Island shape,size, and isolation affect nest‐site selection by Little Terns

ABSTRACT Populations of many seabirds and other species that nest along coasts are declining due to habitat degradation and loss. An improved understanding of the species‐specific factors that determine nest density across a landscape is therefore critical for conservation efforts. We examined factors that affected the density (number per hectare) and abundance (number at a sampling site) of nests of Little Terns (Sternula albifrons) on the Sinai Peninsula, Egypt. Terns preferred to nest on islands rather than the mainland, with islands constituting 64% of the area surveyed, but containing 99% of the 439 tern nests we found. Nest densities were highest on islands that were small, located at moderate distances from the mainland, and irregularly shaped or elongated. Most nests (69%) were on islands with areas < 3 ha, although these islands represented < 5% of total island area, and islands with the highest nest densities were 80–300 m from the mainland. Terrestrial predators were more likely to occur on larger islands, visiting three of the largest four islands. Most tern nests were within 1 m of shorelines, causing island perimeter to be a strong influence on nest density. Island shape was the only factor that significantly affected nest abundance, with more nests on islands with relatively long perimeters for their size. Our results suggest that protection or creation of relatively small, slender islands at moderate distances from shore may be an effective means of increasing the number of breeding sites for Little Terns. Although not generally considered a potential determinant of nest site preferences for seabirds, island shape is likely to be important for species that prefer sites adjacent to water, including species that nest on beaches and seaside cliffs.     

Invasion and eradication of the American mink in the Atlantic Islands National Park (NW Spain): a retrospective analysis

Alien predators exert severe effects on island ecosystems, and their eradication from island habitats may therefore be necessary to conserve the native biota. Efforts are being made to eradicate the American mink (Neovison vison) from the Atlantic Islands of Galicia National Park (NW Spain), a protected site inhabited by vulnerable island fauna. We applied a molecular genetic approach to elucidate the source of the invaders and to evaluate the effectiveness of the trapping programme. We collected mink scats in the field and obtained tissue samples from culled mink. Populations of feral mink were known to be present in coastal areas close to the National Park archipelagos in the 1980–1990s. However, the molecular findings suggest that these populations were not the main source of the mink populations that colonized the islands during the 2000s. Recent releases from farms directly on to the islands are a more likely source of these invaders. Genetic analysis suggested that mink reproduced successfully on the islands and were relatively isolated from other mainland populations. The findings also suggest that most of the culled mink were juveniles, probably because it was more difficult to catch adults. Since mink are short-lived animals, it seems that eradication may also be achieved when a large proportion of juveniles are culled in isolated and small populations.     

Parasites of the feral sheep of Pitt Island,Chatham group

Abstract

Samples from the feral and domestic sheep on Pitt Island were examined for parasites. The feral sheep had never been treated against parasites, and most were due for extermination. The domestic sheep were examined by way of comparison. The sheep ked (Melophagus ovinus) and the chorioptic mange mite (Chorioptes bovis) were found on feral but not domestic sheep. The sheep body louse (Damalinia ovis) was found on domestic but not feral sheep. Lung nodules and liver lesions, presumed to be caused by parasites, were significantly more prevalent in domestic than in feral sheep. The prevalence of Cysticercus tenuicollis cysts and Sarcocystis spp. macrocysts was similar in feral and domestic sheep. The species of intestinal nematode and their relative abundance in feral sheep were similar to those in mainland sheep. Fewer feral sheep were found to have antibodies to Toxoplasma gondii when compared with other breeds; the proportion with antibodies to Sarcocystis ovicanis differed little from that in the mainland flocks, however. The data are compared with information from the Campbell Island feral sheep flock.     

COLOR PATTERN POLYMORPHISM IN THE LAKE ERIE WATER SNAKE,NERODIA SIPEDON INSULARUM

Populations of the water snake, Nerodia sipedon, on islands in western Lake Erie are polymorphic for color pattern. These populations include banded, intermediate, and unbanded morphs while surrounding mainland populations consist solely of the banded morph. The hypothesis that this polymorphism is maintained by strong selection and migration pressures is widely accepted. Unbanded morphs are apparently more cryptic along island shorelines while banded morphs are more cryptic on the mainland. Migration of banded morphs from the mainland explains their persistence in island populations. Data collected in a capture-mark-recapture program on six islands provide no evidence of differential selection among morphs; morph frequencies do not differ among age classes, between once-captured and multiply-captured snakes, or between scarred and unscarred snakes. Furthermore, herring gulls, the most common snake predators in the island area, appear to detect banded and unbanded model snakes with equal ease. High site fidelity of water snakes and the distribution of morphs among islands suggest that migration from the mainland is not common. However, islands close to each other are similar in morph frequency, and water snakes have colonized islands elsewhere in the Great Lakes, indicating that some migration does occur. Recently, the frequency of banded morphs has increased in island populations while adult population sizes have declined. This increase in banded morphs is interpreted as reflecting an increased impact of migration from the mainland into these reduced populations. One scenario for the evolution and maintenance of this polymorphism is that selection was important in establishing unbanded morphs in island populations as they became isolated from the mainland. As populations declined to their present size, the impact of migration from the mainland increased and is now swamping the effect of selection. Further declines in island population size may result in fixation of the banded morph.     

The feral pig (Sus scrofa,Suidae) in Cocos Island,Costa Rica: composition of its diet,reproductive state and genetics

Feral pigs (Sus scrofa) cause different kinds of damage specially on oceanic islands. Pigs were introduced at Cocos Island, Costa Rica, during 1793 and bred successfully. I analyzed feral pigs diet, reproductive state, genetics and the effects of predation, in order to gather data on their ecology and impact on certain Cocos Island communities. The diet was studied, during a dry and a wet period, through stomach contents. The genetic variability was determined through PCR analysis on tissue samples which were taken from feral (Cocos Island) and domestic (mainland) pig ear-lobes. Pigs at Cocos were omnivorous, the most important diet category in both seasons was fruits. More pigs consumed fruits during the wet season but the fruits did occupy more somuch volume during the dry season. Feral pigs did not disperse exotic seeds nor prey on animal endemic species. 56% of the hunted pigs were males and 44% were females. From females in reproductive age, 46% were pregnant or suckling, and the average number of fetuses in a litter was 4.4. I confirmed a reproductive peak during January/February but could not demonstrate a reproductive peak during June/July. The low fetuses number per litter could be related with some levels of stress. The genetic variability for all the evaluated parameters within the feral population was low but not as low as expected. I suggest a compensatory mechanism were the inbreeding depression reduces consanguinity and a species susceptible to stocastic, demographic or environmental factors turns to be an adapted species with high resilience.     

Rapid morphological change in an insular population of feral sheep

Artificially selected qualities can reduce fitness in a wild setting, thus feral domesticates should experience strong selective forces. Domestic sheep Ovis aries have frequently become feral on islands, which differ substantially from mainland environments. We examined changes in body mass and wool traits in feral sheep inhabiting Santa Cruz Island (SCI), California for ≥90 years. To elucidate the influence of nutrition, we compared the mass of feral island sheep with that of island sheep raised in farm conditions. We found that feral sheep on SCI were smaller than purported founder breeds, and that most documented populations of insular feral sheep worldwide have converged to similar body sizes (within 6 kg). SCI rams attained greater mass in farm conditions but ewes did not, suggesting phenotypic plasticity in ram body mass. Ewes exhibited self-shedding of wool at a greater frequency than rams, and sex differences and shedding patterns were consistent with thermoregulation and the risk of fly strike disease as benefits of wool loss. Pigmentation rates did not increase, further supporting the influence of heat stress on wool traits. These changes occurred in <25 generations and may have had a genetic basis, representing a potential example of rapid evolution in insular feral sheep.     

The geographic distribution of pubescence in the sea daisy, Borrichia aborescens, on Bahamian Islands

Borrichia aborescens (L.) DC. is a salt‐tolerant perennial herb that is common on small islands in the central Bahamas. Two morphotypes are present: one with densely pubescent leaves and one with glabrous leaves. I conducted surveys in three archipelagos to document the geographical distribution of pubescence in this species and to infer the underlying mechanisms. B. aborescens was also grown from seed in a greenhouse. The pubescent form of B. aborescens was relatively more abundant on small islands than on nearby large ‘mainland’ islands. In two of the three archipelagoes, pubescence increased with distance on small islands. The pubescent form was relatively more abundant on small islands exposed to the open ocean compared to small islands that were protected by mainland islands or reefs on all sides. On a large mainland island, the pubescent form decreased in relative abundance inland from the coast. B. aborescens cultivated in a greenhouse revealed the effect of a genetic factor on the expression of pubescence. The observed patterns of variation are consistent with a physiological explanation for the adaptive benefit of pubescence. Trichomes may prevent physical blockage of the stomata by accumulation of salt in areas near breaking waves and salt spray.     

Impacts and management of feral cats Felis catus in Australia

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Comparisons of habitat structure and plant,arthropod and bird diversity between mainland and island sites near Perth,Western Australia

Detailed estimations of habitat structure, plant species diversity and diversity of arthropods were made at six 4.0 ha sites, two on mainland Western Australia near Perth and four on adjacent islands. The number of resident passerine bird species was also recorded at each site. Plant species diversity, and horizontal foliage diversity (=patchiness) varied only slightly between sites. There were significant positive correlations between arthropod Order diversity and bird diversity, and between vertical foliage diversity and bird diversity. In both Acacia and dune scrub, the Rottnest Island sites had more individuals of arthropods than the mainland sites but these belonged to fewer Orders. Numerical imbalance between arthropod Orders on Rottnest Island probably results from diminution of predators (passerine birds) there. As the actual number of arthropods is higher on the islands, the absence of so many species of passerine birds may result from other factors (ecological and historical).     

Terrestrial bird community patterns on the coralline islands of the Dahlak Archipelago, Red Sea, Eritrea

Aim This study aims to explain the patterns of species richness and nestedness of a terrestrial bird community in a poorly studied region. Location Twenty‐six islands in the Dahlak Archipelago, Southern Red Sea, Eritrea. Methods The islands and five mainland areas were censused in summer 1999 and winter 2001. To study the importance of island size, isolation from the mainland and inter‐island distance, I used constrained null models for the nestedness temperature calculator and a cluster analysis. Results Species richness depended on island area and isolation from the mainland. Nestedness was detected, even when passive sampling was accounted for. The nested rank of islands was correlated with area and species richness, but not with isolation. Idiosyncrasies appeared among species‐poor and species‐rich islands, and among common and rare species. Cluster analysis showed differences among species‐rich islands, close similarity among species‐poor and idiosyncratic islands, and that the compositional similarity among islands decreased with increasing inter‐island distance. Thus, faunas of species‐poor, smaller islands were more likely to be subsets of faunas of species‐rich, larger islands if the distance between the islands was short. Main conclusions Species richness and nestedness were related to island area, and nestedness also to inter‐island distances but not to isolation from the mainland. Thus, nestedness and species richness are not affected in the same way by area and distance. Moreover, idiosyncrasies may have been the outcome of species distributions among islands being influenced also by non‐nested distributions of habitats, inter–specific interactions, and differences in species distributions across the mainland. Idiosyncrasies in nested patterns may be as important as the nested pattern itself for conservation – and conservation strategies based on nestedness and strong area effects (e.g. protection of only larger islands) may fail to preserve idiosyncratic species/habitats.     

生境片段化对千岛湖地表甲虫物种多样性的影响

在千岛湖片段化景观中选取20个陆桥岛屿和8个大陆样点,从2012年7月到2014年4月,按季度(春、夏、秋季)6次采用巴氏陷阱法收集地表甲虫,分析其物种多度、组成、多样性和季节动态,以及不同岛屿上的地表甲虫的物种多样性与岛屿面积和隔离度等岛屿空间特征的关系.结果表明: 共收集记录到地表甲虫26科101种3370头.大陆和大岛地表甲虫的物种丰富度有显著差异,且小岛地表甲虫密度显著高于大陆;大陆地表甲虫的物种组成变化较大,而岛屿上分布的地表甲虫的物种组成则变化较小.地表甲虫的物种丰富度与岛屿面积呈显著正相关,密度与隔离度呈显著正相关.夏季岛屿上地表甲虫物种丰富度高于春秋两季,岛屿与大陆样地的Shannon指数、Simpson指数和Pielou均匀度指数均在夏季最高、秋季最低.     

Comparison of population numbers of yellow-eyed penguins,

During a comprehensive survey in 1999, 2000 and 2001, we investigated the number of breeding yellow-eyed penguin pairs on Stewart Island, where cats are present, and on adjacent cat-free islands. We found 79 pairs of yellow-eyed penguin breeding in 19 discrete locations on Stewart Island (4.2 pairs per location), and 99 pairs breeding in 10 discrete locations on all cat-free islands (9.9 pairs per location). Large-scale humaninduced habitat modifications have not occurred on Stewart Island, nor on any of its adjacent offshore islands. While the extensive coastline of Stewart Island (673 km) offers potentially large areas of breeding habitat for penguins, the highest number of breeding pairs were found on the smaller, predator-free Codfish Island (25 km coastline), where a total of 61 breeding pairs were recorded. On Stewart Island, where mustelids do not occur, only feral cats can pose a serious threat to penguin offspring. Results from this study suggest that feral cats may prey on yellow-eyed penguins on Stewart Island. Further work is necessary to investigate whether the observed low numbers of yellow-eyed penguins on Stewart Island are caused by feral cat predation. If so, it may be possible to develop appropriate measures to protect this penguin species from a population decline.     

If hippopotamuses cannot swim,how did they colonize islands?

Owing to their aquatic lifestyle, hippopotamuses are normally believed to have reached islands by swimming. Yet, some studies suggest they cannot swim due to their relatively high density. If so, this raises the question of how hippopotamuses would have reached some islands. Their immigration into the British Isles, Sicily, Malta, Zanzibar and Mafia can be accounted for, because these islands sit on continental shelves and were often linked to the mainland during the Pleistocene glacio‐eustatic sea‐level falls. In contrast, their occurrence in Crete, Cyprus and Madagascar would be more difficult to explain. Available geological evidence does not seem to rule out that the latter islands might have been connected with the nearest mainland areas in very recent times. This study intends to consider possibilities about how hippopotamuses reached islands and to show that more effective collaboration is required among specialists involved with the study of insular evolution, colonization and speciation.     

Winter filtering, immigrant selection and species composition of insular mammals of Lake Huron

Patterns in species composition of small mammals on islands of northwestern Lake Huron, USA were studied to test the hypothesis that insular community structure was strongly influenced by immigrant selection, l e, selection for the more vagile species Of 17 insectivores and rodents in the mainland pool nine were detected on at least one of the 25 islands studied These species comprised a biased subset of the mainland pool, biased in favor of species with relatively good winter immigration abilities The five true hibernators were absent from all islands studied and the two winter-inactive species occurred on just two islands Frequency of insular occurrence increased with level of winter activity (hibernator vs winter-inactive vs winter-active) and with body size (p < 0.02)
The winter filtering effect remains one of the best documented forms of immigrant selection In general however, insular community structure is influenced by the combined effects of selective extinction as well as selective immigration Common insular species are those which combine relatively high immigration abilities with low resource requirements     

Biogeography of vascular plants on habitat islands, peninsulas and mainlands in an eascentral Swedish agricultural landscape

The increase of island species richness with area can be explained by an increase in habitat diversity or by an equilibrium of species immigration and extinction. We examined vascular plant species richness in 39 sites (24 habitat islands, 7 'habitat peninsulas' and 8 comparable 'mainland' sites). We sampled at three scales: whole sites, meadows within sites and quadrats (4 m × 4 m) within meadows. All sites (10–10⁴ m²) contained natural vegetation within arable fields in eascentral Sweden. There was a strong correlation between species richness and area for whole sites and for meadows There was no correlation, however, between species richness in quadrats and site area. The difference between site and meadow results on one side and quadrat results on the other suggests that species richness increases with whole site area primarily because large sites are more diverse than smaller ones. Speciearea relationships did not differ between islands, peninsula and mainland sites. Thus, patterns of species richness on our sites were more consistent with habitat diversity than an immigratioextinction equilibrium.     

Colonization of Sphagnum on land uplift islands in the Baltic Sea: time, area, distance and life history

Aim To test whether species richness of Sphagnum mosses on islands in a land uplift archipelago is related to island age, area or connectivity, and whether the frequency of different species can be predicted by their life history and autecology. Location The northern Stockholm archipelago in the Baltic Sea, east‐central Sweden, with a current land uplift rate of 4.4 mm year^?1. Methods We sampled 17 islands differing in area (0.55–55 ha), height (3.6–18 m, representing c. 800–4000 years of age) and distance from mainland (1.6–41 km). For each Sphagnum patch we measured area, height above sea level, horizontal distance from the shore and shading from vascular plants. Factors affecting island species richness, species frequency and habitats on the islands were tested by stepwise regressions. Species frequency was tested on nine life history and autecological variables, including estimated abundance and spore output on the mainland, habitat preference and distribution. Results We recorded 500 patches of 19 Sphagnum species, distributed in 83 rock pools on 14 islands. Island species richness correlated positively with island area and with degree of shelter by surrounding islands, while distance from the mainland, connectivity, height or age did not add to the model. Species frequency (number of colonized islands and rock pools) was mainly predicted by spore output on the mainland and by habitat preference (swamp forest species were more frequent than others), while spore size, for example, did not add to the model. Species differed in mean height above and horizontal distance from the shore, area of occupied rock pools and in the degree of shading of patches. The mean horizontal distance from the shore and the area of occupied rock pools correlated positively with the normal growth position above the water table among species. Spore capsules were found in only 2% of patches, mostly in the bisexual Sphagnum fimbriatum. Main conclusions The presence of Sphagnum in the Stockholm archipelago seems to be governed by regional spore production and habitat demands. Sphagnum does not appear to be dispersal limited at distances up to 40 km and time spans of centuries. Species with a high regional spore output have had a higher colonization rate, which, together with the rarity of spore capsules on the islands, indicate the mainland as a source for colonization rather than dispersal among islands. Swamp forest species seem more tolerant to the island conditions (summer droughts and some salt spray) than open mire species. The different distances from the sea occupied by the species indicate a slow, continuous succession and species replacement towards the island interior as islands are being uplifted and thus expand in area. This partly explains why larger islands harbour more species. Our results thus support some of the island biogeographical theories related to the species–area relationship.     

Feral donkey (<Emphasis Type="Italic">Equus asinus</Emphasis>) eradications in the Galápagos

Introduced herbivores are major drivers of ecosystem change and biodiversity loss, particularly on islands. Tools and techniques now exist to routinely remove introduced herbivores from islands, providing a powerful conservation tool. Here, we summarize the few documented feral donkey removals on islands worldwide, and report on the removal of populations from the Galápagos archipelago, Ecuador. After decades of sporadic control programs on Santiago Island and Alcedo Volcano, Isabela Island, donkey populations were removed from both areas, concurrent with a goat eradication program. Both ground and aerial hunting programs were utilized. The latter method was highly efficient; donkeys were removed from Santiago Island with less than 80 h of aerial hunting. Given the clear impacts of introduced herbivores on islands worldwide, feral donkey populations should be routinely removed from islands.     

Variation in morphology, gait characteristics and speed of locomotion in two populations of lizards

Locomotor behaviour varies between two subspecies of the Spanish wall lizard Podarcis hispanica. One subspecies inhabits the Columbretes islands, the other lives on the Spanish mainland. Size standardized voluntary speeds (as measured in unrestrained laboratory conditions) are lower in the island population (P. h. atrata) than in the mainland population (P. h. hispanica). Maximal running performance (when chased) is much higher in the mainland population than in the island population. High speed video recordings show that subspecies differ in gait characteristics: individuals from the mainland modulate running velocity primarily by modifying stride length, individuals from the island primarily by altering stride frequency. P. h. hispanica's strategy for modulating speed probably allows this mainland subspecies to attain higher maximal speeds than the island subspecies P. h. atrata. Theoretical considerations suggest that at high speeds, P. h. hispanica's running style is energetically more favourable, but this hypothesis awaits experimental verification. We suggest that the differences in locomotion efficiency between the subspecies result from differences in predation pressure between the mainland and the island. The mainland study site has a higher predator diversity and offers less hiding opportunities to the lizards.     

Effects of isolation,logging and dispersal on woody-species richness of islands

Isolation effects on species richness of woody plants were investigated in a system of islands that were created by the filling of the Clarks Hill Reservoir, Georgia. This reservoir was built between 1946–1954. Some islands were logged and cleared of woody plants prior to the filling of the reservoir and others were not logged. The presence of logged versus unlogged islands in the same system allowed us to test whether and how geographical isolation interacts with island history and species-specific dispersal properties in determining patterns of among-island variation in species number. Thirty-six years after the islands were created, logged islands had significantly fewer species of woody plants than unlogged ones. On logged islands, total number of woody species was negatively correlated with distance to the closest mainland (r=–0.95). On unlogged islands, variation in species number was very low (CV=4.9%) and was not correlated with distance to the mainland. These results indicate that the studied system as a whole has not yet reached equilibrium. However, the mean number of species on unlogged islands was very close to the intercept of the regression obtained for logged islands, suggesting that islands close to the mainland have already reached their equilibrium species richness. This conclusion is consistent with predictions of island biogeography theory. When species representing different dispersal properties were analyzed separately, statistically significant distance effects were obtained for bird-dispersed species (r=0.88) and for species with no adaptations to bird or wind dispersal (r=0.81). Wind-dispersed species did not show a decrease in species number with increasing isolation, but their relative frequency was positively and significantly correlated with distance to the mainland (r=0.94). Historical factors, as well as differences among species in dispersal properties, are important in explaining patterns of among-island variation in species number.     

Genetic and phylogenetic consequences of island biogeography

Abstract.— Island biogeography theory predicts that the number of species on an island should increase with island size and decrease with island distance to the mainland. These predictions are generally well supported in comparative and experimental studies. These ecological, equilibrium predictions arise as a result of colonization and extinction processes. Because colonization and extinction are also important processes in evolution, we develop methods to test evolutionary predictions of island biogeography. We derive a population genetic model of island biogeography that incorporates island colonization, migration of individuals from the mainland, and extinction of island populations. The model provides a means of estimating the rates of migration and extinction from population genetic data. This model predicts that within an island population the distribution of genetic divergences with respect to the mainland source population should be bimodal, with much of the divergence dating to the colonization event. Across islands, this model predicts that populations on large islands should be on average more genetically divergent from mainland source populations than those on small islands. Likewise, populations on distant islands should be more divergent than those on close islands. Published observations of a larger proportion of endemic species on large and distant islands support these predictions.