Dispersal of a carabid beetle in farmland is driven by habitat‐specific motility and preference at habitat interfaces

Carabid beetles are common predators of pest insects and weed seeds in agricultural systems. Understanding their dispersal across farmland is important for designing farms and landscapes that support pest and weed biological control. Little is known, however, about the effect of farmland habitat discontinuities on dispersal behaviour and the resulting redistribution of these beetles. We released 1,985 well‐fed and 1,680 food‐deprived individuals of the predatory carabid beetle Pterostichus melanarius (Illiger) (Coleoptera: Carabidae) on a farm in Wageningen, The Netherlands. We recaptured 23.6% of those beetles over a period of 23 days in 2010. The farmland comprised agricultural fields with various crop species and tillage, separated by strips of perennial vegetation. We developed discrete Fokker‐Planck diffusion models to describe dispersal based on motility (m² day^?1) and preferential behaviour at habitat interfaces. We used model selection and Akaike’s information criterion to determine whether movement patterns were driven by variation in motility between habitats, preferential behaviour at habitat interfaces, or both. Model selection revealed differences in motility among habitats and gave strong support for preferential behaviour at habitat interfaces. Behaviour at interfaces between crop and perennial vegetation was asymmetric, with beetles preferentially moving towards the crop. Furthermore, beetles had lower motility in perennial strips than in arable fields. Also between arable habitats movement was asymmetric, with beetles preferentially moving towards the habitat in which motility was lowest. Neither crop type nor tillage explained differences in motility between crop habitats. Recapture data representing dispersal patterns of beetles were best described by a model that accounted for differences in motility between farmland habitats and preferential behaviour at habitat interfaces. Motility in farmland and behaviour at interfaces can also be estimated for other organisms and farmland habitats to support design of farmland conducive to natural pest suppression. Landscape design for early recruitment of carabids into arable fields should take into account the quantity and quality of resource habitats in the landscape, their proximity to crop fields, movement rates, and the possibility of movement responses at interfaces between landscape elements.     

Climate‐driven geographic distribution of the desert locust during recession periods: Subspecies’ niche differentiation and relative risks under scenarios of climate change

The desert locust is an agricultural pest that is able to switch from a harmless solitarious stage, during recession periods, to swarms of gregarious individuals that disperse long distances and affect areas from western Africa to India during outbreak periods. Large outbreaks have been recorded through centuries, and the Food and Agriculture Organization keeps a long‐term, large‐scale monitoring survey database in the area. However, there is also a much less known subspecies that occupies a limited area in Southern Africa. We used large‐scale climatic and occurrence data of the solitarious phase of each subspecies during recession periods to understand whether both subspecies climatic niches differ from each other, what is the current potential geographical distribution of each subspecies, and how climate change is likely to shift their potential distribution with respect to current conditions. We evaluated whether subspecies are significantly specialized along available climate gradients by using null models of background climatic differences within and between southern and northern ranges and applying niche similarity and niche equivalency tests. The results point to climatic niche conservatism between the two clades. We complemented this analysis with species distribution modeling to characterize current solitarious distributions and forecast potential recession range shifts under two extreme climate change scenarios at the 2050 and 2090 time horizon. Projections suggest that, at a global scale, the northern clade could contract its solitarious recession range, while the southern clade is likely to expand its recession range. However, local expansions were also predicted in the northern clade, in particular in southern and northern margins of the current geographical distribution. In conclusion, monitoring and management practices should remain in place in northern Africa, while in Southern Africa the potential for the subspecies to pose a threat in the future should be investigated more closely.     

Sap‐feeding insects on forest trees along latitudinal gradients in northern Europe: a climate‐driven patterns

Knowledge of the latitudinal patterns in biotic interactions, and especially in herbivory, is crucial for understanding the mechanisms that govern ecosystem functioning and for predicting their responses to climate change. We used sap‐feeding insects as a model group to test the hypotheses that the strength of plant–herbivore interactions in boreal forests decreases with latitude and that this latitudinal pattern is driven primarily by midsummer temperatures. We used a replicated sampling design and quantitatively collected and identified all sap‐feeding insects from four species of forest trees along five latitudinal gradients (750–1300 km in length, ten sites in each gradient) in northern Europe (59 to 70°N and 10 to 60°E) during 2008–2011. Similar decreases in diversity of sap‐feeding insects with latitude were observed in all gradients during all study years. The sap‐feeder load (i.e. insect biomass per unit of foliar biomass) decreased with latitude in typical summers, but increased in an exceptionally hot summer and was independent of latitude during a warm summer. Analysis of combined data from all sites and years revealed dome‐shaped relationships between the loads of sap‐feeders and midsummer temperatures, peaking at 17 °C in Picea abies, at 19.5 °C in Pinus sylvestris and Betula pubescens and at 22 °C in B. pendula. From these relationships, we predict that the losses of forest trees to sap‐feeders will increase by 0–45% of the current level in southern boreal forests and by 65–210% in subarctic forests with a 1 °C increase in summer temperatures. The observed relationships between temperatures and the loads of sap‐feeders differ between the coniferous and deciduous tree species. We conclude that climate warming will not only increase plant losses to sap‐feeding insects, especially in subarctic forests, but can also alter plant‐plant interactions, thereby affecting both the productivity and the structure of future forest ecosystems.     

Algorithmic single‐locus species delimitation: effects of sampling effort,variation and nonmonophyly in four methods and 1870 species of beetles

The vast number of undescribed species and the fast rate of biodiversity loss call for new approaches to speed up alpha taxonomy. A plethora of methods for delimiting species or operational taxonomic units (OTUs) based on sequence data have been published in recent years. We test the ability of four delimitation methods (BIN, ABGD, GMYC, PTP) to reproduce established species boundaries on a carefully curated DNA barcode data set of 1870 North European beetle species. We also explore how sampling effort, intraspecific variation, nearest neighbour divergence and nonmonophyly affect the OTU delimitations. All methods produced approximately 90% identity between species and OTUs. The effects of variation and sampling differed between methods. ABGD was sensitive to singleton sequences, while GMYC showed tendencies for oversplitting. The best fit between species and OTUs was achieved using simple rules to find consensus between discordant OTU delimitations. Using several approaches simultaneously allows the methods to compensate for each other's weaknesses. Barcode‐based OTU‐picking is an efficient way to delimit putative species from large data sets where the use of more sophisticated methods based on multilocus or genomic data is not feasible.     

A test for within‐lake niche differentiation in the nine‐spined sticklebacks (Pungitius pungitius)

Specialization for the use of different resources can lead to ecological speciation. Accordingly, there are numerous examples of ecologically specialized pairs of fish “species” in postglacial lakes. Using a polymorphic panel of single nucleotide variants, we tested for genetic footprints of within‐lake population stratification in nine‐spined sticklebacks (Pungitius pungitius) collected from three habitats (viz. littoral, benthic, and pelagic) within a northern Swedish lake. Analyses of admixture, population structure, and relatedness all supported the conclusion that the fish from this lake form a single interbreeding unit.     

Fine‐scale belowground species associations in temperate grassland

Evaluating how belowground processes contribute to plant community dynamics is hampered by limited information on the spatial structure of root communities at the scale that plants interact belowground. In this study, roots were mapped to the nearest one mm and molecularly identified by species on vertical (0–15 cm deep) surfaces of soil blocks excavated from dry and mesic grasslands in Yellowstone National Park (YNP) to examine the spatial relationships among species at the scale that roots interact. Our results indicated that average interspecific root – root distances for the majority of species were within a distance (3 mm) that roots have been shown to compete for resources. Most species placed their roots at random, although low root numbers for many species probably led to overestimating the occurrence of random patterns. According to theory, we expected that most of the remaining species would segregate their root systems to avoid competition. Instead we found that more species aggregated than segregated from others. Based on previous investigations, we hypothesize that species aggregate to increase uptake of water, nitrogen and/or phosphorus made available by neighbouring roots, or as a consequence of a reduction in the pathogenicity of soil biota growing in multispecies mixtures. Our results indicate that YNP grassland root communities are organized as closely interdigitating networks of species that potentially can support strong interactions among many species combinations. Future root research should address the prevalence and functional consequences of species aggregation across plant communities.     

Trapping of European buprestid beetles in oak forests using visual and olfactory cues

Trapping approaches developed for the emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), were adapted for trapping several European oak buprestid species. These approaches included the use of natural leaf surfaces as well as green and purple plastic in sticky trap designs. Plastic surfaces were incorporated into novel ‘branch‐trap’ designs that each presented two 5 × 9‐cm² rectangular surfaces on a cardboard structure wrapped around the leaves of a branch. We used visual adult Agrilus decoys in an attempt to evoke male mating approaches toward the traps. Our first experiment compared the attractiveness of visual characteristics of the surfaces of branch‐traps. The second looked at the effect on trap captures of adding semiochemical lures, including manuka oil, (Z)‐3‐hexen‐1‐ol, and (Z)‐9‐tricosene. In total, 1 962 buprestid specimens including 14 species from the genus Agrilus were caught on 178 traps in a 22‐day time‐span. Overall, the green plastic‐covered branch‐traps significantly out‐performed the other trap designs. We further found that the presence of an EAB visual decoy placed on the trap surface often increased captures on these green traps, but this effect was stronger for certain Agrilus species than for others. The visual decoy was particularly important for the most serious pest detected, Agrilus biguttatus Fabricius, which was captured 13 times on traps with decoys, but only once without a decoy. There were some small but significant effects of odor treatment on the capture of buprestids of two common species, Agrilus angustulus Illiger and Agrilus sulcicollis Lacordaire. There were also 141 Elateridae specimens on these traps, which were not influenced by trap type or decoys. The results suggest that small branch‐traps of this nature can provide a useful new tool for monitoring of buprestids, which have the potential to be further optimized with respect to visual and olfactory cues.     

Temperature‐driven shifts in a host‐parasite interaction drive nonlinear changes in disease risk

Climate change may shift the timing and consequences of interspecific interactions, including those important to disease spread. Because hosts and pathogens may respond differentially to climate shifts, however, predicting the net effects on disease patterns remains challenging. Here, we used field data to guide a series of laboratory experiments that systematically evaluated the effects of temperature on the full infection process, including survival, penetration, establishment, persistence, and virulence of a highly pathogenic trematode (Ribeiroia ondatrae), and the development and survival of its amphibian host. Our results revealed nonlinearities in pathology as a function of temperature, which likely resulted from changes in both host and parasite processes. Both hosts and parasites responded strongly to temperature; hosts accelerated development while parasites showed enhanced host penetration but reduced establishment (encystment) and survival outside the host. While there were no differences in host survival among treatments, we observed a mid‐temperature peak in parasite‐induced deformities (63% at 20 °C), with the lowest frequency of deformities (12%) occurring at the highest temperature (26 °C). This nonlinear effect could result from temperature‐driven changes in parasite burden owing to shifts in host penetration and/or clearance, reductions in host vulnerability owing to faster development, or both. Furthermore, despite strong temperature‐driven changes in parasite penetration, survival, and establishment, the opposing nature of these effects lead to no difference in tadpole parasite burdens shortly after infection. These findings suggest that temperature‐driven changes to the disease process may not be easily observable from comparison of parasite burdens alone, but multi‐tiered experiments quantifying the responses of hosts, parasites and their interactions can enhance our ability to predict temperature‐driven changes to disease risk. Climate‐driven changes to disease patterns will therefore depend on underlying shifts in host and parasite development rates and the timing of their interactions.     

Tectonic vicariance versus Messinian dispersal in western Mediterranean ground beetles

The complex geological history of the western Mediterranean region conceals the interpretation of the evolutionary history of its current fauna, as similar distribution patterns may have very different temporal and geographic origins. Particularly intriguing are some subterranean species in islands, which origin is usually difficult to interpret as their strongly modified morphologies obscure their relationships. We studied subterranean taxa and their likely relatives of two groups of ground beetles in the western Mediterranean: the Duvalius lineage (“isotopic” Trechini) and Molopina (Pterostichini). We included specimens from the islands of Mallorca, Sardinia and Sicily, plus mainland Europe and North Africa. Phylogenetic relationships were reconstructed with a combination of mitochondrial and nuclear data, and divergence dates were estimated with Bayesian methods using the same a priori molecular evolutionary rates for the same gene fragments in the two groups. In the Duvalius lineage, the subgenus Trechopsis, including all the highly modified cave or nivicolous species, was found to be polyphyletic: the species from Mallorca was found to be of Pleistocene origin and sister to the less modified species of subgenus Duvalius from the same island, whereas the Algerian species of Trechopsis were, on the contrary, related to the Sicilian Duvalius, indicating a northern colonisation route during the late Pliocene. Molopina was divided into three main lineages: the genera Abax, Percus, and the Molops groups of genera. The basal diversification of the latter was dated within a temporal window (35–25 Ma) fully congruent with the tectonic opening of the western Mediterranean basin and included six main lineages with uncertain relationships among them: the epigean genera (a) Molops and (b) Tanythrix; and the subterranean (c) Typhlochoromus (Eastern Alps), (d) Speomolops (Sardinia), (e) Henrotius (Mallorca) and (f) a strongly supported clade including the Pyrenean genera Zariquieya, Oscadytes and Molopidius. Despite the similar distribution of some of their subterranean taxa, the two studied groups show a strongly contrasting origin and mode of diversification. While the Duvalius lineage had a recent origin, with complex colonisation patterns and widespread morphological convergence among the subterranean species, the subterranean Molopina had an ancient vicariant origin resulting from the tectonic opening of the western Mediterranean basin.     

Isotopic niche width differentiation between common bottlenose dolphin ecotypes and sperm whales in the Gulf of California

World populations or stock distinction of Tursiops truncatus has been difficult to assess, because of large variations in morphology, habitat, feeding habits, and social structure among areas, which may reflect phylogenetic segregation or ecological plasticity. In the Gulf of California, Mexico, two common bottlenose dolphin ecotypes (inshore and offshore) have been reported. The offshore ecotype is frequently observed in association with sperm whales (Physeter macrocephalus) but the reason for this is still unknown. To explore the degree of resource partitioning/overlap between these species and stocks, we used skin stable isotope values (δ¹³C, δ¹⁵N) to estimate quantitative metrics of isotopic niche width (Bayesian standard ellipse areas, SEA_B) and estimated their diet composition using Bayesian isotopic mixing models. The inshore ecotype in different regions (north, central, and south) of the Gulf of California exhibited distinct δ¹⁵N values and SEA_B, suggesting a latitudinal gradient in nitrogen sources of coastal localities. The SEA_B of inshore and offshore bottlenose dolphin ecotypes was completely distinct, indicating resource partitioning. Associated offshore ecotype and sperm whales had overlapping SEA_B. The isotopic mixing model indicates that a considerable proportion of both species’ diet is large Humbolt squid. Our results suggest that resource partitioning and species association are two strategies that bottlenose dolphin ecotypes use in this zone.     

Fine‐scale variation in natural nitrogen isotope ratios of ants

Stable isotopes provide a powerful means of elucidating the trophic ecology of organisms. Analyses of variation in the ratio of nitrogen isotopes (δ¹⁵N) can provide insights into the trophic position of species with broad diets and the ability to occupy multiple positions in food webs, such as ants. The most powerful studies compare subjects across various spatial scales, but to do so, local variation in δ¹⁵N baselines must be taken into account. To date, a wide variety of baseline calibration methods have been employed, leading some authors to suggest that a standard approach is needed, and that the reality of environmental variation necessitates that this should be at fine scales. In this study, we examine the fine‐scale variation in δ¹⁵N value of colonies of the ant Formica kozlovi Dlussky (Hymenoptera: Formicidae: Formicini) along a sloped transect in Mongolia, and compare these with values for associated soils in an effort to shed further light on this issue. We find variation in ant δ¹⁵N to the order of one trophic level (ca. 3‰), over a distance of only 1 km. Ant δ¹⁵N was highly correlated with soil δ¹⁵N, and variation in mineral soil δ¹⁵N explained ca. 81% of the variation in ant δ¹⁵N. This study underlines the importance of local‐scale baseline corrections for isotopic studies, particularly in environments where baseline variation might be expected. It further suggests that δ¹⁵N of mineral soils may provide a suitable baseline for ecological studies of terrestrial arthropods.     

Behaviour‐related DRD4 polymorphisms in invasive bird populations

It has been suggested that individual behavioural traits influence the potential to successfully colonize new areas. Identifying the genetic basis of behavioural variation in invasive species thus represents an important step towards understanding the evolutionary potential of the invader. Here, we sequenced a candidate region for neophilic/neophobic and activity behaviour – the complete exon 3 of the DRD4 gene – in 100 Yellow‐crowned bishops (Euplectes afer) from two invasive populations in Spain and Portugal. The same birds were scored twice for activity behaviour while exposed to novel objects (battery or slice of apple) in captivity. Response to novel objects was repeatable (r = 0.41) within individuals. We identified two synonymous DRD4 SNPs that explained on average between 11% and 15% of the phenotypic variance in both populations, indicating a clear genetic component to the neophilic/neophobic/activity personality axis in this species. This consistently high estimated effect size was mainly due to the repeated measurement design, which excludes part of the within‐individual nongenetic variance in the response to different novel objects. We suggest that the alternative alleles of these SNPs are likely introduced from the original population and maintained by weak or antagonistic selection during different stages of the invasion process. The identified genetic variants have not only the potential to serve as genetic markers of the neophobic/neophilic/activity personality axis, but may also help to understand the evolution of behaviour in these invasive bird populations.     

What happens in the pith stays in the pith: tissue‐localized defense responses facilitate chemical niche differentiation between two spatially separated herbivores

Herbivore attack is known to elicit systemic defense responses that spread throughout the host plant and influence the performance of other herbivores. While these plant‐mediated indirect competitive interactions are well described, and the co‐existence of herbivores from different feeding guilds is common, the mechanisms of co‐existence are poorly understood. In both field and glasshouse experiments with a native tobacco, Nicotiana attenuata, we found no evidence of negative interactions when plants were simultaneously attacked by two spatially separated herbivores: a leaf chewer Manduca sexta and a stem borer Trichobaris mucorea. T. mucorea attack elicited jasmonic acid (JA) and jasmonoyl‐l ‐isoleucine bursts in the pith of attacked stems similar to those that occur in leaves when M. sexta attacks N. attenuata leaves. Pith chlorogenic acid (CGA) levels increased 1000‐fold to levels 6‐fold higher than leaf levels after T. mucorea attack; these increases in pith CGA levels, which did not occur in M. sexta‐attacked leaves, required JA signaling. With plants silenced in CGA biosynthesis (irHQT plants), CGA, as well as other caffeic acid conjugates, was demonstrated in both glasshouse and field experiments to function as a direct defense protecting piths against T. mucorea attack, but not against leaf chewers or sucking insects. T. mucorea attack does not systemically activate JA signaling in leaves, while M. sexta leaf‐attack transiently induces detectable but minor pith JA levels that are dwarfed by local responses. We conclude that tissue‐localized defense responses allow tissue‐specialized herbivores to share the same host and occupy different chemical defense niches in the same hostplant.     

Intraspecific and interspecific competition induces density‐dependent habitat niche shifts in an endangered steppe bird

Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.