20,777 research outputs found
Timing avian long-distance migration: from internal clock mechanisms to global flights
Migratory birds regularly perform impressive long-distance flights, which are timed relative to the anticipated environmental resources at destination areas that can be several thousand kilometres away. Timely migration requires diverse strategies and adaptations that involve an intricate interplay between internal clock mechanisms and environmental conditions across the annual cycle. Here we review what challenges birds face during long migrations to keep track of time as they exploit geographically distant resources that may vary in availability and predictability, and summarize the clock mechanisms that enable them to succeed. We examine the following challenges: departing in time for spring and autumn migration, in anticipation of future environmental conditions; using clocks on the move, for example for orientation, navigation and stopover; strategies of adhering to, or adjusting, the time programme while fitting their activities into an annual cycle; and keeping pace with a world of rapidly changing environments. We then elaborate these themes by case studies representing long-distance migrating birds with different annual movement patterns and associated adaptations of their circannual programmes. We discuss the current knowledge on how endogenous migration programmes interact with external information across the annual cycle, how components of annual cycle programmes encode topography and range expansions, and how fitness may be affected when mismatches between timing and environmental conditions occur. Lastly, we outline open questions and propose future research directions
On the principle of competitive exclusion in metapopulation models
In this paper we present and analyse a simple two populations model with
migrations among two different environments. The populations interact by
competing for resources. Equilibria are investigated. A proof for the
boundedness of the populations is provided. A kind of competitive exclusion
principle for metapopulation systems is obtained. At the same time we show that
the competitive exclusion principle at the local patch level may be prevented
to hold by the migration phenomenon, i.e. two competing populations may
coexist, provided that only one of them is allowed to freely move or that
migrations for both occur just in one direction
Use of Spotted Knapweed/Star Thistle (Asterales: Asteraceae) as the Primary Source of Nectar by Early Migrating Monarch Butterflies (Lepidoptera: Nymphalidae) from Beaver Island, Michigan
Recent observations over the past decade suggest that the invasive star thistle (aka spotted knapweed (Centaurea stoebe L.) provides much of the nectar that supports monarch butterflies (Danaus plexippus) in their pre-migratory and early migratory flight from the Beaver Island archipelago, an isolated chain of islands located in northern Lake Michigan. With the advent and continuation of global climate change, the opportunistic evolutionary changes that may take place between migrating monarchs and their dependence on non-native nectariferous plants, prior to migration, is worth further documentation and examination
The physiology of movement
Movement, from foraging to migration, is known to be under the influence of the environment. The translation of environmental cues to individual movement decision making is determined by an individual's internal state and anticipated to balance costs and benefits. General body condition, metabolic and hormonal physiology mechanistically underpin this internal state. These physiological determinants are tightly, and often genetically linked with each other and hence central to a mechanistic understanding of movement. We here synthesise the available evidence of the physiological drivers and signatures of movement and review (1) how physiological state as measured in its most coarse way by body condition correlates with movement decisions during foraging, migration and dispersal, (2) how hormonal changes underlie changes in these movement strategies and (3) how these can be linked to molecular pathways. We reveale that a high body condition facilitates the efficiency of routine foraging, dispersal and migration. Dispersal decision making is, however, in some cases stimulated by a decreased individual condition. Many of the biotic and abiotic stressors that induce movement initiate a physiological cascade in vertebrates through the production of stress hormones. Movement is therefore associated with hormone levels in vertebrates but also insects, often in interaction with factors related to body or social condition. The underlying molecular and physiological mechanisms are currently studied in few model species, and show -in congruence with our insights on the role of body condition- a central role of energy metabolism during glycolysis, and the coupling with timing processes during migration. Molecular insights into the physiological basis of movement remain, however, highly refractory. We finalise this review with a critical reflection on the importance of these physiological feedbacks for a better mechanistic understanding of movement and its effects on ecological dynamics at all levels of biological organization
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Parallel changes in gut microbiome composition and function in parallel local adaptation and speciation
The processes of local adaptation and ecological speciation are often strongly shaped by biotic interactions such as competition and predation. One of the strongest lines of evidence that biotic interactions drive evolution comes from repeated divergence of lineages in association with repeated changes in the community of interacting species. Yet, relatively little is known about the repeatability of changes in gut microbial communities and their role in adaptation and divergence of host populations in nature. Here we utilize three cases of rapid, parallel adaptation and speciation in freshwater threespine stickleback to test for parallel changes in associated gut microbiomes. We find that features of the gut microbial communities have shifted repeatedly in the same direction in association with parallel divergence and speciation of stickleback hosts. These results suggest that changes to gut microbiomes can occur rapidly and predictably in conjunction with host evolution, and that host-microbe interactions might play an important role in host adaptation and diversification
Inferring the rules of social interaction in migrating caribou
Social interactions are a significant factor that influence the decision-making of species ranging from humans to bacteria. In the context of animal migration, social interactions may lead to improved decision-making, greater ability to respond to environmental cues, and the cultural transmission of optimal routes. Despite their significance, the precise nature of social interactions in migrating species remains largely unknown. Here we deploy unmanned aerial systems to collect aerial footage of caribou as they undertake their migration from Victoria Island to mainland Canada. Through a Bayesian analysis of trajectories we reveal the fine-scale interaction rules of migrating caribou and show they are attracted to one another and copy directional choices of neighbours, but do not interact through clearly defined metric or topological interaction ranges. By explicitly considering the role of social information on movement decisions we construct a map of near neighbour influence that quantifies the nature of information flow in these herds. These results will inform more realistic, mechanism-based models of migration in caribou and other social ungulates, leading to better predictions of spatial use patterns and responses to changing environmental conditions. Moreover, we anticipate that the protocol we developed here will be broadly applicable to study social behaviour in a wide range of migratory and non-migratory taxa.
This article is part of the theme issue ‘Collective movement ecology’
Comparison of the Survival Rates between Migratory and Resident Birds
Knowledge of survival rates is critical for understanding population change for any species. Migratory species may have lower survival rates than resident species due to the physiological stress of migration and movement through unfamiliar habitat. In this study, we compared the apparent annual survival rate of migrant Gray Catbirds (Dumetella carolinesis) and resident Northern Cardinals (Cardinalis cardinalis). We analyzed eight years (2010-2017) of bird banding data in west-central Ohio using robust design mark-recapture analyses. We caught 51 individual Northern Cardinals and 146 individual Gray Catbirds. Survival varied from year to year, and Gray Catbirds had a marginally higher survival rate as compared to Northern Cardinals. Lastly, we saw differences in species regarding to emigration, immigration, and capture probability, with Northern Cardinals having higher values than Gray Catbirds. Contrary to other studies, our study found that migrants had a higher annual survival rate compared to residents, but the relationship was weak. Future studies should seek to determine what environmental variation may lead to yearly differences in survival.No embargoAcademic Major: Biolog
Modular knowledge systems accelerate human migration in asymmetric random environments
Migration is a key mechanism for expansion of communities. In spatially
heterogeneous environments, rapidly gaining knowledge about the local
environment is key to the evolutionary success of a migrating population. For
historical human migration, environmental heterogeneity was naturally
asymmetric in the north-south (NS) and east-west (EW) directions. We here
consider the human migration process in the Americas, modeled as random,
asymmetric, modularly correlated environments. Knowledge about the environments
determines the fitness of each individual. We present a phase diagram for
asymmetry of migration as a function of carrying capacity and fitness
threshold. We find that the speed of migration is proportional to the inverse
complement of the spatial environmental gradient, and in particular we find
that north-south migration rates are lower than east-west migration rates when
the environmental gradient is higher in the north-south direction.
Communication of knowledge between individuals can help to spread beneficial
knowledge within the population. The speed of migration increases when
communication transmits pieces of knowledge that contribute in a modular way to
the fitness of individuals. The results for the dependence of migration rate on
asymmetry and modularity are consistent with existing archaeological
observations. The results for asymmetry of genetic divergence are consistent
with patterns of human gene flow.Comment: 13 pages, 6 figures, 1 table in Proc. Roy. Soc. Interface 201
Towards Chemical Constraints on Hot Jupiter Migration
The origin of hot Jupiters -- gas giant exoplanets orbiting very close to
their host stars -- is a long-standing puzzle. Planet formation theories
suggest that such planets are unlikely to have formed in-situ but instead may
have formed at large orbital separations beyond the snow line and migrated
inward to their present orbits. Two competing hypotheses suggest that the
planets migrated either through interaction with the protoplanetary disk during
their formation, or by disk-free mechanisms such as gravitational interactions
with a third body. Observations of eccentricities and spin-orbit misalignments
of hot Jupiter systems have been unable to differentiate between the two
hypotheses. In the present work, we suggest that chemical depletions in hot
Jupiter atmospheres might be able to constrain their migration mechanisms. We
find that sub-solar carbon and oxygen abundances in Jovian-mass hot Jupiters
around Sun-like stars are hard to explain by disk migration. Instead, such
abundances are more readily explained by giant planets forming at large orbital
separations, either by core accretion or gravitational instability, and
migrating to close-in orbits via disk-free mechanisms involving dynamical
encounters. Such planets also contain solar or super-solar C/O ratios. On the
contrary, hot Jupiters with super-solar O and C abundances can be explained by
a variety of formation-migration pathways which, however, lead to solar or
sub-solar C/O ratios. Current estimates of low oxygen abundances in hot Jupiter
atmospheres may be indicative of disk-free migration mechanisms. We discuss
open questions in this area which future studies will need to investigate.Comment: Accepted for publication in ApJ Letter
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