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Migration
The formation of the Isthmus of Panama allowed for migrations between the once separated continents of North and South America. This led to one of the greatest documented interchanges of biota in Earth history, wherein an array of species across many groups migrated between the continents. Glyptotherium, a giant extinct armadillo‐like grazer, is an example of a taxon that likely originated in South America and migrated to North America. Here we use Ecological niche modeling to test the extent of suitable conditions for Glyptotherium in Central America and surrounding regions during the intervals when the taxon is thought to have dispersed, allowing for assessment of plausible migration routes and the hypothesis that the genus migrated from North America back to South America during the Rancholabrean (14 000–240 000 years ago). Our niche modeling results show suitable abiotic conditions for Glyptotherium in Central America and the surrounding area throughout the Plio‐Pleistocene, with western South America (the ‘high road') suggested as their ancestors' route northwards. Depending on the extent of suitable conditions, it may have been possible for Glyptotherium to return to South America during the Rancholabrean. The results support previous hypotheses that the range of Glyptotherium was constrained by the need for warm, wet environments.
Changes to migration routes and phenology create novel contact patterns among hosts and pathogens. These novel contact patterns can lead to pathogens spilling over between resident and migrant populations. Predicting the consequences of such pathogen spillover events requires understanding how pathogen evolution depends on host movement behaviour. Following spillover, pathogens may evolve changes in their transmission rate and virulence phenotypes because different strategies are favoured by resident and migrant host populations. There is conflict in current theoretical predictions about what those differences might be. Some theory predicts lower pathogen virulence and transmission rates in migrant populations because migrants have lower tolerance to infection. Other theoretical work predicts higher pathogen virulence and transmission rates in migrants because migrants have more contacts with susceptible hosts.
We aim to understand how differences in tolerance to infection and host pace of life act together to determine the direction of pathogen evolution following pathogen spillover from a resident to a migrant population.
We constructed a spatially implicit model in which we investigate how pathogen strategy changes following the addition of a migrant population. We investigate how differences in tolerance to infection and pace of life between residents and migrants determine the effect of spillover on pathogen evolution and host population size.
When the paces of life of the migrant and resident hosts are equal, larger costs of infection in the migrants lead to lower pathogen transmission rate and virulence following spillover. When the tolerance to infection in migrant and resident populations is equal, faster migrant paces of life lead to increased transmission rate and virulence following spillover. However, the opposite can also occur: when the migrant population has lower tolerance to infection, faster migrant paces of life can lead to decreases in transmission rate and virulence.
Predicting the outcomes of pathogen spillover requires accounting for both differences in tolerance to infection and pace of life between populations. It is also important to consider how movement patterns of populations affect host contact opportunities for pathogens. These results have implications for wildlife conservation, agriculture and human health.
Conservation behavior assists the investigation of species endangerment associated with managing animals impacted by anthropogenic activities. It employs a theoretical framework that examines the mechanisms, development, function, and phylogeny of behavior variation in order to develop practical tools for preventing biodiversity loss and extinction. Developed from a symposium held at the International Congress on Conservation Biology in 2011, this is the first book to offer an in-depth, logical framework that identifies three vital areas for understanding conservation behavior: anthropogenic threats to wildlife, conservation and management protocols, and indicators of anthropogenic threats. Bridging the gap between behavioral ecology and conservation biology, this volume ascertains key links between the fields, explores the theoretical foundations of these linkages, and connects them to practical wildlife management tools and concise applicable advice. Adopting a clear and structured approach throughout, this book is a vital resource for graduate students, academic researchers, and wildlife managers.
Why do some birds migrate during daytime and others at night? Why do some fly at high altitudes and others at lower altitudes? Whereas no comprehensive explanation of the diel schedule and altitude of migration has been proposed, several hypotheses have been advanced to explain nocturnal migration. These hypotheses focus on the need to forage during daylight (Brewster, 1886; Palmgren, 1949; Dorst, 1962), on predator avoidance (Lincoln, 1952), and on avoidance of atmospheric turbulence (Nisbet, 1955; Raynor, 1956; Bellrose, 1967). In addition, some authorities have suggested that the daily timing of migration is related to dietary habits or mode of migratory flight (Dorst, 1962; Baker, 1978). We argue that the diel schedule and altitude of bird migration have evolved in response to predictable variations in the structure of the atmosphere during its daily cycle.
Reviews hypotheses to account for differential migration, ie. where all individuals of a population migrate but distance travelled varies according to sex and/or age, using data from study of dark-eyed junco Junco h. hyemalis. Single-factor hypotheses involve ideas on body size, dominance and arrival time, but a multifactor hypothesis is here proposed, and the idea of a migration threshold mooted, ie. birds move when the advantage of remaining at one site are just outweighed by the advantages of leaving it.-P.J.Jarvis
Management of many species is currently based on an inadequate under- standing of their population dynamics. Lack of age-specific demographic information, particularly for long-lived iteroparous species, has impeded development of useful models. We use a Lefkovitch stage class matrix model, based on a preliminary life table developed by Frazer (1983a), to point to interim management measures and to identify those data most critical to refining our knowledge about the population dynamics of threatened log- gerhead sea turtles (Caretta caretta). Population projections are used to examine the sen- sitivity of Frazer's life table to variations in parameter estimates as well as the likely response of the population to various management alternatives. Current management practices appear to be focused on the least responsive life stage, eggs on nesting-beaches. Alternative protection efforts for juvenile loggerheads, such as using turtle excluder devices (TEDs), may be far more effective.
The impacts of ungulates on small mammals in an East African savanna habitat were investigated by monitoring the population
and community responses of small mammals on replicated 4-ha plots from which ungulates had been excluded. The dominant small
mammal in this habitat is the pouched mouse, Saccostomusmearnsi, a medium-sized murid rodent. Eight other small mammal species, including Arvicanthis sp., Mus sp., Mastomys sp., Dendromus sp., Crocidura sp., and, rarely, Tatera sp., Aethomys sp., and Acomys sp., were also captured. The dominant ungulates are elephant (Loxodonta africana), giraffe (Giraffa camelopardalis), Grevy's and common zebra (Equus grevyi and E. burchelli), buffalo (Syncerus cafer), eland (Taurotragus oryx), Grant's gazelle (Gazella granti), and domestic cattle. Within 1 year, S. mearnsi populations had responded dramatically to the exclusion of large mammals by a two-fold increase in density, a difference
that was maintained through pronounced seasonal fluctuations in the second year. Though individual pouched mice showed no
significant differences in their use of space with and without ungulates, male S. mearnsi maintained significantly higher body weights in the absence of ungulates, indicating that habitat quality had increased.
One other species, Mastomys sp., also increased in the absence of ungulates. Overall, the small mammal community maintained relatively constant species
diversity on the plots to which ungulates did not have access. On the plots to which ungulates did have access, on the other
hand, there was a rapid 75% decrease in diversity in the control plots during one trapping session. Ungulates are most likely
affecting small mammals through their effects on food quality, since there were no detectable differences in their exposure
to predators, as determined by vegetative cover, in the absence of ungulates. These results demonstrate that ungulates can
have strong and rapid impacts on small mammal abundance and diversity in East African savannas, an interaction which has not
previously been given serious consideration.
Whereas migrating birds have been implicated in the spread of West Nile virus (WNV), there is no direct evidence of birds actively migrating while infectious. The role of birds in WNV dispersal is difficult to assess in the field. However, this role can be evaluated experimentally because birds in migratory disposition display increased locomotor activity or restlessness under captive conditions. We tested the following hypotheses: (1) migrating passerine birds continue to exhibit migratory activity while infectious with WNV and (2) the migratory state of the individual affects the magnitude of viremia. We examined the migratory activity of two neoarctic-neotropical passerine migrants, Swainson’s thrush (Catharus ustulatus) and gray catbird (Dumetella carolinensis), during acute WNV infection. All gray catbirds and six of nine Swainson’s thrushes exhibited migratory activity while infectious. Moreover, migratory status did not appear to influence viremia titers, as might be expected if individuals were immunosuppressed during migration. Therefore, we demonstrate that migrating passerine birds are potential dispersal vehicles for WNV.
Migration is one of the possible responses by which an organism can react to changes in its environment. The persistence of biological populations depends on their ability to find those conditions in space and time under which they can survive and reproduce most successfully. For example, seasonally favorable conditions are offered by vast areas of the northern hemisphere. There is a premium on acquiring traits that help to reach such areas (Southwood, 1977), and birds, among others, have responded to this evolutionary challenge. Migration must have evolved several times in different avian taxa over geological times (Cox, 1985), and the diversity of avian migratory systems is very wide (Gauthreaux, 1982).
Migration is used by a number of species as a strategy for dealing with a seasonally variable environment. In many migratory species, only some individuals migrate within a given season (migrants) while the rest remain in the same location (residents), a phenomenon called ‘partial migration’. Most examples of partial migration considered in the literature (both empirically and theoretically) fall into one of two categories: either species where residents and migrants share a breeding ground and winter apart, or species where residents and migrants share an overwintering ground and breed apart. However, a third form of partial migration can occur when non-migrating individuals actually forgo reproduction, essentially a special form of low-frequency reproduction. While this type of partial migration is well documented in many taxa, it is not often included in the partial migration literature, and has not been considered theoretically to date. In this paper we present a model for this partial migration scenario and determine under what conditions an individual should skip a breeding opportunity (resulting in partial migration), and under what conditions individuals should breed every chance they get (resulting in complete migration). In a constant environment, we find that partial migration is expected to occur when the mortality cost of migration is high, and when individuals can greatly increase their fecundity by skipping a year before breeding. In a stochastic environment, we find that an individual should skip migration more frequently with increased risk of a bad year (higher probability and severity), with higher mortality cost of migration, and with lower mortality cost of skipping. We discuss these results in the context of empirical data and existing life history theory.
1. Monarch butterflies Danaus plexippus (L.) (Lepidoptera: Nymphalidae) are susceptible to infection by the obligate protozoan parasite Ophryocystis elektroscirrha (McLaughlin and Myers) (Apicomplexa: Neogregarinida). Because monarchs form resident and migratory populations in different parts of the world, this host–parasite system provides the opportunity to examine how variation in parasite prevalence relates to host movement patterns.
2. Parasite prevalence was evaluated using 14 790 adult monarchs captured between 1968 and 1997. Comparison of three populations in North America indicated that parasite prevalence is associated negatively with host dispersal distances. A continuously breeding, nonmigratory population in southern Florida showed high prevalence (over 70% heavily infected). The western population migrates moderate distances to overwintering sites on the Pacific Coast and has intermediate prevalence (30% heavily infected). The eastern migratory population, which travels the longest distance to Mexican overwintering sites, has exhibited less than 8% infection throughout the past 30 years.
3. Variation in parasite loads within North American migratory populations was investigated to determine whether the prevalence of heavy infection and average parasite loads declined during migration or overwintering. Average parasite loads of summer‐breeding adults in western North America decreased with increasing distance from overwintering sites. This suggests that heavily infected monarchs are less likely to remigrate long distances in spring. No differences in the frequency of heavily infected adults were found among eastern or western North American monarchs throughout the overwintering period, however, suggesting that this parasite does not affect overwintering mortality.
4. Changes in the prevalence of monarchs with low parasite loads demonstrate that spore transfer occurs during migration and overwintering, possibly when adult butterflies contact each other as a result of their clustering behaviour.
5. This study of geographical and temporal variation in O. elektroscirrha among populations of D. plexippus demonstrates the potential role of seasonal migration in mediating interactions between hosts and parasites, and suggests several mechanisms through which migratory behaviour may influence parasite prevalence.
The relationship between the vertical distributions of euphausiids and fish and light intensity has been studied directly by using a photometer in conjunction with an acoustically controlled rectangular midwater trawl. Samples were taken at a position centered on 47N; 17W on 15 and 16 May 1978. Five species of euphausiid and six species of fish have been analysed, both groups contained migrant and non-migrant species. The population of each of these species occurred throughout a light regime spanning at least three orders of magnitude of intensity; none of them was restricted to, or followed, and isolume. There were no sexual or size differences in the distributions of the euphausiids, but the population of Argyropelecus hemigymnus was probably stratified during the day, with smaller individuals occurring shallower than large ones. The results are discussed in relation to previous observations and to the theories of photic regulation of distributions and migrations.