be expected to mitigate the spatial segregation of habitats somewhat, but was scarce, though stream-side outcrops appeared to partially compensate by forcing gravel bars in high-gradient channels.     

GAP management status and regional indicators of threats to biodiversity

Conservation assessment requires quantitative criteria for evaluating the relative degree of threat faced by species or ecological communities. Identifying appropriate criteria for communities is complicated because the species inhabiting them can have many different responses to land uses and other forms of environmental stress. The Gap Analysis Program (GAP) uses summary data on the proportion of the community that is protected as an estimate of its vulnerability. Management status from a gap analysis of California was compared with three ecological indicators (permitted land uses, human population growth, and the spatial extent of road effects) that more directly represent impacts on biodiversity. The classification of management status appears to provide a crude first approximation of these three indicators. Public and private lands that are not formally protected were susceptible to extensive land use conversion or resource extraction in both rural and urban settings. Some plant community types are more susceptible to future infringement by human population increases that were not well predicted by management status alone. Other community types have a high road density despite being moderately well protected. It is suggested that indicators such as future growth and current road effects could complement status in rating the potential vulnerability of plant communities and setting conservation priorities. The choice of indicators will depend on the threatening processes in a given region and the availability of spatial data to map or model them.     

Influence of California halibut (Paralichthys californicus) on the vertical distribution of dissolved oxygen in a raceway and a circular tank at two depths

The design and operation of aquaculture tanks should minimize stagnant areas especially in the immediate vicinity of the fish. In tanks with pelagic fish, mixing caused by the water flow and by fish swimming is sufficient to maintain dissolved oxygen and metabolite concentrations in the immediate vicinity of the fish that are similar to those in the main water body. Given the behavior of sedentary benthic species, such as the California halibut (Paralichthys californicus), and their tendency to remain motionless on the bottom of aquaculture tanks, often in layers that are several fish deep, water quality may stratify with the worse conditions occurring in the area where they fish are lying. The purpose of this study was to evaluate the influence that California halibut (450 g average weight) may have on the vertical profile of oxygen concentration in a raceway (239 cm long, 28 cm wide) and a circular tank (92 cm diameter) operated at two water depths (10 and 20 cm). Oxygen was measured at each centimeter of the vertical profile both in an area with fish and without fish to assess their influence.

Results showed a lower oxygen concentration in the near-bottom region of the raceway and circular tanks. The phenomenon was most pronounced in the raceway operated at a 20 cm depth, but was also observed in the circular tank operated at 20 cm and in the raceway at 10 cm.

Measurements were also taken in samples collected just in front of or directly from a fish's mouth. A zone of depressed oxygen concentration in the immediate vicinity of the fish was documented, with oxygen concentrations as low as 50% of the measured tank effluent concentration. The magnitude of the depression was greater in raceways than in circular tanks and in 20 cm water depth than in 10 cm depth. The fish remained sedentary in these zones of depressed oxygen concentration for extended periods of time and frequently exhibited hyperventilation. The oxygen concentrations in the vicinity of the fish were consistently lower than the concentrations measured in the tank effluent. Therefore, effluent measurements did not provide an accurate representation of conditions to which the fish were exposed.     

Evaluation of weaning performance of California halibut (Paralichthys californicus) larvae using growth,survival and digestive proteolytic activity

This study evaluated weaning success of California halibut, Paralichthys californicus, larvae onto a microdiet at various stages of development utilizing growth, survival and digestive enzyme activity. Weaning onto a microdiet was evaluated at 16, 26, 36 and 46 days posthatch (dph). Alkaline and acid proteases and leucine aminopeptidase activities were measured after weaning and compared between the weaned treatment and Artemia‐fed controls. Survival was significantly lower in the microdiet‐fed treatments compared to the control groups. Growth was significantly reduced in all weaning treatments compared to the control, except for the 46 dph group. No differences in enzyme activities were detected between treatment and diet at 16 and 26 dph; however, activities were higher for the microdiet‐fed larvae at 36 and 46 dph. This study demonstrates that California halibut larvae possess a differentiated and effective digestive system early in development and can be weaned with relative success (>40% survival) before completion of the metamorphosis (i.e., 36 dph). The lack of weaning success at an early date cannot be entirely because of the absence of a functional stomach but could be related to, among other factors, the low‐microdiet ingestion rates observed and higher leaching of smaller microdiets.     

Feeding ecology and habitat of the threespine stickleback, Gasterosteus aculeatus microcephalus, in a remnant population of northwestern Baja California, México

Abstract – The feeding ecology and habitat of the threespine stickleback ( Gasterosteus aculeatus microcephalus Girard, 1854) was studied from November 1996 to May 1997 in a remnant population of northwestern Baja California, México. The analysis of the stomach content of 179 individuals (25 to 56 mm standard length [SL]) showed a diet dominated by cyclopoid copepods (43.8%) and chironomid larvae (39.1%). Diet in relation to size and sex of the fish was dominated by copepods in autumn and winter and by chironomid larvae during spring. Diet overlap (Schoener's index) was significant (≥60%) between fish size-classes in January, March and April and between sexes for most sampling months. The average size of prey consumed was independent of fish mouth size. The feeding strategy of the threespine stickleback shifted from opportunist in winter to specialist in spring.     

Footprints of fixed-gear fisheries in relation to rising whale entanglements on the U.S. West Coast

On the U.S. West Coast, reports of whales entangled in fishing gear increased dramatically in 2014. In this study, a time series of fishing activity maps was developed from 2009 to 2016 for the four fixed-gear fisheries most commonly implicated in entanglements. Maps were generated using vessel monitoring system (VMS) data linked to port-level landings databases, which were related to entangled whale reports over the same time period and with modelled distributions of humpback whales Megaptera novaeangliae Borowski. Over the full study period, neither marked increases in fishing activity nor changes in fisheries footprints within regions with high whale densities were detected. By contrast, a delayed fishery opening in California due to a harmful algal bloom in spring of 2016 led to ~5–7 times average levels of Dungeness crab Metacarcinus magister (Dana) fishing activity, which was consistent with a high rate of entanglement in that year. These results are consistent with current hypotheses that habitat compression caused by a marine heatwave increased the overlap of whales with fishing activity, despite minimal changes in the fisheries themselves. This study adds to literature on bycatch of protected species in otherwise sustainable fisheries, highlighting the value of using VMS data for reducing human–wildlife conflict in the ocean.     

Farmer goals and management styles: Implications for advancing biologically based agriculture

This paper examines differences in the management styles of a purposive sample of almond and winegrape growers in California’s Central Valley, including participants and non-participants in biologically integrated farming systems programs. Using Q methodology, we elicited rankings of economic and social values and goals as they relate to farm production, environmental stewardship, family and community, and leisure. These rankings led to three distinct management styles, labeled as Environmental Stewards, Production Maximizers, and Networking Entrepreneurs. The results demonstrate that farmers make decisions following diverse management strategies and suggest that outreach programs aimed at advancing biologically based farming practices must address these differences to be most effective.