Wild bees and natural enemies prefer similar flower species and respond to similar plant traits

Designing wildflower habitats to support beneficial insects providing pollination and pest control services is important for supporting sustainable crop production. It is often desirable to support both groups of insects, making the selection of resource plants for insect conservation programs more challenging. Moreover, the process of selecting resource plants is complicated by the array of possible options in each region, and the need to provide resources over the entire growing season. Identifying traits shared by resource plants that are attractive to both bees and natural enemies can reduce the need to evaluate new plants in each region, by providing a guide for the types of plants expected to be rewarding to these insects. Using insect visitation data collected from replicated common garden plantings of native wildflower and shrub species from the Great Lakes region of the United States, we found a high degree of correlation between the abundance of bees and natural enemies visiting native plant species. These results were used to identify a set of 15 plant species that can provide resources for these insects throughout the summer. Across all tested species, pollen quantity per flower and the week of bloom were positively correlated with some, but not all, taxonomic groupings of beneficial insects. In contrast, floral area was consistently positively associated with visitation of both natural enemies and wild bees. This trait is easy to document and can allow for efficient local testing of potential resource plants, providing a faster path to implementing insect conservation in working landscapes.     

Spatial autocorrelation analysis allows disentangling the balance between neutral and niche processes in metacommunities

One of the most popular approaches for investigating the roles of niche and neutral processes driving metacommunity patterns consists of partitioning variation in species data into environmental and spatial components. The logic is that the distance decay of similarity in communities is expected under neutral models. However, because environmental variation is often spatially structured, the decay could also be attributed to environmental factors that are missing from the analysis. Here, we use a spatial autocorrelation analysis protocol, previously developed to detect isolation‐by‐distance in allele frequencies, to evaluate patterns of species abundances under neutral dynamics. We show that this protocol can be linked with variation partitioning analyses. Moreover, in an attempt to test the neutral model, we derive three predictions to be applied both to original species abundances and to abundances predicted by a pure spatial model species abundances will be uncorrelated; Moran's I correlograms will reveal similar short‐distance autocorrelation patterns; an increasing degree of non‐neutrality will tend to generate patterns of correlation among abundances within groups of species with similar correlograms (i.e. within species with neutral and non‐neutral dynamics). We illustrate our protocol by analyzing spatial patterns in abundance of 28 terrestrially breeding anuran species from Central Amazonia. We recommend that researchers should investigate spatial autocorrelation patterns of abundances predicted by pure spatial models to identify similar patterns of spatial autocorrelation at short distances and lack of correlation between species abundances. Therefore, the hypothesis that spatial patterns in abundances are primarily due to pure neutral dynamics (rather than to missing spatiallystructured environmental factors) can be confirmed after taking environmental variables into account.     

Common and rare plant species respond differently to fertilisation and competition, whether they are alien or native

Plant traits associated with alien invasiveness may also distinguish rare from common native species. To test this, we grew 23 native (9 common, 14 rare) and 18 alien (8 common, 10 rare) herbaceous species in Switzerland from six plant families under nutrient-addition and competition treatments. Alien and common species achieved greater biomass than native and rare species did overall respectively. Across alien and native origins, common species increased total biomass more strongly in response to nutrient addition than rare species did and this difference was not confounded by habitat dissimilarities. There was a weak tendency for common species to survive competition better than rare species, which was also independent of origin. Overall, our study suggests that common alien and native plant species are not fundamentally different in their responses to nutrient addition and competition.     

Concurrent niche and neutral processes in the competition-colonization model of species coexistence

The importance of neutral dynamics is contentiously debated in the ecological literature. This debate focuses on neutral theory's assumption of fitness equivalency among individuals, which conflicts with stabilizing fitness that promotes coexistence through niche differentiation. I take advantage of competition-colonization trade-offs between species of aquatic micro-organisms (protozoans and rotifers) to show that equalizing and stabilizing mechanisms can operate simultaneously. Competition trials between species with similar colonization abilities were less likely to result in competitive exclusion than for species further apart. While the stabilizing mechanism (colonization differences) facilitates coexistence at large spatial scales, species with similar colonization abilities also exhibited local coexistence probably due to fitness similarities allowing weak stabilizing mechanisms to operate. These results suggest that neutral- and niche-based mechanisms of coexistence can simultaneously operate at differing temporal and spatial scales, and such a spatially explicit view of coexistence may be one way to reconcile niche and neutral dynamics.     

Average niche breadths of species in lake macrophyte communities respond to ecological gradients variably in four regions on two continents

Different species’ niche breadths in relation to ecological gradients are infrequently examined within the same study and, moreover, species niche breadths have rarely been averaged to account for variation in entire ecological communities. We investigated how average environmental niche breadths (climate, water quality and climate–water quality niches) in aquatic macrophyte communities are related to ecological gradients (latitude, longitude, altitude, species richness and lake area) among four distinct regions (Finland, Sweden and US states of Minnesota and Wisconsin) on two continents. We found that correlations between the three different measures of average niche breadths and ecological gradients varied considerably among the study regions, with average climate and average water quality niche breadth models often showing opposite trends. However, consistent patterns were also found, such as widening of average climate niche breadths and narrowing of average water quality niche breadths of aquatic macrophytes along increasing latitudinal and altitudinal gradients. This result suggests that macrophyte species are generalists in relation to temperature variations at higher latitudes and altitudes, whereas species in southern, lowland lakes are more specialised. In contrast, aquatic macrophytes growing in more southern nutrient-rich lakes were generalists in relation to water quality, while specialist species are adapted to low-productivity conditions and are found in highland lakes. Our results emphasise that species niche breadths should not be studied using only coarse-scale data of species distributions and corresponding environmental conditions, but that investigations on different kinds of niche breadths (e.g., climate vs. local niches) also require finer resolution data at broad spatial extents.     

Evolution of dispersal in metacommunities of interacting species

Theoretical studies on the evolution of dispersal in metacommunities are rare despite empirical evidence suggesting that interspecific interactions can modify dispersal behaviour of organisms. To understand the role of species interactions for dispersal evolution, we utilize an individual‐based model of a metacommunity where local population dynamics follows a stochastic version of the Nicholson–Bailey model and dispersal probability is an evolving trait. Our results show that in comparison with a neutral system (commensalism), parasitism promotes dispersal of hosts and parasites, while mutualism tends to reduce dispersal in both partners. Search efficiency of guests (only in the case of parasitism), dispersal mortality and external extinction risk can influence the evolution of dispersal of all partners. In systems composed of two host and two guest species, lower dispersal probabilities evolve under parasitism as well as mutualism than in one host and one guest species systems. This is because of frequency‐dependent modulations of dispersal benefits emerging in such systems for all partners.     

How species respond to multiple extinction threats

It is well established that different species vary in their vulnerability to extinction risk and that species biology can underpin much of this variation. By contrast, very little is known about how the same species responds to different threat processes. The purpose of this paper is therefore twofold: to examine the extent to which a species' vulnerability to different types of threat might covary and to explore the biological traits that are associated with threat-specific responses. We use an objective and quantitative measure of local extinction risk to show that vulnerability to local population decline in primates varies substantially among species and between threat types. Our results show that a species' response to one threat type does not predict its response to others. Multivariate analyses also suggest that different mechanisms of decline are associated with each type of threat, since different biological traits are correlated with each threat-specific response. Primate species at risk from forestry tend to exhibit low ecological flexibility, while those species vulnerable to agriculture tend to live in the canopy and eat low-fruit diets; in further contrast, primates at risk from hunting tend to exhibit large body size. Our analyses therefore indicate that a species' vulnerability to local extinction can be highly variable and is likely to depend on both threat type and biology.     

Zero sum, the niche, and metacommunities: long-term dynamics of community assembly

Recent models of community assembly, structure, and dynamics have incorporated, to varying degrees, three mechanistic processes: resource limitation and interspecific competition, niche requirements of species, and exchanges between a local community and a regional species pool. Synthesizing 30 years of data from an intensively studied desert rodent community, we show that all of these processes, separately and in combination, have influenced the structural organization of this community and affected its dynamical response to both natural environmental changes and experimental perturbations. In addition, our analyses suggest that zero-sum constraints, niche differences, and metacommunity processes are inextricably linked in the ways that they affect the structure and dynamics of this system. Explicit consideration of the interaction of these processes should yield a deeper understanding of the assembly and dynamics of other ecological communities. This synthesis highlights the role that long-term data, especially when coupled with experimental manipulations, can play in assessing the fundamental processes that govern the structure and function of ecological communities.     

Behavioural plasticity and trophic niche shift: How wintering geese respond to habitat alteration

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Dispersal rates affect species composition in metacommunities of Sarracenia purpurea inquilines

Dispersal among local communities can have a variety of effects on species composition and diversity at local and regional scales. Local conditions (e.g., resource and predator densities) can have independent effects, as well as interact with dispersal, to alter these patterns. Based on metacommunity models, we predicted that local diversity would show a unimodal relationship with dispersal frequency. We manipulated dispersal frequencies, resource levels, and the presence of predators (mosquito larvae) among communities found in the water-filled leaves of the pitcher plant Sarracenia purpurea. Diversity and abundance of species of the middle trophic level, protozoa and rotifers, were measured. Increased dispersal frequencies significantly increased regional species richness and protozoan abundance while decreasing the variance among local communities. Dispersal frequency interacted with predation at the local community scale to produce patterns of diversity consistent with the model. When predators were absent, we found a unimodal relationship between dispersal frequency and diversity, and when predators were present, there was a flat relationship. Intermediate dispersal frequencies maintained some species in the inquiline communities by offsetting extinction rates. Local community composition and the degree of connectivity between communities are both important for understanding species diversity patterns at local and regional scales.     

Dispersal stochasticity mediates species richness in source–sink metacommunities

Although it is well‐known that dispersal of organisms within a metacommunity will influence patterns of coexistence and richness, theoretical and experimental studies generally assume that dispersal rates are constant through time. However, dispersal is often a highly variable process that can vary seasonally and/or when stochastic events (e.g. wind storms, droughts, floods) occur. Using a well‐known source–sink metacommunity model, we present novel predictions for local and regional species richness when stochasticity in dispersal is expressly considered. We demonstrate that dispersal stochasticity alters some of the predictions obtained with constant dispersal; the peak of the predicted hump‐shaped relationship between dispersal and local species richness is diminished and shifted towards higher values of dispersal. Dispersal stochasticity increases extinction probabilities of inferior competitor species particularly in metacommunities subjected to severe isolation events (i.e. decreases of dispersal) or homogenization events (i.e. sudden increases of dispersal). Our results emphasize how incorporating dispersal stochasticity into theoretical predictions will broaden our understanding of metacommunities dynamics and their responses to natural and human‐related disturbances.     

Persistence of ecologically similar fungi in a restricted floral niche

Fungi in the genera Knoxdaviesia and Sporothrix dominate fungal communities within Protea flowerheads and seed cones (infructescences). Despite apparently similar ecologies, they show strong host recurrence and often occupy the same individual infructescence. Differences in host chemistry explain their host consistency, but the factors that allow co-occupancy of multiple species within individual infructescences are unknown. Sporothrix splendens and K. proteae often grow on different senescent tissue types within infructescences of their P. repens host, indicating that substrate-related differences aid their co-occupancy. Sporothrix phasma and K. capensis grow on the same tissues of P. neriifolia suggesting neutral competitive abilities. Here we test the hypothesis that differences in host-tissues dictate competitive abilities of these fungi and explain their co-occupancy of this spatially restricted niche. Media were prepared from infructescence bases, bracts, seeds, or pollen presenters of P. neriifolia and P. repens. As expected, K. capensis was unable to grow on seeds whilst S. phasma could. As hypothesised, K. capensis and S. phasma had equal competitive abilities on pollen presenters, appearing to explain their co-occupancy of this resource. Growth of K. proteae was significantly enhanced on pollen presenters while that of S. splendens was the same as the control. Knoxdavesia proteae grew significantly faster than S. splendens on all tissue types. Despite this, S. splendens was a superior competitor on all tissue types. For K. proteae to co-occupy infructescences with S. splendens for extended periods, it likely needs to colonize pollen presenters before the arrival of S. splendens.

     

Immortalized mouse brain endothelial cells are ultrastructurally similar to endothelial cells and respond to astrocyte-conditioned medium

Summary Studies of brain microvessel endothelial cell physiology and blood-brain barrier properties are often hampered by the requirement of repeatedly producing and characterizing primary endothelial cell cultures. The use of viral oncogenes to produce several immortalized brain microvessel cell lines has been reported. The resulting cell lines express many properties of the blood-brain barrier phenotype but do not completely mimic primary endothelial cells in culture. As immortalized brain microvessel endothelial cell lines have not yet been produced from mice, we transformed mouse brain endothelial cells with the adenovirus E1A gene using a retroviral vector (DOL). Eight of 11 clones produced exhibited an endothelial-like cobblestone morphology and were characterized as endothelial with a panel of antibodies, lectins, and ultrastructural criteria. These cells are endothelial in origin and share ultrastructural features with primary cultures of endothelial cells. Examination of freeze fracture and transmission electron micrographs show adherens junctions exist between the transformed cells, and culture in astrocyte-conditioned medium induces the formation of gap junctions. This is one indication that responses to astrocyte-derived factors are retained by the transformed cell lines.     

Limits to the niche and range margins of alien species

We discuss the apparent paradox that while introduced populations often adapt rapidly to conditions in the new range, it is normally assumed that the species’ niche remains unchanged. Focusing on plants, we argue that studies of the niche dynamics of alien species are useful for understanding the constraints acting on species in their native ranges, and vice versa. Most hypotheses about species ecological range margins are more consistent with there being a niche shift than niche stasis in the new range. After reviewing the evidence for niche shifts in alien species, we suggest that the probability of a shift occurring depends primarily upon the ecological and genetic processes limiting the species in its native range. For example, a fundamental niche shift might occur if introduced individuals are released from maladaptive gene flow from central populations, or if genetic diversity is increased by the mixing of individuals from different sources. In addition, other factors such as species characteristics, introduction history and conditions in the new range may also influence whether a niche shift occurs. Based on these considerations, we propose conditions under which niche shifts are most likely. Such understanding is important for predicting and mitigating current and future anthropogenic impacts on species ranges.     

Population and community-level compositional patterns shape the realized niche of the rare arctic-alpine species Carex lachenalii Schkuhr

The ability for vegetative growth and development of generative organs often reflects an adaptation to the environment and may be a suitable proxy for understanding population dynamics of rare relict species. An example of such a plant is Carex lachenalii Schkuhr, an arctic-alpine species, in the temperate zone of Europe only occurring in isolated localities of high-elevation mountain ranges. We aimed to assess whether there were relationships between flower production and clonal growth of C. lachenalii, both at the tuft and plot level, and how co-occurring vegetation could modify this relationship. In the study we focused on population-level traits of C. lachenalii, vegetation traits and components of functional diversity. At the tuft level we found that the proportion of flowering ramets of C. lachenalii decreased with increasing diameter of the tuft. At the plot level, in snowbed vegetation C. lachenalii produced more flowering ramets. We suggest this is due to higher environmental stress, expressed by high importance of habitat filtering (low functional dispersion) in shaping species composition of co-occurring vegetation. In granite grasslands and milder environment (expressed by higher functional dispersion), C. lachenalii produced more vegetative ramets, which we suggest is a result of a more competitive environment. While in snowbeds investment in flowering ramets could promote successful persistence of C. lachenalii, survival of subpopulations occurring in the highly competitive conditions of granite grasslands may be uncertain due to potentially weak adaptation to competition with graminoids and dwarf shrubs.     

Diversity and composition of macroinvertebrate communities in a rare inland salt marsh

Inland salt marshes are rare habitats in the Great Lakes region of North America, formed on salt deposits from the Silurian period. These patchy habitats are abiotically stressful for the freshwater invertebrates that live there, and provide an opportunity to study the relationship between stress and diversity. We used morphological and COI metabarcoding data to assess changes in diversity and composition across both space (a transect from the salt seep to an adjacent freshwater area) and time (three sampling seasons). Richness was significantly lower at the seep site with both datatypes, while metabarcoding data additionally showed reduced richness at the freshwater transect end, consistent with a pattern where intermediate levels of stress show higher diversity. We found complementary, rather than redundant, patterns of community composition using the two datatypes: not all taxa were equally sequenced with the metabarcoding protocol. We identified taxa that are abundant at the salt seep of the marsh, including biting midges (Culicoides) and ostracods (Heterocypris). We conclude that (as found in other studies) molecular and morphological work should be used in tandem to identify the biodiversity in this rare habitat. Additionally, salinity may be a driver of community membership in this system, though further ecological research is needed to rule out alternate hypotheses.     

Changes in the roles of spatial and environmental processes in the structuring of rodent metacommunities

We studied the role of spatial (regional) and environmental (local) processes in the structuring of rodent metacommunities in three contiguous ecoregions that share the same species pool. The two northern ecoregions are mainly affected by anthropogenic processes (agriculture and urbanization) while the southern one is mainly affected by natural processes (flood and drought pulses). Local communities were described based on the analysis of 77 samples of barn owl pellets. To identify which processes (patch dynamics, species sorting, mass effect or neutral theory) structure each metacommunity we evaluated the percentage of variance explained by space (spatial arrangement of communities) and environment (topography, climate and land cover) in three Variation Partitioning Redundancy Analyses. The percentage of variance in rodent metacommunities composition explained by space and environment was between 38 and 61%, and was significant in all three analyses. The pure space fraction was significant for two of the three ecoregions, while the pure environmental fraction was significant for all three ecoregions. The processes that structure rodent metacommunities change across the region. In all three ecoregions the species sorting played a key role, while, mass effect was a structuring factor for northern metacommunities. These results can be explained by species-specific dispersal characteristics and environmental filtering.