History and taxonomy: their roles in the core-satellite hypothesis

Metapopulation models are important in explaining the distribution and abundance of species through time and space. These models combine population dynamics with stochastic variation in extinction and immigration parameters associated with local populations. One of the predictions of metapopulation models is a bimodal distribution of species frequency of occurrence, a pattern that led to the development of the core-satellite species hypothesis. The spatial scale and taxonomic classification of past core-satellite studies has often been undefined. In our study, we have integrated metapopulation dynamics with the roles that differential dispersal ability and history play in the shaping of communities. The differences in distribution patterns between landbridge islands and oceanic islands, and among various taxa (birds, mammals, herptiles, arthropods, fish, and plants) are analyzed. The majority of landbridge islands comprised locally and regionally abundant species (core species), whereas the majority of oceanic islands had a uniform distribution (or no end-peak in their distribution). The patterns of distribution among the taxonomic groups also showed differences. Birds (good dispersers) consistently showed bimodal- and core-distribution patterns. The bimodal prediction of species distribution is best exemplified in the landbridge islands and in birds, and least in oceanic islands and in organisms other than birds. These results illustrate the importance of testing models with various taxonomic groups and at different spatial scales and defining these scales before formally testing the predictions of the models.     

浙江海岛鸟兽地理生态学的初步研究

对浙江洞头岛及舟山五岛的鸟兽调查表明,海岛动物的种数较相邻大陆为低,但种群密度却高于大陆,岛上的某些种类出现生态位扩展的现象。舟山五岛兽类的种数和岛屿面积呈正相关,其关系式为S=2.12A~(0.29),但种群密度随着岛屿面积的增大而下降。文中据此提出了保护和发展岛屿动物资源的某些措施。     

Little evidence for sympatric speciation in island birds

It has been suggested that the presence of sister species in small circumscribed areas, such as isolated lakes or islands, might imply that these species originated sympatrically. To investigate this possibility in birds, we searched for endemic, congeneric species on isolated islands in the ocean. Among 46 islands and small archipelagos chosen because they contain at least one species of endemic land bird, we identified seven pairs of endemic congeners (excluding flightless rails). Of these seven, only four pairs are potentially sister species and thus possible candidates for sympatric speciation. However, three of these four pairs have always been considered the results of double invasion from a mainland source (in two of these cases, molecular-phylogenetic work has either confirmed a double invasion or is ambiguous). The one remaining pair may have speciated allopatrically on a small archipelago. Additional phylogenetic studies are required to understand these cases, and our results should also be considered in light of the large number of island-bird extinctions in historic time. We conclude that, at present, there is little evidence for sympatric speciation in island birds.     

The diet of feral cats on islands: a review and a call for more studies

Cats are among the most successful and damaging invaders on islands and a significant driver of extinction and endangerment. Better understanding of their ecology can improve effective management actions such as eradication. We reviewed 72 studies of insular feral cat diet from 40 islands worldwide. Cats fed on a wide range of species from large birds and medium sized mammals to small insects with at least 248 species consumed (27 mammals, 113 birds, 34 reptiles, 3 amphibians, 2 fish and 69 invertebrates). Three mammals, 29 birds and 3 reptiles recorded in the diet of cats are listed as threatened by the IUCN. However, a few species of introduced mammals were the most frequent prey, and on almost all islands mammals and birds contributed most of the daily food intake. Latitude was positively correlated with the predation of rabbits and negatively with the predation of reptiles and invertebrates. Distance from landmass was positively correlated with predation on birds and negatively correlated with the predation of reptiles. The broad range of taxa consumed by feral cats on islands suggests that they have the potential to impact almost any native species, even the smallest ones under several grams, that lack behavioral, morphological or life history adaptations to mammalian predators. Insular feral cat??s reliance on introduced mammals, which evolved with cat predation, suggests that on many islands, populations of native species have already been reduced.     

A global review of the impacts of invasive cats on island endangered vertebrates

Cats are generalist predators that have been widely introduced to the world's ~179 000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta‐analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non‐native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles.     

Overseas seed dispersal by migratory birds

Long-distance dispersal (LDD) promotes the colonization of isolated and remote habitats, and thus it has been proposed as a mechanism for explaining the distributions of many species. Birds are key LDD vectors for many sessile organisms such as plants, yet LDD beyond local and regional scales has never been directly observed nor quantified. By sampling birds caught while in migratory flight by GPS-tracked wild falcons, we show that migratory birds transport seeds over hundreds of kilometres and mediate dispersal from mainland to oceanic islands. Up to 1.2% of birds that reached a small island of the Canary Archipelago (Alegranza) during their migration from Europe to Sub-Saharan Africa carried seeds in their guts. The billions of birds making seasonal migrations each year may then transport millions of seeds. None of the plant species transported by the birds occurs in Alegranza and most do not occur on nearby Canary Islands, providing a direct example of the importance of environmental filters in hampering successful colonization by immigrant species. The constant propagule pressure generated by these LDD events might, nevertheless, explain the colonization of some islands. Hence, migratory birds can mediate rapid range expansion or shifts of many plant taxa and determine their distribution.     

Plants and birds on the shore of the Sea of Okhotsk: Balance, crisis, adaptation

Mutual relationships between sea colonial birds and plants on the northern shore of the Sea of Okhotsk are considered. The birds form huge flocks on small islands thus transforming the island landscape and providing specific vegetation at nesting sites. The intensity of ornithogenic load determines different relations between the productivity of plant communities and their species richness. As a rule, flora is depleted. The plants thriving at rookeries react to the intensive action of birds by forming specific ecobiomorphs. On the islands of the northern part of the Sea of Okhotsk tussocks of pine purple grass existing on the majority of nesting colonies are of the highest significance.     

Travel schedules to the high arctic: barnacle geese trade-off the timing of migration with accumulation of fat deposits

On their way from the wintering area to the breeding grounds in Spitsbergen, barnacle geese Branta leucopsis stage on islands off the coast of Norway. The aim of this study was to describe when the geese migrate in relation to the body stores deposited and explore questions related to the concept of optimal migration schedules and on the possible mechanisms involved. We estimated fat stores by repeated assessments of the abdominal profile index of individually marked females throughout staging. Reproductive success was derived from observations of the same individuals later in the annual cycle. Females arriving late, or with low fat stores at arrival, achieved higher fat deposition rates, probably by spending more time foraging. But they were unable to match final fat scores of birds that arrived earlier or with larger fat stores. Reproductive success was correlated with the timing of migration and individuals departing at intermediate dates achieved highest success. The exact date of peak reproductive success depended on the size of fat stores accumulated, such that low-quality birds (depositing less fat) benefited most from an early departure to the breeding grounds. Observations in the breeding colonies showed that these birds did not initiate a nest earlier but they spent a longer time in Spitsbergen before settling. The length of stay in Norway was close to the prediction derived from an optimisation model relating spring events to eventual breeding success. Poorest performing birds stayed longer than expected, perhaps depositing more fat to avoid the risk of starvation. Two possible mechanisms of the timing of migration were contrasted and it seemed that the geese departed for migration as soon as they were unable to accumulate any more fat stores.     

Stopover duration of Palearctic passerine migrants in the western Sahara – independent of fat stores?

Birds on migration spend much more time on stopover sites to refuel for the next migration step than aloft, but empirical data on stopover duration are rare, especially for Palearctic trans-Sahara migrants whilst crossing the desert. Previous studies suggest that stopover duration of fat birds in oases is much shorter than that of lean birds. During 2003 and 2004 capture–recapture data of migrating passerines from two inland oases in spring and from one coastal site in autumn in Mauritania, West Africa, were analysed to test whether the probability of being a transient and the stopover duration depend on fuel stores at first capture. The application of capture–recapture models revealed that during autumn migration at the coast the proportion of transients (individuals that stop over only for 1 day) was relatively high (77–90%) in three out of four species investigated and stopover duration was short (1.9–4.6 days). In the inland oases in spring, transients were detected in only four out of 12 analyses. Stopover duration was longer than at the coast in autumn and surprisingly long in some species with durations of up to 30 days. Models taking into account the initial fat load of birds on the first capture occasion were, with one exception, never the most parsimonious ones. This indicates that the time spent after and before capture at the stopover site did not depend on the fat stores at first capture. Therefore, we cannot confirm the assumption that birds arriving at stopover sites in the desert with low fat loads stay longer than birds that arrive with high fat loads.     

Parallel trends in the species diversity of west indian birds and bats

Summary In this paper I compare several biogeographic patterns of West Indian resident land birds and bats, including species-area and trophic diversity-area relationships, the number of islands inhabited per species and levels of endemism, trophic structure as compared with tropical mainland areas, and the degree of faunal simlarity between islands of similar sizes but different locations. In most respects, the bat and bird patterns are strikingly similar. Groups of birds that are conspicuously missing from the Antilles because of the absence of appropriate resources also have missing chiropteran counterparts. Plant-visiting bats and birds are better-represented in terms of relative number of species and, in birds, in biomass, on the Lesser Antilles than on the mainland (e.g. Panama). Small Antillean islands tend to share more species of birds and bats than do larger islands. Stochastic (sensu Simberloff 1978), deterministic, and interactive (e.g. competitive and trophic interactions) factors appear to underly these biogeographic trends. No evidence exists to suggest that Caribbean bats and birds have negatively affected each other's diversity.     

Factors determining the number of land bird species on Islands around South-Western Australia

Summary New evidence from the passerine faunas of islands off Southwestern Australia agrees with the hypothesis that the passerine faunas of Australian and New Zealand islands are impoverished because most passerine species are poor colonizers. Dispersal of landbirds onto Carnac Island near Perth was infrequent, and many of those species that arrived were represented by single birds. Comparison of similarly structured island and mainland habitats showed that island habitats still have fewer passerine bird species than mainland habitats. Island bird faunas are more stable over short periods of time than over long periods; this is contrary to island avifaunas in the Northern Hemisphere.The following features typify the avifaunas of Australian islands: immigration of species of land birds occurs infrequently; (natural) extinction is rare; and the degree of saturation of the avifaunas is low. Without more direct evidence, competitive interactions should not be invoked to account for the species poverty of these insular avifaunas.     

Status of the endangered ivory gull, <Emphasis Type="Italic">Pagophila eburnea</Emphasis>, in Greenland

The ivory gull, a rare high-Arctic species whose main habitat throughout the year is sea ice, is currently listed in Greenland as ‘Vulnerable’, and as ‘Endangered’ in Canada, where the population declined by 80% in 20 years. Despite this great concern, the status of the species in Greenland has been largely unknown as it breeds in remote areas and in colonies for which population data has rarely, if at all, been collected. Combining bibliographical research, land surveys, aerial surveys and satellite tracking, we were able to identify 35 breeding sites, including 20 new ones, in North and East Greenland. Most colonies are found in North Greenland and the largest are located on islands and lowlands. The current best estimate for the size of the Greenland population is approx. 1,800 breeding birds, but the real figure is probably >4,000 adult birds (i.e. >2,000 pairs) since all colonies have not yet been discovered and since only 50% or less of the breeding birds are usually present in the colonies at the time the censuses take place. Although this estimate is four to eight times higher than that previously arrived at, the species seems to be declining in the south of its Greenland breeding range, while in North Greenland the trends are unclear and unpredictable, calling for increased monitoring efforts.     

Regulation of protein breakdown and adrenocortical response to stress in birds during migratory flight

During long-term fasting at rest, protein utilization is maintained at low levels until it increases at a threshold adiposity. This study examines 1) whether such a shift in energy substrate use also occurs during endurance exercise while fasting, 2) the role of corticosterone, and 3) the adrenocortical response to an acute stressor. Ten species of migrating birds caught after an endurance flight over at least 500 km were examined. Plasma uric acid and corticosterone levels were low in birds with fat stores >5% of body mass and high in birds with smaller fat stores. Corticosterone levels were very high in birds with no visible fat stores and emaciated breast muscles. Corticosterone levels increased with handling time only in birds with large fat stores. These findings suggest that 1) migrating birds with appreciable fat stores are not stressed by endurance flight, 2) a metabolic shift (increased protein breakdown), regulated by an endocrine shift (medium corticosterone levels), occurs at a threshold adiposity, as observed in birds at rest, 3) adrenocortical response to an acute stressor is inhibited after this shift, and 4) an adrenocortical response typical for an emergency situation (high corticosterone levels) is only reached when muscle protein is dangerously low.     

The Assembly of an Island Fauna by Natural Invasion: Sources and Temporal Patterns in the Avian Colonization of Barbados

By virtue of their isolation and depauperate faunas, oceanic islands offer unique opportunities to characterize the historical development of ecological communities derived from both natural and anthropogenic invasions. Barbados, an outlying island in the Lesser Antilles, was formed approximately 700,000 YBP by tectonic uplift and was then colonized by birds via natural invasion from the much older volcanic islands in the main Lesser Antillean arc. We investigated the timing and sources of the avian invasion of Barbados by determining levels of mitochondrial DNA (mtDNA) divergence between populations of eight bird species from Barbados and those on the nearby putative source islands of St. Lucia and St. Vincent. Although all Barbados populations appeared to be young relative to the geological age of the island, we found differences among species in their inferred times of colonization and we identified at least two sources of immigrants to Barbados. In contrast to these historical differences across species and populations, our characterization of the mitochondrial genotypes of 231 individual birds suggests that each island population represents the descendants of a single founding maternal lineage. Considered in concert, the results of this molecular survey indicate that the Barbados bird community is composed of species with different invasion histories, which in turn suggests that the island's community composition has changed repeatedly over its 700,000 year history.     

Historical bird and terrestrial mammal extinction rates and causes

Aim Conservation of species is an ongoing concern. Location Worldwide. Methods We examined historical extinction rates for birds and mammals and contrasted island and continental extinctions. Australia was included as an island because of its isolation. Results Only six continental birds and three continental mammals were recorded in standard databases as going extinct since 1500 compared to 123 bird species and 58 mammal species on islands. Of the extinctions, 95% were on islands. On a per unit area basis, the extinction rate on islands was 177 times higher for mammals and 187 times higher for birds than on continents. The continental mammal extinction rate was between 0.89 and 7.4 times the background rate, whereas the island mammal extinction rate was between 82 and 702 times background. The continental bird extinction rate was between 0.69 and 5.9 times the background rate, whereas for islands it was between 98 and 844 times the background rate. Undocumented prehistoric extinctions, particularly on islands, amplify these trends. Island extinction rates are much higher than continental rates largely because of introductions of alien predators (including man) and diseases. Main conclusions Our analysis suggests that conservation strategies for birds and mammals on continents should not be based on island extinction rates and that on islands the key factor to enhance conservation is to alleviate pressures from uncontrolled hunting and predation.     

A model-independent test for the presence of regulatory equilibrium and non-random structure in island species trajectories

Aims To test a key prevision of the dynamic equilibrium theory of island biogeography, namely that changes in species numbers on islands over time (hereafter, species trajectories) are equilibrial, and to characterize aspects of the dynamical properties of species change over time using a model‐independent test. Methods We tested for regulatory equilibrium and non‐random structure in species numbers through time by comparing observed correlation coefficients at lag‐k for species trajectories from four true islands and two habitat islands. First, we estimated the shape of the autocorrelation function for each observed species trajectory by calculating correlation coefficients of the observed data between pairs of values N_t?k and N_t separated by lag‐k (k = 1, 2, …, N ? 1). Second, we tested the observed correlation coefficients at each lag against a distribution of correlation coefficients generated by randomly ordering observed numbers in the species trajectories. Results The patterns of autocorrelation functions for all but one of the observed species trajectories did not exhibit evidence of regulatory equilibrium, and, in fact, closely matched what would be expected from a non‐stationary or ‘random walk’ process. The majority of the correlation coefficients generated from the observed species trajectories did not deviate significantly from correlation coefficients produced by the randomized trajectories. However, there was strong evidence of unusual positive autocorrelation at small time lags for birds on islands measured annually (2‐ to 4‐year lags) and for arthropods on islands measured weekly (7‐ to 8‐week lags), suggesting some degree of structure in change in species richness over time. Main conclusions The autocorrelation function patterns for all but one of the observed species trajectories showed various forms of non‐stationarity. These types of patterns suggest that the numbers of species through time gradually wandered away from their initial sizes. Our model‐independent test of individual correlation coefficients revealed significant structure in the observed species trajectories. These trajectories appear to be non‐random at relatively short lag intervals, indicating a process with short memory.     

Competition Between Insectivorous Lizards and Birds in Central Panama

The following evidence suggests that birds and lizards competefor their arthropod prey on islands in Lake Gatun, Panama: (1)there is extensive overlap between the diets of a representativebird and lizard, (2) at least one insectivorous lizard, Anolislimifrons, appears to be food-limited, (3) birds appear to havea major impact on arthropod abundances, (4) avian abundanceis negatively correlated with the physiological condition and,thus, with the fecundity of female A. limifrons, (5) bird andlizard population densities are negatively correlated. LakeGatun was formed in 1914. In the intervening years, a greatmany bird species have been lost from the smaller islands, butvery few lizard populations have gone extinct. Ninety-six percentof the between-site variation in avian abundances is accountedfor by the number of bird species present at a site. Sites withdepauperate avifaunas are characterized by low avian abundancesbecause the species present do not experience ecological release,and resources which are utilized by birds on species-rich sitesare not exploited by birds on species-poor sites. Thus, avianabundances are controlled by factors extrinsic to the bird-lizardinteraction, and lizards opportunistically increase their abundancesat sites with low avian abundances.     

Comparison of the ecology and evolution of plants with a generalist bird pollination system between continents and islands worldwide

Thousands of plant species worldwide are dependent on birds for pollination. While the ecology and evolution of interactions between specialist nectarivorous birds and the plants they pollinate is relatively well understood, very little is known on pollination by generalist birds. The flower characters of this pollination syndrome are clearly defined but the geographical distribution patterns, habitat preferences and ecological factors driving the evolution of generalist‐bird‐pollinated plant species have never been analysed. Herein I provide an overview, compare the distribution of character states for plants growing on continents with those occurring on oceanic islands and discuss the environmental factors driving the evolution of both groups. The ecological niches of generalist‐bird‐pollinated plant species differ: on continents these plants mainly occur in habitats with pronounced climatic seasonality whereas on islands generalist‐bird‐pollinated plant species mainly occur in evergreen forests. Further, on continents generalist‐bird‐pollinated plant species are mostly shrubs and other large woody species producing numerous flowers with a self‐incompatible reproductive system, while on islands they are mostly small shrubs producing fewer flowers and are self‐compatible. This difference in character states indicates that diverging ecological factors are likely to have driven the evolution of these groups: on continents, plants that evolved generalist bird pollination escape from pollinator groups that tend to maintain self‐pollination by installing feeding territories in single flowering trees or shrubs, such as social bees or specialist nectarivorous birds. This pattern is more pronounced in the New compared to the Old World. By contrast, on islands, plants evolved generalist bird pollination as an adaptation to birds as a reliable pollinator group, a pattern previously known from plants pollinated by specialist nectarivorous birds in tropical mountain ranges. Additionally, I discuss the evolutionary origins of bird pollination systems in comparison to systems involving specialist nectarivorous birds and reconstruct the bird pollination system of Hawaii, which may represent an intermediate between a specialist and generalist bird pollination system. I also discuss the interesting case of Australia, where it is difficult to distinguish between specialist and generalist bird pollination systems.     

BREEDING OF THE WHITE-BACKED AND RÜPPELL'S GRIFFON VULTURES, GYPS AFRICANUS AND G. RUEPPELLII

The breeding season of two species of griffon vultures are described. Rüppell's Griffon Vulture lays 2–3 months earlier than the White-backed Griffon. Young birds were hand-reared to determine their food requirements during growth; these estimates were combined with the food requirements of adult birds to make an estimate of the amount of food a parent bird needs to obtain when it is rearing young. The amount of food actually obtained by a group of birds was recorded from the size of the crops of birds returning to the breeding colony in the afternoon. The comparison of the estimates of the food obtained and the food required through the breeding season suggested that there may be a period during rearing when there was insufficient food available to satisfy the food requirements of both chick and adult. Chicks were found to have a very high survival rate and were probably receiving sufficient food. Presumably adult birds were not therefore receiving sufficient food, and the examination of a sample of adult birds for body condition through the breeding season showed a clear decline in their fat deposits. It was considered that in both species, breeding was timed so that the young left the nest at a period in the year when food conditions were good and the young birds could feed with little competition from adults. The parent birds therefore had to rear young during a season in the year when food conditions were not always adequate and they had to rely on utilising fat reserves. The food conditions for vultures during this study were probably favourable and during years of food shortage breeding may become impossible, or restricted to the most aggressive and dominant individuals.     

Begegnungen in der Arktis Spitzbergens

Encountering Svalbard's nature: plants, birds, and mammals of the high arctic Svalbard is a group of islands in the northernmost Atlantic, only 1300 km south oft the north pole. By the influence of the Gulf Stream, the climate is mild enough to allow for the growth of around 180 vascular plants, among them more then 10 Saxifraga species. The forest is made up of a number of willow species only some centimeters high. There are around 30 common breeding birds, most of them summer visitors. Only the ptarmigan remains throughout the year. This species together with three goose species rely upon vegetarian food, whereas most other birds feed in the sea. Polar bear, several seal species, polar fox, Glaucous gull, and Skua species occur as predators. Some animals, in spite of the ever increasing tourism and local hunting, behave in an extremely confident way.