Life-history characteristics of eleotrid fishes of the western hemisphere, and perils of life in a vanishing environment

The term amphidromous was coined (Myers in Copeia 1949:89–97, 1949b) to describe diadromous life histories that include migrations, not associated with reproduction, that are between fresh and marine waters. This concept has facilitated evaluations of life cycles among a number of groups of fishes including some belonging to the family Eleotridae. Information was gathered on life history patterns of eleotrid fish species that have been recorded from both fresh and brackish or marine waters of the east and west coasts of North, Middle, and South America, including adjacent islands, seeking evidence of diadromy and especially of amphidromy. Convincing evidence was found of diadromy in the life cycles of four species from the east coast (with another two species possibly in this category), and of three species from the west coast of the Americas and adjacent islands. However, there was convincing evidence of amphidromy in only one species from the east coast and adjacent islands, with another three species or species populations possibly in this category, and in three species from the west coast and adjacent islands. It seems possible from the available information that there may be variation among populations in life cycles of some of these species. However, it remains for the use of modern techniques to allow more definitive determinations of life history patterns of these eleotrid species populations. Serious concern exists with respect to the conservation of all diadromous species because of the worldwide emphasis on river manipulations, especially of dam construction. Resident diadromous organisms are being impeded in their migrations, and thus imperiled in their potential for survival, depending on the nature of river alterations and the abilities of the organisms to cope with them.     

Assembly of Alaska‐Yukon boreal steppe communities: Testing biogeographic hypotheses via modern ecological distributions

Beringia (eastern Asia, Alaska, northwest Canada) has been a land‐bridge dispersal route between Asia and North America intermittently since the Mesozoic Era. The Quaternary, the most recent period of exchange, is characterized by large, geologically rapid climate fluctuations and sea‐level changes that alternately expose and inundate the land‐bridge region. Insights into how Quaternary land‐bridge geography has controlled species exchange and assembly of the North American flora comes from focusing on a restricted community with narrow ecological tolerances: species that are today restricted to isolated steppe habitats (dry grasslands) in the Subarctic. We evaluated (i) potential controls over current spatial distributions of steppe plants and their pollinators in Alaska and Yukon and (ii) their ecological distributions in relation to potential biogeographic histories. Taxa present in North America that are disjunct from Asia tended to have larger altitudinal ranges (tolerating colder temperatures) than taxa disjunct from farther south in North America, which were largely restricted to the warmest, lowest‐elevation sites. Ecological findings support the following biogeographic scenarios. Migration from Asia via the land‐bridge occurred during Quaternary glacial periods when conditions were colder and drier than today. While a corridor for migration of cold‐tolerant species of cold steppe and tundra, the land bridge acted as a filter that excluded warmth‐demanding species. Migration from North America occurred under warm, dry interglacial conditions; thermophilous North American disjuncts taking this route may have long histories in Beringia, or they may have migrated recently during the relatively warm and dry early Holocene, when forest cover was incomplete.     

Pattern and process in the geographical ranges of freshwater fishes

North American freshwater fishes were studied to determine whether they displayed the same relationships between log (geographical range size) and log (body size) and the same pattern of range shape as found among North American birds and mammals. The forces that produce these patterns were also investigated. The log (geographical range size) : log (body size) relationship was analysed for 121 North American freshwater fish species. Thirty‐two imperilled species were compared with 89 non‐imperilled species to determine if the overall relationship could result from differential extinction. Range geometries were analysed, within and among habitat guilds, to determine if general patterns could be detected. The log (geographical range size) : log (body size) pattern among freshwater fish species was triangular and qualitatively similar to that found for North American birds and mammals. The results suggest that below a minimum geographical range, the likelihood of extinction increases dramatically for freshwater fishes and that this minimum range size increases with body size. The pattern of fish species’ range shapes differs from that found for other North American vertebrate taxa because, on average, fish possess much smaller ranges than terrestrial species and most fish species’ geographical ranges extend further on a north–south axis than on an east–west axis. The log (geographical range size) : log (body size) pattern reveals that fish species’ geographical ranges are more constrained than those of terrestrial species. The triangular relationship may be caused by differential extinction of species with large bodies and small geographical ranges as well as higher speciation rates of small‐bodied fish. The restricted geographical ranges of freshwater fishes gives them much in common with terrestrial species on oceanic islands. Range shape patterns within habitat guilds reflect guild‐specific historical and current ecological forces. The overall pattern of range shapes emerges from the combination of ecologically different subunits.     

Gradients of life-history variation: an intercontinental comparison of fishes

Multivariate analysis identified atwo-dimensional continuum of life-historyvariation among 301 fish species from Europe,North America, South America and the Atlanticand Pacific coasts of North America. The firstaxis was associated with larger body size,higher fecundity, delayed maturation, fewerreproductive events, and shorter breedingseason on one end and small size, lowfecundity, early maturity, multiplereproductive events per year, and prolongedbreeding season on the other. The second axiscontrasted fishes having larger eggs and moreparental care against fishes with the oppositesuite of traits.Phylogenetic affiliations of species wereapparent in the general patterns of ordinationof species within orders, indicatingevolutionary divergences in life-historypatterns. In fact, partitioning the variance oflife-history traits showed that taxonomic orderand latitude were the most important factorsand geographic region and habitat the least.Despite phylogenetic constraints, basiclife-history patterns showed consistencybetween distantly geographical regions,latitudinal ranges and basic adult habitats,indicating convergences in life-historypatterns. Although the basic life-historypatterns seemed repeatable among distantlyrelated taxa, geographical and latitudinalaffiliations were apparent. Species from SouthAmerica are skewed toward the opportunisticendpoint, whereas North American marine speciesare skewed toward the periodic endpoint of thetrilateral continuum model. Most of the fishspecies from South American data set came fromfluctuating environments, so an opportunisticstrategy of early maturation and continuousspawning permits efficient recolonization ofhabitats over small spatial scales. Incontrast, most species in the North Americanand European data sets came from seasonalhabitats that are nonetheless more hydrologicalstable, so a periodic strategy of delayingmaturation to attain large clutches enhancesadult survivorship during suboptimalenvironmental conditions and recruitment whenearly life stages encounter suitableenvironmental conditions. Similarly,latitudinal affiliations were also observed:opportunistic strategists more common intropical latitudes and periodic strategistsmore common in temperate and Arctic latitudes.     

Do flatland‐ and mountain‐dwelling species show different structuring of their experienced environment over latitude? A western vs. central‐eastern North America rodent multispecies comparison

Species occurrence databases and climate databases were used to examine differences in patterns of species experienced climate across latitude for wide‐ranging rodents in the central‐eastern and western North America. The accumulated data were used to address three questions: (1) Do rodent species in the central and eastern region of North America select habitat at range edges to remain closer to climate conditions at the range core? (2) Is there a trend toward species having greater experienced climate variation consistent with smaller effects of orbitally controlled climate oscillations in the south vs. north? (3) How do species experienced temperature, precipitation, and elevation means and variation in this region compare to rodent species in the adjacent but more heterogeneous western North America? Results showed that central‐eastern North American species occur in as wide a range of environmental conditions as available throughout their ranges. These patterns are different from previous findings for rodents in the adjacent western USA and highlight major differences in current structure of species experienced environmental means and variation over latitude for species in spatially heterogeneous, mountainous areas vs. those that occupy flatter lands. The differences are likely important for determining differential response to climate changes.     

Altitudinal gradients in stream fish diversity and the prevalence of diadromy in the Sixaola River basin,Costa Rica

Landscape-scale patterns of freshwater fish diversity and assemblage structure remain poorly documented in many areas of Central America, while aquatic ecosystems throughout the region have been impacted by habitat degradation and hydrologic alterations. Diadromous fishes may be especially vulnerable to these changes, but there is currently very little information available regarding their distribution and abundance in Central American river systems. We sampled small streams at 20 sites in the Sixaola River basin in southeastern Costa Rica to examine altitudinal variation in the diversity and species composition of stream fish assemblages, with a particular focus on diadromous species. A set of environmental variables was also measured in the study sites to evaluate how changes in fish assemblage structure were related to gradients in stream habitat. Overall, fish diversity and abundance declined steeply with increasing elevation, with very limited species turnover. The contribution of diadromous fishes to local species richness and abundance increased significantly with elevation, and diadromous species dominated assemblages at the highest elevation sites. Ordination of the sampling sites based on fish species composition generally arranged sites by elevation, but also showed some clustering based on geographic proximity. The dominant gradient in fish community structure was strongly correlated with an altitudinal habitat gradient identified through ordination of the environmental variables. The variation we observed in stream fish assemblages over relatively small spatial scales has significant conservation implications and highlights the ecological importance of longitudinal connectivity in Central American river systems.     

Phylogeny and biogeography of Aralia sect. Aralia (Araliaceae)

Aralia sect. Aralia (Araliaceae) consists of approximately eight species disjunctly distributed in Asia and North America. Phylogenetic and biogeographic analyses were conducted using sequences of the internal transcribed spacer regions of the nuclear ribosomal DNA. Aralia racemosa from eastern North America was sister to A. californica from western North America. Aralia cordata from eastern Asia did not form a species-pair relationship with the eastern North American A. racemosa. The two subspecies of A. racemosa formed a monophyletic group. Biogeographic analyses showed a close area relationship between eastern North America and western North America. The Himalayas were cladistically basal and eastern Asia was placed between the Himalayas and North America. The biogeographic analysis supported the origin of the eastern Asian and eastern North American disjunct pattern in Aralia sect. Aralia via the Bering land bridges. Comparisons with results of phylogenetic analyses of other genera suggested that (1) the floristic connection between eastern North America and western North America may be stronger than previously thought; and (2) the biogeographic patterns in the Northern Hemisphere are complex. Furthermore, a lack of correlation between sequence divergence values and phylogenetic positions was observed, suggesting the importance of a phylogenetic framework in biogeographic analyses.     

A Continent-Wide Migratory Divide in North American Breeding Barn Swallows (Hirundo rustica)

Populations of most North American aerial insectivores have undergone steep population declines over the past 40 years but the relative importance of factors operating on breeding, wintering, or stopover sites remains unknown. We used archival light-level geolocators to track the phenology, movements and winter locations of barn swallows (Hirdundo rustica; n = 27) from populations across North America to determine their migratory connectivity. We identified an east-west continental migratory divide for barn swallows with birds from western regions (Washington State, USA (n = 8) and Saskatchewan, Canada (n = 5)) traveling shorter distances to wintering areas ranging from Oregon to northern Colombia than eastern populations (Ontario (n = 3) and New Brunswick (n = 10), Canada) which wintered in South America south of the Amazon basin. A single swallow from a stable population in Alabama shared a similar migration route to eastern barn swallows but wintered farther north in northeast Brazil indicating a potential leap frog pattern migratory among eastern birds. Six of 9 (67%) birds from the two eastern populations and Alabama underwent a loop migration west of fall migration routes including around the Gulf of Mexico travelling a mean of 2,224 km and 722 km longer on spring migration, respectively. Longer migration distances, including the requirement to cross the Caribbean Sea and Gulf of Mexico and subsequent shorter sedentary wintering periods, may exacerbate declines for populations breeding in northeastern North America.     

Scale–bearing Chrysophyceae (Mallomonadaceae) from Central and Northern Canada

In this study, scale–bearing Chrysophyceae (Mallomonadaceae) have been examined by means of transmission and scanning electron microscopy. Lakes in four areas in central and northern Canada, viz. Experimental Lakes Area (ELA), in northwestern Ontario, Whiteshell Provincial Park and Southern Indian Lake in eastern and northern Manitoba, respectively, and Saqvaqjuac on the west coast of Hudson Bay in the Northwest Territories have been investigated. Forty–three species of the genera Mallomonas, Paraphysomonas, Spiniferomonas and Synura have been identified in addition to three species of the genus Chrysochromulina (Prymnesiophyceae). Ten species are new to Canada; five of these have not previously been recorded from North America. Paraphysomonas elegantissima sp. nov. is described. The composition of the Canadian chrysophycean flora is compared with the chrysophycean flora of North America as a whole.     

Informing conservation by identifying range shift patterns across breeding habitats and migration strategies

A species distribution combines the resources and climatic tolerances that allow an individual or population to persist. As these conditions change, one mechanism to maintain favorable resources is for an organism to shift its range. Much of the research examining range shifts has focused on dynamic distribution boundaries wheras the role of species breeding habitat or migration strategies on shift tendencies has received less attention. We expand on previous research by using a large suite of avian species (i.e., 277), analyzing observed abundance-weighted average latitudes, and categorizing species by breeding environment and migration strategy. We used the North American Breeding Bird Survey dataset to address two questions: (1) Has the center of observed abundance for individual species shifted latitudinally? (2) Is there a relationship between migration strategy or breeding habitat and range shifts? Results indicate the majority of species have experienced poleward range shifts over the last 43 years, and birds breeding in all habitat showed trends of poleward shift but only those species breeding in scrub-shrub and grassland environments were different from zero. Additionally, species that are short distance migrants are experiencing significant poleward shifts while Neotropical and permanent residents had shifts that were not different from zero. Our findings do support the general trend expected from climate driven changes (i.e., > 52 % shifting poleward), however, the proportion of species exhibiting equatorial shifts (24 %) or no significant shifts (23 %) illustrates the complex interplay between land cover, climate, species interactions, and other forces that can interact to influence breeding ranges over time. Regardless of the mechanisms driving range shifts, our findings emphasize the need for connecting and expanding habitats for those species experiencing range shifts. This research describes the patterns of breeding birds through central North America and we encourage future research to focus on the mechanisms driving these patterns.     

The biogeography of aquatic macrophytes in North America since the Last Glacial Maximum

Aim To document the post‐glacial migration of the major aquatic macrophytes of North America. Location North America north of Mexico. Methods Aquatic macrophyte pollen were extracted from the North American Pollen Database. The modern pollen distribution was mapped and related to the climate to document the geographical and climatic constraints on these taxa. The fossil pollen were mapped at 2‐ka intervals for the past 21 ka. Results Numerous genera were present in ice‐free Alaska during the Last Glacial Maximum, and south of the Laurentide Ice Sheet in the southeast. Those taxa with the widest modern climatic ranges migrated rapidly into ice‐marginal areas, first in the west and then in the east of North America. Subsequent changes in the range and abundance were smaller. Main conclusions There were four migration routes of aquatic macrophytes during the late‐glacial and post‐glacial periods: a southward migration from Alaska between 14–13 and ka, a northern migration in the west at the same time into the ice‐free Cordilleran region, and movements east and west of Appalachia as early as 19 ka for some taxa into the lower Mississippi and into the upper Mississippi and Great Lakes by 11 ka. As the Laurentide ice sheet wasted, aquatic taxa with the broadest contemporary temperature tolerances rapidly occupied ice‐marginal environments.     

Phylogenetics of the marine sculpins (Teleostei: Cottidae) of the North American Pacific Coast

With 92 species along the North American Pacific Coast, marine sculpins represent the most species-rich radiation of fishes in this region. I used the mitochondrial cytochrome b gene and the nuclear ribosomal S7 intron for 99 species (76 North American, 19 Asian, and four North Atlantic) to produce the most complete phylogenetic hypothesis yet generated for this assemblage. Maximum likelihood and Bayesian analyses produced highly similar tree topologies. While many previously proposed groupings based on morphology are recovered, the molecular data suggest that a number of genera are para- or polyphyletic. However, this analysis supports the monophyly of one large clade that is found exclusively along the North American Pacific Coast (Chitonotous–Ruscarius–Artedius–Orthonopius–Clinocottus–Leiocottus–Oligocottus). Some sibling species have disjunct ranges, suggesting allopatric speciation. However, many other sibling species have largely overlapping ranges, and repeated habitat shifts appear to have facilitated diversification.     

Importance of hybridization between indigenous and nonindigenous freshwater species: an overlooked threat to North American biodiversity

Biodiversity of North American freshwaters is among the greatest in the world. However, due to extensive habitat degradation, pollution, and introductions of nonindigenous species, this biodiversity is also among the most endangered. Unlike habitat degradation and pollution, nonindigenous species represent a permanent loss of biodiversity because their removal or control is often impossible. Most species introduced into nonnative North American ranges, however, are not from Eurasia but have been introduced from geographically isolated regions within North America. Although the ecological effects of introduced species have been widely documented, the effects of hybridization, especially between closely related species, represents an equally serious mechanism of extinction but is much less studied. Identification of which species are likely to hybridize after contact is of critical importance to prevent the further loss of native species. Molecular phylogenetics serves as a powerful tool to identify freshwater species at risk of introgression, if we can assume that genetic distance is a good predictor of the potential for hybridization. Although not a thorough review of all cases of hybridization, this article documents the extent and effects of hybridization in fishes, crayfishes, mussels, and other invertebrates in light of the currently accepted phylogenetic relationships. We suggest this approach may be the first step in addressing the potential threat of hybridization between many of the closely related species in North American fresh waters.     

Transoceanic dispersal of terrestrial species by debris rafting

Rare, long-distance dispersal events are a key process in generating and maintaining patterns in biological diversity and species distributions across space and time. The 9.0 magnitude earthquake that struck the eastern coast of Japan in 2011, and the subsequent 38 m high tsunami washed large amounts of shoreline debris into the Pacific Ocean that led to a large-scale biological rafting event carrying nearly 300 marine species to the western shores of North America. Whether oceanic, trans-Pacific dispersal via rafting generates long distance dispersal events for small, flightless, terrestrial species is unknown. By sampling beach debris associated with known hot-spots of tsunami debris along the north and east shores of Graham Island, Haida Gwaii, Canada, I document significantly dissimilar invertebrate communities associated with tide-line beach debris and the occurrence of several putative Japanese species of soil-dwelling mites (Acari: Oribatida). Previous explanations of Haida Gwaii's unique flora and fauna have been attributed to a proximity to the Beringian land bridge and the accumulated evidence of near-offshore glacial refugia during the last glacial period. However, my research also suggests that stochastic, trans-Pacific rafting events contribute to the biodiversity and biogeography of soil communities on the west coast of North America.     

Otolith microchemistry of tropical diadromous fishes: spatial and migratory dynamics

Otolith microchemistry was applied to quantify migratory variation and the proportion of native Caribbean stream fishes that undergo full or partial marine migration. Strontium and barium water chemistry in four Puerto Rico, U.S.A., rivers was clearly related to a salinity gradient; however, variation in water barium, and thus fish otoliths, was also dependent on river basin. Strontium was the most accurate index of longitudinal migration in tropical diadromous fish otoliths. Among the four species examined, bigmouth sleeper Gobiomorus dormitor, mountain mullet Agonostomus monticola, sirajo goby Sicydium spp. and river goby Awaous banana, most individuals were fully amphidromous, but 9–12% were semi‐amphidromous as recruits, having never experienced marine or estuarine conditions in early life stages and showing no evidence of marine elemental signatures in their otolith core. Populations of one species, G. dormitor, may have contained a small contingent of semi‐amphidromous adults, migratory individuals that periodically occupied marine or estuarine habitats (4%); however, adult migratory elemental signatures may have been confounded with those related to diet and physiology. These findings indicate the plasticity of migratory strategies of tropical diadromous fishes, which may be more variable than simple categorization might suggest.     

Lack of genetic differentiation between monarch butterflies with divergent migration destinations

Monarch butterflies are best known for their spectacular annual migration from eastern North America to Mexico. Monarchs also occur in the North American states west of the Rocky Mountains, from where they fly shorter distances to the California Coast. Whether eastern and western North American monarchs form one genetic population or are genetically differentiated remains hotly debated, and resolution of this debate is essential to understand monarch migration patterns and to protect this iconic insect species. We studied the genetic structure of North American migratory monarch populations, as well as nonmigratory populations in Hawaii and New Zealand. Our results show that eastern and western migratory monarchs form one admixed population and that monarchs from Hawaii and New Zealand have genetically diverged from North American butterflies. These findings suggest that eastern and western monarch butterflies maintain their divergent migrations despite genetic mixing. The finding that eastern and western monarchs form one genetic population also suggests that the conservation of overwintering sites in Mexico is crucial for the protection of monarchs in both eastern and western North America.     

The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the ‘Merry‐Go‐Round’ hypothesis

One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62° N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62° N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high‐seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium‐137 (¹³⁷Cs) levels in S. salar returning to a Quebec river suggested 62·3% had fed at or east of Iceland, whereas levels in 1 sea‐winter (SW) Atlantic Canada returnees indicated 24·7% had fed east of the Faroes. Lower levels of ¹³⁷ Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open‐ocean migrations of epipelagic fishes.     

A review of vital rates and cause‐specific mortality of elk Cervus elaphus populations in eastern North America

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Genetic and morphometric analysis of sixteenth century <Emphasis Type="Italic">Canis</Emphasis> skull fragments: implications for historic eastern and gray wolf distribution in North America

Resolving the taxonomy and historic ranges of species are essential to recovery plans for species at risk and conservation programs that aim to restore extirpated populations. In eastern North America, planning for wolf population restoration is complicated by the disputed historic distributions of two wolf species: the Old World-evolved gray wolf (Canis lupus) and the New World-evolved eastern wolf (C. lycaon). We used genetic and morphometric data from 4- to 500-year-old Canis samples excavated in London, Ontario, Canada to help clarify the historic range of these two wolf species in the eastern temperate forests of North America. We isolated DNA and sequenced the mitochondrial control region and found that none of the samples were of gray wolf origin. Two of the DNA sequences corresponded to those found in present day coyotes (C. latrans), but morphometric comparisons show an eastern wolf, not coyote, origin. The remaining two sequences matched ancient domestic dog haplotypes. These results suggest that the New World-evolved eastern wolf, not the gray wolf, occupied this region prior to the arrival of European settlers, although eastern-gray wolf hybrids cannot be ruled out. Furthermore, our data support the idea of a shared common ancestry between eastern wolves and western coyotes, and that the distribution of gray wolves at this time probably did not include the eastern temperate forests of North America.     

Pollen distribution in the bottom sediments of the western North Atlantic Ocean

An extensive survey of pollen distribution in surficial sediments from the slope and rise between 29° and 72°N, shows patterns which reflect the distribution of vegetation in eastern North America and the effects of aeolian, fluvial, and marine sedimentation. The results of the analysis of 94 core tops show that pollen concentration ranges from 23,000 to 10 grains per gram, and decreases offshore with distance from vegetation sources and northward in relation to lower vegetation density. Maximum concentration occurs in organic-rich, fine-grained lutum deposited off rivers draining the southeastern United States. Low pollen concentrations are associated with high-energy environments, such as the Western Boundary Undercurrent and the Labrador Current. Percentages of dominant pollen types generally correspond with onshore distribution of pollen and vegetation. Oak and other deciduous pollen types are the most abundant in marine sediments off the deciduous forests of eastern United States. Hemlock pollen is essentially restricted to sediments off the hemlock-oak forests of northeastern U.S. and southeastern Canada, and spruce pollen is most abundant adjacent boreal forests and forest-tundra formations. The relative increase in pine pollen seaward reflects the selective effects of marine transport. Synthesis of pollen data by Q-mode factor analysis shows that major vegetation formations of eastern North America produce distinctive, regional marine pollen assemblages.