Canopy insect herbivores in the Azorean Laurisilva forests: key host plant species in a highly generalist insect community

This article explores patterns of insect herbivore distribution in the canopy of the Laurisilva forests on seven islands in the Azores archipelago. To our knowledge, this is one of the first extensive study of this type in tree or shrub canopies of oceanic island ecosystems. One of the most frequently debated characteristics of such ecosystems is the likely prevalence of vague, ill‐defined niches due to taxonomic disharmony, which may have implications for insect‐plant interactions. For instance, an increase in ecological opportunities for generalist species is expected due to the lack of predator groups and reduced selection for chemical defence in host plants. The following two questions were addressed: 1) Are specialists species rare, and insect herbivore species randomly distributed among host plant species in the Azores? 2) Are the variances in insect herbivore species composition, frequency and richness explained by host plants or by regional island effects? We expect a proportional distribution of herbivore species between host plants, influenced by host frequency and distinct island effects; otherwise, deviation from expectation might suggest habitat preference for specific host tree crowns. Canopy beating tray samples were performed on seven islands, comprising 50 transects with 1 to 3 plant species each (10 replicates per species), giving 1320 samples from ten host species trees or shrubs in total. From a total of 129 insect herbivore species, a greater number of herbivore species was found on Juniperus brevifolia (s=65) and Erica azorica (s=53). However, the number of herbivore species per individual tree crown was higher for E. azorica than for any other host, on all islands, despite the fact that it was only the fourth more abundant plant. In addition, higher insect species richness and greater insect abundance were found on the trees of Santa Maria Island, the oldest in the archipelago. Insect species composition was strongly influenced by the presence of E. azorica, which was the only host plant with a characteristic fauna across the archipelago, whereas the fauna of other plant crowns was grouped by islands. The great insect occurrence on E. azorica reflects strong habitat fidelity, but only four species were clearly specialists. Our findings indicate a broadly generalist fauna. The simplicity of Azorean Laurisilva contributed to the understanding of insect‐plant mechanisms in canopy forest habitats.     

Snakes on the Balearic Islands: An Invasion Tale with Implications for Native Biodiversity Conservation

Biological invasions are a major conservation threat for biodiversity worldwide. Islands are particularly vulnerable to invasive species, especially Mediterranean islands which have suffered human pressure since ancient times. In the Balearic archipelago, reptiles represent an outstanding case with more alien than native species. Moreover, in the last decade a new wave of alien snakes landed in the main islands of the archipelago, some of which were originally snake-free. The identification of the origin and colonization pathways of alien species, as well as the prediction of their expansion, is crucial to develop effective conservation strategies. In this study, we used molecular markers to assess the allochthonous status and the putative origin of the four introduced snake species (Hemorrhois hippocrepis, Malpolon monspessulanus, Macroprotodon mauritanicus and Rhinechis scalaris) as well as ecological niche models to infer their patterns of invasion and expansion based on current and future habitat suitability. For most species, DNA sequence data suggested the Iberian Peninsula as the potential origin of the allochthonous populations, although the shallow phylogeographic structure of these species prevented the identification of a restricted source-area. For all of them, the ecological niche models showed a current low habitat suitability in the Balearic, which is however predicted to increase significantly in the next few decades under climate change scenarios. Evidence from direct observations and spatial distribution of the first-occurrence records of alien snakes (but also lizards and worm lizards) suggest the nursery trade, and in particular olive tree importation from Iberian Peninsula, as the main pathway of introduction of alien reptiles in the Balearic islands. This trend has been reported also for recent invasions in NE Spain, thus showing that olive trees transplantation may be an effective vector for bioinvasion across the Mediterranean. The combination of molecular and ecological tools used in this study reveals a promising approach for the understanding of the complex invasion process, hence guiding conservation management actions.     

Species richness, environmental heterogeneity and area: a case study based on land snails in Skyros archipelago (Aegean Sea, Greece)

Aim To test the performance of the choros model in an archipelago using two measures of environmental heterogeneity. The choros model is a simple, easy‐to‐use mathematical relationship which approaches species richness as a combined function of area and environmental heterogeneity. Location The archipelago of Skyros in the central Aegean Sea (Greece). Methods We surveyed land snails on 12 islands of the archipelago. We informed the choros model with habitat data based on natural history information from the land snail species assemblage. We contrast this with habitat information taken from traditional vegetation classification to study the behaviour of choros with different measures of environmental heterogeneity. R² values and Akaike's information criterion (AIC) were used to compare the choros model and the Arrhenius species–area model. Path analysis was used to evaluate the variance in species richness explained by area and habitat diversity. Results Forty‐two land snail species were recorded, living in 33 different habitat types. The choros model with habitat types had more explanatory power than the classic species–area model and the choros model using vegetation types. This was true for all islands of the archipelago, as well as for the small islands alone. Combined effects of area and habitat diversity primarily explain species richness in the archipelago, but there is a decline when only small islands are considered. The effects of area are very low both for all the islands of the archipelago, and for the small islands alone. The variance explained by habitat diversity is low for the island group as a whole, but significantly increases for the small islands. Main conclusions The choros model is effective in describing species‐richness patterns of land snails in the Skyros Archipelago, incorporating ecologically relevant information on habitat occupancy and area. The choros model is more effective in explaining richness patterns on small islands. When using traditional vegetation types, the choros model performs worse than the classic species–area relationship, indicating that use of proxies for habitat diversity may be problematic. The slopes for choros and Arrhenius models both assert that, for land snails, the Skyros Archipelago is a portion of a larger biogeographical province. The choros model, informed by ecologically relevant habitat measures, in conjunction with path analysis points to the importance of habitat diversity in island species richness.     

Diversity of drosophilid flies on Kume-jima, a subtropical island: comparison with diversity on Iriomote-jima

The drosophilid fauna was studied on Kume‐jima, a subtropical island located in the central part of the Ryukyu archipelago, and compared with the fauna of Iriomote‐jima located near the south‐western end of the archipelago. The number of species collected from Kume‐jima was 37, much fewer than that recorded from Iriomote‐jima (95 species). The number of subtropical species was particularly reduced on Kume‐jima, possibly owing either to this island being more distantly located from the sources of subtropical species (e.g. Taiwan) than Iriomote‐jima and/or to winter temperature on Kume‐jima being a little lower (by approximately 1.5°C). The number of fungus‐feeders was also much reduced on Kume‐jima, but the number of fruit‐feeders was only slightly reduced. On Kume‐jima, fungi seem to be less abundant because forests are smaller, resulting in a smaller number of fungus‐feeders. Habitat selection and seasonality were analyzed for species collected using “retainer” type traps baited with banana. For species occurring on both islands, habitat selection differed little between the two islands, whereas the seasonality of some species differed markedly between the two islands.     

Are species–area relationships from entire archipelagos congruent with those of their constituent islands?

Aim To establish the extent to which archipelagos follow the same species–area relationship as their constituent islands and to explore the factors that may explain departures from the relationship. Location Thirty‐eight archipelagos distributed worldwide. Methods We used ninety‐seven published datasets to create island species–area relationships (ISARs) using the Arrhenius logarithmic form of the power model. Observed and predicted species richness of an archipelago and of each of its islands were used to calculate two indices that determined whether the archipelago followed the ISAR. Archipelagic residuals (ArcRes) were calculated as the residual of the prediction provided by the ISAR using the total area of the archipelago, standardized by the total richness observed in the archipelago. We also tested whether any characteristic of the archipelago (geological origin and isolation) and/or taxon accounts for whether an archipelago fits into the ISAR or not. Finally, we explored the relationship between ArcRes and two metrics of nestedness. Results The archipelago was close to the ISAR of its constituent islands in most of the cases analysed. Exceptions arose for archipelagos where (i) the slopes of the ISAR are low, (ii) observed species richness is higher than expected by the ISAR and/or (iii) distance to the mainland is small. The archipelago's geological origin was also important; a higher percentage of oceanic archipelagos fit into their ISAR than continental ones. ArcRes indicated that the ISAR underpredicts archipelagic richness in the least isolated archipelagos. Different types of taxon showed no differences in ArcRes. Nestedness and ArcRes appear to be related, although the form of the relationship varies between metrics. Main conclusions Archipelagos, as a rule, follow the same ISAR as their constituent islands. Therefore, they can be used as distinct units themselves in large‐scale biogeographical and macroecological studies. Departure from the ISAR can be used as a crude indicator of richness‐ordered nestedness, responsive to factors such as isolation, environmental heterogeneity, number and age of islands.     

Pathways of formation of the fauna of the Solovetsky Archipelago,the White Sea,Northwest Russia

The fauna of the Solovetsky Archipelago represents an extremely depleted and reduced variant of the continental northern boreal one. The level of its depletion roughly corresponds to the latitudinal shift by one or two biomes, that is, by the number of species it is comparable to the mainland concrete faunas of the forested or hypoarctic tundra. Only very few arctic species, let alone more southern (nemoral) faunal elements, occur on the archipelago. The compositions of the basic fauna groups and their dominant species are determined there by three main factors: a wide distribution of intrazonal ecosystems (coastal wastelands and grasslands, birch sparse forests, peat bogs), limited living space, and extreme climatic conditions. Among the dominants are eurytopic polyzonal and, to a lesser degree, hypoarctic species. The isolation of the Solovetsky Islands is no significant barrier to the dispersal of numerous animal species, but these islands form a highly specific environment that strongly prevents the invasion of new species lacking relevant preadaptations to the local habitat and climatic conditions. The effect of “density compensation” of lower taxonomic diversity is revealed on the archipelago in many taxa, the range of abundant species being able to vary considerably in time depending on the climatic conditions. The Solovetsky Islands’ fauna is continental by origin, having been mainly formed in the Late Pleistocene and Early Holocene (～9–10 ka before the present).     

A review of Bahamian ant (Hymenoptera: Formicidae) biogeography

Abstract. The results of recent surveys for ants on Staniel Cay, Exumas (and surrounding small cays) and the northeastern region of Andros are presented. These records are compiled with all previously published collection records of ants from the Bahamas into a single database. A list of all known Bahamian species is presented, in accord with current taxonomy. Distributions within the Bahamas are given, along with the status of each species with reference to its origin (endemic, native, or exotic). At present seventy-five named species of ants are known from the Bahamas, which shares 60% of its ant fauna with Florida and 71% with Cuba. More than one third of the species (37%) are exotics, which appear to exist primarily in areas characterized by human disturbance, and apparently have not invaded the native vegetation to a large degree. Both historical and ecological factors are likely to have played important roles in shaping present-day Bahamian ant species diversity and distribution. The number of species on all major Bahamian islands from which ants have been collected is presented as a function of island area. Most islands have not been very thoroughly surveyed. The species-area relationship for the more thoroughly surveyed islands is relatively flat (z= 0.06). Further collecting in this archipelago will probably lead to the discovery of additional species.     

Spider biodiversity patterns and their conservation in the Azorean archipelago,with descriptions of new species

Abstract

In this contribution, we report on patterns of spider species diversity of the Azores, based on recently standardised sampling protocols in different habitats of this geologically young and isolated volcanic archipelago. A total of 122 species is investigated, including eight new species, eight new records for the Azorean islands and 61 previously known species, with 131 new records for individual islands. Biodiversity patterns are investigated, namely patterns of range size distribution for endemics and non‐endemics, habitat distribution patterns, island similarity in species composition and the estimation of species richness for the Azores. Newly described species are: Oonopidae ‐ Orchestina furcillata Wunderlich; Linyphiidae: Linyphiinae ‐ Porrhomma borgesi Wunderlich; Turinyphia cavernicola Wunderlich; Linyphiidae: Micronetinae ‐Agyneta depigmentata Wunderlich; Linyphiidae: Erigoninae ‐ Acorigone gen. nov. with its type species Acorigone zebraneus Wunderlich; Clubionidae ‐ Cheiracanthium floresense Wunderlich; Cheiracanthium jorgeense Wunderlich; Salticidae ‐ Neon acoreensis Wunderlich. Other major taxonomic changes are: Diplocentria acoreensis Wunderlich, 1992 (Linyphiidae) is transferred to Acorigone (comb. nov.), Leucognatha Wunderlich 1995 (Tetragnathidae) is not an endemic genus of the Azores but an African taxon and synonymous with Sancus Tullgren, 1910; Leucognatha acoreensis Wunderlich, 1992 is transferred to Sancus. Minicia picoensis Wunderlich, 1992 is a synonym of M. floresensis Wunderlich, 1992. For each species additional information is presented about its known distribution in the islands, its colonisation status, habitat occurrence and biogeographical origin.     

Persistent inter‐ and intraspecific gene exchange within a parallel radiation of caterpillar hunter beetles (Calosoma sp.) from the Galápagos

When environmental gradients are repeated on different islands within an archipelago, similar selection pressures may act within each island, resulting in the repeated occurrence of ecologically similar species on each island. The evolution of ecotypes within such radiations may either result from dispersal, that is each ecotype evolved once and dispersed to different islands where it colonized its habitat, or through repeated and parallel speciation within each island. However, it remains poorly understood how gene flow during the divergence process may shape such patterns. In the Galápagos islands, three phenotypically similar species of the beetle genus Calosoma occur at higher elevations of different islands, while lowlands are occupied by a fourth species. By genotyping all major populations within this radiation for two nuclear and three mitochondrial gene fragments and seven microsatellite markers, we found strong support that the oldest divergence separates the highland species of the oldest island from the remaining species. Despite their morphological distinctness, highland species of the remaining islands were genetically closely related to the lowland population on each island and within the same magnitude as lowland populations sampled at different islands. Repeated evolution of highland ecotypes out of the lowland species appears the most likely scenario and estimates of geneflow rates revealed extensive admixture among ecotypes within islands, as well as between islands. These findings indicate that gene exchange among the different populations and species may have shaped the phylogenetic relationships and the repeated evolution of these ecotypes.     

中街山列岛岩相潮间带大型底栖动物的群落格局

于2006年9月和2007年7月在中街山列岛4个有居民海岛岩相潮间带设立8个断面,对大型底栖动物的群落结构进行了调查。共获得大型底栖动物34种,其中腔肠动物1种,环节动物3种,甲壳动物10种,软体动物20种。优势种有日本笠藤壶(Tetraclita japonica)、紫贻贝(Mytilus edulis)和节蝾螺(Turb articulatus)等4种。以季节和站位为因子对多样性指数进行双因素方差分析,结果表明只有夏、秋季丰富度指数(P=0.028)存在显著差异,其他指数的方差分析没有显著差异(P>0.05)。3个潮带4个岛屿共12个站位的聚类分析和MDS标序分析表明,12个群落可分为3组(Ⅰ、Ⅱ和Ⅲ组)。大型底栖动物ABC曲线分析表明底栖动物群落尚未受到干扰。     

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.     

Modelling the distribution and interaction of introduced rodents on New Zealand offshore islands

Aim To establish the factors that correlate with the distribution of the four most commonly introduced rodent species on New Zealand offshore islands — ship rat (Rattus rattus), Norway rat (R. norvegicus), Pacific rat or kiore (R. exulans) and house mouse (Mus musculus) — and examine if these distributions are interactive at the archipelago scale. Location The 297 offshore islands of the New Zealand archipelago (latitude: 34° S to 47° S; longitude: 166° E to 179° E). Methods Data on the distribution of all four introduced rodent species and the characteristics of New Zealand offshore islands were collated from published surveys and maps. The distribution of individual rodent species was regressed on island characteristics using a logistic generalized linear model. Interactions were examined by including the distributions of other rodent species as predictors in models. Results All four rodent species appear to be limited by a variety of factors, which differ between species in both number and type. The distribution of ship rats is limited by the most factors, reflecting the extent of its distribution across the archipelago. The distribution of mice is the least explicative. Only the three rat species interacted in their distribution. The distribution of kiore on offshore islands is significantly negatively related to that of ship rats and to a lesser extent Norway rats. The distribution of mice did not appear affected in any way by the number of other rodent species on an island. Main conclusions Differences in competitive ability and dispersal allow all four species to inhabit the New Zealand archipelago. Kiore distribution appears to be most limited by ship rat (and to a lesser extent Norway rat) distribution. The distribution of kiore was not found to interact with the distribution of mice on offshore islands, as has been suggested by others. The distribution of mice on offshore islands was difficult to model, which highlights the difficulties in managing this species. Overall the results offer valuable insights for management methods to assist preventing the invasion of offshore islands.     

Distribution and abundance patterns of bird community and raptor populations in the Andaman archipelago

A qualitative survey of the terrestrial bird community (sixty-five species) and a quantitative analysis of the five-diurnal raptor assemblage were earned out on 33 islands of the oceanic Andaman archipelago in the Bay of Bengal Among seven geographical parameters, island area was the main determinant of species richness for both the whole bird community and each category of species associated with four habitat types Species richness decreased most markedly with island size in the smallest islands and in open habitat species The rarest forest species were the most extinction prone with decreasing island size Specific habitat selection was the most prominent ecological correlate of inter island species distribution Observed species distribution patterns did not fit the random species placement or equprobable occurrence hypotheses Raptors were primarily forest species, two of them restricted to forest interior, two more tolerant of fragmentation and one naturally associated with mangroves Unexpectedly, the two rarest and most area sensitive raptors were the two smallest species with a strong active flight, whereas the most abundant and widespread species was the most forest interior and endemic taxon Both raptor species richness, species frequency of occurrence and abundance indices decreased with island area, which was consistently the most significant determinant of every species' occurrence and abundance There was a significant correlation between abundance or frequency of occurrence of every raptor species and the proportion of their preferred habitat type No relationship was found between habitat niche breadth or local abundance of any species and their distribution range among islands The hypothesis of random composition of species assemblages on islands was not supported because of species specific habitat selection Any evidence of interspecific competitive exclusion was limited to the striking habitat segregation of the two congeneric serpent eagles A metapopulation structure was suggested by small population distribution patterns, observed sea crossing and the circumstances of an apparent extinction     

Contemporary geography dominates butterfly diversity gradients within the Aegean archipelago (Lepidoptera: Papilionoidea, Hesperioidea)

Aim We compare the influence of contemporary geography and historical influences on butterfly diversity for islands in the Aegean archipelago. Location The Aegean archipelago (Greece) and two islands (Cyprus and Megisti) in the Levantine Sea. Methods Thirty‐one islands were examined. Data are taken from own surveys (Coutsis and Olivier) and from the literature. Stepwise multiple regression is used to determine relationships between species richness, frequency, rarity and endemicity against potential geographical predictors. Stepwise logit regression is used to determine geographical predictors of species incidence on islands. Inter‐island and inter‐species associations have been examined using multivariate ordination and clustering techniques. Results The Aegean butterfly fauna is characterized by decreasing diversity and rarity, and increasing homogeneity, from the periphery to the present geographical centre of the archipelago (Cyclades). Diversity and rarity are shown to relate closely to species richness, and species richness, in turn, is largely explained by contemporary geography, particularly the degree of isolation from the nearest mainland sources of Greece or Turkey, and island dimensions. Islands towards the centre of the archipelago are characterized by a group of mobile species (n ≥ 20 species) with extensive ranges across Europe; species that would have recolonized Santorini (Thira) following the VI6 eruption there c. 1630 bc . Endemic components, indicative of autochthonous evolutionary events, are few (5% of species are endemic) compared to known sedentary organisms (molluscs and isopods), but exceed those for more mobile animals (i.e. birds); their distribution is mainly confined to large isolated islands along the Aegean arc (i.e. Kriti) and in the Dodecanese group. Main conclusions Contemporary geography, i.e. processes currently operating in ecological time, dominates butterfly diversity gradients (species richness, frequency, rarity and incidence) in the archipelago. Two reasons are suggested to account for the lack of endemism and the pattern of decreasing diversity into the Cyclades. First, relict butterfly elements may have become extinct on all but a few larger islands, particularly from environmental changes since the Neolithic (fire and overgrazing). Second, colonization from the continental landmasses is ongoing with more mobile species transferring even to the most isolated islands.     

Ant communities on small tropical islands: effects of island size and isolation are obscured by habitat disturbance and ‘tramp’ ant species

Aim Comparisons among islands offer an opportunity to study the effects of biotic and abiotic factors on small, replicated biological communities. Smaller population sizes on islands accelerate some ecological processes, which may decrease the time needed for perturbations to affect community composition. We surveyed ants on 18 small tropical islands to determine the effects of island size, isolation from the mainland, and habitat disturbance on ant community composition. Location Thousand Islands Archipelago (Indonesian name: Kepulauan Seribu) off Jakarta, West Java, Indonesia. Methods Ants were sampled from the soil surface, leaf litter and vegetation in all habitat types on each island. Island size, isolation from the mainland, and land‐use patterns were quantified using GIS software. The presence of settlements and of boat docks were used as indicators of anthropogenic disturbance. The richness of ant communities and non‐tramp ant species on each island were analysed in relation to the islands’ physical characteristics and indicators of human disturbance. Results Forty‐eight ant species from 5 subfamilies and 28 genera were recorded from the archipelago, and approximately 20% of the ant species were well‐known human‐commensal ‘tramp’ species. Islands with boat docks or human settlements had significantly more tramp species than did islands lacking these indicators of anthropogenic disturbance, and the diversity of non‐tramp species decreased with habitat disturbance. Main conclusions Human disturbance on islands in the Thousand Islands Archipelago promotes the introduction and/or establishment of tramp species. Tramp species affect the composition of insular ant communities, and expected biogeographical patterns of ant richness are masked. The island with the greatest estimated species richness and the greatest number of unique ant species, Rambut Island, is a forested bird sanctuary, highlighting the importance of protected areas in preserving the diversity of species‐rich invertebrate faunas.     

Differentiated macrophyte types as a habitat for rotifers in small mid-forest water bodies

The rotifer community structure may be shaped by a variety of environmental factors, including biological parameters, such as predation or competition, as well as by physical-chemical factors, among which the kind of macrophyte substratum and parameters relating to the trophic state and to the catchment area conditions are of great importance. Another impact on rotifer composition, abundance and frequency may be expected when considering differentiated macrophyte types (including helophytes, nymphaeids and elodeids) within a group of eight ponds located within a mid-forest catchment area, which was the main aim of the present study. Detailed analysis on the participation of indicator eutrophic rotifer species provided an additional goal of this investigation in order to qualify the trophic state of this kind of water body located within the Wielkopolska region, in the central western part of Poland. The presence of 117 taxa, including 7 species that are rare or infrequently distributed in the Polish fauna was recorded. The number of taxa and rotifer abundance differed greatly in respect to the specific water body and to the type of substratum. The vegetated zones dominated by elodeids were characterised by the most various and most abundant rotifer communities as well as by the highest values of the Shannon-Weaver index. This reflects a positive relationship between the heterogeneity of habitat and the structure of rotifer communities. It was also found that helophytes and the open water zone possessed the highest, while elodeids the lowest percentage of eutrophic species.     

Vascular plant species richness in relation to habitat diversity and island area in the Finnish Archipelago

Aim The aim of this study is to explore the interrelationships between island area, species number and habitat diversity in two archipelago areas. Location The study areas, Brunskär and Getskär, are located in an archipelago in south‐western Finland. Methods The study areas, 82 islands in Brunskär and 78 in Getskär, were classified into nine habitat types based on land cover. In the Brunskär area, the flora (351 species) was surveyed separately for each individual habitat on the islands. In the Getskär area, the flora (302 species) was surveyed on a whole‐island basis. We used standard techniques to analyse the species–area relationship on a whole‐island and a habitat level. We also tested our data for the small island effect (SIE) using breakpoint and path analysis models. Results Species richness was significantly associated with both island area and habitat diversity. Vegetated area in particular, defined as island area with the rock habitat subtracted, proved to be a strong predictor of species richness. Species number had a greater association with island area multiplied by the number of habitats than with island area or habitat number separately. The tests for a SIE in the species–area relationship showed the existence of a SIE in one of the island groups. No SIE could be detected for the species–vegetated area relationship in either of the island groups. The strength of the species–area relationship differed considerably between the habitats. Main conclusions The general principles of island biogeography apply well to the 160 islands in this study. Vascular plant diversity for small islands is strongly influenced by physiographic factors. For the small islands with thin and varying soil cover, vegetated area was the most powerful predictor of species richness. The species–area curves of various habitats showed large variations, suggesting that the measurement of habitat areas and establishment of habitat‐based species lists are needed to better understand species richness on islands. We found some evidence of a SIE, but it is debatable whether this is a ‘true’ SIE or a soil cover/habitat characteristics feature.     

Island size, isolation, or interspecific competition? The breeding distribution of the Parus guild in the Danish archipelago

The Parus guild (Parus spp., Sitta, Certhia, and Regulus) is distributed as a complex mosaic within the Danish archipelago, with from one to eight species on different islands. We assessed the roles of island isolation, island size, and interspecific competition in determining the breeding species compositions of this guild on 53 Danish islands. Small, isolated islands supported fewer species than larger, nearshore islands. These effects, however, were largely restricted to a few sedentary species (P. cristatus, P. palustris, S. europaea) that are known to be poor dispersers/colonizers. In some cases, these three species were also absent from large, nearshore islands with suitable habitat, suggesting that habitat availability was not always responsible for the absence of a species. Monte Carlo simulations suggested that the pattern of species presence/absence was not a result of interspecific interactions. Thus, although a number of previous studies have documented interspecific competition among members of the Parus guild, our results suggest that such competition is not responsible for the unusual pattern of species distribution within the Danish archipelago. Received: 28 October 1996 / Accepted: 7 February 1997     

Zoogeography of Pacific Ocean islands: a comparison of the rotifer faunas of Easter Island and the Galápagos archipelago

During September 1990, an extensive sampling of the freshwaters of Easter Island was conducted. The resulting list of rotifer species, supplemented by taxa present in samples collected during a previous trip to the island, is compared with that of another oceanic island of volcanic origin, namely Santa Cruz, Galápagos archipelago. In spite of less research, Santa Cruz has a richer rotifer fauna which, unlike Easter Island, includes endemic species. Possible causes for the faunal poverty of Easter Island are: large source-to-target distance, small target size, uniformity of the target island's ecosystems and limited age of its aquatic biotopes.