Postmating barriers to hybridization between an island’s native eucalypts and an introduced congener

We evaluate postmating barriers to hybridization between an exotic eucalypt and a group of native congeners on the island of Tasmania. We aimed to better understand the basis of reproductive isolation between the species, glean insights into the evolution of isolating mechanisms, and inform genetic risk management. Compatibility between the exotic plantation species Eucalyptus nitens (pollen parent) and 18 native Tasmanian taxa was assayed using experimental crossing for 17 taxa (13,458 flowers pollinated to produce 1058 female × male cross combinations), and previous data for one species. Compatibility was assessed in terms of F₁ hybrid production, as well as F₁ hybrid survival and growth after 5 years. This data was combined with measurements of style length, and genetic distance from E. nitens to each maternal species, in order to determine the importance of a sequence of prezygotic and postzygotic barriers. We found that the early-acting barrier of style length (prezygotic) had the strongest isolating effect, while later-acting (postzygotic) barriers, affecting early-age growth and survival, contributed little to reproductive isolation. Style length alone explained 46 % of the variation in hybridization rate. Conversely, there was no significant relationship between genetic distance and prezygotic or postzygotic compatibility in these closely related species. This pattern is consistent with selection driving the rapid evolution of prezygotic barriers, while drift-like-processes lead to the more gradual evolution of intrinsic barriers. Although other premating and postmating barriers clearly contribute, our results highlight the important role of early-acting postmating barriers in preventing gene flow from exotic E. nitens plantations.     

Shrub cover expressed as an ‘arthropod island’ in xeric environments

Based on the vague importance of shrub cover, an attempt was made to create a theoretical concept framework known as an ‘arthropod-island’ analytical model. These models were based on the multi-bond correlation between shrubs, soil properties, and above- and below-ground biotic communities. By utilizing published datasets on (i.e., above- and below-ground) arthropod communities related to shrub species and age, the proposed models for an ‘arthropod island’ were applied in order to determine their fitness for xeric ecosystems. It was found that the ‘arthropod-island’ concept could be the result of statistical differences in ecologically adaptive (i.e., preferable) redistribution of arthropods among the microhabitats beneath the shrub canopy and in the open spaces. Taxon density, relative to the richness and Shannon indices, was found to be more sensitive to the selected models. The relative interaction intensity index [RII = (A ? B)/(A + B), A = shrub canopy value, B = intershrub value] was found to be more suitable for the ‘arthropod island’ at the community level. The relative neighbor effect [RNE = (B ? A)/max(A, B)] and RII were found to be suitable at the population level, while the fitted model heavily depended on the variety of arthropod taxon. It was suggested that there were consistent ‘arthropod island’–shrub relationships between shrub species and between shrub ages in terms of arthropod density at the community level. The arthropod taxon was found to indicate an inconsistent ‘arthropod island’–shrub relationship between shrub species that differed from shrub ages at the population level.     

Genetic variation and structure of house sparrow populations: is there an island effect?

Population genetic structure and intrapopulation levels of genetic variation have important implications for population dynamics and evolutionary processes. Habitat fragmentation is one of the major threats to biodiversity. It leads to smaller population sizes and reduced gene flow between populations and will thus also affect genetic structure. We use a natural system of island and mainland populations of house sparrows along the coast of Norway to characterize the different population genetic properties of fragmented populations. We genotyped 636 individuals distributed across 14 populations at 15 microsatellite loci. The level of genetic differentiation was estimated using F‐statistics and specially designed Mantel tests were conducted to study the influence of population type (i.e. mainland or island) and geographic distance on the genetic population structure. Furthermore, the effects of population type, population size and latitude on the level of genetic variation within populations were examined. Our results suggest that genetic processes on islands and mainland differed in two important ways. First, the intrapopulation level of genetic variation tended to be lower and the occurrence of population bottlenecks more frequent on islands than the mainland. Second, although the general level of genetic differentiation was low to moderate, it was higher between island populations than between mainland populations. However, differentiation increased in mainland populations somewhat faster with geographical distance. These results suggest that population bottleneck events and genetic drift have been more important in shaping the genetic composition of island populations compared with populations on the mainland. Such knowledge is relevant for a better understanding of evolutionary processes and conservation of threatened populations.     

An island within an island: genetic differentiation of Anopheles gambiae in São Tomé, West Africa, and its relevance to malaria vector control

Islands are choice settings for experimental studies of vector control strategies based on transgenic insects. Before considering this approach, knowledge of the population structure of the vector is essential. Genetic variation at 12 microsatellite loci was therefore studied in samples of the malaria vector Anopheles gambiae s.s., collected from six localities of S?o Tomé island (West Africa). The objectives were (i) to assess the demographic stability and effective population size of A. gambiae from these sites, (ii) to determine population differentiation and (iii) to relate the observed patterns of population structure with geographic, ecological and historical aspects of the vector on the island. Significant population differentiation, revealed by FST and RST statistics, was found between the southernmost site, Porto Alegre, and northern localities. The observed patterns of population substructure are probably a result of restrictions to gene flow in the less inhabited, more densely forested and mountainous south. In all localities surveyed, A. gambiae appeared to be experiencing a demographic expansion, consistent with a relatively recent (ca. 500 years) founder effect. The results are discussed with respect to current and future prospects of malaria vector control.     

Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.

     

Does interspecific competition with a stronger competitor explain the rarity of an endangered snake on a Mediterranean island?

Interspecific competition has been demonstrated to be an important shaping force for snake communities worldwide, but relatively few studies have investigated its occurrence and extent with island assemblages of snakes. In Sardinia (Mediterranean Sea), two species of whip snakes (Colubridae) co-occur, one of them being abundant and widespread (Hierophis viridiflavus) and the other being localized and critically endangered (Hemorrhois hippocrepis). A previous hypothesis suggested that the latter species would be confined to suboptimal habitats by the former species, which is a stronger competitor for food. As a consequence, He. hippocrepis would not only be rare but would also be smaller in body size in Sardinia than in other regions of its range where Hi. viridiflavus does not occur. In 1999?C2010, we studied habitat selection, food habits, and body sizes of these two snakes in sympatric populations, applying a suite of statistical tools including null models and Monte Carlo simulations. We observed that dietary habits were different between species (compared to Hi. viridiflavus, He. hippocrepis more frequently preyed upon rodents and less frequently on lizards, and within rodent prey, more frequently upon Rattus and less frequently upon Mus), but not in a way compatible with competitively induced trophic niche partitioning. The two species were similar in terms of prey size and predator-size?Cprey-size relationships. They also differed in habitat selection (maquis was the preferred habitat for both, but Hi. viridiflavus was found significantly more often than He. hippocrepis in grasslands, cultivations, and artificial pinewoods) but again in a non-competitively directed way. In addition, there was no evidence for the hypothesis that He. hippocrepis was confined to suboptimal habitats. Body sizes were similar between species (with males being significantly larger than females), and Sardinian He. hippocrepis were not smaller than conspecifics inhabiting regions without Hi. viridiflavus. Overall, our study showed that the two species differed in some aspects of their ecology, but these differences could not be due to competitive interactions. The conservation implications of these results are also discussed.     

Behavioral and physiological adjustments to new predators in an endemic island species, the Galápagos marine iguana

For the past 5 to 15 million years, marine iguanas (Amblyrhynchus cristatus), endemic to the Galápagos archipelago, experienced relaxed predation pressure and consequently show negligible anti-predator behavior. However, over the past few decades introduced feral cats and dogs started to prey on iguanas on some of the islands. We investigated experimentally whether behavioral and endocrine anti-predator responses changed in response to predator introduction. We hypothesized that flight initiation distances (FID) and corticosterone (CORT) concentrations should increase in affected populations to cope with the novel predators. Populations of marine iguanas reacted differentially to simulated predator approach depending on whether or not they were previously naturally exposed to introduced predators. FIDs were larger at sites with predation than at sites without predation. Furthermore, the occurrence of new predators was associated with increased stress-induced CORT levels in marine iguanas. In addition, age was a strong predictor of variation in FID and CORT levels. Juveniles, which are generally more threatened by predators compared to adults, showed larger FIDs and higher CORT baseline levels as well as higher stress-induced levels than adults. The results demonstrate that this naive island species shows behavioral and physiological plasticity associated with actual predation pressure, a trait that is presumably adaptive. However, the adjustments in FID are not sufficient to cope with the novel predators. We suggest that low behavioral plasticity in the face of introduced predators may drive many island species to extinction.     

When considering no man is an island—assessing bioenergy systems in a regional and LCA context: a review

Purpose

With many environmental burdens associated with bioenergy production occurring at the regional level, there is a need to produce more regional and spatially representative life cycle assessment of bioenergy systems. On the other hand, such assessments also need to account for the global and cumulative impacts along the full bioenergy life cycle in order to support effective regional policy measures and decision making. Therefore, the challenge is to find a balance. In other words, how should we define the regional context for bioenergy system assessments in order to complement life cycle thinking? The aim of this review is to answer this question by providing an overview of important considerations when assessing bioenergy systems in a regional and LCA context and how these two contexts intersect. It also aims to help guide and orientate LCA practitioners interested in including more regional aspects in their bioenergy studies. Until now, such a review which explores the integration of regional and life cycle contexts in relation to bioenergy systems and their products has not been done.

Methods

As a first step, we define what we mean by the term region. We then look at the potential burdens relating to bioenergy systems and their relationship with the regional context. In a next step, we explore life cycle thinking and the intersection between the regional and LCA contexts by providing some examples from the literature. We then discuss the benefits and limitations of such regionally contextualized life cycle approaches in relation to bioenergy production systems and indeed other alternative biomass uses.

Results and discussion

Three regional contexts were identified to help orientate life cycle thinking aiming to assess the regional and nonregional environmental implications of bioenergy production. These contexts were as follows: “within regional,” “regional and ROW,” and “regionalized.” The added value of implementing a regionally contextualized life cycle approach is the ability, therefore, to include greater regional and spatial details in the assessments of bioenergy production systems, without losing the links to the diversity of global supply chains. Thus, providing greater geographical and regional insight into how such potential burdens can be reduced or shifted burdens avoided or how associated regional production activities could be optimized to mitigate such burdens.

Conclusions

The use of different regional contexts as proposed in this paper is not only useful to orientate life cycle thinking in relation to bioenergy systems but also for the assessment of alternative novel bio-based systems.

     

Biological invasion on an oceanic island mountain: Do alien plant species have wider ecological ranges than native species?

Abstract. Spatial distribution patterns of alien plant species were compared with those of native species on a windward slope of Mt. Haleakala (3055 m). Oceanic islands are considered susceptible to biological invasion, and this study numerically tested this circumstantial evidence with the following questions: Are all habitats equally susceptible; and, do successful invaders have wider realized niches than natives? The mountain slope consists of three distinct altitudinal bioclimatic zones (hot moist lowland, wet montane cloud, and cool arid high-altitude zones). Ordination indicated that alien species' ranges and population expansions were clustered in the lowland and high-altitude zones. The lowland zone had been subjected to natural canopy dieback, and the high-altitude zone to grazing by domestic and feral ungulates. By contrast, the montane cloud forest was relatively intact in terms of number and cover of native species. Thus, susceptibility to alien invasion clearly differed among zones, and the primary causes seemed to be the obvious disturbance factors. The mean ecological range along the altitude-rainfall gradient was significantly (P < 0.05) greater for native than for alien species in most life-form groups. The reasons for the greater number of climate generalists among the natives vs. the range-restricted aliens appear to be related to: (1) the pre-alien condition with a depauperate flora which allowed for ‘ecological release’ of successful native colonizers, and (2) the climatic pre-adaptation of alien invaders which restricts them from penetrating over a broader spectrum of climatic zones in a floristic matrix subjected to increasing interspecific competition.     

A fascinating island: 2n = 4

Abstract

Among Angiosperms, only six species are known to possess the lowest identified chromosome number, i.e. 2n = 4. These plants are the monocotyledons Zingeria biebersteiniana, Colpodium versicolor, Ornithogalum tenuifolium and Rhynchospora tenuis, and the dicotyledons Haplopappus gracilis and Brachyscome dichromosomatica. The low chromosome number may be cytogenetically derived from a different ancestral basic number, characteristic of each genus, by different processes, including tandem fusion or unequal reciprocal translocations with loss of centric fragments. All these plants possess low nuclear 4C DNA contents, ranging from 1.56 pg (R. tenuis) to 8.20 pg (H. gracilis), and they generally display a similar chromosome size and a similar position of the nucleolus organising region (NOR), that is often located in the terminal or subterminal region of the small chromosome pair. All these characteristics could be a consequence of common adaptative mechanisms. Peculiar characteristics within these karyotypes are the holocentric chromosomes of R. tenuis and the presence of B chromosomes in B. dichromosomatica. Plants with a very low chromosome number may be considered to constitute a fascinating “island of interest”; moreover, they represent simple systems helpful for the examination of the structural organisation and evolution of Angiosperm chromosomes.     

New Caledonia: a very old Darwinian island?

New Caledonia has generally been considered a continental island, the biota of which largely dates back to Gondwanan times owing to its geological origin and the presence of phylogenetic relicts. This view is contradicted by geological evidence indicating long Palaeocene and Eocene submersions and by recent biogeographic and phylogenetic studies, with molecular or geophysical dating placing the biota no older than the Oligocene. Phylogenetic relicts do not provide conclusive information in this respect, as their presence cannot be explained by simple hypotheses but requires assumption of many ad hoc extinction events. The implication of this new scenario is that all the New Caledonian biota colonized the island since 37 Ma Local richness can be explained by local radiation and adaptation after colonization but also by many dispersal events, often repeated within the same groups of organisms. Local microendemism is another remarkable feature of the biota. It seems to be related to recent speciation mediated by climate, orography, soil type and perhaps unbalanced biotic interactions created by colonization disharmonies. New Caledonia must be considered as a very old Darwinian island, a concept that offers many more fascinating opportunities of study.     

The island rule: made to be broken?

The island rule is a hypothesis whereby small mammals evolve larger size on islands while large insular mammals dwarf. The rule is believed to emanate from small mammals growing larger to control more resources and enhance metabolic efficiency, while large mammals evolve smaller size to reduce resource requirements and increase reproductive output. We show that there is no evidence for the existence of the island rule when phylogenetic comparative methods are applied to a large, high-quality dataset. Rather, there are just a few clade-specific patterns: carnivores; heteromyid rodents; and artiodactyls typically evolve smaller size on islands whereas murid rodents usually grow larger. The island rule is probably an artefact of comparing distantly related groups showing clade-specific responses to insularity. Instead of a rule, size evolution on islands is likely to be governed by the biotic and abiotic characteristics of different islands, the biology of the species in question and contingency.     

Metacommunity,mainland‐island system or island communities? Assessing the regional dynamics of plant communities in a fragmented landscape

Understanding the regional dynamics of plant communities is crucial for predicting the response of plant diversity to habitat fragmentation. However, for fragmented landscapes the importance of regional processes, such as seed dispersal among isolated habitat patches, has been controversially debated. Due to the stochasticity and rarity of among‐patch dispersal and colonization events, we still lack a quantitative understanding of the consequences of these processes at the landscape‐scale. In this study, we used extensive field data from a fragmented, semi‐arid landscape in Israel to parameterize a multi‐species incidence‐function model. This model simulates species occupancy pattern based on patch areas and habitat configuration and explicitly considers the locations and the shapes of habitat patches for the derivation of patch connectivity. We implemented an approximate Bayesian computation approach for parameter inference and uncertainty assessment. We tested which of the three types of regional dynamics – the metacommunity, the mainland‐island, or the island communities type – best represents the community dynamics in the study area and applied the simulation model to estimate the extinction debt in the investigated landscape. We found that the regional dynamics in the patch‐matrix study landscape is best represented as a system of highly isolated ‘island’ communities with low rates of propagule exchange among habitat patches and consequently low colonization rates in local communities. Accordingly, the extinction rates in the local communities are the main drivers of community dynamics. Our findings indicate that the landscape carries a significant extinction debt and in model projections 33–60% of all species went extinct within 1000 yr. Our study demonstrates that the combination of dynamic simulation models with field data provides a promising approach for understanding regional community dynamics and for projecting community responses to habitat fragmentation. The approach bears the potential for efficient tests of conservation activities aimed at mitigating future losses of biodiversity.     

A sponge diversity centre within a marine ‘island’

The exposed and gulf-stream warmed south-west coast of Ireland has a Lusitanean fauna composed of elements of the colder waters to the north and east, and others from the warmer Mediterranean Sea. Lough Hyne, a small marine body, is unusual on this coast in being very sheltered, but also in being characterised by many different niches within a small space (1 km²). Sponges are particularly abundant, morphologically varied and more than 100 species have been described. Species diversity was measured at 6 m intervals on vertical and inclined profiles (to a maximum of 30 m) at six sites, spanning a range of flow rate and sedimentation regimes. Diversity, richness, evenness and density varied significantly with both flow regime and depth, but was much lower on the surrounding Atlantic coast. Four different sponge communities were differentiated on the basis of sponge species assemblages which correlated with different environmental conditions. At sites of turbulent and fast flow conditions, sponge diversity and richness were lowest, with the highest values being found at the sites of moderate and high sedimentation. Significant differences were observed in all four ecological variables with respect to substratum angle with the exception of the site experiencing the most turbulent flow conditions. Lough Hyne was found to possess the second highest sponge species diversity (H=3.626) and richness (77 species) of all available figures from temperate, polar and tropical areas (of similar sized sampling area). The uniqueness, diversity and species composition of the sponge community at this location suggests Lough Hyne is, biologically, a marine island within the island of Ireland.     

Contrasting levels of extra-pair paternity in mainland and island populations of the house sparrow (Passer domesticus): is there an 'island effect'?

Despite the many studies that have investigated the genetic mating system of socially monogamous birds, very little is known about the underlying causes of extra-pair paternity and few studies have attempted to test those hypotheses which have been suggested. This study describes die analysis of die genetic mating system of two populations of the house sparrow [Passer domesticus) , and uses the results from four other populations to test existing hypodieses using an intra-specific comparative approach. The parentage analysis was conducted using a combination of published and newly presented microsatellite loci isolated from the house sparrow. One population in Kentucky, U.S.A. was found to contain what may be considered to be a typical level of extra-pair paternity for mis species (10.5%, 19/185 offspring). The second, a population on the island of Lundy, UK, exhibited a very low level (1.3%, 4/305 offspring), significandy lower dian that in all the other populations studied so far. The finding of such diverse rates of extra-pair paternity, along with the existing estimates from ofher populations, has allowed us to test the effects of breeding density and genetic variation on die level of extra-pair paternity. We found no effect of either factor on the frequency of extra-pair paternity in the house sparrow, leaving the cause of this variation open to fresh ideas.     

The small‐island effect: fact or artefact?

Positive relationships between species richness and sampling area are perhaps the most pervasive patterns in nature. However, the shape of species–area relationships is often highly variable, for reasons that are poorly understood. One such source of variability is the "small-island effect", which refers to a decrease in the capacity of sampling area to predict species richness on small islands. Small-island effects have been attributed to a variety of processes, including spatial subsidies, habitat characteristics and ocean-born disturbances. Here, we show that small-island effects can be generated by logarithmic data transformations, which are commonly applied to both axes of species–area relationships. To overcome this problem, we derive several null models to test for non-random variability in the capacity of island area to predict species richness and apply them to data sets on island plant communities in Canada and New Zealand. Both archipelagos showed evidence for small-island effects using traditional breakpoint regression techniques on log-log axes. However, null model analyses revealed different results. The capacity of sampling area to predict species richness in the Canadian archipelago was actually lowest at intermediate island size classes. In the New Zealand archipelago, island area was similarly capable of predicting species richness across the full range of island sizes, indicating the small-island effect detected by breakpoint regression is an artifact of logarithm data transformation. Overall results show that commonly used regression techniques can generate spurious small-island effects and that alternative analytic procedures are needed to detect non-random patterns in species richness on small islands.     

The contribution of island populations to in situ genetic conservation

Genetic variation is often lower within island populations, however islands may also harbor divergent genetic variation. The likelihood that insular populations are genetically diverse or divergent should be influenced by island size and isolation. We tested this assumption by comparing patterns of genetic variation across all major island song sparrow populations along the Pacific North American coast. Allelic richness was moderately lowered even on islands which are close to large, potential sources. The most significant differences in allelic richness occurred on very small or highly remote islands. Gene diversity was significantly lower only on remote or very small islands. We found that island populations contribute to regional genetic variation through both the amount of genetic variation and the uniqueness of that variation. The partitioning of this contribution was associated with the size and isolation of the island populations.     

Are island plant communities more invaded than their mainland counterparts?

Questions: Are island vegetation communities more invaded than their mainland counterparts? Is this pattern consistent among community types? Location: The coastal provinces of Catalonia and the para‐oceanic Balearic Islands, both in NE Spain. These islands were connected to the continent more than 5.35 million years ago and are now located <200 km from the coast. Methods: We compiled a database of almost 3000 phytosociological relevés from the Balearic Islands and Catalonia and compared the level of invasion by alien plants in island versus mainland communities. Twenty distinct plant community types were compared between island and mainland counterparts. Results: The percentage of plots with alien species, number, percentage and cover percentage of alien species per plot was greater in Catalonia than in the Balearic Islands in most communities. Overall, across communities, more alien species were found in the mainland (53) compared to the islands (only nine). Despite these differences, patterns of the level of invasion in communities were highly consistent between the islands and mainland. The most invaded communities were ruderal and riparian. Main conclusion: Our results indicate that para‐oceanic island communities such as the Balearic Islands are less invaded than their mainland counterparts. This difference reflects a smaller regional alien species pool in the Balearic Islands than in the adjacent mainland, probably due to differences in landscape heterogeneity and propagule pressure.