Population genetics of wolf spiders of fragmented habitat in the wheat belt of New South Wales

Possible effects of habitat fragmentation on the population genetics of a species of wolf spider (Lycosidae) from remnant Callitris woodland in the wheat belt of central western New South Wales in Australia are examined. Single-strand conformational analysis of mitochondrial cytochrome oxidase (subunit 1) was used to characterize the haplotypes of 295 spiders in six blocks each of four woodland sites. DNA sequences were collected from 119 of these spiders to confirm haplotype scoring, allow phylogeny estimation and permit calculation of sequence-based statistics. Intra-block tests do not suggest widespread effects of fragmentation. Genetic diversity is high in all blocks, with 25 haplotypes being identified. Nucleotide diversity is relatively low, as all of the haplotypes are closely related. One block had a significantly low value for the Ewens/Watterson test of neutrality and one block's value was nearly significantly high. Two blocks had nearly significant values of the Harpending Raggedness Index testing for recent population bottlenecks. No other intrablock tests approach significance. Interpopulation comparisons show significant nonhomogeneity of haplotype frequencies globally and in all pairwise comparisons. Relationships between woodland blocks based on haplotype frequencies are discordant with geographical proximity. Haplotype distribution patterns suggest that population structuring existed prior to fragmentation. We develop two measures of genetic distinctiveness to identify subpopulations of interest for conserving evolutionary processes in a species' regional population. One is based on the sum of pairwise FST values and one on the spatial distribution of genetic variation. High values of the measure suggest a subpopulation might have been recently perturbed and low values that it is relatively undisturbed. The two measures identify different blocks as being of particular interest.     

Edge effects on the prevalence and mortality factors of Phytomyza ilicis (Diptera, Agromyzidae) in a suburban woodland

Although the effects of edges on the biotas of habitat patches have been widely discussed, there have been few empirical studies of the mechanistic basis of population and community differences between patch edges and interiors. This is particularly true of differential effects of edges on species' mortalities, and on interactions in insect populations and communities. Here we examine edge-associated differences in the prevalence and mortality factors of the holly leaf-miner Phytomyza ilicis , in a suburban woodland in Sheffield, U.K. Leaf miner prevalence was higher and survivorship to adulthood lower at the woodland edge. Natural enemies and other mortality factors contributed differently to total mortality at the edge and interior. Mechanisms underlying edge effects on P. ilicis arose from the interaction between microclimate, adult movement and host-plant quality. The differential induction of species mortality found, confirms the complexity of species' responses to habitat edges and the importance of understanding the effects of edges on species interactions.     

Novel methods improve prediction of species' distributions from occurrence data

Prediction of species' distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species' distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species' occurrence data. Presence-only data were effective for modelling species' distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.     

Developmental stability across the breeding distribution of the scissor-tailed flycatcher (Tyrannus forficatus)

A central question in ecology is how individual fitness interacts with the spatial variation in population density and habitat characteristics across species' ranges. We used fluctuating asymmetry (FA) as a measure of developmental stability (DS) in individuals of Tyrannus forficatus to estimate the suitability of sites of varying abundance and position within the species' range. FA in the inner-tail feathers of males and females is not spatially correlated across the species' range. FA in males increases towards the centre of the range and is not correlated with abundance. FA in females is not correlated with position in the range or abundance. Our results suggest that optimal sites are found throughout the range of the species, whereas suboptimal sites are mainly found towards the centre of the range. Additionally, our results suggest that abundance may not reflect the suitability of sites across species' ranges.     

The rise and fall of isolation by distance in the anadromous brook charr (Salvelinus fontinalis Mitchill)

Geographic patterns of genetic diversity depend on a species' demographic properties in a given habitat, which may change over time. The rates at which patterns of diversity respond to changes in demographic properties and approach equilibrium are therefore pivotal in our understanding of spatial patterns of diversity. The brook charr Salvelinus fontinalis is a coastal fish exhibiting limited marine movements, such that a stable one-dimensional isolation-by-distance (IBD) pattern should be observed over the whole range. Its range, however, recently shifted northward such that northern populations may still be in the process of reaching equilibrium. We investigated variation in IBD patterns, genetic divergence, and allelic richness at six microsatellite markers in 2087 anadromous brook charr from 59 rivers along the most likely postglacial colonization route. We observed a decrease in allelic richness, together with an increase in differentiation and a decrease in IBD in the most recently colonized northern populations, as expected following recent colonization. Contrary to expectation, however, similar patterns were also observed at the southernmost part of the range, despite the fact that these populations are not considered to be newly colonized. We propose that the loss of dispersal capabilities associated with anadromy may have caused the southernmost populations to evolve relatively independently of one another. This study thus demonstrated that changes in a species' geographic range and dispersal capabilities may contribute to shaping geographic patterns of genetic diversity.     

Glacial history of the North Atlantic marine snail, Littorina saxatilis, inferred from distribution of mitochondrial DNA lineages

The North Atlantic intertidal gastropod, Littorina saxatilis (Olivi, 1792), exhibits extreme morphological variation between and within geographic regions and has become a model for studies of local adaptation; yet a comprehensive analysis of the species' phylogeography is lacking. Here, we examine phylogeographic patterns of the species' populations in the North Atlantic and one remote Mediterranean population using sequence variation in a fragment of the mitochondrial cytochrome b gene (607 bp). We found that, as opposed to many other rocky intertidal species, L. saxatilis has likely had a long and continuous history in the Northwest Atlantic, including survival during the last glacial maximum (LGM), possibly in two refugia. In the Northeast Atlantic, several areas likely harboured refugial populations that recolonized different parts of this region after glacial retreat, resulting in strong population structure. However, the outlying monomorphic Venetian population is likely a recent anthropogenic introduction from northern Europe and not a remnant of an earlier wider distribution in the Mediterranean Sea. Overall, our detailed phylogeography of L. saxatilis adds an important piece to the understanding of Pleistocene history in North Atlantic marine biota as well as being the first study to describe the species' evolutionary history in its natural range. The latter contribution is noteworthy because the snail has recently become an important model species for understanding evolutionary processes of speciation; thus our work provides integral information for such endeavours.     

Theoretical models of species' borders: single species approaches

The range of potential mechanisms limiting species' distributions in space is nearly as varied and complex as the diversity of life itself. Yet viewed abstractly, a species' border is a geographic manifestation of a species' demographic responses to a spatially and temporally varying world. Population dynamic models provide insight into the different routes by which range limits can arise owing to gradients in demographic rates. In a metapopulation context, for example, range limits may be caused by gradients in extinction rates, colonization rates or habitat availability. We have consider invasion models in uniform and heterogeneous environments as a framework for understanding non-equilibrium range limits, and explore conditions under which invasions may cease to spread leaving behind a stationary range limit. We conclude that non-equilibrial range dynamics need further theoretical and empirical attention.     

Degree of landscape fragmentation influences genetic isolation among populations of a gliding mammal

Forests and woodlands are under continuing pressure from urban and agricultural development. Tree-dependent mammals that rarely venture to the ground are likely to be highly sensitive to forest fragmentation. The Australian squirrel glider (Petaurus norfolcensis) provides an excellent case study to examine genetic (functional) connectivity among populations. It has an extensive range that occurs in a wide band along the east coast. However, its forest and woodland habitat has become greatly reduced in area and is severely fragmented within the southern inland part of the species' range, where it is recognised as threatened. Within central and northern coastal regions, habitat is much more intact and we thus hypothesise that genetic connectivity will be greater in this region than in the south. To test this we employed microsatellite analysis in a molecular population biology approach. Most sampling locations in the highly modified south showed signatures of genetic isolation. In contrast, a high level of genetic connectivity was inferred among most sampled populations in the more intact habitat of the coastal region, with samples collected 1400 km apart having similar genetic cluster membership. Nonetheless, some coastal populations associated with urbanisation and agriculture are genetically isolated, suggesting the historic pattern observed in the south is emerging on the coast. Our study demonstrates that massive landscape changes following European settlement have had substantial impacts on levels of connectivity among squirrel glider populations, as predicted on the basis of the species' ecology. This suggests that landscape planning and management in the south should be focused on restoring habitat connectivity where feasible, while along the coast, existing habitat connectivity must be maintained and recent losses restored. Molecular population biology approaches provide a ready means for identifying fragmentation effects on a species at multiple scales. Such studies are required to examine the generality of our findings for other tree-dependent species.     

Spatial-temporal population dynamics across species range: from centre to margin

Understanding the boundaries of species' ranges and the variations in population dynamics from the centre to margin of a species' range is critical. This study simulated spatial-temporal patterns of birth and death rates and migration across a species' range in different seasons. Our results demonstrated the importance of dispersal and migration in altering birth and death rates, balancing source and sink habitats, and governing expansion or contraction of species' ranges in changing environments. We also showed that the multiple equilibria of metapopulations across a species' range could be easily broken following climatic changes or physical disturbances either local or regional. Although we refer to our models as describing the population dynamics across whole species' range, they should also apply to small-scale habitats (metapopulations) in which species abundance follows a humped pattern or to any ecosystem or landscape where strong central-marginal (C-M) environmental gradients exist. Conservation of both central and marginal populations would therefore be equally important considerations in making management decisions.     

Seed and pollen flow in expanding a species' range

The distinct processes of gene flow via seeds and pollen in hermaphrodite plants provide a biological basis for interpreting their different roles in expanding a species' range. A species' range is primarily expanded through the colonization process by seed dispersal and followed by the joint effects of both seed and pollen flow. Here we examined the effects of seed and pollen flow on shaping a species' distribution in one-dimensional space. Our results demonstrate that pollen flow can enhance range expansion when immigrating genes are adaptive to recipient populations, but can shrink a species' range when immigrating genes are maladaptive. The incompletely purging of maladaptive genes from immigrating pollen grains at the gametophyte stage can reinforce the biological barrier to range expansion. The linkage disequilibria attained by immigrating seeds and pollen grains indirectly amplify the effects of the reaction component and further limit a species' range. The cumulative effect from multiple loci each with a small effect can be substantial on altering a species' range when these genes are maladaptive. These theoretical predictions can help understand the role of pollen flow that is incapable of colonizing new habitats in range expansion.     

Are protected areas maintaining bird diversity?

Evaluating the effectiveness of protected areas for sustaining biodiversity is crucial to achieving conservation outcomes. While studies of effectiveness have improved our understanding of protected‐area design and management, few investigations (< 5%) have quantified the ecological performance of reserves for conserving species. Here, we present an empirical evaluation of protected‐area effectiveness using long‐term measures of a vulnerable assemblage of species. We compare forest and woodland bird diversity in the Australian Capital Territory over 11 yr on protected and unprotected areas located in temperate eucalypt woodland and matched by key habitat attributes. We examine separately the response of birds to protected areas established prior to 1995 and after 1995 when fundamental changes were made to regional conservation policy. Bird diversity was measured in richness, occurrence of vulnerable species, individual species trajectories and functional trait groups. We found that protected areas were effective in maintaining woody vegetation cover in the study region, but were less effective in the protection of the target bird species assemblage. Protected areas were less species rich than unprotected areas, with significant declines in richness across sites protected prior to 1995. Small, specialised and vulnerable species showed stronger associations with unprotected areas than protected areas. Our findings indicate that recently established reserves (post‐1995) are performing similarly to unprotected woodland areas in terms of maintaining woodland bird diversity, and that both of these areas are more effective in the conservation of woodland bird populations than reserves established prior to 1995. We demonstrate that the conservation value of protected areas is strongly influenced by the physical characteristics, as well as the landscape context, of a given reserve and can diminish with changes in surrounding land use over time. Both protected areas and off‐reserve conservation schemes have important roles to play in securing species populations.     

The relation of density regulation to habitat specialization, evolution of a species' range, and the dynamics of biological invasions

Prior studies of the evolution of species' niches and ranges have identified the importance of within-population genetic variance, migration rate, and environmental heterogeneity in determining evolutionarily stable patterns of species' range and habitat use. Different combinations of these variables can produce either habitat specialists or generalists and cause either stable range limits or unbounded expansion. We examine the effect of density regulation on a species' range and habitat use within a landscape comprised of two discrete habitats and along continuous environmental gradients. Using the theta-logistic formulation, we demonstrate the following. (1) Spatially uniform density regulation generally weakens gene swamping and opposes habitat specialization and range limitation. (2) The form of density regulation should play an important role in determining whether the equilibrium species' range is limited by gene flow. (3) Even when no long-term limited-range equilibrium occurs, quasi-stable (or even contracting) range limits may be maintained for a long period during the initial phases of an invasion; the length of this period depends on the form of density regulation. (4) The steady state invasion speed in heterogeneous environments depends on the form of density regulation. Implications for the study of biological invasions are discussed, and directions for further exploration are sketched.     

Impacts of Restored Patch Density and Distance from Natural Forests on Colonization Success

Abstract The reduction and fragmentation of forest habitats is expected to have profound effects on plant species diversity as a consequence of the decreased area and increased isolation of the remnant patches. To stop the ongoing process of forest fragmentation, much attention has been given recently to the restoration of forest habitat. The present study investigates restoration possibilities of recently established patches with respect to their geographical isolation. Because seed dispersal events over 100 m are considered to be of long distance, a threshold value of 100 m between recent and old woodland was chosen to define isolation. Total species richness, individual patch species richness, frequency distributions in species occurrences, and patch occupancy patterns of individual species were significantly different among isolated and nonisolated stands. In the short term no high species richness is to be expected in isolated stands. Establishing new forests adjacent to existing woodland ensures higher survival probabilities of existing populations. In the long term, however, the importance of long‐distance seed dispersal should not be underestimated because most species showed occasional long‐distance seed dispersal. A clear distinction should be made between populations colonizing adjacent patches and patches isolated from old woodland. The colonization of isolated stands may have important effects on the dynamics and diversity of forest networks, and more attention should be directed toward the genetic traits and viability of founding populations in isolated stands.     

Ecological traits influence the current distribution and range of an island endemic bird

Aim  The aim of this paper is to investigate the causes of the current restricted distribution of a narrow-range endemic bird species, the Canary Islands stonechat, Saxicola dacotiae .
Location  Eastern islands of the Canary Islands archipelago.
Methods  We compared climatic patterns (temperature and rainfall), habitat and microhabitat structure, food availability during a full annual cycle, and the abundance of native avian competitors and predators inside and outside the species' range. Three study areas, located in similar habitats on nearby islands, were studied: northern Fuerteventura, close to the northern border of the species' range; southern Lanzarote, 22 km from the nearest site occupied by stonechats; and the Lobos islet, 10 km from the nearest occupied site and 2 km from the coast of Fuerteventura.
Results  The cover of suitable habitats (slopes with high cover of large shrubs, stony fields and ravines) and microhabitats (shrubs and boulders) and the abundance of arthropods during the breeding period of Canary Islands stonechats were lower outside than inside the species' range. Temperature, rainfall and the abundance of competitors and predators inside and outside the species' range did not differ significantly.
Main conclusions  Ecological requirements explaining the distribution of the Canary Islands stonechat within its range seem to be the main factor hindering its settlement on nearby islands. Geological and palaeoclimatic processes, as well as past and current human impact, could also have constrained the distribution of this narrow-range endemic bird species.     

Tales of the unexpected: Phylogeography of the arctic-alpine model plant Saxifraga oppositifolia (Saxifragaceae) revisited

Arctic-alpine biota occupy enormous areas in the Arctic and the northern hemisphere mountain ranges and have undergone major range shifts during their comparatively short history. The origins of individual arctic-alpine species remain largely unknown. In the case of the Purple saxifrage, Saxifraga oppositifolia, an important model for arctic-alpine plants, phylogeographic studies have remained inconclusive about early stages of the species' spatiotemporal diversification but have provided evidence for long-range colonization out of a presumed Beringian origin to cover today's circumpolar range. We re-evaluated the species' large-scale range dynamics based on a geographically extended sampling including crucial areas such as Central Asia and the (south-)eastern European mountain ranges and employing up-to-date phylogeographic analyses of a plastid sequence data set and a more restricted AFLP data set. In accordance with previous studies, we detected two major plastid DNA lineages also reflected in AFLP divergence, suggesting a long and independent vicariant history. Although we were unable to determine the species' area of origin, our results point to Europe (probably the Alps) and Central Asia, respectively, as the likely ancestral areas of the two main lineages. AFLP data suggested that contact areas between the two clades in the Carpathians, Northern Siberia and western Greenland were secondary. In marked contrast to high levels of diversity revealed in previous studies, populations from the major arctic refugium Beringia did not exhibit any plastid sequence polymorphism. Our study shows that adequate sampling of the southern, refugial populations is crucial for understanding the range dynamics of arctic-alpine species.     

Differential habitat utilization by patas monkeys (Erythrocebus patas) and tantalus monkeys (Cercopithecus aethiops tantalus) living sympatrically in northern Cameroon.

In order to obtain reliable evidence for differences in habitat preferences between two closely related savanna-dwelling primate species, namely, patas monkeys (Erythrocebus patas) and tantalus monkeys (Cercopithecus aethiops tantalus), I collected data on vegetation and patterns of range use concurrently at a single study site, Kala Maloue, Cameroon, in a similar manner for a group of each species. Kala Maloue consisted of 64% grassland mostly dominated by Gramineae spp. and the rest was woodland. Tantalus monkeys showed preference for woodland, especially gallery forest, much more than did the patas irrespective of the season. Moreover, patas preferentially established their home range in grassland in the wet season. Interspecific and seasonal differences in habitat preferences could be interpreted on the basis of interspecific and seasonal differences in preferences for main food. In dry season, tantalus utilized water-containing areas at a frequency closely in proportion to the availability of such areas while the patas utilized water-containing areas more frequently than expected. This is because tantalus established a smaller home range along the river where water was never completely depleted throughout the dry season. Both the patas and the tantalus preferred woodland to grassland as sleeping sites possibly owing to predation avoidance. Both the daily travel distance per group weight and the home range size per group weight were greater for patas than for tantalus partly because of higher preference for grassland with low habitat quality in the case of patas. It is suggested, however, that high locomotive ability enabled patas to effectively utilize small and widely dispersed items of food such as grasshoppers and to explore areas with high availability of food and water and with preferable sleeping sites.     

Range size heritability in Carnivora is driven by geographic constraints

Range size heritability refers to an intriguing pattern where closely related species occupy geographic ranges of similar extent. Its existence may indicate selection on traits emergent only at the species level, with interesting consequences for evolutionary processes. We explore whether range size heritability may be attributable to the fact that range size is largely driven by the size of geographic domains (i.e., continents, biomes, areas given by species' climatic tolerance) that tend to be similar in phylogenetically related species. Using a well-resolved phylogeny of Carnivora, we show that range sizes are indeed constrained by geographic domains and that the phylogenetic signal in range sizes diminishes if the domain sizes are accounted for. Moreover, more detailed delimitation of species' geographic domain leads to a weaker signal in range size heritability, indicating the importance of definition of the null model against which the pattern is tested. Our findings do not reject the hypothesis of range size heritability but rather unravel its underlying mechanisms. Additional analyses imply that evolutionary conservatism in niche breadth delimits the species' geographic domain, which in turn shapes the species' range size. Range size heritability patterns thus emerge as a consequence of this interplay between evolutionary and geographic constraints.     

The ‘abundant centre’ distribution: to what extent is it a biogeographical rule?

Several ecological and evolutionary hypotheses are based on the assumption that species reach their highest abundance in the centre of their range and decline in abundance toward the range edges. We reviewed empirical tests of this assumption, which we call the 'abundant centre' hypothesis. We found that of 145 separate tests conducted as part of 22 direct empirical studies, only 56 (39%) support the abundant centre hypothesis. More problematic than the percentage of studies that support the hypothesis is the finding that most studies inadequately sampled the species' ranges. Only two of the studies analysed data that were collected throughout the species' range. The remaining studies relied on data from a small number of points in their analysis, meaning that the range edges were severely under-sampled. Patterns of abundance across the entire range must be known to draw testable hypotheses about the consequences of species' geographical abundance distributions. Indirect tests of the abundant centre hypothesis, in which ecological or evolutionary expectations of abundant centre distributions were examined, did not support or reject the abundant centre hypothesis overall. We conclude that more exploration of species' abundance distributions is necessary and we suggest methods to use in future studies.     

Allee effects, invasion pinning, and species' borders

All species' ranges are the result of successful past invasions. Thus, models of species' invasions and their failure can provide insight into the formation of a species' geographic range. Here, we study the properties of invasion models when a species cannot persist below a critical population density known as an "Allee threshold." In both spatially continuous reaction-diffusion models and spatially discrete coupled ordinary-differential-equation models, the Allee effect can cause an invasion to fail. In patchy landscapes (with dynamics described by the spatially discrete model), range limits caused by propagation failure (pinning) are stable over a wide range of parameters, whereas, in an uninterrupted habitat (with dynamics described by a spatially continuous model), the zero velocity solution is structurally unstable and thus unlikely to persist in nature. We derive conditions under which invasion waves are pinned in the discrete space model and discuss their implications for spatially complex dynamics, including critical phenomena, in ecological landscapes. Our results suggest caution when interpreting abrupt range limits as stemming either from competition between species or a hard environmental limit that cannot be crossed: under a wide range of plausible ecological conditions, species' ranges may be limited by an Allee effect. Several example systems appear to fit our general model.     

The dynamics of climate-induced range shifting; perspectives from simulation modelling

Predicted future climate change will alter species' distributions as they attempt to track the most suitable 'climate window'. Climate envelope models indicate the direction of likely range changes but do not incorporate population dynamics, therefore observed responses may differ greatly from these projections. We use simulation modelling to explore the consequences of a period of environmental change for a species structured across an environmental gradient. Results indicate that a species' range may lag behind its climate envelope and demonstrate that the rate of movement of a range can accelerate during a period of climate change. We conclude that the inclusion of both population dynamics and spatial environmental variability is vital to develop models that can both predict, and be used to manage, the impact of changing climate on species' biogeography.