Expanding Range Margins Research Articles

A range‐expanding butterfly is susceptible to cold and long winters but shows no signs of local adaptation to winter conditions

Abstract Numerous species shift or expand their ranges poleward in response to climate change. Even when expanding species follow their climatic niches, expanding range margin populations are likely to face unfamiliar environmental conditions and thus natural selection for local adaptation. The wall brown butterfly (Lasiommata megera) has expanded northward in Sweden in the years 2000–2020, most likely as a result of climate change, and has previously been shown to have evolved local adaptations to northern daylength conditions. This evolution has occurred despite hypothesised genetic constraints to adaptation at range margins. We studied local adaptation to winter conditions in four of the previously‐studied L. megera populations, using a common garden laboratory experiment with a warm and short, an intermediate, and a cold and long winter treatment. We compared the winter and post‐winter survival of caterpillars from two southern core range and two northern range margin populations in Sweden. During the experiment, we measured metabolic rates of a subset of diapausing caterpillars to test whether populations differ in metabolic suppression during diapause. Further, we measured supercooling points, which reflect lower lethal temperature in L. megera, of the same subset of caterpillars. We also compared supercooling points between L. megera and three closely related species with more northern distributions. Few individuals survived the coldest treatment all the way to successful adult emergence, so L. megera seems susceptible to cold winters. Individuals of northern descent did not survive cold winters any better than individuals from southern populations. Similarly, there were no signs of local adaptation in metabolic rates or supercooling points. The comparison among species did not reveal any clear relationship between geographical distribution and supercooling point. Although northern winters probably exert strong selection on L. megera, we provide comprehensive evidence for the lack of local adaptation to winter conditions. This contrasts with the previous finding of quickly evolved local adaptation in diapause timing, highlighting the need to consider how traits associated with different seasons differ in how they may evolve and facilitate climate change‐induced range expansions. Read the free Plain Language Summary for this article on the Journal blog.

Comparisons of habitat types and host tree species across a threatened Caribbean orchid’s core and edge distribution

AbstractTropical forest ecosystems are rich in epiphytes that make up a significant portion of the overall plant diversity. However, epiphytic plants are often understudied due to inaccessibility and the lack of basic ecological information poses challenges to their conservation, particularly in a time of rapid global change. The mule-ear orchid,Trichocentrum undulatum(Orchidaceae), is a large flowering epiphyte found in southern Florida (USA), the Greater, and Lesser Antilles including Cuba. The plant is Florida state-listed as endangered with only one remaining small and declining population in a coastal mangrove forest due to historical extraction and habitat destruction. Currently, there is no systematic understanding of the species’ habitat requirements. To fill this void, we compared the habitat and microhabitat of the species on its northern distribution edge (southern Florida) and the core range (in Cuba). The Florida population has only one host species,Conocarpus erectus, found in one habitat type. This is in sharp contrast to the 92 documented hosts and 5 habitats across 8 provinces in Cuba. Based on our findings from Cuba, we suggest conservation and restoration options in Florida by proposing potential suitable host plants and habitats. Proactive restoration of this species will help to ease the threat from sea-level rise to the species by securing and expanding range margins.

Sex differences in morphology across an expanding range edge in the flightless ground beetle, Carabus hortensis.

Species’ ranges are dynamic, changing through range shifts, contractions, and expansions. Individuals at the edge of a species’ shifting range often possess morphological traits that increase movement capacity, that are not observed in individuals farther back within the species’ range. Although morphological traits that increase in proportion toward the range edge may differ between the sexes, such sex differences are rarely studied.Here, we test the hypotheses that body size and condition increase with proximity to an expanding range edge in the flightless ground beetle, Carabus hortensis, and that these trait changes differ between the sexes.Male, but not female, body size increased with proximity to the range edge. Body size was positively correlated with male front and mid tibia length and to female hind tibia length, indicating that body size is indicative of movement capacity in both sexes. Body condition (relative to body size) decreased with increasing population density in males but not females. Population density was lowest at the range edge.Our results indicate that sex is an important factor influencing patterns in trait distribution across species’ ranges, and future studies should investigate changes in morphological traits across expanding range margins separately for males and females. We discuss the implications for sex differences in resource allocation and reproductive rates for trait differentiation across species’ shifting ranges.

Colonizations cause diversification of host preferences: A mechanism explaining increased generalization at range boundaries expanding under climate change.

As species' poleward range limits expand under climate change, generalists are expected to be better colonists than specialists, extending their ranges faster. This effect of specialization on range shifts has been shown, but so has the reverse cause-effect: in a global meta-analysis of butterfly diets, it was range expansions themselves that caused increases in population-level diet breadth. What could drive this unexpected process? We provide a novel behavioral mechanism by showing that, in a butterfly with extensive ecotypic variation, Edith's checkerspot, diet breadths increased after colonization events as diversification of individual host preferences pulled novel hosts into population diets. Subsequently, populations that persisted reverted toward monophagy. We draw together three lines of evidence from long-term studies of 15 independently evolving populations. First, direct observations showed a significant increase in specialization across decades: in recent censuses, eight populations used fewer host genera than in the 1980s while none used more. Second, behavioral preference-testing experiments showed that extinctions and recolonizations at two sites were followed, at first by diversification of heritable preference ranks and increases in diet breadth, and subsequently by homogenization of preferences and contractions of diet breadth. Third, we found a significant negative association in the 1980s between population-level diet breadth and genetic diversity. Populations with fewer mtDNA haplotypes had broader diets, extending to 3-4 host genera, while those with higher haplotype diversity were more specialized. We infer that diet breadth had increased in younger, recently colonized populations. Preference diversification after colonization events, whether caused by (cryptic) host shifts or by release of cryptic genetic variation after population bottlenecks, provides a mechanism for known effects of range shifts on diet specialization. Our results explain how colonizations at expanding range margins have increased population-level diet breadths, and predict that increasing specialization should accompany population persistence as current range edges become range interiors.

Improving predictions of range expansion for invasive species using joint species distribution models and surrogate co‐occurring species

AbstractAimsSpecies distribution models (SDMs) are often used to forecast potential distributions of important invasive or rare species. However, situations where models could be the most valuable ecologically or economically, such as for predicting invasion risk, often pose the greatest challenges to SDM building. These challenges include non‐equilibrium range expansion, low or uneven prevalence, and projecting distributions into environments that are non‐analogous to the environments used for model building.LocationMinnesota, USA.TaxonCardamine impatiens (Narrowleaf Bittercress), Celastrus orbiculatus (Oriental Bittersweet), and Humulus japonicus (Japanese Hops).MethodsWe took a novel approach to build robust species distribution models of invasive species using occurrence‐environment correlations between invasive species and co‐occurring native community members. The correlations were obtained from a joint species distribution model (JSDM) of a densely sampled database of 10,336 MN plant communities from across the state of Minnesota, USA. Positively and negatively associated native species were incorporated into the model as surrogate presences and pseudoabsences (weighted by their environmental correlations) along with invasive species occurrences records (surrogate SDMs).ResultsSurrogate models performed better than traditional SDMs in predicting occurrences along the northern invasion margin (outside the training area). Both types of models had similarly high cross‐validation metrics in the area of training. Surrogate models also predicted greater range expansion beyond the current geographic range.Main conclusionsThese results demonstrate that modelers can take advantage of detailed community data to develop SDMs that leverage surrogate native species as phytometers of environments beyond the current area of occupancy. The additional information in surrogate models generates highly effective predictions of invasive species along expanding range margins.

Kin competition accelerates experimental range expansion in an arthropod herbivore.

With ongoing global change, life is continuously forced to move to novel areas, which leads to dynamically changing species ranges. As dispersal is central to range dynamics, factors promoting fast and distant dispersal are key to understanding and predicting species ranges. During range expansions, genetic variation is depleted at the expanding front. Such conditions should reduce evolutionary potential, while increasing kin competition. Organisms able to recognise relatives may be able to assess increased levels of relatedness at expanding range margins and to increase their dispersal in a plastic manner. Using individual-based simulations and experimental range expansions of a spider mite, we demonstrate that plastic responses to kin structure can be at least as important as evolution in driving range expansion speed. Because recognition of kin or kind is increasingly documented across the tree of life, we anticipate it to be a highly important but neglected driver of range expansions.

Habitat Use of the Piñon Mouse (Peromyscus truei) in the Toiyabe Range, Central Nevada

Pinon-juniper woodland is expanding across much of western North America. In the Great Basin, woodland expansion has encroached on native shrublands, threatening species that have close associations with the sagebrush ecosystem. Pinon-juniper woodlands also harbor great biodiversity, and the response of woodland specialists to expansion has been less well studied than that of shrubland specialists. Here, we use occupancy and abundance modeling, accounting for imperfect detection, to assess habitat use of a woodland specialist, the pinon mouse (Peromyscus truei). Our study occurred in the Toiyabe Range of central Nevada, an area P. truei is thought to have recently colonized. Understanding habitat use at an expanding range margin can have important implications for dispersal-mediated woodland expansion. Peromyscus truei was documented in a wide range of conditions, including nonwoodland and woodland habitats, across the latitudinal and elevational extent of the mountain range. Occupancy models suggest that P. truei occurrences are most associated with the presence of pinon pine. For abundance, our global model was the best supported, indicating that no one environmental factor or set of factors considered were found to structure abundance. Chi-square tests indicate that use of woodland versus nonwoodland habitats by P. truei is not structured by age or sex. Although P. truei was found in a range of habitat types, we cannot conclude whether it is more appropriate to characterize this species as a habitat generalist, or whether postcolonization abiotic and biotic filtering is not yet complete. Research on woodland specialists at expanding local and landscape-scale range margins provides a unique opportunity to study how habitat selection and ecological filtering impact community assembly under environmental change.

Changes in habitat associations during range expansion: disentangling the effects of climate and residence time

The distributions of many species are not at equilibrium with their environment. This includes spreading non-native species and species undergoing range shifts in response to climate change. The habitat associations of these species may change during range expansion as less favourable climatic conditions at expanding range margins constrain species to use only the most favourable habitats, violating the species distribution model assumption of stationarity. Alternatively, changes in habitat associations could result from density-dependent habitat selection; at range margins, population densities are initially low so species can exhibit density-independent selection of the most favourable habitats, while in the range core, where population densities are higher, species spread into less favourable habitat. We investigate if the habitat preferences of the non-native common waxbill Estrilda astrild changed as they spread in three directions (north, east and south-east) in the Iberian Peninsula. There are different degrees of climatic suitability and colonization speed across range expansion axes, allowing us to separate the effects of climate from residence time. In contrast to previous studies we find a stronger effect of residence time than climate in influencing the prevalence of common waxbills. As well as a strong additive effect of residence time, there were some changes in habitat associations, which were consistent with density-dependent habitat selection. The combination of broader habitat associations and higher prevalence in areas that have been colonised for longer means that species distribution models constructed early in the invasion process are likely to underestimate species’ potential distribution.

Expanding population edges: theories, traits, and trade-offs.

Recent patterns of global change have highlighted the importance of understanding the dynamics and mechanisms of species range shifts and expansions. Unique demographic features, spatial processes, and selective pressures can result in the accumulation and evolution of distinctive phenotypic traits at the leading edges of expansions. We review the characteristics of expanding range margins and highlight possible mechanisms for the appearance of phenotypic differences between individuals at the leading edge and core of the range. The development of life history traits that increase dispersal or reproductive ability is predicted by theory and supported with extensive empirical evidence. Many examples of rapid phenotypic change are associated with trade-offs that may influence the persistence of the trait once expansion ends. Accounting for the effects of edge phenotypes and related trade-offs could be critical for predicting the spread of invasive species and population responses to climate change.

Two Species with an Unusual Combination of Traits Dominate Responses of British Grasshoppers and Crickets to Environmental Change.

There are large variations in the responses of species to the environmental changes of recent decades, heightening interest in whether their traits may explain inter-specific differences in range expansions and contractions. Using a long-term distributional dataset, we calculated range changes of grasshoppers and crickets in Britain between the 1980s and the 2000s and assessed whether their traits (resource use, life history, dispersal ability, geographic location) explain relative performance of different species. Our analysis showed large changes in the distributions of some species, and we found a positive relationship between three traits and range change: ranges tended to increase for habitat generalists, species that oviposit in the vegetation above ground, and for those with a southerly distribution. These findings accord well with the nature of environmental changes over this period (climatic warming; reductions in the diversity and increases in the height of vegetation). However, the trait effects applied mainly to just two species, Conocephalus discolor and Metrioptera roeselii, which had shown the greatest range increases. Once they were omitted from the analysis, trait effects were no longer statistically significant. Previous studies on these two species emphasised wing-length dimorphism as the key to their success, resulting in a high phenotypic plasticity of dispersal and evolutionary-ecological feedback at their expanding range margins. This, combined with our results, suggests that an unusual combination of traits have enabled these two species to undertake extremely rapid responses to recent environmental changes. The fact that our results are dominated by two species only became apparent through cautious testing of the results’ robustness, not through standard statistical checks. We conclude that trait-based analyses may contribute to the assessment of species responses to environmental change and provide insights into underlying mechanisms, but results need to be interpreted with caution and may have limited predictive power.

Dispersal and species’ responses to climate change

Dispersal is fundamental in determining biodiversity responses to rapid climate change, but recently acquired ecological and evolutionary knowledge is seldom accounted for in either predictive methods or conservation planning. We emphasise the accumulating evidence for direct and indirect impacts of climate change on dispersal. Additionally, evolutionary theory predicts increases in dispersal at expanding range margins, and this has been observed in a number of species. This multitude of ecological and evolutionary processes is likely to lead to complex responses of dispersal to climate change. As a result, improvement of models of species’ range changes will require greater realism in the representation of dispersal. Placing dispersal at the heart of our thinking will facilitate development of conservation strategies that are resilient to climate change, including landscape management and assisted colonisation.SynthesisThis article seeks synthesis across the fields of dispersal ecology and evolution, species distribution modelling and conservation biology. Increasing effort focuses on understanding how dispersal influences species' responses to climate change. Importantly, though perhaps not broadly widely‐recognised, species' dispersal characteristics are themselves likely to alter during rapid climate change. We compile evidence for direct and indirect influences that climate change may have on dispersal, some ecological and others evolutionary. We emphasise the need for predictive modelling to account for this dispersal realism and highlight the need for conservation to make better use of our existing knowledge related to dispersal.

Testing species distribution models across space and time: high latitude butterflies and recent warming

AbstractAimTo quantify whether species distribution models (SDMs) can reliably forecast species distributions under observed climate change. In particular, to test whether the predictive ability ofSDMsdepends on species traits or the inclusion of land cover and soil type, and whether distributional changes at expanding range margins can be predicted accurately.LocationFinlandMethodsUsing 10‐km resolution butterfly atlas data from two periods, 1992–99 (t1) and 2002–09 (t2), with a significant between‐period temperature increase, we modelled the effects of climatic warming on butterfly distributions with boosted regression trees (BRTs) and generalized additive models (GAMs). We evaluated model performance by using the split‐sample approach with data fromt1(‘non‐independent validation’), and then compared model projections based on data fromt1with species' observed distributions int2(‘independent validation’). We compared climate‐onlySDMs toSDMs including land cover, soil type, or both. Finally, we related model performance to species traits and compared observed and predicted distributional shifts at northern range margins.ResultsSDMs showed fair to good model fits when modelling butterfly distributions under climate change. Model performance was lower with independent compared with non‐independent validation and improved when land cover and soil type variables were included, compared with climate‐only models.SDMs performed less well for highly mobile species and for species with long flight seasons and large ranges. When forecasting changes at northern range margins, correlations between observed and predicted range shifts were predominantly low.Main conclusionsSDMs accurately describe current distributions of most species, yet their performance varies with species traits and the inclusion of land cover and soil type variables. Moreover, their ability to predict range shifts under climate change is limited, especially at the expanding edge. More tests with independent validations are needed to fully understand the predictive potential ofSDMsacross taxa and biomes.

Strong genetic differentiation due to multiple founder events during a recent range expansion of an introduced wall lizard population

Biological invasions represent ideal sys- tems for the study of evolutionary processes associated with colonization events. It has been hypothesized that the genetic diversity is generally decreasing from the centre of the range to the margins due to multiple founder events. Invasive populations offer the oppor- tunity to test this hypothesis at a fine spatial and temporal scale. We analysed the genetic structure of a large expanding non-native population of the Com- mon Wall Lizard (Podarcis muralis) in Passau (Ger- many) using thirteen microsatellite loci. We analyzed the genetic structure and levels of admixture across a transect reflecting the expansion process and tested for a loss of genetic diversity and an increase of genetic differentiation from the centre to the invasion front. Our results demonstrate that significant genetic pop- ulation structure can emerge rapidly at a small spatial scale. We found a trend for an increase in genetic differentiation and a decrease in genetic diversity from the invasion centre to the expanding range margin, suggesting that genetic drift is the major factor causing this pattern. The correlation between genetic diversity and average genetic differentiation was significant among sites. We hypothesize that the territoriality of P. muralis generates sufficient rates of noncontiguous and stratified dispersal from longer established sites to maintain significant genetic diversity at the invasion front. Simultaneously, territoriality might restrict the colonization success of migrants at established sites, so that in combination with founder events a strong differentiation arises.

Adapting conservation to a changing climate

In the last 5 years, research into adaptation for conservation and land management has developed rapidly, and a wide range of initiatives have started within conservation organizations. This rapid growth prompted Natural England and the British Ecological Society to sponsor a conference on Adapting Conservation to a Changing Climate (Morecroft et al. 2011) in January 2011 in London. The conference brought together scientists, conservationists and policy makers to review recent research and the development of practical application measures. This special profile sees the publication of five papers resulting from that meeting. The papers present an interesting insight into some current directions in work on climate change adaptation. Research on the impact of climate change has placed considerable emphasis on changing species distributions and projections for how the climate envelope of species might shift under different climate change scenarios. Initial thinking on adaptation often took this as a starting point and focused on how to facilitate changes in species ranges. This continues to be an important issue but there has been increasing recognition of the importance of landscape and site scale issues, controlling whether and how a species might move across a landscape. So, in this series of papers, Lawson et al. (2012) look at the expanding range margin and how the capacity of a species to spread into new areas will be controlled by land management decisions. Oliver et al. (2012) look at the relationship between distribution and population density and stability – important factors in determining long-term persistence of species. Changing distributions are not the only aspect of climate change adaptation, however. There has been an increasing realization that there are a range of factors that make species and communities more or less likely to persist within their current distribution – adaptation is not simply about facilitating changing distributions. Maximizing the potential to maintain species where they are is particularly important for species with limited capacity to disperse and Norris, Hobson & Ibisch (2012) look at how different microclimates are associated with different forest characteristics. In different ways, all these papers contribute to our understanding of ecological networks and the role they can play in climate change adaptation. Newton et al. (2012) also consider ecological networks and investigate how ecosystem services can be evaluated within the conceptual frame work of networks. One of the major developments in ecology over the last decade has been the development of approaches to assessing ecosystem services, and it is important that climate change adaptation and the ecosystem approach go hand in hand. Morecroft et al. 2012 present an approach to translating scientific understanding of resilience into practical climate change adaptation. This is an example of a more general point: climate change adaptation is an intrinsically applied issue and needs both the practical conservationist and the research ecologist. Climate change poses a profound challenge to conservationists. The starting point for conservation has been protecting the species, habitats and landscapes we have and where possible restoring what has been lost. Going into the future, this may not be possible in many cases. Similarly, tried and tested techniques may start to lose their effectiveness. As climate change – and other environmental changes – develop further, there will be a critical need to develop and test adaptation measures. A strong partnership between conservation practitioners and researchers will be essential to making this happen.

Wrong place, wrong time: climate change‐induced range shift across fragmented habitat causes maladaptation and declined population size in a modelled bird species

AbstractMany species are locally adapted to decreased habitat quality at their range margins, and therefore show genetic differences throughout their ranges. Under contemporary climate change, range shifts may affect evolutionary processes at the expanding range margin due to founder events. In addition, populations that are affected by such founder events will, in the course of time, become located in the range centre. Recent studies investigated evolutionary changes at the expanding range margin, but have not assessed eventual effects across the species' range. We explored the possible influence of range shift on the level of adaptation throughout the species' total range. For this we used a spatially explicit, individual‐based simulation model of a woodland bird, parameterized after the middle spotted woodpecker ( Dendrocopos medius) in fragmented habitat. We simulated its range under climate change, and incorporated genetic differences at a single locus that determined the individual's degree of adaptation to optimal temperature conditions. Generalist individuals had a large thermal tolerance, but relatively low overall fitness, whereas climate specialists had high fitness combined with a small thermal tolerance. In equilibrium, the populations in the range centre were comprised of the specialists, whereas the generalists dominated the margins. In contrast, under temperature increase, the generalist numbers increased at the expanding margin and eventually also occupied the centre of the shifting range, whereas the specialists were located in the retracting margins. This was caused by founder events and led to overall maladaptation of the species, which resulted in a reduced metapopulation size and thus impeded the species' persistence. We therefore found no evidence for a complementary effect of local adaptation and range shifts on species' survival. Instead, we showed that founder events can cause local maladaptation which can amplify throughout the species' range, and, as such, hamper the species' persistence under climate change.

Update: From acorns mighty micropockets grow

ISSN 1948-6596 news and update update From acorns mighty micropockets grow Dispersal processes may be critical in determining rates of species range shifts under future climate change. Travis Marsico, Jessica Hellman and Jeanne Romero-Severson, writing in the Journal of Biogeography, shed new light on the future by examining the past shifts in Oregon oak since the Last Glacial Maximum (LGM) (Marsico et al. 2009). They find that it doesn't take a village, it just takes a single tree. This helps support an emerging new view of how plant range shifts are realized when climate shifts rapidly. Until recently, prevailing concepts of bio- logical response to rapid warming in North Amer- ica and Europe were of large, monolithic range shifts in which species totally vacated habitat of waning suitability, moving to new, completely dis- junct range. This view began to change in 1995 when Matt McGlone and Vera Markgraf pre- sented a starkly contrasting model of vegetation shift in the Southern Hemisphere. In New Zealand, McGlone found recolonization of the South Island to be much more rapid than could be accounted for by long-distance dispersal (McGlone 1995). In southern South America, Markgraf documented vegetation change keeping pace with extremely rapid climate 'flickers' (Markgraf and Kenny 1995). Both authors suggested that micropockets of vegetation could explain the very rapid observed changes in dominant vegetation. Such micropock- ets of vegetation were very plausible in these southern settings where no large continental ice sheets existed. Evidence has since grown that micropockets may be important in Northern Hemisphere set- tings as well (recent literature is briefly reviewed by Marsico et al.). Tree remains very close to the boundary of the ice sheet have been found in pa- leorecords of both Europe and North America. Pollen signatures that were previously assumed to be from long-distance blow-in are now being rein- terpreted as possible evidence of vegetation mi- cropockets. If the growing consensus around micro- pockets is correct, the implications for vegetation response to future, human-induced climate change is profound. Patches of vegetation of a few tens of meters on a side might provide source material at rapidly expanding range margins. Long-distance dispersal might establish micro- pockets of vegetation that would serve as step- ping-stones for additional long-distance dispersal. Marsico et al. show that in Oaks in the Pa- cific Northwest, dispersal was primarily from indi- viduals on the leading edge of the range. Chloro- plast DNA markers were remarkably homogenous in their samples. At 16 of 22 sites all individuals sampled shared a single chloroplast haplotype. Having identical chloroplast haplotype indicates a common maternal ancestor, so these populations were established from single colonizations or mul- tiple colonizations by seeds from the same tree (which seems much less likely). The implication is that single trees are criti- cal for establishing populations in newly suitable range. Micropockets of vegetation would have ample sources of seeds for range shifts, if all it takes is a single tree. Marsico et al. found much more diversity in nuclear DNA, indicating that once single colonizations occur, populations grow and are diversified by wide pollen flow from many individuals. Colonists from micropockets and di- versity from broader populations may be a key mechanism in rapid range shifts as rapid human- induced climate change gathers force. Markgraf, V. & Kenny, R. (1995) Character of rapid vegetation and climate change during the late- glacial in southernmost South America. In Hunt- ley, B., Cramer, W., Morgan, A.V., Prentice, H.C. and Allen, J.R.M. (eds.) Past and Future Rapid Environmental Changes: The Spatial and Evolu- tionary Responses of Terrestrial Biota, pp. 81- 102. Springer-Verlag, Berlin. Marsico, T.D., Hellmann, J.J. & Romero-Severson, J. (2009) Patterns of seed dispersal and pollen flow in Quercus garryana (Fagaceae) following post-glacial climatic changes. Journal of Bio- geography, 36, 929-941. McGlone, M.S. (1995) The responses of New Zealand forest diversity to Quaternary climates. In Hunt- ley, B., Cramer, W., Morgan, A.V., Prentice, H.C. frontiers of biogeography 1.1, 2009 — © 2009 the authors; journal compilation © 2009 The International Biogeography Society

Local and landscape management of an expanding range margin under climate change

Summary1. There is a pressing need to understand how to facilitate species’ range shifts under climate change. However, few empirical studies are available to inform decision‐making, particularly at fine spatial and temporal resolutions.2. We present a case study of a thermally constrained habitat specialist, the silver‐spotted skipper butterflyHesperia comma, at its expanding range margin in south‐eastern Britain. Using data from 724 habitat patches over a 9‐year interval (2000–2009), we examined local and landscape determinants of colonization, survival and population density. We then predicted probabilities of colonization and survival for habitat patches under the observed 1982 and 2009 distributions to investigate how the factors limiting range expansions change through space and time.3. Between 2000 and 2009,Hesperia commacontinued to expand its range in Britain, but the 67 recorded colonization events were offset by 48 local extinctions. Extinctions were strongly linked to climate, occurring predominantly in cooler regions and on shaded north‐facing slopes.4. Population density and probability of survival were closely related to conditions within a site, whereas probability of colonization was largely determined by functional connectivity. Survival probability was also influenced by connectivity, suggesting that immigration helped to support extinction‐prone populations (a ‘rescue effect’).5. Patch occupancy beyond the range margin was primarily constrained by colonization, but close to the expanding front, population survival became the key limiting factor. This pattern was conserved during range expansion, altering management priorities at individual sites.6. Synthesis and applications. Previous studies on facilitating range shifts have stressed the need to increase landscape‐scale connectivity to remove constraints on colonization, and our data substantiate this advice. However, we show that enhancing population survival can also help to facilitate range expansions, because populations at leading range edges face high extinction risk. Population survival can be improved directly through local management actions, such as enlarging patch size and increasing habitat quality, or indirectly by improving connectivity. Thus, local management can secure vulnerable populations at the range edge and provide larger and more stable migrant sources for future expansion and deserves consideration when facilitating range shifts under climate change.

Dispersal limitation at the expanding range margin of an evergreen tree in urban habitats?

Dispersal limitations contribute to shaping plant distribution patterns and thus are significant for biodiversity conservation and urban ecology. In fleshy-fruited plants, for example, any preference of frugivorous birds affects dispersal capacities of certain fruit species. We conducted a removal experiment with fruits of Ilex aquifolium, a species that is currently expanding its range margin in northern Europe in response to climate change. The species is also a popular ornamental tree and naturalization has been observed in many parts of its range. Fruits of native I. aquifolium and of three cultivars were offered to birds at the expanding range margin in urban habitats in eastern Denmark. The four fruit types were removed at different rates and red fruits were preferred over a yellow cultivar. Small fruit diameter was positively related to fruit removal, and removal was faster under tree canopies compared with open habitats. The preference for red cultivars compared with native I. aquifolium may contribute to naturalization and potential invasion of garden escapes. Preferential foraging under closed canopies indicates trees and shrubs as recruitment foci for fleshy-fruited plants in urban landscapes. The results should be included in urban forestry and planting of potentially invasive ornamental species.

The role of macropters during range expansion of a wing-dimorphic insect species

Marked changes in distribution in consequence of global warming have been observed not only for highly mobile insect taxa, which are capable of flight, but also for wing-dimorphic species with predominantly short-winged individuals. In the special case of wing-dimorphic species, it is likely that the rarer long-winged (macropterous) morph plays an important role in the dispersal process, but little is known about how and to what extent it is involved. The aim of our study was to provide more information on the mechanisms behind dispersal processes in wing-dimorphic insects at expanding range margins. As solitary individuals are believed to play an important role in the range expansion of wing-dimorphic species (potential dispersers), we recorded the number of long-winged and short-winged solitary males at the local range margin of our model organism Metriopteraroeselii (Orthoptera: Tettigoniidae) in NW Germany. To investigate differences in dispersal capability (% macropters) between populations with different colonisation histories, we studied 43 populations of M. roeselii. Our results show that about 2/3 of the solitary males were long-winged and these long-winged individuals were significantly more frequent in recently colonised areas. Moreover, M. roeselii had a significantly higher dispersal capability (% macropters) in high-density populations and in recently established populations at the expanding range margin compared to populations characterised by medium- or long-term establishment nearer to the range core. Our study is the first that quantifies the importance of macropters for the recent range expansion of a wing-dimorphic species and it provides for the first time detailed insights into the complex dispersal processes that take place at the expanding range margin. It is likely that density stress and a changed genetic predisposition to become macropterous, and thus a combination of both ecological and evolutionary effects, leads to a high percentage of macropters in recently colonised areas.

PgiGenotype Influences Flight Metabolism at the Expanding Range Margin of the European Map Butterfly

In species expanding their ranges in response to climate warming or for other reasons, individuals with superior dispersal capacity are often more likely than others to establish new populations beyond the current range boundary. Previous studies on butterflies have shown that molecular variation in the glycolytic enzyme phosphoglucose isomerase (Pgi) is associated with variation in flight metabolic rate, flight capacity under unfavourable conditions, and dispersal rate. We examined allelic variation in Pgi in the European map butterfly (Araschnia levana), which has rapidly expanded northwards in Finland. We show that the kinetically fastest Pgi allele, Pgi-1, is associated with superior flight metabolic rate and is more frequent at the eastern Finnish expansion front than in old established populations in Estonia. In eastern Finland, the Pgi-1 allele is significantly more frequent in newly-established (age ca. 4 years) than in older populations (age 11 to 22 years), and the Pgi-1 allele is more frequent ...