Divergent Habitat Preferences Research Articles

Phylogeographic incongruence between two related Geranium species with divergent habitat preferences in East Asia

AbstractPlant species with overlapping distributions are expected to experience the same historical events. In contrast, species with different preferred habitat types may exhibit incongruent phylogeographic patterns because of their habitat‐dependent demographic changes in spite of their overlapping distributions. On the western side of the Japanese Archipelago, boreal forest and non‐forest vegetation were dominant during the last glacial period; subsequently, temperate forests expanded, and open vegetation (e.g., grasslands) decreased. Such vegetation shifts can result in incongruent phylogeographic patterns among temperate forest and grassland species; however, few phylogeographic studies have investigated this hypothesis. Here, we evaluated the phylogeographic structure of two related Geranium species that occur in grassland (Geranium krameri) and temperate forest (Geranium shikokianum) habitats using chloroplast genome sequencing and nuclear genome‐wide single‐nucleotide polymorphisms genotyping. The phylogeographic structure was stronger for the temperate forest species than the grassland species, despite its currently scattered distribution for grassland species. The observed patterns indicate that the phylogeographic histories of these species were influenced by their habitat configurations since the last glacial period. During the ice age, grasslands in Japan were much more widespread than today; this would have enabled the grassland species to form a continuous distribution, leading to low divergence among regional populations. In contrast, the significant genetic divergence within the forest species can be attributed to the glacial isolation of regional populations. Our genetic results suggest that vegetation transitions have variously controlled the population dynamics of two species with overlapping distributions.

Interpreting the mammal deposits of Cloggs Cave (SEAustralia),GunaiKurnaiAboriginal Country, through community‐led partnership research

AbstractPalaeontological animal bone deposits are rarely investigated through research partnerships where the local First Nations communities have a defining hand in both the research questions asked and the research processes. Here we report research undertaken through such a partnership approach at the iconic archaeological site of Cloggs Cave (GunaiKurnai Country, East Gippsland), in the southern foothills of SE Australia's Great Dividing Range.A new excavation was combined with detailed chronometric dating, high‐resolution 3D mapping and geomorphological studies. This allowed interpretation of a sequence of stratigraphic layers spanning from a lowermost excavated mixed layer dated to between 25,640 and 48,470 cal BP, to a dense set of uppermost, ash layers dated to between 1460 and 3360 cal BP. This long and well‐dated chronostratigraphic sequence enabled temporal trends in the abundant small mammal remains to be examined.The fossil assemblage consists of at least 31 taxa of mammals which change in proportions through time. Despite clear evidence that the Old Ancestors repeatedly carried vegetation into the cave to fuel cool fires (no visible vegetation grows in Cloggs Cave), we observed little to no evidence of cooking fires or calcined bone, suggesting that people had little involvement with the accumulation of the faunal remains. Small mammal bones were most likely deposited in the cave by large disc‐faced owls,Tyto novaehollandae(Masked Owl) orTyto tenebricosa(Sooty Owl).Despite being well dated and largely undisturbed, the Cloggs Cave assemblage does not appear to track known Late Quaternary environmental change. Instead, the complex geomorphology of the area fostered a vegetation mosaic that supported mammals with divergent habitat preferences. The faunal deposit suggests a local ancestral landscape characterised by a resilient mosaic of habitats that persisted over thousands of years, signalling that the Old Ancestors burned landscape fires to encourage and manage patches of different vegetation types and ages within and through periods of climate change.Read the freePlain Language Summaryfor this article on the Journal blog.

Weak asymmetric interspecific aggression and divergent habitat preferences at an elevational contact zone between tropical songbirds

Closely related tropical bird species often occupy mutually exclusive elevational ranges, but the mechanisms generating and maintaining this pattern remain poorly understood. One hypothesis is that replacement species are segregated by interference competition (e.g. territorial aggression), but the extent to which competition combines with other key factors such as specialization to distinct habitats remains little studied. Using vegetation surveys and reciprocal playback experiments, we explored the dynamics of interspecific aggression between two Nightingale‐Thrushes Catharus sp. in Central America. We show that lower‐elevation Black‐headed Nightingale‐Thrushes Catharus mexicanus are aggressive towards higher‐elevation Ruddy‐capped Nightingale‐Thrushes Catharus frantzii where they meet at contact zones. However, interspecific aggressive responses were weak and unidirectional, and the two species were associated with different habitats. We conclude that the contact zone is maintained and located primarily by habitat selection, and is probably reinforced by interspecific aggression. This has important implications for understanding how montane species will respond to climate change because the pace and extent of range shifts will not depend solely on habitat shifts or interspecific competition, but instead on interactions between these two factors.

Is there a need for accepting paraphyletic taxa? A case study in the Sardinian endemic Cymbalaria muelleri (Plantaginaceae)

AbstractEvolution does not always result in dichotomous phylogenetic trees. For instance, in anacladogenetic speciation, where a new species originates by budding, the ancestral taxon is often initially paraphyletic. Here we study Cymbalaria muelleri (Plantaginaceae), a chasmophytic species endemic to Sardinia, a major island in the Mediterranean Basin. Its distribution range is divided into two well-delimited geographical groups with some morphological differences. Using a combination of morphology, molecular data (amplified fragment length polymorphism fingerprinting) and relative genome size, we found that the two geographical groups should be considered two separate taxa, which split through anacladogenesis. Accordingly, we formally describe the new paraphyletic subspecies C. muelleri subsp. villosa as the ancestor, from which C. muelleri subsp. muelleri originated by budding. Morphological analyses support the differentiation of the two subspecies, and there are strong diagnostic characters to differentiate them. In addition to morphology and genetics, slightly divergent habitat preferences and the disjunct distribution of the two subspecies also support the recognition of two taxa. Genome size data obtained for the two subspecies are consistent with the previously established hexaploidy of C. muelleri.

Land‐use change alters the mechanisms assembling rainforest mammal communities in Borneo

The assembly of species communities at local scales is thought to be driven by environmental filtering, species interactions and spatial processes such as dispersal limitation. Little is known about how the relative balance of these drivers of community assembly changes along environmental gradients, especially man-made environmental gradients associated with land-use change. Using concurrent camera- and live-trapping, we investigated the local-scale assembly of mammal communities along a gradient of land-use intensity (old-growth forest, logged forest and oil palm plantations) in Borneo. We hypothesised that increasing land-use intensity would lead to an increasing dominance of environmental control over spatial processes in community assembly. Additionally, we hypothesised that competitive interactions among species might reduce in concert with declines in α-diversity (previously documented) along the land-use gradient. To test our first hypothesis, we partitioned community variance into the fractions explained by environmental and spatial variables. To test our second hypothesis, we used probabilistic models of expected species co-occurrence patterns, in particular focussing on the prevalence of spatial avoidance between species. Spatial avoidance might indicate competition, but might also be due to divergent habitat preferences. We found patterns that are consistent with a shift in the fundamental mechanics governing local community assembly. In support of our first hypothesis, the importance of spatial processes (dispersal limitation and fine-scale patterns of home-ranging) appeared to decrease from low to high intensity land-uses, whilst environmental control increased in importance (in particular due to fine-scale habitat structure). Support for our second hypothesis was weak: whilst we found that the prevalence of spatial avoidance decreased along the land-use gradient, in particular between congeneric species pairs most likely to be in competition, few instances of spatial avoidance were detected in any land-use, and most were likely due to divergent habitat preferences. The widespread changes in land-use occurring in the tropics might be altering not just the biodiversity found in landscapes, but also the fundamental mechanics governing the local assembly of communities. A better understanding of these mechanics, for a range of taxa, could underpin more effective conservation and management of threatened tropical landscapes.

Links between Genetic Groups, Indole Alkaloid Profiles and Ecology within the Grass-Parasitic Claviceps purpurea Species Complex.

The grass parasitic fungus Claviceps purpurea sensu lato produces sclerotia with toxic indole alkaloids. It constitutes several genetic groups with divergent habitat preferences that recently were delimited into separate proposed species. We aimed to 1) analyze genetic variation of C. purpurea sensu lato in Norway, 2) characterize the associated indole alkaloid profiles, and 3) explore relationships between genetics, alkaloid chemistry and ecology. Approximately 600 sclerotia from 14 different grass species were subjected to various analyses including DNA sequencing and HPLC-MS. Molecular results, supported by chemical and ecological data, revealed one new genetic group (G4) in addition to two of the three known; G1 (C. purpurea sensu stricto) and G2 (C. humidiphila). G3 (C. spartinae) was not found. G4, which was apparently con-specific with the recently described C. arundinis sp. nov, was predominantly found in very wet habitats on Molinia caerulea and infrequently in saline habitats on Leymus arenarius. Its indole-diterpene profile resembled G2, while its ergot alkaloid profile differed from G2 in high amounts of ergosedmam. In contrast to G1, indole-diterpenes were consistently present in G2 and G4. Our study supports and complements the newly proposed species delimitation of the C. purpurea complex, but challenges some species characteristics including host spectrum, habitat preferences and sclerotial floating ability.

The landscape genetics of syntopic topminnows (Fundulus notatusandF. olivaceus) in a riverine contact zone

The metapopulation dynamics of a species are influenced by the spatial arrangement of preferred habitats across a landscape. Increasing habitat patchiness can result in greater population subdivision, leading to more pronounced population genetic structure. Therefore, even subtle differences in habitat preferences among species could lead to substantial differences in genetic structure. Members of the Fundulus notatus species complex of topminnows include a headwater specialist and a large river specialist with broadly overlapping geographical distributions. Both species are often found in the same drainage systems, but partially isolated by divergent habitat preferences. The purpose of this research was to determine whether distribution along a stream continuum in a contact zone influences population genetic patterns in two species of topminnow (Fundulus olivaceus and Fundulus notatus). Fish were collected in the summers of 2010–2012, and habitat data were collected in summer 2012, within all major tributaries of the Saline River in southern Illinois. In total, 523 fish were genotyped using seven microsatellite loci to assess genetic variation. Species distributions in F. notatus and F. olivaceus were associated with habitat factors that covaried with cumulative drainage area. Populations of F. olivaceus showed a greater level of genetic structure reflected in a significant pattern of isolation by distance, while populations of F. notatus showed no such pattern. Spatial autocorrelation analysis revealed that at an individual level, both species became increasingly divergent with waterway distance. Overall, clear interspecific differences in habitat preferences were translated into measurable but relatively subtle differences in population genetic structure.

Contrasting Population and Life History Responses of a Young Morph-Pair of European Whitefish to the Invasion of a Specialised Coregonid Competitor, Vendace

Invasions of non-native species represent a global problem of great scientific interest. Here we study in detail the response in population and life history characteristics of closely related native species, with divergent habitat preferences, that are impacted by an invading species over a sufficient time period to allow a new stable state to become established. A time series of 20 years starting at the first occurrence of the invader (vendace Coregonus albula (L.)) allows exploration of the long term population and life history response of two ecologically, morphologically, and genetically different native sympatric morphs (DR- and SR-) of congeneric whitefish C. lavaretus (L.). The whitefish morphs are taxonomically equally related to the invading vendace, but only the planktivorous DR-whitefish share its pelagic niche. We would expect that the ecological differences between the whitefish morphs may be used as a predictor of competitive effects. Vendace exhibited an initial boom-and-bust development, and has continued to fluctuate in density. The responses of the pelagic DR-whitefish were: i) an immediate habitat shift, ii) a subsequent population decline caused by increased annual mortality, and iii) a new stable state at a lower density and apparently relaxed competition. The ecologically more distant benthivorous SR-whitefish also showed significant, but a much more limited response during this process, indicating damped indirect interactions through the food-web. This long-term case-study found that in two native eco-species equally related to the invader, only one of the eco-species was highly affected. Direct competition for resources is obviously important for species interactions, whereas the taxonomic relatedness per se seems to offer little predictive power for invasion effects.

The Impact of Exotic Purple Loosestrife (Lythrum salicaria) on Wetland Bird Abundances

The exotic invasive wetland plant purple loosestrife (Lythrum salicaria) is often considered to have negative impacts on native plant and animal species, but this is debated. Clarifying its influence would provide insight into appropriate management actions following invasion. We investigated the influence of L. salicaria cover and density on abundances of wetland bird species that are associated with a variety of vegetation structures. We found evidence of relationships between L. salicaria measures and abundance for most species we examined, but these relationships did not always agree with our predictions based on species' habitat associations. Some bird species positively responded whereas others negatively responded to increasing L. salicaria cover or density. Response curves varied in complexity and included linear and quadratic relationships as well as interactions. Our results suggested that L. salicaria did not categorically decrease habitat quality for all wetland bird species, and it may have had a positive influence on quality for some species. This ambiguity is not unique to L. salicaria invasion but applies to many changing habitat features. Therefore, there is likely no single appropriate strategy for managing L. salicaria when the goal is to maintain a diverse avian community in which species have divergent habitat preferences.

Hybridization among Caribbean damselfish species correlates with habitat degradation

Caribbean damselfish species (genus Stegastes) are permanently territorial, display obvious aggressive behavior related to territory defense, and have divergent habitat preferences for primary territory substrates. Territory quality is directly tied to variation in reproductive success among individuals, which suggests that ecological isolation plays a key role in the maintenance of species boundaries in this genus. If so, hybridization is expected to occur among closely-related damselfish species when there is a limitation in the availability of preferred primary habitat. To test this prediction, we collected damselfish from both high disturbance (Jamaica) and low disturbance (Barbados) coral reef environments, and looked for evidence of hybridization among species based on both morphological variation and discordance between mitochondrial and nuclear genetic markers. Consistent with the hypothesis that species boundaries in this system are maintained by strong substrate preferences and aggressive territoriality, we found evidence for extensive hybridization in Jamaica, where intense hurricanes have led to considerable habitat degradation over the last 30years. In light of ongoing climate change, this result suggests that hybridization leading to a blurring of ecological species boundaries may represent an increasingly common yet underappreciated threat to many coral reef fish species.

Mechanisms of reinforcement in natural and simulated polymorphic populations

Reinforcement speciation is the process whereby selection against hybrids drives the evolution of enhanced pre-mating reproductive isolation. Work has focused on divergent mating preferences (assortative mating) but pre-mating isolation can also arise via various migration modification behaviours, such as divergent habitat preferences. The relative importance of these two different mechanisms of reinforcement remains unclear. A recent theoretical model (Yukilevich–True model) found that relative fixation probabilities between these mechanisms can vary. Additionally, natural populations of Timema cristinae walking-sticks exhibit variation (polymorphism) in both mechanisms, generating questions about the patterns expected for allele frequencies prior to fixation, during the early stages of the speciation process. In the present study, we report: (1) new analyses examining the correlation between fixation probabilities for assortative mating and migration modification in the Yukilevich–True model; (2) novel simulations examining allele frequencies in polymorphic populations; and (3) empirical patterns of reinforcement in T. cristinae in the context of theoretical predictions. Simulations of both types yielded congruent results, revealing that the outcome of reinforcement was dependent on the strength of selection. Under weak selection, reinforcement by either mechanism is unlikely. Under intermediate selection, the conditions favoring the rise and fixation of one mechanism favored the rise and fixation of the other. However, assortative mating evolved somewhat more readily than migration modification. Populations of T. cristinae, which experience such intermediate selection, supported these predictions. Under strong selection, the evolution of migration modification generally interfered with the evolution of assortative mating by decreasing migration between populations, thereby reducing selection for assortative mating. Congruence of the results for allele frequencies versus fixation probabilities suggests that similar patterns of reinforcement are expected during different stages of the speciation process. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 305–319.

The evolution of host preference in allopatric vs. parapatric populations of Timema cristinae walking-sticks

Divergent habitat preferences can contribute to speciation, as has been observed for host-plant preferences in phytophagous insects. Geographic variation in host preference can provide insight into the causes of preference evolution. For example, selection against maladaptive host-switching occurs only when multiple hosts are available in the local environment and can result in greater divergence in regions with multiple vs. a single host. Conversely, costs of finding a suitable host can select for preference even in populations using a single host. Some populations of Timema cristinae occur in regions with only one host-plant species present (in allopatry, surrounded by unsuitable hosts) whereas others occur in regions with two host-plant species adjacent to one another (in parapatry). Here, we use host choice and reciprocal-rearing experiments to document genetic divergence in host preference among 33 populations of T. cristinae. Populations feeding on Ceanothus exhibited a stronger preference for Ceanothus than did populations feeding on Adenostoma. Both allopatric and parapatric pairs of populations using the different hosts exhibited divergent host preferences, but the degree of divergence tended to be greater between allopatric pairs. Thus, gene flow between parapatric populations apparently constrains divergence. Host preferences led to levels of premating isolation between populations using alternate hosts that were comparable in magnitude to previously documented premating isolation caused by natural and sexual selection against migrants between hosts. Our findings demonstrate how gene flow and different forms of selection interact to determine the magnitude of reproductive isolation observed in nature.

Spatial and ecological isolation in cicadas: First data from Tibicina (Hemiptera: Cicadoidea) in France

The seven taxa of the cicada genus Tibicina (T.corsica corsica, T. corsica fairmairei, T. garricola, T. haematodes, T. nigronervosa, T. quadrisignata, T. tomentosa) which occur in continental France and Corsica were investigated. Extrinsic factors (geographical barriers) and factors intrinsic to the ecology of species were considered in an effort to understand the biogeography of Tibicina. Three patterns related to intrinsic factors were recognised: (1) pairs of taxa with sympatric distributions but with divergent habitat preferences; (2) pairs of taxa with sympatric distributions and similar habitat but with allochronic occurrence; (3) pairs of taxa with similar ecology but with allopatric distributions. When taxa were separated by their habitat, the height of vegetation appeared to be more important than the floristic composition of the habitat. These factors lead to the partitioning of resources in time and space. All taxa occur in secondary vegetations. Human agro-pastoral activity has probably influenced the dynamics of cicada populations and the maintenance of isolation between them.

Spatial Interactions and Microhabitat Selections of Two Locally Sympatric Voles, Microtus Montanus and Microtus Pennsylvanicus

Microtus pennsylvanicus and Microtus montanus are sympatric in south central Montana, and the two occur in intermixed populations. This study attempted to assess the relative importance of interspecific interactions and habitat preference on movements and habitat selection of the two species. Radioisotope telemetry in 20—m x 20—m field enclosures showed that M. montanus had larger home ranges in the presence of M. pennsylvanicus than in single species treatment. Spacing between individuals was closer for M. montanus when alone as compared to mixed treatments. There was more overlap in M. montanus home ranges in single species treatments than in mixed treatments. Microtus montanus selected different vegetation when alone than in the presence of M. pennsylvanicus. The vegetation selected by each species was different from that selected by the other in all treatments. Enclosure experiments indicated only slight differences in emigration rates, survival rates, or weight changes for either species between single and mixed species treatments. Trap lines in natural areas outside of the enclosures showed that the two species are sympatric throughout the year but have different habitat preferences. Both interspecific interactions and divergent habitat preferences are important in maintaining separation between M. pennsylvanicus and M. montanus but the importance of each changes along habitat gradients. As habitats become uniformly optimal for M. pennsylvanicus, they are able to exclude M. montanus from an area.