气候变化对大兴安岭北部蒙古栎种群动态的影响

通过对气象因子和样地数据分析表明,20余年来大兴安岭北部气候趋于变暖,低海拔地带蒙古栎呈现明显的进展趋势,演替趋于以蒙古栎为优势种的阔叶林,海拔较高地带蒙古栎更新不良,演替趋于兴安落叶松和几种阔叶树的混生林,蒙古栎种群发展与干暖化具有一致性,在各类气象因子中,5月均低温是影响蒙古栎更新的决定性因子,由海拔升高引起的区域干燥度降低也是影响更新的重要因子,这也说明蒙古栎对冷湿生境的不适应性。     

Distance-based population classification software using mean-field annealing

We describe a distance-based clustering method using a proximity matrix of genetic distances to partition populations into genetically similar groupings. The optimization heuristic mean-field annealing (MFA) was used to find locally optimal solutions where exhaustive search was not possible. To illustrate this method, we analysed both simulated and real data sets. Simulated data indicated that MFA successfully differentiated population groups, even with small F(ST) values, as long as there was separation of within and between group distances. Reanalysis of microsatellite data from various human populations using mean-fields found similar ethnic groups corresponding to major geographic regions reported by Rosenberg et al. (2002) who used the model-based computer program Structure. However, with MFA, the Kalash population was found to group with other Central/South Asian populations instead of being the only member of its own genetic cluster. Europe/Middle East populations formed a separate group from Central/South Asian populations instead of being a single group in the Structure analysis. The MFA analysis determined the greatest genetic distances (largest mean intracluster distance) occurred in native American populations, identifying three groups instead of only one found with Structure. For conservation purposes, it is not only important to identify genetically similar groupings but also to determine the relative level of genetic differentiation captured within these groups. To illustrate this, we compare two separate MFA analyses of Chinook salmon (Oncorhynchus tshawytscha) populations from British Columbia, Canada. The software called PORGS-MFA used in this article can be downloaded from http://www.pac.dfo-mpo.gc.ca/science/facilities-installations/pbs-sbp/mgl-lgm/apps/porgs/index-eng.htm.     

Winter and summer upwelling modes and their biological importance in the California Current Ecosystem

Analysis of monthly coastal upwelling intensities revealed two seasonal and biologically relevant upwelling ‘modes’ in the California Current Ecosystem (CCE). The first mode reflected upwelling during the summer months and was characterized by low‐frequency (multidecadal) processes, including significant (P<0.01) linear trends at some latitudes. In contrast, the second mode reflected wintertime upwelling and was defined by higher‐frequency variability associated with the North Pacific High and El Niño Southern Oscillation events. These modes were compared with multidecadal time series of splitnose rockfish (Sebastes diploproa) otolith growth, yelloweye rockfish (S. ruberrimus) otolith growth, Chinook salmon (Oncorhynchus tshawytscha) scale growth, and indices of Cassin's auklet (Ptychoramphus aleuticus) and common murre (Uria aalge) reproduction in the central‐northern CCE. In redundancy and correlation analyses, salmon growth and Cassin's auklet fledgling success associated with the summer upwelling mode while all other time series associated with the winter upwelling mode, indicating that CCE biology was differentially sensitive to these seasonal upwelling patterns. Thus, upwelling occurred in unrelated seasonal modes with contrasting trends, atmospheric forcing mechanisms, and impacts on the biology of the CCE, underscoring the importance of seasonality when evaluating ecosystem response to climate variability and change.     

A Cover Story: Fisheries May Drive Stocks to Extinction

The cover of the 1993 reprint of Beverton and Holt's book bears a diagram, its significance previously unrecognized, that expresses extinction due to fishing. This paper traces the concept to self-regenerating yield models in their 1957 book, its numerical development therein far in advance of its reinvention 30 years later. Local extinction constitutes a critical impact of fisheries on aquatic ecosystems that has been too often downplayed by fisheries science.     

Density‐dependent mortality in Pacific salmon: the ghost of impacts past?

Conservation biologists often ignore density dependence because at‐risk populations are typically small relative to historical levels. However, if populations are reduced as a result of impacts that lower carrying capacity, then density‐dependent mortality may exist at low population abundances. Here, we explore this issue in threatened populations of juvenile chinook salmon (Oncorhynchus tshawytscha). We followed the fate of more than 50 000 juvenile chinook in the Snake River Basin, USA to test the hypothesis that their survival was inversely associated with juvenile density. We also tested the hypotheses that non‐indigenous brook trout and habitat quality affect the presence or strength of density dependence. Our results indicate that juvenile chinook suffer density‐dependent mortality and the strength of density dependence was greater in streams in which brook trout were absent. We were unable to detect an effect of habitat quality on the strength of density dependence. Historical impacts of humans have greatly reduced population sizes of salmon, and the density dependence we report may stem from a shortage of nutrients normally derived from decomposing salmon carcasses. Cohorts of juvenile salmon may experience density‐dependent mortality at population sizes far below historical levels and recovery of imperiled populations may be much slower than currently expected.     

Extrapolating Growth Reductions in Fish to Changes in Population Extinction Risks: Copper and Chinook Salmon

Fish commonly respond to stress, including stress from chemical exposures, with reduced growth. However, the relevance to wild populations of subtle and sometimes transitory growth reductions may not be obvious. At low-level, sustained exposures, Cu is one substance that commonly causes reduced growth but little mortality in laboratory toxicity tests with fish. To explore the relevance of growth reductions under laboratory conditions to wild populations, we (1) estimated growth effects of low-level Cu exposures to juvenile Chinook salmon (Oncorhynchus tshawytscha), (2) related growth effects to reduced survival in downriver Chinook salmon migrations, (3) estimated population demographics, (4) constructed a demographically structured matrix population model, and (5) projected the influence of Cu-reduced growth on population size, extinction risks, and recovery chances. Reduced juvenile growth from Cu in the range of chronic criteria concentrations was projected to cause disproportionate reductions in survival of migrating juveniles, with a 7.5% length reduction predicting about a 23% to 52% reduction in survival from a headwaters trap to the next census point located 640 km downstream. Projecting reduced juvenile growth out through six generations (～30 years) resulted in little increased extinction risk; however, population recovery times were delayed under scenarios where Cu-reduced growth was imposed.     

Confirmation of the presence and use of sandy beach surf-zones by juvenile Chinook salmon

Migration patterns and habitat use of sub-yearling Chinook salmon during initial ocean entrance is poorly understood. Twenty-five years ago, sub-yearling Chinook salmon were hypothesized to stay close to shore (<5 km). To test this hypothesis we sampled the surf-zone of a southern Oregon dissipative sandy beach throughout the summer of 2006 (06/07–09/29) using a beach seine in 1 m of water depth. We caught 48 sub-yearlings over six dates (07/22 to 09/01). Mean standard length of Chinook salmon caught in the surf-zone increased from 9.1 ± 0.6 (07/22/06) to 11.6 ± 0.7 cm (09/01/06), suggesting a mean increase of 0.6 mm in standard length (S.L.) per day. Early in the summer, smaller fish fed mostly on amphipods. Later in the summer, larger juveniles fed primarily on larval and juvenile fish. All prey items were common in the surf-zone. Juveniles appear to migrate from the estuary to the surf-zone where they feed on the local zooplankton for up to two summer months before migrating offshore.