Linking climate change and species invasion: an illustration using insect herbivores

Climate change and invasive species are two of the most important ecological issues facing the world today. Yet, to date these two factors have largely been viewed independently. In order to prevent large-scale economic and environmental damage and as a first step towards predicting and preventing invasions, it is important to understand the factors affecting invasions. Here, we focus on insect herbivores and link the climate change and invasive research fields. We illustrate using existing published research that life history traits can be useful indicators of future invasive potential. However, climate change will also affect propagule pressure and the communities into which invaders will arrive. With the aid of a meta-analysis we show that climate-induced community changes are likely to increase niche-availability in the future, further exacerbating the problem of invasive species. It is timely and important that further research linking these two important ecological threats is undertaken.     

Functional diversity of crustacean zooplankton communities: towards a trait-based classification

1. While studies of phytoplankton and terrestrial plant communities have increasingly emphasised the use of functional traits in ecological research, few have yet to apply this approach to zooplankton communities.
2. This study reviews laboratory and observational studies on zooplankton feeding and life history and provides a series of functional trait tables for the North American freshwater zooplankton. Qualitative and quantitative trait tables highlight areas where data were more scarce and point to which types of studies could fill in gaps in our knowledge of zooplankton niches.
3. Data were most complete for the Cladocera across most traits, while feeding information for cyclopoids was most sparse. Qualitative data that distinguished congeneric species were lacking for most groups.
4. A regional community dendrogram for common north-eastern North American zooplankton species was generated and shows that taxonomic differences between species do not capture fully functional differences based on the traits of body length, habitat, trophic group and feeding type.
5. The data collected here, combined with readily measurable species attributes, can be used to generate a multivariate measure of the functional niche of each species found in a community. Armed with this information, functional relationships that are useful for ecological studies of lake ecosystems can be more easily conducted.     

Assembly rules of ground-foraging ant assemblages are contingent on disturbance, habitat and spatial scale

Aim A major endeavour of community ecology is documenting non‐random patterns in the composition and body size of coexisting species, and inferring the processes, or assembly rules, that may have given rise to the observed patterns. Such assembly rules include species sorting resulting from interspecific competition, aggregation at patchily distributed resources, and co‐evolutionary dynamics. However, for any given taxon, relatively little is known about how these patterns and processes change through time and vary with habitat type, disturbance history, and spatial scale. Here, we tested for non‐random patterns of species co‐occurrence and body size in assemblages of ground‐foraging ants and asked whether those patterns varied with habitat type, disturbance history, and spatial scale. Location Burned and unburned forests and fens in the Siskiyou Mountains of southern Oregon and northern California, USA. Methods We describe ground‐foraging ant assemblages sampled over two years in two discrete habitat types, namely Darlingtonia fens and upland forests. Half of these sites had been subject to a large‐scale, discrete disturbance – a major fire – in the year prior to our first sample. We used null model analyses to compare observed species co‐occurrence patterns and body‐size distributions in these assemblages with randomly generated assemblages unstructured by competition both within (i.e. at a local spatial scale) and among (i.e. at a regional scale) sites. Results At local spatial scales, species co‐occurrence patterns and body‐size ratios did not differ from randomness. At regional scales, co‐occurrence patterns were random or aggregated, and there was evidence for constant body‐size ratios of forest ants. Although these patterns varied between habitats and years, they did not differ between burned and unburned sites. Main conclusions Our results suggest that the operation of assembly rules depends on spatial scale and habitat type, but that it was not affected by disturbance history from fire.     

Correlates of range size and dispersal ability: a comparative analysis of sphingid moths from the Indo-Australian tropics

Aim  We tested various species-level traits for their potential to explain species' range sizes and dispersal abilities.
Location  Southeast Asia and Malay Archipelago.
Methods  We used published maps of geographical distribution estimates for sphingid moths to calculate range areas and classify species according to their dispersion across (present or historical) water straits in the Malay Archipelago. We tested forewing length (FWL), wing load (thorax width/FWL), presence or absence of a functional proboscis (i.e. adult feeding), larval diet breadth and larval diet composition for univariate correlations with range size and inter-island dispersion. We used multivariate, phylogenetically controlled models to test for independent effects of parameters.
Results  Range size correlated strongly with larval diet breadth, a result that was also confirmed in the multivariate model. Adult feeding had a significant impact on range sizes only within the multivariate model, but not in the univariate correlation. Dispersal class also correlated with larval diet breadth, but was additionally influenced by forewing length, wing load and larval diet composition. A univariate effect of adult feeding became non-significant in the multivariate, phylogenetically controlled model.
Main conclusions  Larval diet breadth is the best predictor of range size as well as inter-island dispersion, confirming the importance of niche breadth on the geographic ranges of species. A number of other factors are shown to have additional impact on predictions of range size or inter-island dispersal ability. Our analyses cannot determine the causal mechanisms of these correlations, but may stimulate further research on the adaptive significance of traits affecting range size and dispersal in this system.     

Ultrastructure of the putative stem cell niche in rat mammary epithelium

There is now strong evidence that the stem cells of many tissues reside in specialized structures termed niches. The stem cell niche functions to house and regulate symmetric and asymmetric mitosis of stem cells in mammalian skin, mouse and human bone marrow, mouse brain, gut, and hair follicle, and Drosophila ovary and testis. This regulation is effected through the action of various signaling pathways such as Notch, Hedgehog, Wnt and others. The hormones of the estrous cycle, pregnancy and lactation that initiate growth in mouse mammary epithelium appear to act at a paracrine level to regulate mitosis through Notch receptors. Previous work has established that the putative stem cells of the mammary epithelium in several animal species reside near the basement membrane and never make contact with the ductal lumen. We show that these putative stem cells are found in anatomically specialized places created by the cytoplasmic extensions and modifications of neighboring differentiated cells. Such specializations may help to regulate stem cell activity by modulating molecular traffic to putative stem cells and contact with signaling molecules in the basement membrane. The histological characteristics of these putative niches vary as to the kinds of relationships the cells can have with the basement membrane and neighboring cells and as to how many stem or progenitor cells they may contain. This suggests a plasticity that may be relevant to the response of niches to tissue demands, such as wound healing, the periodic growth and regression of mammary epithelium, the process of mammary tumorigenesis therapeutic strategies for breast cancer.     

Molecular phylogeny of congeneric monogenean parasites (Dactylogyrus): a case of intrahost speciation

Dactylogyrus species (Dactylogyridae: Monogenea) are a group of monogenean gill parasites that are highly specific to freshwater fish of the family Cyprinidae. Dactylogyrus species were sampled from 19 cyprinids and one percid collected in Europe. Using partial 18S rDNA and ITS1 sequences, a phylogeny of 51 Dactylogyrus species was reconstructed to investigate the patterns of parasite speciation and diversification. Three main Dactylogyrus lineages were recognized from all phylogenetic trees, that is, analysis of 18S rDNA alone and combined 18SrDNA and ITS1. The first lineage associates the Dactylogyrus species of Cyprinus carpio and Carassius auratus of the Cyprininae; the second associates Dactylogyrus species of the Gobioninae, Pseudorasbora parva of the Rasborinae, and Ctenopharyngodon idella of the Cyprininae; and the third associates Dactylogyrus species of the Leuciscinae and Alburninae and Barbus barbus of the Cyprininae. Our results suggest that the genus Dactylogyrus is of quite recent origin and that these three lineages separated from each other in a very short period of time. Host subfamily mapping onto the parasite tree inferred from analysis of the combined dataset showed that the Cyprininae could be plesiomorphic hosts for Dactylogyrus. Dactylogyrus parasites would have secondarily colonized the Percidae and representatives of the Leuciscinae, Alburninae, Gobioninae, and Rasborinae. Comparison of host and parasite phylogenetic relationships indicated that a very high number of parasite duplications occurred within two of the three Dactylogyrus lineages. Dactylogyrus diversification can be mainly explained by sympatric intrahost speciation events that seem to be correlated to strict host specificity. Moreover, the present study shows that the congeneric parasites speciating within one host tend to occupy niches within hosts differing at least in one niche parameter.     

Evolution of niche width and adaptive diversification

Theoretical models suggest that resource competition can lead to the adaptive splitting of consumer populations into diverging lineages, that is, to adaptive diversification. In general, diversification is likely if consumers use only a narrow range of resources and thus have a small niche width. Here we use analytical and numerical methods to study the consequences for diversification if the niche width itself evolves. We found that the evolutionary outcome depends on the inherent costs or benefits of widening the niche. If widening the niche did not have costs in terms of overall resource uptake, then the consumer evolved a niche that was wide enough for disruptive selection on the niche position to vanish; adaptive diversification was no longer observed. However, if widening the niche was costly, then the niche widths remained relatively narrow, allowing for adaptive diversification in niche position. Adaptive diversification and speciation resulting from competition for a broadly distributed resource is thus likely if the niche width is fixed and relatively narrow or free to evolve but subject to costs. These results refine the conditions for adaptive diversification due to competition and formulate them in a way that might be more amenable for experimental investigations.     

Phylogenetic relationships between environmental and clinical isolates of Pseudomonas fluorescens and related species deduced from 16S rRNA gene and OprF protein sequences

The major surface protein of the genus Pseudomonas, OprF, is a non-specific porin that plays an important role in maintenance of cell shape, in growth in a low osmolarity environment, and in adhesion to various supports. The objectives of our study were (i) to carry out a comparative analysis of phylogenies obtained from the OprF protein and from the 16S rRNA gene in 41 isolates from various sources (water, soil, milk and the hospital) and (ii) to investigate the physiological characteristics correlated with the phylogeny of OprF. We report here an important incongruence between the phylogenies of the 16S rRNA gene and the OprF protein. Phylogenetic analysis of 16S rRNA genes grouped Pseudomonas fluorescens isolates into one cluster (termed fluorescens r-cluster) whilst the phylogeny of the OprF protein divided Pseudomonas fluorescens isolates into two quite distinct clusters (termed fluorescens 1 o-cluster and fluorescens 2 o-cluster) that may be related to the original habitat of the strain. The fluorescens 1 o-cluster contained the majority of non-rhizospheric soil isolates, while the fluorescens 2 o-cluster contained all our clinical isolates and most of the rhizospheric isolates (which are fixed to the roots). In order to check this correlation, we studied two physiological characteristics: the range of growth temperature and the capacity for non-specific adhesion to polystyrene. The temperature range study for strains did not explain the existence of the two o-clusters but it did confirm the capacity of certain P. fluorescens strains to grow at 37 degrees C. The adhesion capacities of the isolates in the two o-clusters seems to be correlated with ecological niche.     

Comparative ecology of eleotrid fishes in Central American coastal streams

The population structure, abundance, reproductive status, and feeding interrelationships of eleotrid fishes from two freshwater streams of the Caribbean coast of Costa Rica were investigated over 10 continuous months. Eleotris amblyopsis was abundant in both streams. Dormitator maculatus, Eleotris pisonis, and Gobiomorus dormitor were present in both streams but common only in the larger stream that contained dense growth of floating aquatic macrophytes. Dormitator maculatus is a detritivore and overlaps with the other three eleotrids, all of which had diets dominated by shrimp and fishes. Intraguild predation and cannibalism was documented with E. amblyopsis as the prey. Except for the benthic G. dormitor, eleotrids were associated with dense mats of floating macrophytes in the large stream, and leaf peaks in the small stream. Diet similarity among the three carnivorous eleotrids declined during the wet seasons, the period when their prey disperse at lower per-unit-area densities within the flooded forests that surround the streams. Analysis of population size distributions and gonadal maturation indicated that at least some reproduction occurs on a nearly year-round basis within these eleotrid populations. The spring dry period may be associated with migration of ripe eleotrids to estuarine habitats for spawning. Juvenile Eleotris are the dominant fishes in the tismiche, mass migrations of juvenile shrimp and fish larvae and juveniles that enter and ascend the estuary, especially during the summer wet season.     

Abundance–range size relationships in the herbaceous flora of central England

1 Using data from a survey of over 10 000 1-m² quadrats in a 3000-km² area, we examined the relationship between abundance and range for the vascular plant flora of central England.
2 At the level of the whole landscape, abundance was not related to local, regional or national range. Local, regional and national range were closely related to each other.
3 At the level of the whole landscape, range was significantly and positively related to both niche breadth (expressed as the range of habitats exploited) and to habitat availability, although niche breadth appeared to be more important. Abundance was not related to niche breadth or habitat availability. Since specialist species are mainly confined to uncommon habitats (especially wetlands), we conclude that the relationship between range and niche breadth is not an artefact of widespread species passively sampling more habitats.
4 At the level of individual habitat types, significant positive relationships between range and abundance were common. These relationships remained after controlling for the effects of phylogeny. For predominantly annual weed communities, the relationship was linear, but for perennial communities it was markedly 'upper triangular', i.e. all combinations of range and abundance were found except wide range/low abundance. The evidence suggests that this difference can be attributed to the greater mobility of annual weeds.