Poleward shifts in winter ranges of North American birds

Climate change is thought to promote the poleward movement of geographic ranges; however, the spatial dynamics, mechanisms, and regional anthropogenic drivers associated with these trends have not been fully explored. We estimated changes in latitude of northern range boundaries, center of occurrence, and center of abundance for 254 species of winter avifauna in North America from 1975 to 2004. After accounting for the effect of range size and the location of the northern boundary, positive latitudinal trends were evident for the northern boundary (1.48 km/yr), center of occurrence (0.45 km/yr), and center of abundance (1.03 km/yr). The northern boundary, when examined across individual species, had the most variable trends (SD = 7.46 km/yr) relative to the center of occurrence (SD = 2.36 km/yr) and center of abundance (SD = 5.57 km/yr). Trends did not differ based on migratory status, but there was evidence that trends differed for species with ranges centered in the southern vs. northern portion of the study area. Species occurred more sporadically over time at northern range boundaries, and northern boundaries were associated with a concentration of colonization and extirpation events, with a greater prevalence of colonization events likely promoting poleward trends. Regional anthropogenic drivers explained approximately 8% of the trend for the northern boundary, 14% for the center of occurrence, and 18% for the center of abundance; however, these effects were localized in the northern portion of species' ranges and were associated with distributional changes within ranges, primarily abundance, producing patterns that mimicked poleward movements. We conclude that poleward distributional shifts represent the interaction between climate change and regional factors whose outcome is determined by the scale of the analysis and the biotic and abiotic features in the region, and how anthropogenic activities have impacted these features.     

Weight and chemical composition of some important oceanic zooplankton in the North Pacific Ocean

Wet and dry weight, total carbon, nitrogen, hydrogen, and ash contents were determined on 33 species of zooplankton distributed predominantly in the open sea region of the North Pacific. Sampling covered the waters from 44°N to the equator. Average percentage of dry weight to wet weight was about 19% of all samples from the whole area. Percentage dry weight of carbon in copepods was on an average 51.5%. The highest value, 66.6%, was obtained in eggs of the copepod Pareuchaeta sarsi. Mixed zooplankton was assumed to contain carbon comprising about 35 to 45% of the dry weight. Carbon contained in the zooplankton biomass existing in the upper 200 m in the western parts of the northern North Pacific and Bering Sea during spring and summer was estimated to range from 20 to 85 mg C/m³. Nitrogen content varied considerably with localities. Average ratio of carbon to nitrogen was 8.5 in subarctic copepods, and 4.1 in subtropic-tropic copepods. This ratio also varied with season. In the copepod Calanus cristatus the ratio was highest (10.0) in May, immediately after the spring bloom of phytoplankton, when the animals contained much fat. The ratio fell to 5.1 in December. There seemed to be a large seasonal variation in boreal zooplankton due to great fluctuations of environmental conditions, especially the amount of food available; in tropical species the range was small because of environmental uniformity. Average hydrogen content was about 6 to 10%. The percentage of ash to dry weight amounted to 39.3% in pteropods and 3.4% in copepods.     

Symbiosis between bacteria and oceanic clonal sea star larvae in the western North Atlantic Ocean

Bacteria were present in the majority of clonal sea star bipinnariae (Luidia sp.) collected between June 1987 and August 1990 from oceanic populations in the subtropical western North Atlantic Ocean. Light and electron microscopy revealed dense aggregations of bacteria within lobes of the epidermal cuticle in the gastric region of larvae. Gram-negative rods and less-common elongate spiral bacteria were observed, always in close association with branching epidermal microvilli. Intact and partially digested bacteria occurred in vesicles and phagosomes within epidermal cells, a probable indication of phagocytotic activity by the host. The association of larvae of Luidia sp. and bacteria ranged widely on both geographical and temporal scales. During July and August 1988, larvae were abundant (1.6 to 11.1 m³) in the mixed surface layer (<10 to 100 m) of stations in the Gulf Stream, the Sargasso Sea and the North Equatorial Drift, and 96% (mean of 5 stations, n=8 to 10 larvae in each station) of the individuals surveyed harbored bacteria beneath their cuticle. In a single station on the Florida Current sampled during winter, spring, and summer months between 1989 and 1991, 79 to 90% of the larvae harbored bacteria. The incidence of symbiosis was higher in actively cloning larvae than in non-cloning larvae. This is the first documentation of a symbiosis in field populations of echinoderm larvae.     

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.     

Evolution of mating systems and sexual size dimorphism in North American cyprinids

Mating systems evolve with sexual size dimorphism (SSD) in many animals. Mating systems with males larger than females occur when males compete for female access or guard territories, while mating systems with group mating tend to occur in species where females are the same size or larger than males. In addition to variation in SSD with mating system, sperm competition varies among mating systems in predictable patterns. We examined the evolution of mating systems with SSD and testes mass in 111 North American Cyprinidae fishes using phylogenetic comparative methods. Our results demonstrate that the evolution of mating systems in Cyprinidae fishes is from ancestral taxa that are group spawners with females the same size or larger than males to pair spawning systems where males tend to be larger than females. We used an additive model to predict male and female body size from testes mass and mating system. Only mating system varied predictably with SSD. Our results for analyses of hyperallometry (Rensch’s rule) were that individual species of Cyprinidae can have hyperallometry for SSD, but the pattern is not present across all taxa.     

Changes in body size, abundance, and energy allocation in rockfish assemblages of the northeast Pacific.

Fish body size, a key driver of many aspects of fish population biology and ecology, is affected by fisheries that deplete the largest individuals. Rockfish (genus Sebastes) are a diverse group that has been heavily fished on the U.S. West Coast in recent decades. We examined trawl survey data from 1980 to 2001 to determine spatial and temporal trends in body size and density of 16 shelf rockfish species, including six that are considered overfished. Mean individual mass and maximum observed mass declined in the majority of species in one or more zoogeographic regions between central California and Washington. Density changes were far more variable in time and space, but in all regions, density declines were most often associated with large-bodied rockfish. We next estimated the impact of size and density changes on energy consumption and fecundity in a five-species rockfish assemblage that includes bocaccio (S. paucispinis), a large-bodied, overfished species. Indexes of both consumption and fecundity by the assemblage increased in the southern portion of the study area between 1980 and 2001 but decreased in the northern portion. Allocation of energy and reproductive potential within the assemblage shifted dramatically: relative to bocaccio, total energy consumption and fecundity indexes for the other four species increased by orders of magnitude from 1980 to 2001. These changes in community structure may affect the ability of bocaccio and other large rockfish species to recover from overfishing, especially in light of long-term declines in zooplankton production that may also be affecting rockfish size and production. Addressing these issues may require a regional, multispecies management approach.     

Flightlessness and the energetic cost of wing molt in a large sea duck

Although the replacement of feathers apparently represents the major event of somatic production in the annual cycle of wild birds, knowledge about the energetics of molt has always been hampered by logistical and technical difficulties, which are exacerbated by the fact that birds are able to compensate behaviorally to buffer any variation in energy demand. During wing molt, sea ducks (Mergini) and other diving birds lose all of their wing feathers at once, leading to a period of temporary flightlessness of variable duration, a condition that considerably restricts their movements and increases the probability of predation. In the present study, we present the first results aimed at quantifying the duration of flightlessness, energy expenditure, and foraging effort during molt of a wing-propelled diving bird, the Common Eider (Somateria mollissima). Data loggers were implanted in the body cavity of 13 females to record heart rate and hydrostatic pressure (depth) every two seconds for a period of 220 days. Flight frequency and duration were assessed from elevated and constant heart rate, and the absence of flight was used to quantify the duration of flightlessness, which lasted, on average, 36 +/- 8 days (mean +/- SD). Using a period of four weeks before and four weeks after the flightless period, we found that dive depth (ranging from 1 to 2 m, on average) and daily diving time did not vary during the course of the study. Daily metabolic rate increased by 9%, and resting metabolic rate by 12% from the pre-molt period to the flightless period and remained high during the post-molt period. This study indicates that the energetic costs of replacing flight remiges in female eiders are substantial, although this is not associated with any change in foraging effort, which suggests that female Common Eiders lose mass during wing molt. Finally, estimates of energy savings associated with the total absence of flights during wing molt represent 6% of daily metabolic rate or 14% of resting metabolic rate. This finding contrasts with the classical view that little or no benefit is associated with a flightless condition. We suggest that such energy savings may have favored the evolution of temporary flightlessness in diving birds.     

Electrophoretic and biometric variability in the abyssal grenadier Coryphaenoides armatus of the western North Atlantic,eastern South Pacific and eastern North Pacific Oceans

Specimens of the abyssal grenadier Coryphaenoides armatus (Hector, 1875), from the western North Atlantic and eastern North Pacific Oceans were compared electrophoretically at 27 presumptive gene loci. At 6 of the 7 polymorphic loci there were only minor differences in allelic frequencies but a nearly fixed difference was found at one locus, phosphogluconate dehydrogenase. Eastern North Pacific grenadiers typically have a narrower interorbital space, a shorter dorsal interspace, more soft rays in the 1st dorsal fin (9–10 versus 8–9) and more pelvic fin rays (21–23 versus 18–21) than grenadiers from the western North Atlantic (as well as grenadiers from the eastern South Pacific, which were included in the biometric analysis). There is an apparent disjunction in the distribution of C. armatus in the eastern Pacific at the Gulf of Panamá which coincides with the change of morphology. It is suggested that North Pacific grenadiers comprise a subspecies, C. armatus variabilis Günther, 1878, which is morphologically distinct from the subspecies C. armatus armatus (Hector, 1875) of the other areas.     

Deep distributions of oceanic cirripede larvae in the Sargasso Sea and surrounding North Atlantic Ocean

From deep ( 1000 m), multi-depth zooplankton samples taken in the Azores frontal region from November 1980 to June 1981, high numbers of the two larval forms ofLepas pectinata, the commonest lepadid cirripede in this area, were sampled. The nauplii and cyprid larvae are large and long-lived. Nauplii were sampled where they feed, in the upper 150 m, closely associated with the fluorescence maximum. The cyprids were mainly sampled between 300 and 400 m, with a sharp cut-off in numbers just below the distribution peak. This deep distribution is intriguing, as the cyprids, which were not migrating diurnally, are non-feeding. To complete their life cycle they must settle on floating debris at the surface, where very few were sampled. They are negatively buoyant and there is no apparent physical reason for this deep distribution. There was no obvious pattern of changes in individual length or length/dry weight distribution with depth, the population appeared homogeneous. There was also no accumulation of other zooplankton at the same depth, or evidence from gut contents of large carnivores that the distribution pattern was caused by selective predation. A close association exists betweenL. pectinata andSargassum spp. weed, the cyprids preferentially settling on small fragments of weathered weed, the supply of which may be enhanced after winter. During winter, the harsh environment at the surface of the northern Sargasso Sea may discourage cyprid settlement. The deep distribution may be an ontogenetic migration conferring some survival advantage and saving energy due to the lower temperature and oxygen levels at depth. If it is a behavioural mechanism, duration of the cyprid stage will be extended until a more clement time of year, allowing them to settle over a longer period. The cyprids of other species were also sampled at depth, so the phenomenon appears to be widespread. If subsequent research confirms these observations as an ontogenetic migration, our current understanding of the fouling behaviour of oceanic lepadid cirripedes would be considerably modified.     

Major shifts in Amazon wildlife populations from recent intensification of floods and drought

In the western Amazon Basin, recent intensification of river‐level cycles has increased flooding during the wet seasons and decreased precipitation during the dry season. Greater than normal floods occurred in 2009 and in all years from 2011 to 2015 during high‐water seasons, and a drought occurred during the 2010 low‐water season. During these years, we surveyed populations of terrestrial, arboreal, and aquatic wildlife in a seasonally flooded Amazonian forest in the Loreto region of Peru (99,780 km²) to study the effects of intensification of natural climatic fluctuations on wildlife populations and in turn effects on resource use by local people. Shifts in fish and terrestrial mammal populations occurred during consecutive years of high floods and the drought of 2010. As floods intensified, terrestrial mammal populations decreased by 95%. Fish, waterfowl, and otter (Pteronura brasiliensis) abundances increased during years of intensive floods, whereas river dolphin and caiman populations had stable abundances. Arboreal species, including, macaws, game birds, primates, felids, and other arboreal mammals had stable populations and were not affected directly by high floods. The drought of 2010 had the opposite effect: fish, waterfowl, and dolphin populations decreased, and populations of terrestrial and arboreal species remained stable. Ungulates and large rodents are important sources of food and income for local people, and large declines in these animals has shifted resource use of people living in the flooded forests away from hunting to a greater reliance on fish.     

Sympatry and allopatry of song in North American tanagers

Summary The possibility that the hypotheses of character convergence and character displacement might explain interspecific variation in song features among North American tanagers is examined. Scarlet and summer tanagers (Piranga olivacea and P. rubra) are the most sympatric among the four species and have the largest differences in song characteristics. However, songs of scarlet tanagers do not differ significantly between sympatry and allopatry. Songs of summer tanagers more resemble those of scarlet tanagers in allopatry, but this geographical variation has been explained by variation in habitat characteristics. Both species countersing in sympatry, and react aggressively to each other's songs in sympatry as well as in allopatry, probably due to similarities in the song. The limited data from the narrow sympatric zone between western and hepatic tanagers (P. ludoviciana and P. flava) indicate that their songs differ to a great extent. Therefore, the results do not support the hypothesis of character convergence. Character displacement might explain partially interspecific differences in song features between scarlet and summer tanagers but cannot be tested further.     

Density and composition of heterotrophic bacterial populations in North Sea sediments

The bacteria from 119 sediment samples collected off the Belgian and Dutch North Sea coast were enumerated on marine agar. Geographical and seasonal variations were observed. The colony formers were mainly obligate aerobes. Coliform organisms were relatively rare. An exhaustive analysis of a few samples revealed a great number of species belonging to different taxonomic groups. A survey of physiological and biochemical characteristics of 71 isolates is presented.     

Breeding and larval distribution of the pteropod Clione limacina in the North Atlantic,Subarctic and North Pacific Oceans

The pteropod Clione limacina (Phipps, 1774) is an arcticboreal, circumpolar species, which is widely distributed in the North Atlantic and Subarctic Oceans; it also occurs in the North Pacific Ocean (in the Oyashio and neighbouring waters) and along the Atlantic coast of North America in the waters of the cold Labrador current to the Cape Hatteras region (35° N). The distribution of C. limacina larvae in the plankton of the Norwegian, Barents and White Seas, the Bear Island-Spitsbergen region of the Greenland Sea, the Newfoundland Grand Bank and the Flemish-Cap Bank region of the North-western Atlantic Ocean, and the Kurile-Kamchatka region of the North-western Pacific Ocean has been studied, and information from literature concerning the reproduction and larval occurrence of the species is summarized. Throughout its distributional are, spawning of C. limacina is characterized by the same general ecological pattern. This species breeds and spawns in all types of water masses occurring within the vertical range which it commonly inhabits — from surface layers to 500 m water depth. In all local populations of the species, the most intensive spawning is correlated with the spring/summer period of annual heating of the local waters, and the highest abundance parallels maximum growth of phytoplankton which serves as food for veligers and early polytrochous larvae. After the end of this period, spawning intensity in all local C. limacina populations declines sharply, but spawning continues at low intensity during the autumn/winter season, being practically continuous throughout the year. Distribution patterns of C. limacina larvae are determined by those of their parental forms (the parental forms spawn in the zones permanently inhabited). The earliest larval stages of C. limacina (veligers) are present predominantly in the upper 100 or 200 m water layer, i.e. in the zone of high phytoplankton abundance. Polytrochous larvae, after becoming predaceous feeders, are distributed throughout the whole water column from the surface to 500 m depth, similar to adult C. limacina. As with the adults, larvae are present (within the species' distribution area) in all types of water masses. Since the beginning of the twentieth century, in the course of the warming of the Arctic Ocean, the southern race of C. limacina (formerly a summer/autumn seasonal invader in the Norwegian Sea) has become a permanent component of the plankton fauna of the Norwegian and Barents Seas in regions influenced by the Norwegian-Northcape Current System.     

Distribution of male and female mtDNA lineages in populations of blue mussels,Mytilus trossulus and M. galloprovincialis,along the Pacific coast of North America

Geographic variation in mitochondrial large subunit (16S) ribosomal RNA haplotypes was examined for blue mussels, Mytilus trossulus Gould, 1850 and M. galloprovincialis Lamarck, 1819, sampled from ten sites along the Pacific coast of the USA in January of 1993. Using polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assays we determined haplotype frequencies for both the male and female mussel mitochondrial DNA (mtDNA) lineages. Populations from Morro Bay south to San Diego, California, contained only M. galloprovincialis male and female haplotypes, while those from Arcata Bay, California, north to Port Orford, Oregon, were fixed for M. trossulus haplotypes. Populations from Monterey Bay to Bodega Bay, California, contained a mixture of M. trossulus and M. galloprovincialis haplotypes. Overall only 2 of 97 heteroplasmic individuals had a mixed M. trossulus/M. galloprovincialis mitochondrial genotype indicating that hybridization is uncommon in the populations sampled. Further, there was no evidence of extensive introgression between these mussel taxa at the level of mtDNA. This is in contrast to previously published results which suggested the significant introgression of M. trossulus haplotypes into southern populations containing primarily M. galloprovincialis nuclear genotypes. We feel the discrepancy lies in the ability of our assays to detect haplotypes corresponding to both the male and female mtDNA lineages. Potential explanations for the lack of mtDNA introgression include, low levels of backcrossing between hybrids and parental taxa, epistatic interaction between nuclear and mitochondrial genes and the breakdown of a sex-specific inheritance pattern for mtDNA in hybrids.     

Physiology and chemical composition of nitrogen-fixing phytoplankton in the central North Pacific Ocean

The magnitude and physiological characteristics of biological nitrogen fixation have been studied in the oligotrophic waters of the North pacific gyre. The filamentous blue-green algae Trichodesmium spp. and Richelia intracellularis were the important nitrogen-fixing phytoplankton. Most of the nitrogen fixation occurs in the upper 40 m of the water column, with detectable fixation as deep as 90 m, which corresponds to about the 1 % light depth. There was no evidence of photoinhibition of nitrogen fixation, although CO₂ reduction was depressed slightly at the highest light levels. The rate of nitrogen fixation in the water column varied throughout the day, being highest in mid-morning and in late afternoon. Relatively high fixation rates were also found during periods of darkness. Elevated oxygen concentrations had a marked inhibitory effect on rates of nitrogen fixation, a pO₂ of 0.4 atm causing a 75% inhibition. Data from studies of nitrogen fixation and assimilation rates of ¹⁵N-labelled nitrate, ammonium, and urea indicate that nitrogen fixation furnished about 3% of the total daily fixed nitrogen requirement for phytoplankton growth. Studies with isolated colonies of Trichodesmium spp. indicated that 100% of their nitrogen requirement was met by nitrogen fixation. Chemical composition of the Trichodesmium colonies showed that the C:N ratio was 4.1 and that their phosphorus content relative to carbon or nitrogen was much lower than that of the total particulate material in the water column. Elevated ratios of carbon: adenosine triphosphate (ATP) also suggest that phosphorus deficiency may be limiting the growth of Trichodesmium. The magnitude of nitrogen fixation in the gyre is seasonally dependent, with high rates in late summer and autumn. At these times the water column is stratified, with phosphate and nitrate barely detectable in the upper 100 m. Our data suggest that during these months of stratification, biological fixation of nitrogen amounts to about 33 g-at N/m²/day.     

Abundance and size distribution dynamics of abyssal epibenthic megafauna in the northeast Pacific

The importance of interannual variation in deep-sea abundances is now becoming recognized. There is, however, relatively little known about what processes dominate the observed fluctuations. The abundance and size distribution of the megabenthos have been examined here using a towed camera system at a deep-sea station in the northeast Pacific (Station M) from 1989 to 2004. This 16-year study included 52 roughly seasonal transects averaging 1.2 km in length with over 35600 photographic frames analyzed. Mobile epibenthic megafauna at 4100 m depth have exhibited interannual scale changes in abundance from one to three orders of magnitude. Increases in abundance have now been significantly linked to decreases in mean body size, suggesting that accruals in abundance probably result from the recruitment of young individuals. Examinations of size-frequency histograms indicate several possible recruitment events. Shifts in size-frequency distributions were also used to make basic estimations of individual growth rates from 1 to 6 mm/month, depending on the taxon. Regional intensification in reproduction followed by recruitment within the study area could explain the majority of observed accruals in abundance. Although some adult migration is certainly probable in accounting for local variation in abundances, the slow movements of benthic life stages restrict regional migrations for most taxa. Negative competitive interactions and survivorship may explain the precipitous declines of some taxa. This and other studies have shown that abundances from protozoans to large benthic invertebrates and fishes all have undergone significant fluctuations in abundance at Station M over periods of weeks to years.     

A comparison of zooplankton patterns in the California Current and North Pacific Central Gyre

This study compares the small-scale (100's to 1000's of meters) horizontal spatial distribution of zooplankton from stations in the California Current (29°N; 118°W) and in the North Pacific Central Gyre (31°N; 155°W). Patterns were inferred from the spacing of vertical tows and the variability in abundance of 15 taxonomic categories caught in these tows. In the California Current, 4 tows were taken at random positions within 2000 m of a drogue or fixed geographic position and 4 replicate tows were taken at the drougue or the fixed point. Four series of these 8 tows were taken around noon and midnight during two days. At the Central Gyre station, two similar series (one day and one night) were taken while following a drogue. Estimates of the scale of structure based on comparisons of replicate and random tow variability suggest that aggregated patterns in the Central Gyre are larger than a few hundred meters, while the California Current structures may be less than 100 m in size. Day-night changes in patch size were not apparent in either area. Evidence for multispecies patches was found only for the Central Gyre station. Replication samples in both areas gave more consistent measures of community structure (relative proportions of species) than the random tows. Similarity of community structure decreased with increasing distance between tows being compared. The decrease was much greater for the California Current station, a further indication of smaller patch size in this area. Diurnal changes in community structure occurred in both areas.Based in part on a dissertation submitted in partial fulfillment of the requirements of the Ph.D. degree at the University of California, San Diego. Portions of this research were supported by the Marine Life Research Program of the Scripps Institution of Oceanography.     

A century of increasing pine density and associated shifts in understory plant strategies

We analyzed one of the longest-term ecological data sets to evaluate how forest overstory structure is related to herbaceous understory plant strategies in a ponderosa pine forest. Eighty-two permanent 1-m2 chart quadrats that were established as early as 1912 were remeasured in 2007. We reconstructed historical forest structure using dendrochronological techniques. Ponderosa pine basal area increased from an average of 4 m2/ha in the early 1900s to 29 m2/ha in 2007. Understory plant foliar cover declined by 21%, species richness declined by two species per square meter, and functional diversity also declined. The relative cover of C4 graminoids decreased by 18% and C3 graminoids increased by 19%. Herbaceous plant species with low leaf and fine root nitrogen concentrations, low specific leaf area, high leaf dry matter content, large seed mass, low specific root length, short maximum height, and early flowering date increased in relative abundance in sites where pine basal area increased the most. Overall, we observed a long-term shift in composition toward more conservative shade- and stress-tolerant herbaceous species. Our analysis of temporal changes in plant strategies provides a general framework for evaluating compositional and functional changes in terrestrial plant communities.