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"Natural History Note"
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Field notes on science & nature
Pioneering a new niche in the study of plants and animals in their natural habitat, this book allows readers to peer over the shoulders and into the notebooks of a dozen eminent field workers, to study firsthand their observational methods, materials, and fleeting impressions.
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Differences in Speed and Duration of Bird Migration between Spring and Autumn
It has been suggested that birds migrate faster in spring than in autumn because of competition for arrival order at breeding grounds and environmental factors such as increased daylight. Investigating spring and autumn migration performances is important for understanding ecological and evolutionary constraints in the timing and speed of migration. We compiled measurements from tracking studies and found a consistent predominance of cases showing higher speeds and shorter durations during spring compared to autumn, in terms of flight speeds (airspeed, ground speed, daily travel speed), stopover duration, and total speed and duration of migration. Seasonal differences in flight speeds were generally smaller than those in stopover durations and total speed/duration of migration, indicating that rates of foraging and fuel deposition were more important than flight speed in accounting for differences in overall migration performance. Still, the seasonal differences in flight speeds provide important support for time selection in spring migration.
Journal Article
Bimodal Pollination Systems in Andean Melastomataceae Involving Birds, Bats, and Rodents
Floral adaptation to a single most effective functional pollinator group leads to specialized pollination syndromes. However, adaptations allowing for pollination by two functional groups (bimodal pollination systems) remain a rarely investigated conundrum. We tested whether floral scent and nectar traits of species visited by two functional pollinator groups indicate specialization on either of the two pollinator groups or adaptations of both (bimodal systems). We studied pollination biology in four species of Meriania (Melastomataceae) in the Ecuadorian Andes. Pollinator observations and exclusion experiments showed that each species was effectively pollinated by two functional groups(hummingbirds/bats, hummingbirds/rodents, flower-piercers/rodents), nectar composition followed known bird preferences, and scent profiles gave mixed support for specialization on bats and rodents. Our results suggest that nectar-rewarding Meriania species have evolved stable bimodal pollination strategies with parallel adaptations to two functional pollinator groups. The discovery of rodent pollination is particularly important given its rarity outside of South Africa.
Journal Article
Purring Crickets
Opportunities to observe contemporary signal change are incredibly rare but critical for understanding how diversity is created and maintained. We discovered a population of the Pacific field cricket (Teleogryllus oceanicus) with a newly evolved song (purring), different from any known cricket. Male crickets use song to attract females from afar and to court females once near. Teleogryllus oceanicus is well known for sexual signal evolution, as exemplified by a recent signal loss. In this study, we characterized the new purring sound and investigated the role of the purr in long-distance and short-distance communication. The purring sound differed from typical ancestral calls in peak frequency, amplitude, and bandwidth. Further, the long-distance purring song facilitated mate location, though the role of courtship purring song is less clear. Our discovery of purring male crickets is an unprecedented opportunity to watch the emergence of a newly evolved sexual signal unfold in real time and has potential to illuminate the mechanisms by which evolutionary novelties arise and coevolve between the sexes.
Journal Article
The Comparative Effects of Large Carnivores on the Acquisition of Carrion by Scavengers
Pumas (Puma concolor) and black bears (Ursus americanus) are large carnivores that may influence scavenger population dynamics. We used motion-triggered video cameras deployed at deer carcasses to determine how pumas and black bears affected three aspects of carrion acquisition by scavengers: presence, total feeding time, and mean feeding-bout duration. We found that pumas were unable to limit acquisition of carrion by large carnivores but did limit aspects of carrion acquisition by both birds and mesocarnivores. Through their suppression of mesocarnivores and birds, pumas apparently initiated a cascading pattern and increased carrion acquisition by small carnivores. In contrast, black bears monopolized carrion resources and generally had larger limiting effects on carrion acquisition by all scavengers. Black bears also limited puma feeding behaviors at puma kills, which may require pumas to compensate for energetic losses through increasing their kill rates of ungulates. Our results suggest that pumas provide carrion and selectively influence species acquiring carrion, while black bears limit carrion availability to all other scavengers. These results suggest that the effects of large carnivores on scavengers depend on attributes of both carnivores and scavengers (including size) and that competition for carcasses may result in intraguild predation as well as mesocarnivore release.
Journal Article
Mountain Pine Beetle Develops an Unprecedented Summer Generation in Response to Climate Warming
The mountain pine beetle (MPB;Dendroctonus ponderosae) is native to western North America, attacks most trees of the genusPinus, and periodically erupts in epidemics. The current epidemic of the MPB is an order of magnitude larger than any previously recorded, reaching trees at higher elevation and latitude than ever before. Here we show that after 2 decades of air-temperature increases in the Colorado Front Range, the MPB flight season begins more than 1 month earlier than and is approximately twice as long as the historically reported season. We also report, for the first time, that the life cycle in some broods has increased from one to two generations per year. Because MPBs do not diapause and their development is controlled by temperature, they are responding to climate change through faster development. The expansion of the MPB into previously inhospitable environments, combined with the measured ability to increase reproductive output in such locations, indicates that the MPB is tracking climate change, exacerbating the current epidemic.
Journal Article
Sex-specific ventral dichromatism and melanization in harlequin toads (Atelopus): a common but overlooked character of unknown function
Hidden colors are a widespread phenomenon in the animal kingdom, particularly in anurans. In some cases, hidden colors are suddenly exposed during defensive displays to startle predators, others seemingly remain hidden—particularly from researchers. Amazonian species of Neotropical harlequin toads (genus Atelopus) show striking and consistent ventral sexual dichromatism where females show and males generally lack melanization. Inspired by these observations we undertook a deeper inquiry across this species-rich genus. We collected data on ventral sexual dichromatism in Atelopus species and scored expression of sex-specific ventral melanization (i.e. black, brown and/or grey coloration). Ventral sexual dichromatism was present throughout the entire range of the genus and in almost all phylogenetic groups. However, there was a clear geographic signal with this trait being most common and widespread in Amazonian Atelopus species. Ventral melanization was correlated with temperature and elevation. Focusing on the Amazonian species, we present hypotheses on potential functions of sexually dimorphic ventral patterns and sex-specific ventral melanization as a baseline to further investigate the dynamics of sexual and natural selection as potential drivers of these traits. Selective pressures on less exposed body parts, such as ventral sides, likely differ considerably from those on dorsal appearance. Given the amount of research on amphibian coloration, it is remarkable how little we know about the evolution, function and underlying mechanisms of ventral appearance. We hope our work will spark more interest in the flip side of amphibians, thereby broadening our understanding of animal coloration.
Journal Article
Transitions between the Terrestrial and Epiphytic Habit Drove the Evolution of Seed-Aerodynamic Traits in Orchids
Orchids are globally distributed, a feature often attributed to their tiny dustlike seeds. They were ancestrally terrestrial but in the Eocene expanded into tree canopies, with some lineages later returning to the ground, providing an evolutionarily replicated system. Because seeds are released closer to the ground in terrestrial species than in epiphytic ones, seed traits in terrestrials may have been under selective pressure to increase seed dispersal efficiency. In this study, we test the expectations that seed airspace—a trait known to increase seed flotation time in the air—is (i) larger in terrestrial lineages and (ii) has increased following secondary returns to a terrestrial habit. We quantified and scored 20 seed traits in 121 species and carried out phylogenetically informed analyses. Results strongly support both expectations, suggesting that aerodynamic traits even in dust seeds are under selection to increase dispersal ability, following shifts in average release heights correlated with changes in habit.
Journal Article