Adjacent Mainland Areas Research Articles

RAD-seq data for Engelhardia roxburghiana provide insights into the palaeogeography of Hainan Island and its relationship to mainland China since the late Eocene

Hainan Island in southern China is situated within the Indo-Burma biodiversity hotspot, and has attracted the attention of evolutionary biologists, geologists, and biogeographers. However, the palaeogeography of Hainan Island and its relationship with mainland China remains contested. In this paper, we report RAD-seq data for Engelhardia roxburghiana populations from Hainan Island and adjacent mainland areas to identify genetic diversity, structure, divergence time, and demographic dynamics over geologic time. Findings were assessed using climate model data to constrain suitable distribution areas. Results indicate that E. roxburghiana dispersed from the Chinese mainland to Hainan Island via a hypothetical land bridge during the late Eocene so that the drift of Hainan Island was impossible. We cast doubt on the hypothesis that Hainan Island was connected to Vietnam and Guangxi at this time. We emphasize that higher genetic diversity in the Yunnan-Guizhou Plateau and Chiang-nan regions is the result of mixed populations or the existence of refugia, and lower genetic diversity in the Indochina Peninsula is due to a historical bottleneck. From the late Eocene to Oligocene, the arid belt that dominated East Asia retreated, facilitating the expansion of E. roxburghiana from the Indochina Peninsula to southern China. The main diversification of E. roxburghiana occurred in the Miocene following the strengthening precipitation within the East Asian Summer Monsoon. Climatic oscillations during the Quaternary led to the contraction of E. roxburghiana in the Indochina Peninsula, with expansion after Last Glacial Period (LGP; 119 to 11.7 ka). Southern China has served as a refugium and continues to do so in the future. In summary, our study elucidates the evolutionary trajectory of E. roxburghiana through large-scale sampling, providing insights into the palaeogeography of Hainan Island and itsbiogeographic relationships with adjacent mainlands.

Divergence of the freshwater sleeper, Neodontobutishainanensis (Chen, 1985) (Teleostei, Odontobutidae), in the Pearl River basin and on Hainan Island of southern China.

Study of divergence of freshwater fish populations between island and adjacent mainland areas can shed light on the phylogeographical relationships of these regions. Neodontobutishainanensis is a freshwater fish species restricted to Hainan Island and in Guangdong and Guangxi provinces in the southern mainland China. We examine the phylogenetic relationship and population structure of N.hainanensis based on 3,176 nuclear loci using a gene-capture method. STRUCTURE analysis and principal coordinate analyses (PCA) indicate that populations from Guangdong, Guangxi and Hainan are each distinct, except that some individuals of the Guangdong population share minor genetic components with individuals of the Guangxi population. In the concatenated gene tree, the Hainan population is grouped with the Guangdong population, but the coalescent tree groups the Hainan population as the sister to the Guangxi population. Finally, coalescent simulations confirmed the divergence pattern supported by the coalescent tree and revealed a one-way introgression from the Guangxi population to the Guangdong population, which can explain the discordant results supported by the concatenated and coalescent phylogenetic analyses. Due to recent decline of N.hainanensis populations and the genetic patterns in this species, as revealed in this study, the populations in the three areas should be treated as separate conservation units.

Pre-eradication assessment of feral cat density and population size across Kangaroo Island, South Australia

Abstract Context Feral cats (Felis catus) are a significant threat to wildlife in Australia and globally. In Australia, densities of feral cats vary across the continent and also between the mainland and offshore islands. Densities on small islands may be at least an order of magnitude higher than those in adjacent mainland areas. To provide cat-free havens for biodiversity, cat-control and eradication programs are increasingly occurring on Australian offshore islands. However, planning such eradications is difficult, particularly on large islands where cat densities could vary considerably. Aims In the present study, we examined how feral cat densities vary among three habitats on Kangaroo Island, a large Australian offshore island for which feral cat eradication is planned. Methods Densities were compared among the following three broad habitat types: forest, forest–farmland boundaries and farmland. To detect cats, three remote-camera arrays were deployed in each habitat type, and density around each array was calculated using a spatially explicit capture–recapture framework. Key results The average feral cat density on Kangaroo Island (0.37 cats km−2) was slightly higher than that on the Australian mainland. Densities varied from 0.06 to 3.27 cats km−2 and were inconsistent within broad habitat types. Densities were highest on farms that had a high availability of macropod and sheep carcasses. The relationship between cat density and the proportion of cleared land in the surrounding area was weak. The total feral cat population of Kangaroo Island was estimated at 1629±661 (mean±s.e.) individuals. Conclusions Cat densities on Kangaroo Island are highly variable and may be locally affected by factors such as prey and carrion availability. Implications For cat eradication to be successful, resources must be sufficient to control at least the average cat density (0.37 cats km−2), with additional effort around areas of high carcass availability (where cats are likely to be at a higher density) potentially also being required.

Network biogeography of a complex island system: the Aegean Archipelago revisited

AbstractAimThe Aegean Archipelago has been the focal research area for identifying and testing several ecological and evolutionary patterns, yet its biogeographical subdivision has been somewhat overlooked, with the processes driving the assembly of the Aegean island plant communities still remaining largely unclear. To bridge this gap, we identify the biogeographical modules (highly linked subgroups of islands and plant taxa) within the Aegean Archipelago.LocationThe Aegean Archipelago, Greece.MethodsWe used a network approach to detect island biogeographical roles and modules, based on a large and detailed database including 1498 Aegean endemic and subendemic plant taxa distributed on 59 Aegean Islands and five adjacent mainland areas.ResultsThe Aegean was divided into six biogeographical modules; the network was significantly modular. None of the modules displayed all four possible biogeographical roles (connectors, module hubs, network hubs, peripherals). Six new biogeographical regions in the Aegean were identified.Main conclusionsThe borders of the six biogeographical regions in the Aegean correspond well to the region's palaeogeographical evolution from the middle Miocene to the end of the Pleistocene. The Central Aegean acts as an ecogeographical filter for the distribution of several plant lineages across the Aegean Sea, while there seems to be a N–S‐oriented biogeographical barrier in the Aegean corresponding to the palaeogeographical situation during the middle Ionian. These biogeographical barriers have been fundamental for both plants and animals.

Observations of the summer birds of Tukarak Island (Belcher Islands, Nunavut), Nastapoka Islands (Nunavut), and Lac Guillaume-Delisle (northern Quebec)

In a survey of land and water birds of Tukarak and Nastapoka Islands and Lac Guillaume-Delisle in summer 2011, we recorded 22 of the 30 species known to breed on the Belcher Islands, as well as five non-breeding species, and we observed 32 species in Lac Guillaume-Delisle. In all areas surveyed, we observed a total of 43 species: 10 waterfowl, 2 gallinaceous birds, 3 loons, 2 hawks, 3 shorebirds, 1 auk, 3 gulls, 2 falcons, and 17 songbirds. In this area of Hudson Bay, a number of species reach the southern or northern limit of their breeding distribution in eastern Canada. In light of the impact that climate change may have on bird distribution in northerly latitudes, the Belcher Islands and adjacent mainland areas could be particularly useful locations for monitoring changes in the breeding range of birds.

Non-indigenous introgression into the Norwegian red deer population

Rates of introgression from non-indigenous into native populations are increasing worldwide, often as a result of anthropogenic translocation events. In ungulates translocations have been common, especially among deer. European red deer consists of two distinct lineages, one western and one eastern. These probably originate from different glacial refuges, but it is unknown to what extent they hold different adaptations. Here we address dispersal and introgression into the Norwegian mainland population from an introduced island stock consisting of an admixture of both European lineages. The last decade this stock has grown considerably in number and dispersal could be expected to have increased. We therefore used samples separated by a 5 year interval from Otteroya, adjacent mainland areas and a more distant sub-population. Bayesian assignment analysis verified the genetic structure and identified dispersal between the Otteroya stock and the adjacent mainland coastal areas. Three individuals (two newly sampled) with second or third generation non-indigenous origin were found among the adjacent mainland samples (5 and 3 %, respectively). Two individuals with first and second generation mainland-origin were found on Otteroya (old samples). This suggests some non-indigenous introgression from Otteroya into the mainland Norwegian population.

Deep, hierarchical divergence of mitochondrial DNA in Amplirhagada land snails (Gastropoda: Camaenidae) from the Bonaparte Archipelago, Western Australia

Continental islands have experienced cycles of isolation and connection. Although complex genetic patterns have been described for mainland species affected by glacial cycles of isolation, island biotas have received little attention. We examined mitochondrial DNA in Amplirhagada land snails from 16 islands and two adjacent mainland areas of the Bonaparte Archipelago, in the Kimberley region of northern Western Australia. Four major clades, with sequence divergence of 16–27% in the 16S ribosomal RNA gene, correspond to the major geographic groupings, separated by 10–160 km. Distinct lineages also characterize islands that are only a few kilometres apart. The large differences indicate that the lineages are much older than the islands themselves, and show no evidence of geologically recent connection. Three of the major clades match the morphological description of Amplirhagada alta. Either this named species comprises several morphologically cryptic species, or it is a single, genetically very diverse species, distributed over much of the Bonaparte Archipelago. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 141–153.

Top-down and bottom-up consequences of unchecked ungulate browsing on plant and animal diversity in temperate forests: lessons from a deer introduction

Debate on the relative importance of competition for resources and trophic interactions in shaping the biological diversity of living communities remains unsettled after almost a century. Recently, dramatic increases in ungulate populations have provided a useful quasi-experiment on the effects of unrestrained ungulates on forest ecology. The islands of Haida Gwaii (Canada) offer a unique situation to investigate the potential of large herbivores to control temperate forest community structure and diversity. Black-tailed deer Odocoileus hemionus Merriam, native to adjacent mainland areas of British Columbia, were introduced in 1878 and spread to all but a few islands. Because deer were not native to the archipelago, islands that still lack deer provide a rare instance of temperate forest vegetation and fauna that developed in the absence of large herbivores. The colonisation of different islands at different times, and the absence of significant predation allow us to assess whether and how a large herbivore can exert “top-down” control on vegetation and its associated fauna. We studied plant communities in forest interior and shoreline, on seven small islands of varying browse history. Three islands were untouched by deer, deer had been resident for about 15 years on two, and on another two deer had been present for more than 50 years. Without deer, vegetation in the understorey and/or shrub layer was dense or very dense. Structure and composition varied markedly within and between shoreline and interior communities. Without deer, shoreline communities were dominated by species absent from islands with deer. Where deer had been present for less than 20 years most plant species characteristic of shorelines on islands without deer were already absent or scarce, but in the forest interior species richness was less affected and extensive shrub thickets remained. On islands where deer had been present for >50 years vegetation below the browse line was extremely simplified, converging in both forest interior and shoreline towards an open assemblage of a few deer-tolerant species, basically two coniferous trees. This top down effect on the plant community reflected up the food chain so that understorey invertebrate and shrub-dependent songbird communities became simplified. In contrast, species densities of litter arthropods (especially weevils and millipedes) were highest where deer were present for >50 years. Canopy birds were unaffected by deer presence. In the absence of predators, major climatic stress or other means to control the herbivore, deer browsing created greatly simplified plant and animal communities.

The role of seasonal migration in the near-total loss of caribou on south-central Canadian Arctic Islands

The role of seasonal migration in the near-total loss of caribou on south-central Canadian Arctic Islands

The utility of site‐based datasets and regional ecosystem mapping for biodiversity conservation in the Southeast Queensland Bioregion: Past, present, future

The utility of site-based datasets and regional ecosystem mapping for biodiversity conservation in the Southeast Queensland Bioregion: Past, present, future. Ben E. Lawson. School of Natural and Rural Systems Management (NRSM) & School of Geography, Planning and Architecture (GPA), The University of Queensland, Brisbane 4072, Australia. Email: b.lawson@uq.edu.au. Key words: conservation, ecosystem mapping, regional ecosystems, site-based data. Ecosystem mapping and site-based datasets are core components of conservation planning and management schemes. In Queensland, regional ecosystem mapping is used for landscape-level planning, underpinned by site-based data. This doctoral research assesses their utility as surrogates for biodiversity patterns with a view to future needs. The research is supervised by Dr Grant Wardell-Johnson, Associate Professor Bob Beeton (NRSM) and Dr David Pullar (GPA) from the University of Queensland. The ecologically diverse Southeast Queensland (SEQ) Bioregion is the focus of this research. Issues and limitations in the two datasets, which underpin this research, were the first component examined. Regional ecosystem mapping showed a decrease in the number of heterogeneous polygons (i.e. a polygon with multiple ecosystems assigned) across successive versions. Polygon heterogeneity levels were positively correlated with endangered ecosystems and lower polygon accuracy, and strongly related to particular regional ecosystem and geomorphology types (see Lawson 2006). Retrospective analysis of the Queensland Herbarium's site-based floristic dataset, ‘CORVEG’, showed improved data quality and completeness in the past decade as a consequence of more explicit sampling protocols, although missing information continues to limit data utility (see Lawson in press). Case studies were used to explore the application of regional ecosystem mapping in varied circumstances. The first case study examined SEQ sand islands where high levels of map unit homogeneity relative to adjacent mainland areas were observed. Analysis showed that mapping effectively portrayed ecological patterns and that homogeneity existed across various map scales and map authors across the islands, suggesting that high polygon homogeneity were ecological, not cartographic, phenomena (see Lawson & Wardell-Johnson in press). The second case study came from Toohey Forest in southern SEQ, an area mapped as a single regional ecosystem type at 1:100 000 scale despite its recognized biotic and abiotic diversity. Fine-scale mapping approaches were explored to assess the representation of floristic patterns, indicating that ongoing reduction in regional ecosystem mapping scale and incorporation of fine-scale geomorphic mapping were vital to improve the representation of floristic diversity. Core components of the research which are yet to be completed will elucidate species richness and dissimilarity patterns within and between map units and reveal the ecosystem types that are (and aren't) well portrayed by the mapped patterns, the reasons for this, and measures to improve representation. Queensland's regional ecosystem mapping program shows continued improvement in the representation of biodiversity patterns, with some areas more effectively portrayed than others. The use of heterogeneous polygons to identify ecosystems otherwise unrecognizable at particular map scales is simultaneously a major advantage and disadvantage to representing biodiversity patterns. Opportunities are available to focus limited resources on particular geomorphological and regional ecosystem types, and for alternate methods of representing geographically restricted ecosystems. Greater consideration of current and future uses of site-based floristic data is necessary. For example, hierarchical datasets serving multiple biodiversity objectives should be considered. These issues are directly relevant to the mapping of biodiversity condition.

Macro‐scale bird species richness patterns of the East Asian mainland and islands: energy, area and isolation

AbstractAim To create a map of bird species richness (BSR) in East Asia and to examine the effect of area, isolation, primary productivity, topographic heterogeneity, and human population density on BSR.Location East Asia (from 70° E to 180° E longitude), including the eastern half of the Palaearctic Region, the entire Oriental Region, and the entire Wallacea Subregion.Methods The breeding ranges of 2406 terrestrial bird species were mapped and overlaid to create a species richness map. The BSR map was transformed into a 100 × 100 km quadrat system, and BSR was analysed in relation to land area, average normalized difference vegetation index (NDVI), elevation range, and average population density.Results In general, BSR declined from the Tropics to the Arctic. In mainland East Asia, however, BSR was highest around the Tropic of Cancer, and fluctuated between 30° and 50° N. Islands had lower BSR than adjacent mainland areas. The NDVI was strongly positively correlated with BSR in mainland areas and on islands. For mainland areas, NDVI explained 65% of the BSR variation, and topographic heterogeneity explained an additional 6% in ordinary least‐squares regression. On islands, NDVI explained 66% of BSR variation, island area explained 13%, and distance to mainland accounted for 1%.Main conclusions In East Asia, we suggest that primary productivity is the key factor underpinning patterns of BSR. Primary productivity sets the upper limits of the capacity of habitats to support bird species. In isolated areas such as islands and peninsulas, however, BSR might not reach the richness limits set by primary productivity because the degree of isolation and area size also can affect species richness. Other factors, such as spatial heterogeneity, biotic interactions, and perturbations, may also affect species richness. However, their effects are secondary and are not as strong as primary productivity, isolation, and area size.

Relating spatial and temporal patterns in floristics with vegetation mapping: an example from Fraser Island, south-east Queensland, Australia

The use of mapped polygons to represent vegetation patterns is becoming more widespread in conservation planning and natural resource management. The degree of homogeneity (i.e., one vegetation unit per polygon) of these polygons influences the efficacy of mapped patterns. It was observed that Fraser Island, south-east Queensland (SEQ) exhibited near complete map unit homogeneity relative to adjacent mainland areas. We sought to establish whether this homogeneity had an ecological or cartographic basis. Floristic presence-absence data from 50 quadrats, each sampled over three consecutive years, were analysed using cluster analysis (UPGMA) and ordination (SSH MDS) to define and compare eight numerically-derived plant community types with eight a priori regional ecosystem types derived from mapping of the island. Strong congruence between the two approaches was evident, suggesting that the mapping effectively portrayed ecological patterns. Floristic composition and species richness remained consistent at most quadrats for three consecutive years. Perennial woody species (including tree and shrub species) showed significant (P < 0.05) variation between regional ecosystem units and between plant community groups, but was stable through time. Conversely, the herb assemblage showed significant temporal variation and poor fidelity to vegetation classifications. High levels of map unit homogeneity were shown to extend to five barrier sand islands of SEQ across various map scales and map authors in these sandy environs. We conclude that homogeneity in mapped polygons on Fraser Island is a consequence of discrete boundaries and the associated distinctive floristics of the vegetation communities in this area. We suggest focussing limited mapping resources to areas of high polygon heterogeneity, instead of areas such as the SEQ sand islands which appear well represented by existing mapping.

Genetic differentiation of three species of Matthiola (Brassicaceae) in the Sicilian insular system

We examined the genetic variation of 12 isozyme loci in 14 populations of Matthiola (Brassi- caceae) representing the geographic distribution of the species M. incana, M. fruticulosa ssp. fruticulosa and M. tricuspidata in the Sicilian insular system and the adjacent mainland areas to estimate the levels and distribution of genetic variation in the insular populations and to understand their popu- lation dynamics. The disparity in the distribution of polymorphism in populations of M. incana ssp. incana (low within populations but with high values of FST and GST) contrasts with the homogeneity in the inter-population distribution of the high genetic variation detected in M. tricuspidata and M. fruticulosa ssp. fruticulosa. While the low polymorphism found in M. incana ssp. incana is consistent with its origin through cultivation and the associated lack of gene flow, the Sicilian populations of the other two taxa probably derived from multiple founder events from nearby conti- nental areas and, according to our estimates, have maintained high interpopulational gene flow. Unlike M. incana, the Sicilian populations of M. tricuspidata and M. fruticulosa ssp. fruticulosa could have survived the glaciations in refugia. This higher antiquity, together with the maintenance of abundant gene flow, largely explains their high values of genetic variation. In contrast, M. incana ssp. pulchella and M. incana ssp. rupestris have low indices of polymorphism and they are probably neo-endemics, as their distribution areas were severely affected by the Plio-Pleistocene glaciations.

Failure of two consecutive annual treatments with ivermectin to eradicate the reindeer parasites (Hypoderma tarandi, Cephenemyia trompe and Linguatula arctica) from an island in northern Norway

The highly efficient endectocide ivermectin is used to reduce the burden of parasites in many semidomestic reindeer herds in northern Fennoscandia. In the autumn of 1995 and 1996 all reindeer on the island of Silda (42 km2) were treated with ivermectin in an attempt to eradicate the warble fly (Hypoderma (=Oedemagena) tarandi (L.)), the nose bot fly (Cephenemyia trompe (Modeer)) (Diptera: Oestridae) and the sinus worm (Linguatula arctica Riley, Haugerud and Nilssen) (Pentastomida: Linguatulidae). Silda is situated 2-3 km off the mainland of Finnmark, northern Norway, and supports about 475 reindeer in summer. A year after the first treatment, the mean abundance of H. tarandi was reduced from 3.5 to 0.6, but a year after the second treatment the mean abundance unexpectedly had increased to 4.5. After one year without treatment, the mean abundance and prevalence of the three target parasites were at the same level, or higher, than pre-treatment levels. The main hypothesis for the failure to eliminate the parasites is that gravid H. tarandi and C. trompe females originating from untreated reindeer in adjacent mainland areas dispersed to the island during the warm summer of 1997 (possibly also in 1998). As these oestrids are strong flyers, it may not be too difficult for them to cross >2-3 km of oceanic waters. There are no good explanations for the failure to eradicate L. arctica, but the results indicate that there may be elements in its life cycle that are unknown. The conclusion of the study is that it may be difficult or impossible to eradicate these parasites permanently, even locally such as on islands unless adjacent areas on the mainland are also cleared.

Effects of population size and isolation on reproductive output in Aquilegia canadensis (Ranunculaceae)

It is generally expected that small, isolated populations will suffer reduced fitness due to inbreeding, yet few studies have investigated the relation between population characteristics, inbreeding and fitness. Among Ontario populations of the short‐lived, perennial plant Aquilegia canadensis, large populations (N>90 flowering plants) outcross twice as frequently as small populations (N=30–40), and inbreeding depression is extremely strong. We tested the prediction that reproductive output, a major component of population fitness, should be positively associated with population size. Data from a survey of 33 populations located on small islands in the St. Lawrence River, Canada and 23 populations on adjacent mainland areas supported this prediction. Population size correlated positively with reproductive output, measured as the number of seedlings produced per plant in 1995 (average r=+0.39 pooled P=0.019), and the number of fruits per plant in 1997 (r=+0.30, P=0.056). We also tested the prediction that fitness should decline with increasing spatial isolation between populations by measuring the distance separating all island populations. However, reproductive output did not correlate with isolation in either year. We compared island and mainland populations to test the prediction that reproductive output should be lower for populations on small islands than those occurring in more continuous mainland habitat. In contrast to our predictions, island populations exhibited, if anything, higher reproductive output than mainland populations. We also found no support for the prediction that the positive association between population size and reproductive output should be stronger for presumably isolated populations on small islands than for those on adjacent mainland areas. While the mechanisms underlying the association between population size and fitness are impossible to identify with correlations alone, our results are consistent with the hypothesis that inbreeding can significantly reduce the fitness of natural populations.

Neotropical Land-Bridge Avifaunas: New Approaches to Null Hypotheses in Biogeography

The construction of null hypotheses and statistical tests for non-random avian distributions has been vigorously debated by island biogeographers. Less attention has been given to the underlying quality of the data, which often consist of species lists from islands and adjacent mainland areas. We believe three major problems with past analyses make it difficult to interpret the results. 1. Source pools for statistical tests are constructed unrealistically. Arbitrary geopolitical units are used to define source pools. Archipelagos are analyzed as closed systems with equivalent source pools for all islands. 2. Habitat preferences and availability are not explicitly incorporated in null models. 3. Estimates of colonization potential based on species incidence functions may not be satisfactory. Incidence functions do not incorporate available and distance effects. We propose new organism-based methods for the analysis of birds on islands that incorporate geometrically standardized source pools, availability, and geographic ranges of source pool species. We apply these methods in an analysis of seven Neotropical land-bridge island avifaunas. With few exceptions, land-bridge island communities appear to be a random subset of the mainland habitat pool, at the family level. A comparison of total and habitat pool shows that the pool is a superior predictor of species richness in each family. Finally, species with widespread mainland ranges are disproportionately common on islands. Our results suggest that availability and area of a species range are responsible for some of the differences between island and mainland communities.

Zoogeography of the Grasshoppers and Their Relatives (Orthoptera) on the California Channel Islands

Twelve of fifty-four Orthoptera species (22-2 %) found on the eight California Channel Islands off the coast of Southern California are endemic, 11 9% in the northern four-island subgroup and 22 2 % in the southern four-island subgroup. A general analysis of the distribution of these endemics, especially those in the cricket genus Cnemotettix and those endemic species capable of flight, was conducted. The results indicate that autochthonous speciation, and not the occurrence of mainland relicts, explains these high endemic numbers. A regression analysis of log island area versus log number of Orthoptera species yields results similar to those of other plant and animal species. Faunistically rich land masses that lie within 20 km of one Channel Island are disproportionately more important as source areas than those land masses at distances exceeding 20 km. Simple regression of environmental components correlated with faunal diversity shows that for untransformed data, Orthoptera species numbers are significantly explained by area (82 %) and elevation (74 %). For log transformed data, the significance of area in explaining Orthoptera species number is diminished to 5700, while elevation explains 78 %, which is almost unchanged from before transformation. * Present address: David B. Weissman, University of California, Irvine, College of Medicine, Medical Student Affairs, Irvine, California 92717. Introduction Island biogeography, with its conceptual base largely laid by early works of Preston (1962) and MacArthur & Wilson (1963, 1967), is rapidly becoming an explicit, predictive portion of ecological theory. Insights into explanations of species distributions, community structure, and competitive interactions among species on islands come from many sources (see Diamond, 1973; Simberloff, 1974). Several such works (i.e. Diamond, 1969, 1971; Power, 1972; Lynch & Johnson, 1974; Hunt & Hunt, 1974; Johnson, Mason & Raven, 1968; Savage, 1967; von Bloeker, 1967) were specifically conducted on the California Channel Islands (see Fig. 1). These islands are particularly useful for testing many biogeographical tenets because only eight islands are involved: the Channel Islands are closer, fewer, and smaller than other island groups (i.e. Hawaiian, Galapagos, Canary, West Indies, etc.) from which extensive empirical biogeographical data have also come. Additionally, all eight Channel Islands are presently located near the mainland. This permits identification and comparison of island and mainland (source) faunas and assessment of probable speciation patterns. Also, the four northern (San Miguel, Santa Rosa, Santa Cruz, and Anacapa) and four southern (San Nicolas, Santa Catalina, San Clemente, and Santa Barbara) islands are themselves cohesive subgroups with reference to (i) geological similarity (see below) and (ii) gradients of size (and corresponding topographic diversity) and isolation (see Table 2). This paper is the first to present a comprehensive zoogeographical analysis of any insect group (specifically the Orthoptera) found on the Channel Islands. Six years (1969-74) of extensive field work on all the Channel Islands and adjacent mainland areas form the foundation for this analysis. Detailed census methods and complete species list are presented elsewhere (Rentz & Weissman, 1973, 1976).

An Ecological Analysis of Chaparral and Pine Forest Bird Communities on Santa Cruz Island and Mainland California

A comparative study of chaparral and pine forest bird communities on Santa Cruz Island and adjacent mainland areas was made during 1969—72. Five fewer species occurred in the island chaparral bird community and four fewer species in the island pine forest bird communities. Changes in bird species composition occurred most notably in the island pine forest, which is utilized by species commonly found in the chaparral. No significant changes in niche breadths were observed for the communities in general; however, a slight tendency for increased foraging height diversities on the island was observed. Average niche overlap values between species present on both the mainland and the island are greater on the island, mainly because of an increased vertical habitat overlap. By use of the observed mainland densities and competition coefficients composed of mainland overlap values, island densities were predicted for four bird species that show greater densities in the island chaparral community. Hence, competitive release occurs in the chaparral bird community. All communities studied are in a state of equilibrium, and the island communities are at least approaching a state of saturation equivalent to that of the mainland communities.

The structural evolution of the Tarskavaig and Moine nappes in Skye

Synopsis The structural complex comprising the Tarskavaig and Moine nappes of Skye has been re-mapped and analysed in detail. Large scale folds belong to only two generations and these can be correlated with generations of large folds in adjacent mainland areas. Small folds belong to at least four more generations in addition to the two generations already mentioned. Some of these small folds are, however, of little regional importance and are found only in zones of highly deformed rocks. These zones have developed at two separate times in the structural evolution; and, like thrust planes, belong to two other separate periods. General considerations indicate that the displacements on the thrust planes could be very much less than assumed, and there is the possibility that the Loch Alsh fold may well be a late stage structure, in contrast to earlier views.

COMPETITIVE EXCLUSION BETWEEN THE RODENT GENERAMICROTUSANDCLETHRIONOMYS

Comparative studies of the faunas occurring on islands and adjacent mainland areas have revealed instances of what have been interpreted as examples of competitive exclusion in a number of vertebrate groups, particularly birds (Amadon, 1953; Lack, 1942; Mayr, 1942, 1963; Serventy, 1951) and reptiles (Brown and Marshall, 1953; Underwood, 1962). In these cases it has been found that closely related forms with similar habits may occur sympatrically on a mainland area but often only one species has succeeded in becoming established on an adjacent island, because, it is assumed, of the poverty of available ecological niches. It further appears, in many instances, that the particular species which first reaches an island is the one which will become established there and once it has done so it can apparently prevent subsequent colonization by other closely related forms. Similar cases of competitive exclusion on islands have not been reported upon in detail for mammals, and it therefore seems desirable to place on record what appears to be a clear-cut example of ecological competition between the Holarctic rodent genera Micratus (North America: meadow vole; Britain: short-tailed vole) and Clethrionomys (North America: redbacked vole; Britain: bank vole). North American data apply only to Microtus pennsylvanicus and Clethrionomys gapperi due to the lack of detailed information on other species of these genera. The data presented here are based primarily on field studies carried out by the writer at various times over a 10-year period; otherwise, material has been drawn from the published works of other zoologists. On the mainland of temperate North America where both genera occur, Microtus pennsylvanicus is essentially a grassland form whereas Clethrionomys gapperi is virtually confined to forested, or at least, scrubby areas. In peak years of population density, Microtus may invade open woodlands in small numbers and may even occur in isolated grassy areas which are completely surrounded by forest. Scrubby areas, especially in swamps, may be invaded at such times. Clethrionomys, on the other hand, seems never to invade exclusively grassy areas, regardless of population density. This is not to imply that C. gapperi is incapable of living in grassland habitats, but no instance is known to the writer where this is the case. That Microtus may well be restricted to grasslands on the North American continent because it is excluded from the woodlands by Clethrionomys is quite apparent from the fact that on large, ecologically diversified islands such as Newfoundland where Clethrionomys is absent, Microtus occurs commonly throughout the woodlands as well as the grasslands (Cameron, 1958). Twenty-seven of the 43 specimens collected on the island were taken in forested areas; one specimen was collected in a mature spruce woodland 20 miles from the nearest known grassland area. Similarly, Microltus was found to be most abundant in upland coniferous woodlands on the Magdalen Islands (Quebec) in the summer of 1959. Thirty-six of the 50 specimens collected were taken in woodlands. Cletlrionomys does not occur there but the deer mouse, Peromyscus maniculatus, is native and presumably a limited degree of competition does exist between it and Microtus when the latter is at a peak in population density, as was the case in the summer of 1959 (Cameron, 1962a). On a number of smaller inshore islands in eastern Canada studied by the writer, Microtus was also found in heavily forested