The importance of within-system spatial variation in drivers of marine ecosystem regime shifts

Comparative analyses of the dynamics of exploited marine ecosystems have led to differing hypotheses regarding the primary causes of observed regime shifts, while many ecosystems have apparently not undergone regime shifts. These varied responses may be partly explained by the decade-old recognition that within-system spatial heterogeneity in key climate and anthropogenic drivers may be important, as recent theoretical examinations have concluded that spatial heterogeneity in environmental characteristics may diminish the tendency for regime shifts. Here, we synthesize recent, empirical within-system spatio-temporal analyses of some temperate and subarctic large marine ecosystems in which regime shifts have (and have not) occurred. Examples from the Baltic Sea, Black Sea, Bengula Current, North Sea, Barents Sea and Eastern Scotian Shelf reveal the largely neglected importance of considering spatial variability in key biotic and abiotic influences and species movements in the context of evaluating and predicting regime shifts. We highlight both the importance of understanding the scale-dependent spatial dynamics of climate influences and key predator–prey interactions to unravel the dynamics of regime shifts, and the utility of spatial downscaling of proposed mechanisms (as evident in the North Sea and Barents Sea) as a means of evaluating hypotheses originally derived from among-system comparisons.     

Hypoderma actaeon: an emerging myiasis in roe deer (Capreolus capreolus)

Subcutaneous larvae of Hypoderma spp. (Diptera: Oestridae) were detected in the dorsal region in 10 roe deer, Capreolus capreolus (Artiodactyla: Cervidae), hunted in central Spain between January and March 2016. All larvae were found in the inner side of the hide during the skinning of the animals. The study of the morphological features of eight larvae of different stages collected from two animals allowed the identification of Hypoderma actaeon Brauer. The small size (4–5 mm) of some of the first instars suggests that the internal lifecycle of H. actaeon may be exclusively subcutaneous. This is the first confirmation of H. actaeon in roe deer; however, further studies to assess the spread of the parasite and to follow the evolution of this myiasis in roe deer are needed.     

West Nile virus cluster analysis and vertical transmission in Culex pipiens complex mosquitoes in Sacramento and Yolo Counties,California, 2011

West Nile virus (WNV) is now endemic in California, with annual transmission documented by the statewide surveillance system. Although much is known about the horizontal avian‐mosquito transmission cycle, less is known about vertical transmission under field conditions, which may supplement virus amplification during summer and provide a mechanism to infect overwintering female mosquitoes during fall. The current study identified clusters of WNV‐infected mosquitoes in Sacramento and Yolo Counties, CA, during late summer 2011 and tested field‐captured ovipositing female mosquitoes and their progeny for WNV RNA to estimate the frequency of vertical transmission. Space‐time clustering of WNV‐positive Culex pipiens complex pools was detected in the northern Elk Grove area of Sacramento County between July 18 and September 18, 2011 (5.22 km radius; p<0.001 and RR=7.80). Vertical transmission by WNV‐infected females to egg rafts was 50% and to larvae was 40%. The estimated minimal filial infection rate from WNV‐positive, ovipositing females was 2.0 infected females/1,000. The potential contribution of vertical transmission to WNV maintenance and amplification are discussed.     

Dynamic macroecology on ecological time-scales

Aim The discipline of macroecology is increasingly being regarded as an effective vehicle for the evaluation of recent population‐ to ecosystem‐level responses to widespread human and environmental influences. However, due to the prevalent use of time‐averaged and cumulative data in macroecological analyses, the majority of the patterns that emerge from research in this field can be regarded as static. Here we review the application of dynamic macroecological analyses to changes in relationships between macroecological variables on seasonal to decadal scales. We illustrate the strength of this perspective for documenting changing patterns and testing hypotheses related to these dynamics on ecological time‐scales. Location Studies were compiled and reviewed from terrestrial and aquatic ecosystems. Methods We review examples of temporal changes in macroecological patterns driven by recent anthropogenic influences and environmental change. Results The dynamic nature of macroecological patterns on ecological time‐scales has been revealed in recent years across a wide range of ecosystems, largely through the development, maintenance and analysis of biotic and environmental monitoring time series. The resultant analyses complement examinations of dynamics over evolutionary time and have similarly revealed that static portrayals can conceal important temporal dynamics that underlie the patterns of interest. As a consequence, static depictions, resting as they do on comparative analyses in which the validity of space‐for‐time substitutions is assumed, may be of limited use for testing hypotheses related to the mechanisms underlying the patterns revealed and, by extension, the development of reliable predictions of future states. Main conclusions Recent dynamic macroecological analyses have demonstrated the utility of combined spatial and temporal replication, and have contributed to hypothesis testing related to the mechanistic processes underlying changes in macroecological patterns on ecological time‐scales. We suggest four specific avenues of future research to further the development and application of temporal approaches on similar time‐scales within the field of macroecology.     

The dynamics of exploited marine fish populations and Humpty Dumpty: similarities and differences

Marine fish populations of the global oceans and particularly large-bodied, continental shelf-dwelling groundfish species of the North Atlantic, such as cod (Gadus morhua), have been strongly perturbed by over-fishing, frequently beyond levels that may have altered their capacity to recover. Age and size structure, spatial structure, reproductive potential, and other traits that convey fitness advantages are commonly lost when prolonged and excessive fishing pressure is exerted. Fisheries management protocols implemented to recover collapsed populations have been numerous and varied with all attempting to reduce or eliminate fishing pressure. Such measures, employed singly or in multiple combinations, typically involve quota reductions or fishing moratoria, area closures and other technical measures, as well as enhanced enforcement of fishing practices. A striking geographic pattern exists in the efficacy of such measures to regain lost population attributes and hence recovery. Some regional populations have recovered while others, despite management interventions lasting decades, notably, but not exclusively, those aimed at cod populations of the Northwest Atlantic, have yet to fully recover, an endpoint analogous to the conclusion of the famous nursery rhyme of Humpty Dumpty. Here we examine the dynamics of multiple collapsed populations exhibiting varying responses to recovery initiatives from the perspective of the Humpty Dumpty metaphor.     

具size结构种群竞争系统的最优控制

研究基于size结构的种群模型的控制问题,利用特征线法给出了系统的形式解,由Banach不动点定理和Gronwall不等式推导了系统及其共轭系统的适定性,并依靠法锥相关知识证明了最优控制问题解的存在必要条件.     

Osmotic stress and mortality in adult American shad during transfer from saltwater to freshwater

Thirty-five adult American shad (Alosa sapidissima) were moved quickly (2.5 h) from saltwater to freshwater. Changes in the levels of osmotically active blood constituents and of mortality were observed during and after the transfer. These were compared with levels of corresponding constituents and of mortality in 20 shad maintained in saltwater under similar conditions and to 44 shad sampled immediately after capture in saltwater and in freshwater (40 km from the saltwater-freshwater interface). Sodium and chloride levels in theblood of the transferred group declined sharply during and after transfer. Calcium, glucose and lactic acid levels increased, and potassium and magnesium levels remained stable. Transferred shad experienced heavy mortality beginning 5 h after the initial reduction in salinity associated with movement into freshwater. No mortality was experienced in the group held in saltwater.
It was concluded that the extensive meandering exhibited by adult shad at the upper limit of the salt-freshwater interface during their spring migration in the Connecticut River is a behavioural response designed to slow the transition from the saltwater to the freshwater environment, thereby minimizing the physiological stress involved and/or allowing full recovery from this stress before proceeding upriver.     

Genetic relationships among the shads (Alosa) revealed by mitochondrial DNA analysis

We surveyed restriction site differences in mitochondrial DNA. (mtDNA) among five species of shad ( Alosa ) from North America and Europe. Allis shad, Alosa alosa and twaite shad, Alosa fallax shared two divergent genotype groups, suggesting that the two forms are either a single species, or are distinct species that have hybridized. Phenetic and cladistic analyses of the relationships among the mitochondrial genotypes defined two groups of shad, corresponding to the subgenera, Alosa and Pomolobus . The mean estimated sequence divergence between the mtDNAs of these two groups of shad was 6.5%. Taken in conjunction with fossil data, this divergence estimate suggests that the rate of mtDNA divergence between the two subgenera has been almost 10-fold lower than the 'conventional' clock calibration for mtDNA.